Leon Axel, M.D., Ph.D.

Quantitative contrast-enhanced first-pass cardiac perfusion MRI at 3 tesla with accurate arterial input function and myocardial wall enhancement
Breton E; Kim D; Chung S; Axel L
2011 Jul 14;:?-?, Journal of magnetic resonance imaging
PURPOSE: To develop, and validate in vivo, a robust quantitative first-pass perfusion cardiovascular MR (CMR) method with accurate arterial input function (AIF) and myocardial wall enhancement. MATERIALS AND METHODS: A saturation-recovery (SR) pulse sequence was modified to sequentially acquire multiple slices after a single nonselective saturation pulse at 3 Tesla. In each heartbeat, an AIF image is acquired in the aortic root with a short time delay (TD) (50 ms), followed by the acquisition of myocardial images with longer TD values ( approximately 150-400 ms). Longitudinal relaxation rates (R(1) = 1/T(1) ) were calculated using an ideal saturation recovery equation based on the Bloch equation, and corresponding gadolinium contrast concentrations were calculated assuming fast water exchange condition. The proposed method was validated against a reference multi-point SR method by comparing their respective R(1) measurements in the blood and left ventricular myocardium, before and at multiple time-points following contrast injections, in 7 volunteers. RESULTS: R(1) measurements with the proposed method and reference multi-point method were strongly correlated (r > 0.88, P < 10(-5) ) and in good agreement (mean difference +/-1.96 standard deviation 0.131 +/- 0.317 / 0.018 +/- 0.140 s(-1) for blood/myocardium, respectively). CONCLUSION: The proposed quantitative first-pass perfusion CMR method measured accurate R(1) values for quantification of AIF and myocardial wall contrast agent concentrations in 3 cardiac short-axis slices, in a total acquisition time of 523 ms per heartbeat. J. Magn. Reson. Imaging 2011;. (c) 2011 Wiley-Liss, Inc
— id: 138509, year: 2011, vol: , page: ?, stat: Journal Article,

Liver stiffness assessment by tagged MRI of cardiac-induced liver motion
Chung, Sohae; Breton, Elodie; Mannelli, Lorenzo; Axel, Leon
2011 Apr;65(4):949-955, Magnetic resonance in medicine
Cirrhosis is an important and growing public health problem, affecting millions of Americans and many more people internationally. A pathological hallmark of the progression to cirrhosis is the development of liver fibrosis, so that monitoring the appearance and progression of liver fibrosis can be used to guide therapy. Here, we report a method to use magnetization-tagged magnetic resonance imaging to measure the cardiac-induced motion and deformation in the liver, as a means for noninvasively assessing liver stiffness, which is related to fibrosis. The initial results show statistically significant differences between healthy and cirrhotic subjects in the direct comparisons of the maximum displacement (mm), and the maximum (P1) and minimum (P2) two-dimensional strains, through the cardiac cycle (3.514 +/- 0.793, 2.184 +/- 0.611; 0.116 +/- 0.043, 0.048 +/- 0.011; -0.094 +/- 0.020, -0.041 +/- 0.015; healthy, cirrhosis, respectively; P < 0.005 for all). There are also significant differences in the displacement-normalized P1 and P2 strains (mm(-1) ) (0.030 +/- 0.008, 0.017 +/- 0.007; -0.024 +/- 0.006, -0.013 +/- 0.004; healthy, cirrhosis, respectively; P < 0.005 for all). Therefore, this noninvasive imaging-based method is a promising means to assess liver stiffness using clinically available imaging tools. Magn Reson Med, 2011. (c) 2011 Wiley-Liss, Inc
— id: 127232, year: 2011, vol: 65, page: 949, stat: Journal Article,

Patient-specific modeling and visualization of blood flow through the heart
Kulp, S; Metaxas, D; Qian, Zhen; Voros, S; Axel, L; Mihalef, V
2011 ;2011:1692-1697, Proceedings (IEEE International Symposium on Biomedical Imaging : from nano to macro)
— id: 135353, year: 2011, vol: 2011, page: 1692, stat: Journal Article,

Functional imaging and modeling of the heart
Metaxas, Dimitris N.; Axel, Leon
Berlin : Springer, 2011,
— id: 2308, year: 2011, vol: , page: , stat: ,

Combination of compressed sensing and parallel imaging with respiratory motion correction for highly-accelerated cardiac perfusion MRI
Otazo R.; Kim D.; Axel L.; Sodickson D.K.
2011 ;13:?-?, Journal of cardiovascular magnetic resonance
Introduction: Cardiac perfusion MRI requires fast data acquisition to achieve an appropriate combination of temporal resolution, spatial resolution and spatial coverage for clinical studies [1]. We have recently presented a combination of compressed sensing and parallel imaging (k-t SPARSESENSE) to highly accelerate perfusion studies [2]. However, this method is sensitive to respiratory motion, which decreases temporal sparsity and produces temporal blurring in the reconstructed images. In this work, we present a rigid respiratory motion correction method which allows highly-accelerated first-pass cardiac perfusion MRI to be performed without strict breath-holding. Purpose: To develop a respiratory motion correction method for joint compressed sensing and parallel imaging acceleration of first-pass cardiac perfusion MRI. Methods: Free-breathing first-pass cardiac perfusion MRI with 0.1 mmol/kg of Gd-DTPA (Magnevist) was performed using a modified multi-slice TurboFLASH pulse sequence. Healthy volunteers were imaged on a whole-body 3T scanner (Siemens; Tim-Trio) using the standard 12- element body matrix coil array. The relevant imaging parameters include: FOV = 320mmx320mm, image resolution = 1.7mmx1.7mm, slice-thickness = 8mm, TE/ TR = 1.3/2.5ms, repetitions=40. An acceleration factor of 8 was used to acquire 10 slices per heartbeat with temporal resolution of 60ms/slice. Data undersampling was performed using a pseudo-random ky-t pattern [2]. Fully-sampled low-resolution coil sensitivity reference data were acquired in the first heartbeat. Image reconstruction was performed in two-steps using the k-t SPARSE-SENSE algorithm [2] with temporal FFT as sparsifying transform. First, an intermediate k-t SPARSESENSE reconstruction is generated for respiratory motion correction. Rigid motion between frames is detected by computing the displacement of each frame from this intermediate k-t SPARSE-SENSE reconstruction with respect to the coil sensitivity reference using a crosscorrelation approach in the image domain [3]. Second, motion correction is performed by aligning all the frames in the accelerated data. The final k-t SPARSESENSE reconstruction is computed using the aligned accelerated data. Results: Rigid respiratory motion correction significantly increased sparsity in the temporal Fourier domain, which is due to better alignment among frames (Fig. 1). Fig. 2 shows k-t SPARSE-SENSE reconstruction of a representative slice from the free-breathing perfusion scan without and with motion correction. The utilization of motion correction decreased temporal blurring and presented images with higher quality. Conclusions: This work demonstrates feasibility of highly-accelerated first-pass cardiac perfusion MRI without strict breathholding with rigid respiratory motion correction. Future work will explore the use of non-rigid motion correction. The proposed technique may be useful for imaging patients with impaired breath-hold capabilities(figure present)
— id: 135612, year: 2011, vol: 13, page: ?, stat: Journal Article,

Identifying Regional Cardiac Abnormalities From Myocardial Strains Using Nontracking-Based Strain Estimation and Spatio-Temporal Tensor Analysis
Qian, Zhen; Liu, Qingshan; Metaxas, Dimitris N.; Axel, Leon
2011 DEC ;30(12):2017-2029, IEEE Transactions on medical imaging
Myocardial strain is a critical indicator of many cardiac diseases and dysfunctions. The goal of this paper is to extract and use the myocardial strain pattern from tagged magnetic resonance imaging (MRI) to identify and localize regional abnormal cardiac function in human subjects. In order to extract the myocardial strains from the tagged images, we developed a novel nontracking-based strain estimation method for tagged MRI. This method is based on the direct extraction of tag deformation, and therefore avoids some limitations of conventional displacement or tracking-based strain estimators. Based on the extracted spatio-temporal strain patterns, we have also developed a novel tensor-based classification framework that better conserves the spatio-temporal structure of the myocardial strain pattern than conventional vector-based classification algorithms. In addition, the tensor-based projection function keeps more of the information of the original feature space, so that abnormal tensors in the subspace can be back-projected to reveal the regional cardiac abnormality in a more physically meaningful way. We have tested our novel methods on 41 human image sequences, and achieved a classification rate of 87.80%. The regional abnormalities recovered from our algorithm agree well with the patient's pathology and clinical image interpretation, and provide a promising avenue for regional cardiac function analysis
— id: 147721, year: 2011, vol: 30, page: 2017, stat: Journal Article,

Mechanisms of Myocardial Infarction in Women Without Angiographically Obstructive Coronary Artery Disease
Reynolds HR; Srichai MB; Iqbal SN; Slater JN; Mancini GB; Feit F; Pena-Sing I; Axel L; Attubato MJ; Yatskar L; Kalhorn RT; Wood DA; Lobach IV; Hochman JS
2011 Sep 27;124(13):1414-1425, Circulation
BACKGROUND: . Unique identifier: NCT00798122
— id: 137093, year: 2011, vol: 124, page: 1414, stat: Journal Article,

Quantitative assessment of atrioventricular plane displacement in normal and diastolic heart failure - A cine MRI study
Anand R.; Chung S.; Bhagavatula S.; Axel L.
2010 ;12:137-137, Journal of cardiovascular magnetic resonance
Introduction: Left atrioventricular plane displacement reflects the dysfunction in patients with heart failure. In previous studies, it has been reported that the displacement was decreased with progression of diastolic dysfunction [1, 2]. The purpose of our study is to use conventional cine magnetic resonance imaging to measure the displacement of the atrioventricular plane of the left ventricle in normal subjects and in patients with diastolic dysfunction. Purpose: To assess the change in position of the AVJ plane by noninvasive, conventional cine MRI to diagnose early diastolic dysfunction. Methods: Cine MRI was performed at 1.5 T MRI scanner (Symphony, Siemens) on eight normal volunteers (Nl) (29 +/- 4.4 years old) and eight patients with heart failure Figure 1 (abstract P69) (64 +/- 17 years old) in two-, three-and four-chamber long axis views. Five patients had a history of mild cardiomyopathy with normal wall thickness (NT), and three patients had left ventricular hypertrophy (H). All patients had normal or near normal ejection fraction (>= 45%). Analysis used software custom written in Matlab (Natick, MA). To measure the displacement of the atrio-ventricular plane, a reference line was drawn from the ventricular apex towards the base of the left ventricle (green line in Figure 1(a)). The position of the atrioventricular junction (AVJ) was tracked during the cardiac cycle (red dot in Figure 1(a)) and was projected onto the reference line. The displacement of the AVJ along the reference line was measured relative to the position at end-diastole. Two parameters were selected for the analysis: (1) Maximum displacement (mm) of the AVJ towards apex and (2) Thm (ms), the time period between the half maximum systolic and half maximum diastolic displacement points. Results: Results are shown in Figure 1: (b) the time courses of the 2-chamber AVJ displacement are shown for the representative Nl, NT and H during the cardiac cycle, (c) box plots of the 2-chamber maximum displacements (mean;-17.9,-14,-11.1; Nl, NT, H; respectively), and (d) box plots of the 2-chamber Thm (mean; 317.4, 552.1, 756.6; Nl, NT, H; respectively). The AVJ displacement is decreased in NT and H as compared to Nl. Conclusion: Cine MRI measurement of the AVJ displacement provides a simple and potentially valuable noninvasive method to assess early left ventricular diastolic dysfunction. This method can be used on any conventional MRI system
— id: 135282, year: 2010, vol: 12, page: 137, stat: Journal Article,

Intracavitary "fountains" in left ventricular noncompaction
Axel, Leon
2010 Jul 20;56(4):e7-e7, Journal of the American College of Cardiology
— id: 111387, year: 2010, vol: 56, page: e7, stat: Journal Article,

Image-guided radio-frequency gain calibration for high-field MRI
Breton, Elodie; McGorty, Kellyanne; Wiggins, Graham C; Axel, Leon; Kim, Daniel
2010 May;23(4):368-374, NMR in biomedicine
High-field (>/= 3T) MRI provides a means to increase the signal-to-noise ratio, due to its higher tissue magnetization compared with 1.5T. However, both the static magnetic field (B(0)) and the transmit radio-frequency (RF) field (B 1+) inhomogeneities are comparatively higher at higher field strengths than those at 1.5T. These challenging factors at high-field strengths make it more difficult to accurately calibrate the transmit RF gain using standard RF calibration procedures. An image-based RF calibration procedure was therefore developed, in order to accurately calibrate the transmit RF gain within a specific region-of-interest (ROI). Using a turbo fast low-angle shot (TurboFLASH) pulse sequence with centric k-space reordering, a series of 'saturation-no-recovery' images was acquired by varying the flip angle of the preconditioning pulse. In the resulting images, the signal null occurs in regions where the flip angle of the preconditioning pulse is 90 degrees . For a given ROI, the mean signal can be plotted as a function of the nominal flip angle, and the resulting curve can be used to quantitatively identify the signal null. This image-guided RF calibration procedure was evaluated through phantom and volunteer imaging experiments at 3T and 7T. The image-guided RF calibration results in vitro were consistent with standard B(0) and B 1+ maps. The standard automated RF calibration procedure produced approximately 20% and 15-30% relative error in the transmit RF gain in the left kidney at 3T and brain at 7T, respectively. For initial application, a T(2) mapping pulse sequence was applied at 7T. The T(2) measurements in the thalamus at 7T were 60.6 ms and 48.2 ms using the standard and image-guided RF calibration procedures, respectively. This rapid, image-guided RF calibration procedure can be used to optimally calibrate the flip angle for a given ROI and thus minimize measurement errors for quantitative MRI and MR spectroscopy
— id: 138388, year: 2010, vol: 23, page: 368, stat: Journal Article,

Automated 3D motion tracking using Gabor filter bank, robust point matching, and deformable models
Chen, Ting; Wang, Xiaoxu; Chung, Sohae; Metaxas, Dimitris; Axel, Leon
2010 Jan;29(1):1-11, IEEE Transactions on medical imaging
Tagged magnetic resonance imaging (tagged MRI or tMRI) provides a means of directly and noninvasively displaying the internal motion of the myocardium. Reconstruction of the motion field is needed to quantify important clinical information, e.g., the myocardial strain, and detect regional heart functional loss. In this paper, we present a three-step method for this task. First, we use a Gabor filter bank to detect and locate tag intersections in the image frames, based on local phase analysis. Next, we use an improved version of the robust point matching (RPM) method to sparsely track the motion of the myocardium, by establishing a transformation function and a one-to-one correspondence between grid tag intersections in different image frames. In particular, the RPM helps to minimize the impact on the motion tracking result of 1) through-plane motion and 2) relatively large deformation and/or relatively small tag spacing. In the final step, a meshless deformable model is initialized using the transformation function computed by RPM. The model refines the motion tracking and generates a dense displacement map, by deforming under the influence of image information, and is constrained by the displacement magnitude to retain its geometric structure. The 2D displacement maps in short and long axis image planes can be combined to drive a 3D deformable model, using the moving least square method, constrained by the minimization of the residual error at tag intersections. The method has been tested on a numerical phantom, as well as on in vivo heart data from normal volunteers and heart disease patients. The experimental results show that the new method has a good performance on both synthetic and real data. Furthermore, the method has been used in an initial clinical study to assess the differences in myocardial strain distributions between heart disease (left ventricular hypertrophy) patients and the normal control group. The final results show that the proposed method is capable of separating patients from healthy individuals. In addition, the method detects and makes possible quantification of local abnormalities in the myocardium strain distribution, which is critical for quantitative analysis of patients' clinical conditions. This motion tracking approach can improve the throughput and reliability of quantitative strain analysis of heart disease patients, and has the potential for further clinical applications
— id: 134972, year: 2010, vol: 29, page: 1, stat: Journal Article,

Rapid B(1) (+) mapping using a preconditioning RF pulse with TurboFLASH readout
Chung, Sohae; Kim, Daniel; Breton, Elodie; Axel, Leon
2010 Aug;64(2):439-446, Magnetic resonance in medicine
In MRI, the transmit radiofrequency field (B(1) (+)) inhomogeneity can lead to signal intensity variations and quantitative measurement errors. By independently mapping the local B(1) (+) variation, the radiofrequency-related signal variations can be corrected for. In this study, we present a new fast B(1) (+) mapping method using a slice-selective preconditioning radiofrequency pulse. Immediately after applying a slice-selective preconditioning pulse, a turbo fast low-angle-shot imaging sequence with centric k-space reordering is performed to capture the residual longitudinal magnetization left behind by the slice-selective preconditioning pulse due to B(1) (+) variation. Compared to the reference double-angle method, this method is considerably faster. Specifically, the total scan time for the double-angle method is equal to the product of 2 (number of images), the number of phase-encoding lines, and approximately 5T(1), whereas the slice-selective preconditioning method takes approximately 5T(1). This method was validated in vitro and in vivo with a 3-T whole-body MRI system. The combined brain and pelvis B(1) (+) measurements showed excellent agreement and strong correlation with those by the double-angle method (mean difference = 0.025; upper and lower 95% limits of agreement were -0.07 and 0.12; R = 0.93; P < 0.001). This fast B(1) (+) mapping method can be used for a variety of applications, including body imaging where fast imaging is desirable. Magn Reson Med, 2010. (c) 2010 Wiley-Liss, Inc
— id: 111368, year: 2010, vol: 64, page: 439, stat: Journal Article,

Highly-accelerated first-pass cardiac perfusion MRI using compressed sensing and parallel imaging
Otazo R.; Kim D.; Axel L.; Sodickson D.K.
2010 ;12:62-62, Journal of cardiovascular magnetic resonance
Introduction: Robust implementation of first-pass cardiac perfusion MRI for clinical use can be particularly challenging due to competing constraints of spatial and temporal resolution, and spatial coverage [1]. k-t SENSE [2] can be used to achieve high accelerations, but dynamic training data are required which reduces the effective acceleration rate. An alternative acceleration technique is compressed sensing (CS) [3], where spatial and temporal correlations result in sparsity of image series content, which may in turn be exploited to achieve high levels of undersampling without losing image information. We have recently presented the combination of compressed sensing and parallel imaging (JOCS: JOint-CS [4]) to increase the acceleration rate of CS alone. In this work, we demonstrate first-pass cardiac perfusion MRI with whole-heart coverage and high spatial and temporal resolution using the JOCS technique. Purpose: Evaluate the feasibility of highly-accelerated first-pass cardiac perfusion MRI with whole-heart coverage per heartbeat using JOCS. Methods: First-pass cardiac perfusion MRI with 0.1 mmol/kg of Gd-DTPA (Magnevist) was performed in two healthy volunteers and one patient with coronary artery disease. A modified multislice TurboFLASH sequence was employed on a whole-body 3 T scanner (Siemens;Tim-Trio) using the 12-element body matrix coil array. The relevant imaging parameters include: FOV = 320 mm x 320 mm, image-resolution = 1.7 mm x 1.7 mm, slice-thickness = 8 mm, TE/TR = 1.3 ms/2.5 ms, repetitions = 40. Acceleration was accomplished using ky-t random undersampling to produce the required incoherence. Breath-hold measurements with acceleration factor of R = 8 (allowing 10 (Figure presented) (Figure presented) acquired slices per heartbeat, temporal-resolution = 60 ms/slice) were performed. In the patient, delayed-enhancement images were obtained using a phase-sensitive inversion recovery (PSIR) [6] pulse sequence, 15 minutes after the administration of the contrast agent. Image reconstruction was performed using the JOCS algorithm [5]. A Fourier transform along the time dimension and finite differences along the spatial dimensions were used as sparsifying transforms. Results: Fig. 1 shows the reconstructed images (10 slices) for the peak blood and peak myocardial wall enhancement phases for one volunteer study. The reconstructed images covered most of the heart with adequate blood and myocardial wall enhancement and good image quality. Fig. 2 shows perfusion images at peak myocardial wall enhancement in three short-axis views (mid-to-apical) with perfusion defects for the patient study. The corresponding PSIR delayed-enhancement images show myocardial scarring regions that correlate well with the perfusion defect regions. Conclusion: JOCS enables first-pass cardiac perfusion MRI studies with whole-heart coverage and high spatial (<2 mm) and temporal (60 ms/slice) resolution. Future work will explore 3D imaging and the use of larger numbers of coils
— id: 135284, year: 2010, vol: 12, page: 62, stat: Journal Article,

Combination of compressed sensing and parallel imaging for highly accelerated first-pass cardiac perfusion MRI
Otazo, Ricardo; Kim, Daniel; Axel, Leon; Sodickson, Daniel K
2010 Sep;64(3):767-776, Magnetic resonance in medicine
First-pass cardiac perfusion MRI is a natural candidate for compressed sensing acceleration since its representation in the combined temporal Fourier and spatial domain is sparse and the required incoherence can be effectively accomplished by k-t random undersampling. However, the required number of samples in practice (three to five times the number of sparse coefficients) limits the acceleration for compressed sensing alone. Parallel imaging may also be used to accelerate cardiac perfusion MRI, with acceleration factors ultimately limited by noise amplification. In this work, compressed sensing and parallel imaging are combined by merging the k-t SPARSE technique with sensitivity encoding (SENSE) reconstruction to substantially increase the acceleration rate for perfusion imaging. We also present a new theoretical framework for understanding the combination of k-t SPARSE with SENSE based on distributed compressed sensing theory. This framework, which identifies parallel imaging as a distributed multisensor implementation of compressed sensing, enables an estimate of feasible acceleration for the combined approach. We demonstrate feasibility of 8-fold acceleration in vivo with whole-heart coverage and high spatial and temporal resolution using standard coil arrays. The method is relatively insensitive to respiratory motion artifacts and presents similar temporal fidelity and image quality when compared to Generalized autocalibrating partially parallel acquisitions (GRAPPA) with 2-fold acceleration
— id: 138195, year: 2010, vol: 64, page: 767, stat: Journal Article,

Non-gadolinium-enhanced 3-dimensional magnetic resonance angiography for the evaluation of thoracic aortic disease: a preliminary experience
Srichai, Monvadi B; Kim, Sooah; Axel, Leon; Babb, James; Hecht, Elizabeth M
2010 ;37(1):58-65, Texas Heart Institute journal
We compared image quality and diagnostic accuracy of a noncontrast 3-dimensional magnetic resonance angiography (NC-MRA) technique (balanced steady-state free-precession sequence) to contrast-enhanced MRA (CE-MRA) for evaluation of thoracic aortic disease.The CE-MRA provides 3-dimensional high-resolution images of the thoracic aorta that are important in the evaluation of patients with aortic disease. However, recent concerns with the potential nephrotoxic effects of gadolinium contrast medium limit the application of CE-MRA for patients who have significant renal insufficiency.Twenty-one patients (mean age, 51 yr; 18 men) who underwent NC-MRA and CE-MRA for evaluation of thoracic aortic disease were retrospectively identified. Data sets were reviewed by 2 readers who were blinded to the patients' information. The thoracic aorta was divided into 5 segments. Image quality and reader confidence for diagnosis of aortic pathology were rated on 5-point scales. The Wilcoxon matched-pairs signed rank test and the Student t test were used for comparisons.The NC-MRA identified all pathologic findings with 100% diagnostic accuracy and similar reader confidence, when compared with CE-MRA. Although overall image quality was not significantly different, superior image quality was observed at the aortic root (4.4 +/- 0.8 vs 3.2 +/- 0.9, P <0.0005) and ascending aorta (4.1 +/- 1 vs 3.7 +/- 0.9, P=0.05) respectively.In conclusion, NC-MRA is a useful alternative for evaluation and follow-up of thoracic aortic disease, especially for patients with poor intravenous access or contraindications to gadolinium use
— id: 107791, year: 2010, vol: 37, page: 58, stat: Journal Article,

MRI of the microarchitecture of myocardial infarction: are we seeing new kinds of structures?
Axel, Leon
2009 May;2(3):169-170, Circulation. Cardiovascular imaging
— id: 138511, year: 2009, vol: 2, page: 169, stat: Journal Article,

Numerical and in vivo validation of fast cine displacement-encoded with stimulated echoes (DENSE) MRI for quantification of regional cardiac function
Feng, Li; Donnino, Robert; Babb, James; Axel, Leon; Kim, Daniel
2009 Sep;62(3):682-690, Magnetic resonance in medicine
Quantitative assessment of regional cardiac function can improve the accuracy of detecting wall motion abnormalities due to heart disease. While recently developed fast cine displacement-encoded with stimulated echoes (DENSE) MRI is a promising modality for the quantification of regional myocardial function, it has not been validated for clinical applications. The purpose of this study, therefore, was to validate the accuracy of fast cine DENSE MRI with numerical simulation and in vivo experiments. A numerical phantom was generated to model physiologically relevant deformation of the heart, and the accuracy of fast cine DENSE was evaluated against the numerical reference. For in vivo validation, 12 controls and 13 heart-disease patients were imaged using both fast cine DENSE and myocardial tagged MRI. Numerical simulation demonstrated that the echo-combination DENSE reconstruction method is relatively insensitive to clinically relevant resonance frequency offsets. The strain measurements by fast cine DENSE and the numerical reference were strongly correlated and in excellent agreement (mean difference = 0.00; 95% limits of agreement were 0.01 and -0.02). The strain measurements by fast cine DENSE and myocardial tagged MRI were strongly correlated (correlation coefficient = 0.92) and in good agreement (mean difference = 0.01; 95% limits of agreement were 0.07 and -0.04)
— id: 101933, year: 2009, vol: 62, page: 682, stat: Journal Article,

Special section on the 12th International Conference on Medical Imaging and Computer Assisted Intervention. Editorial
Metaxas, Dimitris N; Axel, Leon
2009 Oct;13(5):771-772, Medical image analysis
— id: 138510, year: 2009, vol: 13, page: 771, stat: Journal Article,

CT and MR Appearances of Cardiac Pseudomasses: Imaging Pearls and Pitfalls (CME Credit Available)
Rueff, L; Srichai, M; Jacobs, J; Chandarana, H; Axel, L; Kim, D; Lim, R
2009 MAY ;192(5):646-651, American journal of roentgenology
— id: 99182, year: 2009, vol: 192, page: 646, stat: Journal Article,

Semiautomated segmentation of myocardial contours for fast strain analysis in cine displacement-encoded MRI
Chen, Ting; Babb, James; Kellman, Peter; Axel, Leon; Kim, Daniel
2008 Aug;27(8):1084-1094, IEEE Transactions on medical imaging
The purposes of this study were to develop a semiautomated cardiac contour segmentation method for use with cine displacement-encoded MRI and evaluate its accuracy against manual segmentation. This segmentation model was designed with two distinct phases: preparation and evolution. During the model preparation phase, after manual image cropping and then image intensity standardization, the myocardium is separated from the background based on the difference in their intensity distributions, and the endo- and epi-cardial contours are initialized automatically as zeros of an underlying level set function. During the model evolution phase, the model deformation is driven by the minimization of an energy function consisting of five terms: model intensity, edge attraction, shape prior, contours interaction, and contour smoothness. The energy function is minimized iteratively by adaptively weighting the five terms in the energy function using an annealing algorithm. The validation experiments were performed on a pool of cine data sets of five volunteers. The difference between the semiautomated segmentation and manual segmentation was sufficiently small as to be considered clinically irrelevant. This relatively accurate semiautomated segmentation method can be used to significantly increase the throughput of strain analysis of cine displacement-encoded MR images for clinical applications
— id: 80338, year: 2008, vol: 27, page: 1084, stat: Journal Article,

Fast motion tracking of tagged MRI using angle-preserving meshless registration
Chen, Ting; Wang, Xiaoxu; Metaxas, Dimitris; Axel, Leon
2008 ;11(Pt 2):313-320, Medical image computing & computer-assisted intervention : MICCAI
Fast tracking of motion is the key step towards tagged MRI-based quantitative cardiac analysis. Existing motion tracking approaches, including the widely used HARP method, are either time consuming or qualitatively inconsistent, or both. We present in this paper a new fast motion tracking method based on a meshless kernel. For MR image sequences containing multiple image frames, tag intersections are automatically detected in all frames and indexed in the first frame. Then a thin plate spline approach is used to establish a point-to-point correspondence between tag intersections in the initial and the current frame. Lastly, we use a meshless registration kernel to generate a dense displacement map that minimizes the residual of sparse motion at intersections. To further improve the motion tracking, we develop a special technique to preserve tangential angles of tags at tag intersections. We tested our new method on both numerical phantoms and in vivo heart data. The motion tracking results are evaluated against the ground truth and manually drawn tags. Clinical application potential is demonstrated by cardiac strain analysis based on the proposed methodology
— id: 91456, year: 2008, vol: 11, page: 313, stat: Journal Article,

Myocardial first-pass perfusion cardiovascular magnetic resonance: history, theory, and current state of the art
Gerber, Bernhard L; Raman, Subha V; Nayak, Krishna; Epstein, Frederick H; Ferreira, Pedro; Axel, Leon; Kraitchman, Dara L
2008 ;10(1):18-18, Journal of cardiovascular magnetic resonance
In less than two decades, first-pass perfusion cardiovascular magnetic resonance (CMR) has undergone a wide range of changes with the development and availability of improved hardware, software, and contrast agents, in concert with a better understanding of the mechanisms of contrast enhancement. The following review provides a perspective of the historical development of first-pass CMR, the developments in pulse sequence design and contrast agents, the relevant animal models used in early preclinical studies, the mechanism of artifacts, the differences between 1.5T and 3T scanning, and the relevant clinical applications and protocols. This comprehensive overview includes a summary of the past clinical performance of first-pass perfusion CMR and current clinical applications using state-of-the-art methodologies
— id: 93972, year: 2008, vol: 10, page: 18, stat: Journal Article,

Tag separation in cardiac tagged MRI
Huang, Junzhou; Qian, Zhen; Huang, Xiaolei; Metaxas, Dimitris; Axel, Leon
2008 ;11(Pt 2):289-297, Medical image computing & computer-assisted intervention : MICCAI
In this paper we introduce a tag separation method for better cardiac boundary segmentation and tag tracking. Our approach is based on two observations in the cardiac tagged MR images: 1) the tag patterns have a regular texture; 2) the cardiac images without tag patterns are piecewise smooth with sparse gradients. These observations motivate us to use two dictionaries, one based on the Discrete Cosine Transform for representing tag patterns and the other based on the Wavelet Transform for representing the underlying cardiac image without tag patterns. The two dictionaries are built such that they can lead to sparse representations of the tag patterns and of the piece-wise smooth regions without tag patterns. With the two dictionaries, a new tag separation approach is proposed to simultaneously optimize w.r.t. the two sparse representations, where optimization is directed by the Total Variation regularization scheme. While previous methods have focused on tag removal, our approach to acquiring both optimally-decomposed tag-only image and the cardiac image without tags simultaneously can be used for better tag tracking and cardiac boundary segmentation. We demonstrate the superior performance of the proposed approach through extensive experiments on large sets of cardiac tagged MR images
— id: 93966, year: 2008, vol: 11, page: 289, stat: Journal Article,

Comparison of the effectiveness of saturation pulses in the heart at 3T
Kim, Daniel; Gonen, Oded; Oesingmann, Niels; Axel, Leon
2008 Jan;59(1):209-215, Magnetic resonance in medicine
Cardiac MRI at 3T provides a means to increase the contrast-to-noise ratio (CNR) for first-pass perfusion MRI. However, both the static magnetic field (B(0)) and radio frequency (RF) field (B(1)) variations within the heart are comparatively higher at 3T than at 1.5T. The increased field variations can degrade the performance of a single rectangular saturation pulse that is conventionally used for magnetization preparation. The accuracy of T(1)-weighted signal measurement depends on the uniformity of the magnetization saturation. The purpose of this study was to assess the relative effectiveness of the rectangular, pulse train, and adiabatic composite (BIR-4) saturation pulses in the human heart at 3T. In volunteers, after nominal saturation, the mean residual magnetization within the left ventricle (LV) was different between all three pulses (0.13 +/- 0.06 vs. 0.03 +/- 0.02 vs. 0.03 +/- 0.01, respectively; P < 0.001). Within paired groups, the mean residual magnetization was significantly higher for the rectangular pulse than for either the pulse train and BIR-4 pulses (P < 0.001), but not different between the pulse train and BIR-4 pulses. The performances of all three saturation pulses were comparatively poorer in the right ventricle (RV) than in the LV, respectively. Magn Reson Med, 2007. (c) 2007 Wiley-Liss, Inc
— id: 75184, year: 2008, vol: 59, page: 209, stat: Journal Article,

11th International Conference, New York, NY, USA, September 6-10, 2008. Proceedings, Part II. Preface
Metaxas, Dimitris; Axel, Leon; Fichtinger, Gabor; Szekely, Gabor
2008 ;11(Pt 2):V-VIII, Medical image computing & computer-assisted intervention : MICCAI
— id: 93967, year: 2008, vol: 11, page: V, stat: Journal Article,

Medical image computing and computer-assisted intervention--MICCAI2008. Preface
Metaxas, Dimitris; Axel, Leon; Fichtinger, Gabor; Szekely, Gabor
2008 ;11(Pt 1):V-VII, Medical image computing & computer-assisted intervention : MICCAI
— id: 93971, year: 2008, vol: 11, page: V, stat: Journal Article,

Images in cardiovascular medicine. Lyme carditis
Naik, Mohit; Kim, Danny; O'Brien, Francis; Axel, Leon; Srichai, Monvadi B
2008 Oct 28;118(18):1881-1884, Circulation
— id: 91481, year: 2008, vol: 118, page: 1881, stat: Journal Article,

Identifying regional cardiac abnormalities from myocardial strains using spatio-temporal tensor analysis
Qian, Zhen; Liu, Qingshan; Metaxas, Dimitris N; Axel, Leon
2008 ;11(Pt 1):789-797, Medical image computing & computer-assisted intervention : MICCAI
Myocardial deformation is a critical indicator of many cardiac diseases and dysfunctions. The goal of this paper is to use myocardial deformation patterns to identify and localize regional abnormal cardiac function in human subjects. We have developed a novel tensor-based classification framework that better conserves the spatio-temporal structure of the myocardial deformation pattern than conventional vector-based algorithms. In addition, the tensor-based projection function keeps more of the information of the original feature space, so that abnormal tensors in the subspace can be back-projected to reveal the regional cardiac abnormality in a more physically meaningful way. We have tested our novel method on 41 human image sequences, and achieved a classification rate of 87.80%. The recovered regional abnormalities from our algorithm agree well with the patient's pathology and doctor's diagnosis and provide a promising avenue for regional cardiac function analysis
— id: 93968, year: 2008, vol: 11, page: 789, stat: Journal Article,

Active volume models with probabilistic object boundary prediction module
Shen, Tian; Zhu, Yaoyao; Huang, Xiaolei; Huang, Junzhou; Metaxas, Dimitris; Axel, Leon
2008 ;11(Pt 1):331-341, Medical image computing & computer-assisted intervention : MICCAI
We propose a novel Active Volume Model (AVM) which deforms in a free-form manner to minimize energy. Unlike Snakes and level-set active contours which only consider curves or surfaces, the AVM is a deforming object model that has both boundary and an interior area. When applied to object segmentation and tracking, the model alternates between two basic operations: deform according to current object prediction, and predict according to current appearance statistics of the model. The probabilistic object prediction module relies on the Bayesian Decision Rule to separate foreground (i.e., object represented by the model) and background. Optimization of the model is a natural extension of the Snakes model so that region information becomes part of the external forces. The AVM thus has the efficiency of Snakes while having adaptive region-based constraints. Segmentation results, validation, and comparison with GVF Snakes and level set methods are presented for experiments on noisy 2D/3D medical images
— id: 93970, year: 2008, vol: 11, page: 331, stat: Journal Article,

LV motion and strain computation from tMRI based on meshless deformable models
Wang, Xiaoxu; Chen, Ting; Zhang, Shaoting; Metaxas, Dimitris; Axel, Leon
2008 ;11(Pt 1):636-644, Medical image computing & computer-assisted intervention : MICCAI
We propose a novel meshless deformable model for in vivo Left Ventricle (LV) 3D motion estimation and analysis based on tagged MRI (tMRI). The meshless deformable model can capture global deformations such as contraction and torsion with a few parameters, while track local deformations with Laplacian representation. In particular, the model performs well even when the control points (tag intersections) are relatively sparse. We test the performance of the meshless model on a numeric phantom, as well as in vivo heart data of healthy subjects and patients. The experimental results show that the meshless deformable model can fully recover the myocardial motion and strain in 3D
— id: 93969, year: 2008, vol: 11, page: 636, stat: Journal Article,

Is subendocardial ischaemia present in patients with chest pain and normal coronary angiograms? A cardiovascular MR study
Axel, Leon
2007 Nov;28(21):2687-2687, European heart journal
— id: 93978, year: 2007, vol: 28, page: 2687, stat: Journal Article,

2D motion analysis of long axis cardiac tagged MRI
Chen, Ting; Chung, Sohae; Axel, Leon
2007 ;10(Pt 2):469-476, Lecture notes in computer science
The tracking and reconstruction of myocardial motion is critical to the diagnosis and treatment of heart disease. Currently, little has been done for the analysis of motion in long axis (LA) cardiac images. We propose a new fully automated motion reconstruction method for grid- tagged MRI that combines Gabor filters and deformable models. First, we use a Gabor filter bank to generate the corresponding phase map in the myocardium and estimate the location of grid tag intersections. Second, we use a non-rigid registration module driven by thin plate splines (TPS) to generate a transformation function between tag intersections in two consecutive images. Third, deformable spline models are initialized using Fourier domain analysis and tracked during the cardiac cycle using the TPS generated transformation function. The splines will then locally deform under the influence of gradient flow and image phase information. The final motion is decomposed into tangential and normal components corresponding to the local orientation of the heart wall. The new method has been tested on LA phantoms and in vivo heart data, and its performance has been quantitatively validated. The results show that our method can reconstruct the motion field in LA cardiac tagged MR images accurately and efficiently
— id: 75418, year: 2007, vol: 10, page: 469, stat: Journal Article,

Adaptive metamorphs model for 3D medical image segmentation
Huang, Junzhou; Huang, Xiaolei; Metaxas, Dimitris; Axel, Leon
2007 ;10(Pt 1):302-310, Medical image computing & computer-assisted intervention : MICCAI
In this paper, we introduce an adaptive model-based segmentation framework, in which edge and region information are integrated and used adaptively while a solid model deforms toward the object boundary. Our 3D segmentation method stems from Metamorphs deformable models. The main novelty of our work is in that, instead of performing segmentation in an entire 3D volume, we propose model-based segmentation in an adaptively changing subvolume of interest. The subvolume is determined based on appearance statistics of the evolving object model, and within the subvolume, more accurate and object-specific edge and region information can be obtained. This local and adaptive scheme for computing edges and object region information makes our segmentation solution more efficient and more robust to image noise, artifacts and intensity inhomogeneity. External forces for model deformation are derived in a variational framework that consists of both edge-based and region-based energy terms, taking into account the adaptively changing environment. We demonstrate the performance of our method through extensive experiments using cardiac MR and liver CT images
— id: 93974, year: 2007, vol: 10, page: 302, stat: Journal Article,

Ultrasound myocardial elastography and registered 3D tagged MRI: quantitative strain comparison
Qian, Zhen; Lee, Wei-Ning; Konofagou, Elisa E; Metaxas, Dimitris N; Axel, Leon
2007 ;10(Pt 1):800-808, Medical image computing & computer-assisted intervention : MICCAI
Ultrasound Myocardial Elastography (UME) and Tagged Magnetic Resonance Imaging (tMRI) are two imaging modalities that were developed in the recent years to quantitatively estimate the myocardial deformations. Tagged MRI is currently considered as the gold standard for myocardial strain mapping in vivo. However, despite the low SNR nature of ultrasound signals, echocardiography enjoys the widespread availability in the clinic, as well as its low cost and high temporal resolution. Comparing the strain estimation performances of the two techniques has been of great interests to the community. In order to assess the cardiac deformation across different imaging modalities, in this paper, we developed a semi-automatic intensity and gradient based registration framework that rigidly registers the 3D tagged MRIs with the 2D ultrasound images. Based on the two registered modalities, we conducted spatially and temporally more detailed quantitative strain comparison of the RF-based UME technique and tagged MRI. From the experimental results, we conclude that qualitatively the two modalities share similar overall trends. But error and variations in UME accumulate over time. Quantitatively tMRI is more robust and accurate than UME
— id: 93973, year: 2007, vol: 10, page: 800, stat: Journal Article,

Dynamic CMR cardiac anatomy: The 'cypress tree' papillary muscle root
Biederman, RW; Doyle, M; Axel, L
2006 OCT 31 ;114(18):778-778, Circulation
— id: 69564, year: 2006, vol: 114, page: 778, stat: Journal Article,

Theory-based signal calibration with single-point T1 measurements for first-pass quantitative perfusion MRI studies
Cernicanu, Alexandru; Axel, Leon
2006 Jun;13(6):686-693, Academic radiology
RATIONALE AND OBJECTIVES: The aim of the study is to develop a theory-based signal calibration approach to be used for the conversion of signal-time curves to absolute contrast concentration-time curves for first-pass contrast-enhanced quantitative myocardial perfusion studies. MATERIALS AND METHODS: A normalization procedure was used to obtain a theoretical relationship between image signal and T1 and perform rapid single-point T1 measurements. T1 measurements were compared with reference T1 measurements. The method also was used in preliminary in vivo contrast-enhanced first-pass perfusion studies, and its applicability for dual-delay-time acquisitions was shown. A theory-based error sensitivity analysis was used to characterize the robustness of the method. RESULTS: The normalization procedure was implemented with minimal noise enhancement and insensitivity to small misregistrations through postprocessing techniques. The rapid T1 measurements are in excellent agreement with the reference measurements (R = 0.99, slope = 1.05, bias = -5.96 milliseconds). For in vivo studies, it is possible to simultaneously calibrate the arterial input function and myocardial enhancement curves acquired with different effective trigger delays through appropriate use of the theory-based signal calibration model. With this method, errors of in vivo baseline T1 estimates are large, but the effect of these large errors on the accuracy of contrast agent concentration estimates is limited. CONCLUSION: This theory-based signal calibration approach can be used to perform rapid T1 mapping and provides flexibility for in vivo calibration of signal-time curves resulting from dual-delay-time first-pass contrast-enhanced acquisitions
— id: 93980, year: 2006, vol: 13, page: 686, stat: Journal Article,

Using Gabor filter banks and temporal-spatial constraints to compute 3D myocardium strain
Chen, Ting; Axel, Leon
2006 ;1:4755-4758, Conference Proceedings (IEEE Engineering in Medicine & Biology Society)
In this paper, we describe a new approach for reconstructing 3D strains in the myocardium using tagged MR images. We first segment the myocardium using a 3D deformable model driven by image gradients and Gabor filter responses. Tags are automatically detected and tracked as deformable thin plates during systole and early diastole. To keep the tracking results more stable and consistent, we use a combination of gradient information, an intensity probabilistic model, the phase information, and a temporal-spatial smoothness constraint. Based on the tag deformation, we compute a dense displacement in the myocardium around both ventricles. The displacements in x-, y-, and z- directions are calculated separately and are combined to form the final displacement maps. We do not use the information outside the segmented surface of the myocardium to avoid displacement errors caused by noises, artifacts, and correlations between different regions in the myocardium. The strain in the myocardium during the heart cycle is derived from the displacement. This method accepts images of either a tag grid or separate horizontal and vertical tag lines as its input. Experimental results on phantom and real data demonstrate good performance of this method in calculating the myocardial strain
— id: 93975, year: 2006, vol: 1, page: 4755, stat: Journal Article,

Multislice, dual-imaging sequence for increasing the dynamic range of the contrast-enhanced blood signal and CNR of myocardial enhancement at 3T
Kim, Daniel; Axel, Leon
2006 Jan;23(1):81-86, Journal of magnetic resonance imaging
PURPOSE: To develop a multislice, first-pass perfusion imaging sequence for increasing the effective dynamic range of the contrast-enhanced blood signal and the contrast-to-noise ratio (CNR) of myocardial wall enhancement. MATERIALS AND METHODS: A hybrid echo-planar imaging (EPI) pulse sequence was modified to acquire data for both the arterial input function (AIF) and the myocardium, using two different saturation-recovery time delays (TDs) and spatial resolutions, after a single saturation pulse. Five healthy subjects were scanned at 3T in three short-axis levels of the heart per heartbeat during passage of a high-dose bolus of contrast agent. The T(1)-weighted signal-time curve of the blood was converted to AIF using empirical conversion tables derived from phantom experiments. RESULTS: In all subjects the calculated AIF was consistently less distorted and higher for the short-TD protocol than for the long-TD protocol (peak concentration: 5.0 +/- 1.0 mM vs. 3.0 +/- 0.6 mM; P < 0.01). A combination of EPI, long TD, high-dose bolus of contrast agent, and 3T imaging yielded relatively strong peak enhancement in the myocardium (CNR = 11.9 +/- 3.3). CONCLUSION: Our dual-imaging approach at 3T seems promising for acquiring both a relatively accurate AIF and a high CNR of myocardial wall enhancement in multiple slices per heartbeat
— id: 66761, year: 2006, vol: 23, page: 81, stat: Journal Article,

A segmentation and tracking system for 4D cardiac tagged MR images
Metaxas, Dimitris N; Axel, Leon; Qian, Zhen; Huang, Xiaolei
2006 ;1:1541-1544, Conference Proceedings (IEEE Engineering in Medicine & Biology Society)
In this paper we present a robust method for segmenting and tracking cardiac contours and tags in 4D cardiac MRI tagged images via spatio-temporal propagation. Our method is based on two main techniques: the Metamorphs segmentation for robust boundary estimation, and the tunable Gabor filter bank for tagging lines enhancement, removal and myocardium tracking. We have developed a prototype system based on the integration of these two techniques, and achieved efficient, robust segmentation and tracking with minimal human interaction
— id: 93976, year: 2006, vol: 1, page: 1541, stat: Journal Article,

Clinical application of a semiautomatic 3D fusion tool where automatic fusion techniques are difflicult to use
Noz, ME; Maguire, GQ; Zeleznik, MP; Olivecrona, L; Olivecrona, H; Axel, L; Srichai, MB; Moy, L; Murphy-Walcott, A
2006 ;4057:195-205, Lecture notes in computer science
The purpose of this paper is to demonstrate the clinical advantages of using semiautomatic volume registration where automatic registration is problematic due to large deformations, small bone anatomy, or extraneous structures. Examples are drawn from clinical cases of MRI/PET breast studies, CT angiography/SPECT cardiac studies, and total wrist arthroplasty. These types of studies should be contrasted with those involving the head, thorax, and pelvis where there is much less deformation and the existence of (some) large bones facilitates automatic matching
— id: 69353, year: 2006, vol: 4057, page: 195, stat: Journal Article,

Advances in MRI tagging techniques for determining regional myocardial strain
Pai, Vinay M; Axel, Leon
2006 Feb;8(1):53-58, Current cardiology reports
MRI of the heart with magnetization tagging provides a potentially useful new way to assess cardiac mechanical function, through revealing the local motion of otherwise indistinguishable portions of the heart wall. Although still an evolving area, tagged cardiac MRI is already able to provide novel quantitative information on cardiac function. Exploiting this potential requires developing tailored methods for both imaging and image analysis. In this article, we review some of the progress that has been made in developing imaging methods for tagged cardiac MRI
— id: 64784, year: 2006, vol: 8, page: 53, stat: Journal Article,

Boosting and nonparametric based tracking of tagged MRI cardiac boundaries
Qian, Zhen; Metaxas, Dimitris N; Axel, Leon
2006 ;9(Pt 1):636-644, Medical image computing & computer-assisted intervention : MICCAI
In this paper we present an accurate cardiac boundary tracking method for 2D tagged MRI time sequences. This method naturally integrates the motion and the static local appearance features and generates accurate boundary criteria via a boosting approach. We extend the conventional Adaboost classifier into a posterior probability form, which can be embedded in a particle filtering-based shape tracking framework. To make the tracking process more robust and faster, we use a PCA subspace shape representation to constrain the shape variation and lower the dimensionality. We also learn two shape-dynamic models for systole and diastole separately, to predict the shape evolution. Our tracking method incorporates the static appearance, the motion appearance, the shape constraints, and the dynamic prediction in a unified way. The proposed method has been implemented on 50 tagged MRI sequences. The experimental results show the accuracy and robustness of our approach
— id: 93979, year: 2006, vol: 9, page: 636, stat: Journal Article,

Extraction and tracking of MRI tagging sheets using a 3D Gabor filter bank
Qian, Zhen; Metaxas, Dimitris N; Axel, Leon
2006 ;1:711-714, Conference Proceedings (IEEE Engineering in Medicine & Biology Society)
In this paper, we present a novel method for automatically extracting the tagging sheets in tagged cardiac MR images, and tracking their displacement during the heart cycle, using a tunable 3D Gabor filter bank. Tagged MRI is a non-invasive technique for the study of myocardial deformation. We design the 3D Gabor filter bank based on the geometric characteristics of the tagging sheets. The tunable parameters of the Gabor filter bank are used to adapt to the myocardium deformation. The whole 3D image dataset is convolved with each Gabor filter in the filter bank, in the Fourier domain. Then we impose a set of deformable meshes onto the extracted tagging sheets and track them over time. Dynamic estimation of the filter parameters and the mesh internal smoothness are used to help the tracking. Some very encouraging results are shown
— id: 93977, year: 2006, vol: 1, page: 711, stat: Journal Article,

Comparison of left atrial volume and left atrial appendage contribution in patients with and without persistent atrial fibrillation
Srichai, MB; Jacobs, JE; Bernstein, N; Chinitz, L; Axel, L
2006 FEB 21 ;47(4):125A-125A, Journal of the American College of Cardiology
— id: 63302, year: 2006, vol: 47, page: 125A, stat: Journal Article,

Dense myocardium deformation estimation for 2D tagged MRI
Axel, L; Chen, T; Manglik, T
2005 AUG ;3504(8):446-456, Lecture notes in computer science
Magnetic resonance tagging technique measures the deformation of the heart wall by overlying darker tag lines onto the brighter myocardiurn and tracking their motion during the heart cycle. In this paper, we propose a new spline-based methodology for constructing a dense cardiac displacement map based on the tag tracking result. In this new approach, the deformed tags are tracked using a Gabor filter-based technique and smoothed using implicit splines. Then we measure the displacement in the myocardium of both ventricles using a new spline interpolation model. This model uses rough segmentation results to set up break points along tag tracking spline so that the local myocardium deformation will not be influenced by the tag information in the blood or the deformation in other parts of the myocardium. The displacements in x- and y- directions are calculated separately and are combined later to form the final displacement map. This method accepts either a tag grid or separate horizontal and vertical tag lines as its input by adjusting the offsets of images taken at different breath hold. The method can compute dense displacement maps of the myocardiurn for time phases during systole and diastole. The approach has been quantatively validated on phantom images and been tested on more than 20 sets of in-vivo heart data
— id: 98172, year: 2005, vol: 3504, page: 446, stat: Journal Article,

Tagged magnetic resonance imaging of the heart: a survey
Axel, Leon; Montillo, Albert; Kim, Daniel
2005 Aug;9(4):376-393, Medical image analysis
Magnetic resonance imaging (MRI) of the heart with magnetization tagging provides a potentially useful new way to assess cardiac mechanical function, through revealing the local motion of otherwise indistinguishable portions of the heart wall. While still an evolving area, tagged cardiac MRI is already able to provide novel quantitative information on cardiac function. Exploiting this potential requires developing tailored methods for both imaging and image analysis. In this paper, we review some of the progress that has been made in developing such methods for tagged cardiac MRI, as well as some of the ways these methods have been applied to the study of cardiac function
— id: 55960, year: 2005, vol: 9, page: 376, stat: Journal Article,

Three-dimensional systolic kinematics of the right ventricle
Haber, Idith; Metaxas, Dimitris N; Geva, Tal; Axel, Leon
2005 Nov;289(5):H1826-H1833, American journal of physiology. Heart & circulatory physiology
The right ventricle (RV) of the heart is responsible for pumping blood to the lungs. Its kinematics are not as well understood as that of the left ventricle (LV) due to its thin wall and asymmetric geometry. In this study, the combination of tagged MRI and three-dimensional (3-D) image-processing techniques was used to reconstruct 3-D RV-LV motion and deformation. The reconstructed models were used to quantify the 3-D global and local deformation of the ventricles in a set of normal subjects. When compared with the LV, the RV exhibited a similar twisting pattern, a more longitudinal strain pattern, and a greater amount of displacement
— id: 134943, year: 2005, vol: 289, page: H1826, stat: Journal Article,

Computational modeling and simulation of heart ventricular mechanics from tagged MRI
Hu, ZH; Metaxas, D; Axel, L
2005 AUG ;3504(8):369-383, Lecture notes in computer science
Heart ventricular mechanics has been investigated intensively in the last four decades. The passive material properties, the ventricular geometry and muscular architecture, and the myocardial activation are among the most important determinants of cardiac mechanics. The heart muscle is anisotropic, inhomogeneous, and highly nonlinear. The heart ventricular geometry is irregular and object dependent. The muscular architecture includes the organization of the fiber and the connective tissues. Studies of the myocardial activation have been carried out at both cell and tissue levels. Previous work from our research group has successfully estimated the in-vivo motion and deformation of both the left and the right ventricles. In this paper, we present an iterative model to estimate the in-vivo myocardium material properties, the active forces generated along fiber orientation, and strain and stress distribution in both ventricles. Compared to the strain energy function approach, our model is more intuitively understandable. Using the model, we have simulated the mechanical events of a few different heart diseases. Noticeable strain and stress differences are found between normal and diseased hearts
— id: 98171, year: 2005, vol: 3504, page: 369, stat: Journal Article,

B(0) and B(1)-insensitive uniform T(1)-weighting for quantitative, first-pass myocardial perfusion magnetic resonance imaging
Kim, Daniel; Cernicanu, Alexandru; Axel, Leon
2005 Dec;54(6):1423-1429, Magnetic resonance in medicine
Myocardial perfusion can be estimated, in principle, from first-pass MR images by converting the T(1)-weighted signal-time curves to contrast agent concentration-time curves. Typically, T(1) weighting is achieved by saturating the magnetization with a nonselective radiofrequency (RF) pulse prior to the imaging sequence. The accuracy of the perfusion estimate derived from the single-point T(1)-weighted signal depends on the initial residual longitudinal magnetization (RLM) produced by the saturation pulse. In this study we demonstrate that single-shot, echo-planar imaging can be used to show initial RLM resulting from incomplete saturation due to static magnetic field and RF field inhomogeneities in the heart at 1.5 T. Three saturation pulses, single, composite simple, and composite B(1)-insensitive rotation (BIR-4) were evaluated in phantom and cardiac experiments. The RLM image was calculated by normalizing the saturated image by a proton-density-weighted image. Mean RLM produced by the three saturation pulses was significantly different in noncontrast cardiac imaging (RLM(single) = 0.108 +/- 0.078; RLM(composite) = 0.051 +/- 0.052; RLM(BIR-4) = 0.011 +/- 0.009; P < 0.001; n = 20). Using a BIR-4 pulse to perform saturation of magnetization seems promising for improving the effectiveness and uniformity of T(1) weighting for first-pass perfusion imaging
— id: 66762, year: 2005, vol: 54, page: 1423, stat: Journal Article,

A learning framework for the automatic and accurate segmentation of cardiac tagged MRI images
Qian, Z; Metaxas, DN; Axel, L
2005 OCT-DEC ;3765(4):93-102, Lecture notes in computer science
In this paper we present a fully automatic and accurate segmentation framework for 2D tagged cardiac MR images. This scheme consists of three learning methods: a) an active shape model is implemented to model the heart shape variations, b) an Adaboost learning method is applied to learn confidence-rated boundary criterions from the local appearance features at each landmark point on the shape model, and c) an Adaboost detection technique is used to initialize the segmentation. The set of boundary statistics learned by Adaboost is the weighted combination of all the useful appearance features, and results in more reliable and accurate image forces compared to using only edge or region information. Our experimental results show that given similar imaging techniques, our method can achieve a highly accurate performance without any human interaction
— id: 98085, year: 2005, vol: 3765, page: 93, stat: Journal Article,

Magnetic resonance imaging in the management of pericardial disease
Srichai, Monvadi B; Axel, Leon
2005 Dec;7(6):449-457, Current treatment options in cardiovascular medicine
The pericardium, although seldom the primary cause of systemic illness, can be involved in almost every type of disease. Pericardial involvement may be subtle and escape detection unless specifically sought, or it can overshadow features of the underlying systemic disease. Suspected pericardial disease is usually initially evaluated with echocardiography. However, magnetic resonance imaging can offer additional valuable information. In addition to the excellent resolution and unlimited imaging planes available for visualization of the entire pericardial sac, the wide field of view allows for evaluation of involvement of adjacent cardiac structures. Dynamic functional imaging and tissue characterization with and without contrast can further characterize disease and provide information regarding concomitant myocardial disease and effects on cardiac motion. The treatment of specific pericardial conditions ultimately depends on the underlying disease process. Magnetic resonance imaging can provide useful information to aid in diagnosis, management, and guidance of therapy for pericardial disease
— id: 133569, year: 2005, vol: 7, page: 449, stat: Journal Article,

Saphenous vein graft aneurysm masquerading as a right atrial mass
Yatskar, Leonid; Rosenzweig, Barry P; Attubato, Michael; Axel, Leon; Tunick, Paul A; Kronzon, Itzhak
2005 Mar;22(3):263-265, Echocardiography
We report a case of a large saphenous vein graft (SVG) aneurysm masquerading as a right atrial mass on transesophageal echocardiogram. Cardiac magnetic resonance angiography reliably made a diagnosis of SVG aneurysm extrinsically compressing right atrium. This case illustrates the importance of using combined imaging modalities for the diagnosis and management of cardiac masses
— id: 55961, year: 2005, vol: 22, page: 263, stat: Journal Article,

Assessment of pericardial disease by magnetic resonance and computed tomography
Axel, Leon
2004 Jun;19(6):816-826, Journal of magnetic resonance imaging
Pericardial disease and its consequences can be well shown with magnetic resonance imaging (MRI) and computed tomography (CT). Here I review the normal and pathologic anatomy and physiology of the pericardium, approaches to MRI and CT imaging of the pericardium, and some specific considerations in common conditions affecting the pericardium
— id: 43745, year: 2004, vol: 19, page: 816, stat: Journal Article,

Cerebral perfusion CT techniques
Axel, Leon
2004 Dec;233(3):935-935, Radiology
— id: 138512, year: 2004, vol: 233, page: 935, stat: Journal Article,

Papillary muscles do not attach directly to the solid heart wall
Axel, Leon
2004 Jun 29;109(25):3145-3148, Circulation
BACKGROUND: The papillary muscles (PMs) play an important role in normal cardiac function, helping to prevent leakage through the AV valves during systole. The nature of their attachment to the heart wall can affect the understanding of their function. This attachment is conventionally portrayed as a direct connection of their bases to the solid portion of the heart wall. X-ray multidetector CT provides a new, noninvasive way to investigate this connection in vivo. METHODS AND RESULTS: With the use of x-ray multidetector CT with interactive 3D reconstruction, the bases of the PMs are seen to attach to the trabeculae carneae lining the ventricular wall rather than directly to the solid portion of the wall, as has been conventionally believed. This is true for both the left and right ventricular PMs. CONCLUSIONS: This new picture of the geometry of the attachment of the PMs to the heart wall may have important implications for the understanding of their function, including the nature of the transmission of the forces between the PMs and the heart wall
— id: 47775, year: 2004, vol: 109, page: 3145, stat: Journal Article,

Pulmonary micronodule detection from 3D chest CT
Chang, S; Emoto, H; Metaxas, DN; Axel, L
2004 OCT 14 ;3217(2):821-828, Lecture notes in computer science
Computed Tomography (CT) is one of the most sensitive medical imaging modalities for detecting pulmonary nodules. Its high contrast resolution allows the detection of small nodules and thus lung cancer at a very early stage. In this paper, we propose a method for automating nodule detection from high-resolution chest CT images. Our method focuses on the detection of discrete types of granulomatous nodules less than 5 mm in size using a series of 3D filters, Pulmonary nodules can be anywhere inside the lung, e.g., on lung walls near vessels, or they may even be penetrated by vessels,. For this reason,, we first develop a new cylinder filter to suppress vessels, and noise. Although nodules usually have higher intensity values than surrounding regions, many malignant nodules are of low contrast. In order not to ignore low contrast nodules, we develop a spherical filter to, further enhance nodule intensity values, which is a novel 3D extension of Variable N-Quoit filter. As with most automatic nodule detection methods, our method generates false positive nodules. To address this, we also develop a filter for false positive elimination. Finally, we present promising results of applying our method to various clinical chest CT datasets with over 90% detection rate
— id: 98195, year: 2004, vol: 3217, page: 821, stat: Journal Article,

3D cardiac anatomy reconstruction using high resolution CT data
Chen, T; Metaxas, D; Axel, L
2004 NOV ;3216(11):411-418, Lecture notes in computer science
Recent advances in CT technology have allowed the development of systems with multiple rows of detectors and rapid rotation. These new imaging systems have permitted the acquisition of high resolution, spatially registered, and cardiac gated 3D heart data. In this paper, we present a framework that makes use of these data to reconstruct the 3D cardiac anatomy with resolutions that were not previously possible. We use an improved 3D hybrid segmentation framework which integrates Gibbs prior models, deformable models, and the marching cubes method to achieve a sub-pixel accuracy of the reconstruction of cardiac objects. To improve the convergence at concavities on the object surface, we introduce a new type of external force, which we call the scalar gradient. The scalar gradient is derived from a gray level edge map using local configuration information and can help the deformable models converge into deep concavities on object's surface. The 3D segmentation and reconstruction have been conducted on 8 high quality CT data sets. Important features, such as the structure of papillary muscles, have been well captured, which may lead to a new understanding of the cardiac anatomy and function. All experimental results have been evaluated by clinical experts and the validation shows the method has a very strong performance
— id: 46469, year: 2004, vol: 3216, page: 411, stat: Journal Article,

Increasing the signal-to-noise ratio in DENSE MRI by combining displacement-encoded echoes
Kim, Daniel; Epstein, Frederick H; Gilson, Wesley D; Axel, Leon
2004 Jul;52(1):188-192, Magnetic resonance in medicine
A new technique was developed to increase the signal-to-noise ratio (SNR) in displacement encoding with stimulated echoes (DENSE) MRI. This signal-averaged DENSE (sav-DENSE) technique is based on the SNR advantage of extracting a pair of DENSE images with uncorrelated noise from the complex complementary spatial modulation of the magnetization image, and combining them during image reconstruction. Eleven healthy volunteers were imaged at three short-axis locations with the use of sav-DENSE, cine DENSE, and myocardial tagging pulse sequences. In this study, sav-DENSE increased the SNR by 15-34% as compared to cine DENSE. Circumferential strain values measured by sav-DENSE and myocardial tagging were strongly correlated (slope = 0.95, intercept = -0.02, R = 0.92) and within the 95% limits of agreement. The breath-hold sav-DENSE technique yielded relatively accurate and precise quantification of 2D intramyocardial function, with a 40.2-ms temporal resolution and a 3.5 x 3.5 mm2 spatial resolution
— id: 43743, year: 2004, vol: 52, page: 188, stat: Journal Article,

Gabor filter-based automated strain computation from tagged MR images
Manglik, T; Cernicanu, A; Pai, V; Kim, D; Chen, T; Dugal, P; Batchu, B; Axel, L
2004 OCT 14 ;3217(2):1064-1066, Lecture notes in computer science
Myocardial tagging is a non-invasive MR imaging technique; it generates a periodic tag pattern in the magnetization that deforms with the tissue during the cardiac cycle. It can be used to assess regional myocardial function, including tissue displacement and strain. Most image analysis methods require labor-intensive tag detection and tracking. We have developed an accurate and automated method for tag detection in order to calculate strain from tagged magnetic resonance images of the heart. It detects the local spatial frequency and phase of the tags using a bank of Gabor filters with varying frequency and phase. This variation in tag frequency is then used to calculate the local myocardial strain. The method is validated using computer simulations
— id: 98196, year: 2004, vol: 3217, page: 1064, stat: Journal Article,

Quantification of the curvature and shape of the interventricular septum
Moses, Daniel A; Axel, Leon
2004 Jul;52(1):154-163, Magnetic resonance in medicine
The interventricular septum (IVS) occupies a unique position within the heart, lying between the left (LV) and right (RV) ventricular cavities. Changes in its normal geometry may signify not only abnormalities of the septal myocardium, but also abnormal pressure differences between the LV and RV. Flattening of the IVS has been noted with cross-sectional imaging in association with pulmonary hypertension, but the septal curvature and shape have not previously been measured in three dimensions. This paper describes a method to model the RV surface of the IVS from spatially registered cross-sectional images for measurements of curvature. A smoothing 2D spline surface is constructed through the RV septal surface at regular times during the cardiac cycle, and the principal curvatures, as well as the Gaussian and mean curvatures, shape index, and curvedness, are calculated. Vector and color surface maps and graphs of average curvature and shape indices are constructed. Consistent curvature patterns were observed in four normal subjects. This method of measuring septal geometry can provide potentially useful new information on the effects of RV disease. We examine the problem of describing septal motion, and describe a simple measure of septal curvature that may be of clinical value
— id: 43744, year: 2004, vol: 52, page: 154, stat: Journal Article,

Tagged MRI-based studies of cardiac function
Axel, L
2003 SEP 3 ;2674(9):1-7, Lecture notes in computer science
Tagged MRI provides a potentially powerful new way to non-invasively assess the regional function of the heart. Although its potential has not yet been fully realized, due to remaining technical limitations in image acquisition and analysis, good progress is being made to overcome these limitations. Current research focuses on improving imaging methods to obtain high resolution 3D spatially registered tagged images, designing more efficient methods to extract the heart wall contours and tag positions within the wall from the tagged images, and implementing efficient ways to reconstruct the 3D motion of the heart from this data. In addition to the new regional motion and deformation data that tagged MRI can provide on normal and abnormal cardiac function, we can potentially use this motion data to model the corresponding forces within the heart wall
— id: 38509, year: 2003, vol: 2674, page: 1, stat: Journal Article,

MR Imaging of arrhythmogenic right ventricular cardiomyopathy: morphologic findings and interobserver reliability
Bluemke, David A; Krupinski, Elizabeth A; Ovitt, Theron; Gear, Kathleen; Unger, Evan; Axel, Leon; Boxt, Lawrence M; Casolo, Giancarlo; Ferrari, Victor A; Funaki, Brian; Globits, Sebastian; Higgins, Charles B; Julsrud, Paul; Lipton, Martin; Mawson, John; Nygren, Anders; Pennell, Dudley J; Stillman, Arthur; White, Richard D; Wichter, Thomas; Marcus, Frank
2003 ;99(3):153-162, Cardiology
BACKGROUND: Magnetic resonance (MR) imaging is frequently used to diagnose arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D). However, the reliability of various MR imaging features for diagnosing ARVC/D is unknown. The purpose of this study was to determine which morphologic MR imaging features have the greatest interobserver reliability for diagnosing ARVC/D. METHODS: Forty-five sets of films of cardiac MR images were sent to 8 radiologists and 5 cardiologists with experience in this field. There were 7 cases of definite ARVC/D as defined by the Task Force criteria. Six cases were controls. The remaining 32 cases had MR imaging because of clinical suspicion of ARVC/D. Readers evaluated the images for the presence of (a) right ventricle (RV) enlargement, (b) RV abnormal morphology, (c) left ventricle enlargement, (d) presence of high T(1) signal (fat) in the myocardium, and (e) location of high T(1) signal (fat) on a Likert scale with formatted responses. RESULTS: Readers indicated that the Task Force ARVC/D cases had significantly more (chi(2) = 119.93, d.f. = 10, p < 0.0001) RV chamber size enlargement (58%) than either the suspected ARVC/D (12%) or no ARVC/D (14%) cases. When readers reported the RV chamber size as enlarged they were significantly more likely to report the case as ARVC/D present (chi(2)(= )33.98, d.f. = 1, p < 0.0001). When readers reported the morphology as abnormal they were more likely to diagnose the case as ARVC/D present (chi(2) = 78.4, d.f. = 1, p < 0.0001), and the Task Force ARVC/D (47%) cases received significantly more abnormal reports than either suspected ARVC/D (20%) or non-ARVC/D (15%) cases. There was no significant difference between patient groups in the reported presence of high signal intensity (fat) in the RV (chi(2) = 0.9, d.f. = 2, p > 0.05). CONCLUSIONS: Reviewers found that the size and shape of abnormalities in the RV are key MR imaging discriminates of ARVD. Subsequent protocol development and multicenter trials need to address these parameters. Essential steps in improving accuracy and reducing variability include a standardized acquisition protocol and standardized analysis with dynamic cine review of regional RV function and quantification of RV and left ventricle volumes
— id: 43747, year: 2003, vol: 99, page: 153, stat: Journal Article,

Scan-conversion algorithm for ridge point detection on tubular objects
Chang, S; Metaxas, DN; Axel, L
2003 JAN ;2879(3):158-165, Lecture notes in computer science
Anatomical structures contain various types of curvilinear or tube-like structures such as blood vessels and bronchial trees. In medical imaging, the extraction and representation of such structures are of clinical importance. Complex curvilinear structures can be best represented by their center lines (or skeletons) along their elongated direction. In this paper, a gradient-based method for ridge point extraction on tubular objects is presented. Using the gradients of distance maps or intensity profiles usually generates skeleton surfaces for 3D objects, which is not desirable for representing tubular objects. To extract only the points on the centerline, we first employ the gradient vector flow (GVF) technique and then apply eigenanalysis of the Hessian matrix to remove false positive points. We present various results of the method using CLSM (Confocal Laser Scanning Microscopy) images of blood fibrins and CT images of a skull and lungs. Our method is efficient and allows for completely automatic extraction of points along the centerline of a tubular object in its elongated direction
— id: 98217, year: 2003, vol: 2879, page: 158, stat: Journal Article,

Left ventricle composite material model for stress-strain analysis
Hu, ZH; Metaxas, D; Axel, L
2003 MAR ;2673(5):218-229, Lecture notes in computer science
Mechanical properties of the myocardium. have been investigated intensively in the last four decades. Due to the nonlinearity and history dependence of the myocardial deformation, many complex strain energy functions have been used to describe the stress-strain relationship of myocardium. These functions are good at fitting in-vitro experimental data from myocardial stretch testing. However it is difficult to model in-vivo myocardium by using the strain energy functions. In a previous paper [24], we have implemented transversely anisotropic material model to estimate in-vivo strain-stress analysis in the myocardium. In this work, the fiber orientation is updated at each time step from the end of diastole to the end of systole, and the stiffness matrix is recalculated using the current fiber orientation. We also extended our model to include residual ventricular stresses and time dependent blood pressure in the left ventricle cavity
— id: 98231, year: 2003, vol: 2673, page: 218, stat: Journal Article,

In vivo strain and stress estimation of the heart left and right ventricles from MRI images
Hu, Zhenhua; Metaxas, Dimitris; Axel, Leon
2003 Dec;7(4):435-444, Medical image analysis
Mechanical properties of the myocardium have been investigated intensively in the last four decades. Many complex strain energy functions have been used to estimate the stress-strain relationship of myocardium because the heart muscle is an inhomogeneous, anisotropic, and nearly incompressible material, which undergoes large deformations. These functions can be effective for fitting in vitro experimental data from myocardial stretch testing. However, it is difficult to model in vivo myocardium using these strain energy functions. Moreover, such estimates have so far been carried out almost exclusively on the left ventricle, because of the relative thinness and complex geometry of the right ventricle. Previous work from our research group has successful estimated the motion and deformation of both the left and the right ventricles, using data from noninvasive tagged magnetic resonance imaging. In this paper, we present a novel statistical model to estimate the in vivo material properties and strain and stress distribution in both ventricles, using such data. Two normal hearts and two hearts with right-ventricular hypertrophy (RVH) were studied and noticeable differences were found between the strain and stress distributions for normal volunteers and RVH patients. Compared to the strain energy function approach, our model is more intuitively understandable
— id: 43746, year: 2003, vol: 7, page: 435, stat: Journal Article,

A finite element model for functional analysis of 4D cardiac-tagged MR images
Park, K; Metaxas, D; Axel, L
2003 JAN ;2878(1):491-498, Lecture notes in computer science
This paper proposes a new approach for functional analysis of cardiac images. A generic heart model is coupled with finite element methods to assess global and regional function from tagged magnetic resonance images. A model including both the left ventricle (LV) and right ventricle (RV) up to the basal area is needed for comprehensive understanding of cardiac physiology and anatomy. Most existing techniques can only handle the LV. Although some have attempted modeling the whole heart, these models have no geometric reference frame, so that it is difficult to compare different heart shapes and their motion. This paper uses a generic bi-ventricular heart model for functional analysis of heart motion. Three orthogonal tagging directions provide temporal correspondence of material points and enable tracking material points over time. The generic finite element model deforms due to forces exerted from material points by solving governing equations based on physical laws. The resulting model parameters can be used to characterize myocardial motion and deformation, including the basal area. We discuss the possibility of classifying parameters associated with normal and pathological hearts
— id: 42514, year: 2003, vol: 2878, page: 491, stat: Journal Article,

Biomechanical dynamics of the heart with MRI
Axel, Leon
2002 ;4(Pt 1):321-347, Annual review of biomedical engineering
Magnetic resonance imaging (MRI) provides a noninvasive way to evaluate the biomechanical dynamics of the heart. MRI can provide spatially registered tomographic images of the heart in different phases of the cardiac cycle, which can be used to assess global cardiac function and regional endocardial surface motion. In addition, MRI can provide detailed information on the patterns of motion within the heart wall, permitting calculation of the evolution of regional strain and related motion variables within the wall. These show consistent patterns of spatial and temporal variation in normal subjects, which are affected by alterations of function due to disease. Although still an evolving technique, MRI shows promise as a new method for research and clinical evaluation of cardiac dynamics
— id: 43749, year: 2002, vol: 4, page: 321, stat: Journal Article,

Fast imaging of phosphocreatine in the normal human myocardium using a three-dimensional RARE pulse sequence at 4 Tesla
Greenman, Robert L; Axel, Leon; Ferrari, Victor A; Lenkinski, Robert E
2002 Apr;15(4):467-472, Journal of magnetic resonance imaging
PURPOSE: To investigate the use of a three-dimensional rapid acquisition with relaxation enhancement (RARE) pulse sequence for direct acquisition of phosphocreatine (PCr) images of the human myocardium. MATERIALS AND METHODS: A short elliptical birdcage radiofrequency (RF) body coil was constructed to produce a uniform flip angle throughout the chest cavity. In vivo images using a spectrally-selective RARE sequence with a spatial resolution of 1.2 cm x 1.2 cm x 2.5 cm (4 cm(3)) were acquired in nine minutes and 40 seconds. RESULTS: Scans of phantoms demonstrated excellent spectral selectivity. The signal-to-noise ratio in the myocardium ranged from 12.6 in the anterior wall to 5.3 in the mid septum. CONCLUSION: This study demonstrates that PCr data can be acquired using a three-dimensional RARE sequence with greater spatial and temporal resolution than spectroscopic techniques
— id: 43750, year: 2002, vol: 15, page: 467, stat: Journal Article,

In-vivo strain and stress estimation of the left ventricle from MRI images
Hu, ZH; Metaxas, D; Axel, L
2002 DEC ;2488(17):706-713, Lecture notes in computer science
Little information is known about in-vivo heart strain and stress distribution. In this paper, we present a novel statistical model to estimate. the in-vivo material properties and strain and stress distribution in the left ventricle. The displacements of the heart wall are reconstructed in previous work of our group by using MRI-SPAMM tagging technique and deformable model. Based on the reconstructed displacements, we developed the statistical model to estimate strain and stress by using EM algorithm. Two normal hearts and two hearts with right-ventricular hypertrophy are studied. We find noticeable differences in the strain and stress estimated for normal and abnormal hearts
— id: 98215, year: 2002, vol: 2488, page: 706, stat: Journal Article,

LV-RV shape modeling based on a blended parameterized model
Park, K; Metaxas, DN; Axel, L
2002 NOV 14 ;2488(16):753-761, Lecture notes in computer science
Making a generic heart deformable model to be able to analyze normal and pathological hearts is important. Such a generic model gives more stability and accuracy for segmentation, analysis and classsification. Due to the conflicting demands of shape generality and shape compactness, such a generic heart model is difficult to define. In order to be useful, a generic heart model should be defined with a few number of parameters. In all the previous work on the modeling of the LV-RV shape the deformable model is built from the given datasets. Therefore such methods have limitations that the quality of shape estimation are dependent on the quality of the datasets. In this paper, we introduce a blended deformable model approach with parameter functions which is generic enough to deal with the different heart shapes. Using a method we are able to model the 3D shape of the heart which include the left ventricle(LV) and the right ventricle(RV). We also include the inflow and outflow tract of the RV basal area, so that the full LV-RV shape can be estimated
— id: 42466, year: 2002, vol: 2488, page: 753, stat: Journal Article,

Penile leiomyosarcoma: sonographic and magnetic resonance imaging findings
Dobos N; Nisenbaum HL; Axel L; Van Arsdalen K; Tomaszewski JE
2001 May;20(5):553-557, Journal of ultrasound in medicine
— id: 43752, year: 2001, vol: 20, page: 553, stat: Journal Article,

Ultrafast three-dimensional contrast-enhanced magnetic resonance angiography and imaging in the diagnosis of partial anomalous pulmonary venous drainage
Ferrari VA; Scott CH; Holland GA; Axel L; Sutton MS
2001 Mar 15;37(4):1120-1128, Journal of the American College of Cardiology
OBJECTIVES: The purpose of our study was to evaluate patients with suspected anomalous pulmonary veins (APVs) and atrial septal defects (ASDs) using fast cine magnetic resonance imaging (MRI) and ultrafast three-dimensional magnetic resonance angiography (MRA). BACKGROUND: Precise anatomic definition of anomalous pulmonary and systemic veins, and the atrial septum are prerequisites for surgical correction of ASDs. Cardiac catheterization and transesophageal echocardiography (TEE) are currently used to diagnose APVs, but did not provide complete information in our patients. METHODS: Twenty consecutive patients with suspected APVs were studied by MRA after inconclusive assessment by catheterization, TEE or both. The MRI images were acquired with a fast cine sequence and a novel ultrafast three-dimensional sequence before and after contrast injection. RESULTS: Partial anomalous pulmonary venous drainage was demonstrated in 16 of 20 patients and was excluded in four patients. Magnetic resonance imaging correctly diagnosed APVs and ASDs in all patients (100%) who underwent surgery. For the diagnosis of APVs, the MRI and catheterization results agreed in 74% of patients and the MRI and TEE agreed in 75% of patients. For ASDs, MRI agreed with catheterization and TEE in 53% and 83% of patients, respectively. CONCLUSIONS: Fast cine MRI with three-dimensional contrast-enhanced MRA provides rapid and comprehensive anatomic definition of APVs and ASDs in patients with adult congenital heart disease in a single examination
— id: 43753, year: 2001, vol: 37, page: 1120, stat: Journal Article,

Validation of in vivo myocardial strain measurement by magnetic resonance tagging with sonomicrometry
Yeon SB; Reichek N; Tallant BA; Lima JA; Calhoun LP; Clark NR; Hoffman EA; Ho KK; Axel L
2001 Aug;38(2):555-561, Journal of the American College of Cardiology
OBJECTIVES: This study was designed to validate strain measurements obtained using magnetic resonance tagging with spatial modulation of magnetization (SPAMM). We compared circumferential segment shortening measurements (%S) obtained using SPAMM to sonomicrometry %S in a canine model with (n = 28) and without (n = 3) coronary artery ligation. BACKGROUND: Magnetic resonance tagging enables noninvasive measurement of myocardial strain, but such strain measurements have not yet been validated in vivo. METHODS: Circumferential sonomicrometry crystal pairs were placed in apical myocardium at ischemic risk in ligation studies and in adjacent and remote myocardium. The %S was obtained from closely juxtaposed sonomicrometry and SPAMM sites. RESULTS: Paired data were available from 19 of 31 studies. Both methods distinguished remote from ischemic function effectively (p = 0.014 for SPAMM and p = 0.002 for sonomicrometry). SPAMM %S was similar to sonomicrometry %S in ischemic myocardium (2 +/- 3 vs. 0 +/- 3 p = 0.067) but was slightly higher than sonomicrometry %S in remote myocardium (11 +/- 10 vs. 7 +/- 5, p = 0.033). End-systolic (n = 30) and late systolic (n = 34) SPAMM %S correlated well with sonomicrometry %S (r = 0.84, p < 0.0001 and r = 0.88, p < 0.0001). CONCLUSIONS: Magnetic resonance tagging using SPAMM can quantitate myocardial strain in ischemic and remote myocardium. This study validates its application in scientific investigation and clinical assessment of patients with myocardial ischemia
— id: 43751, year: 2001, vol: 38, page: 555, stat: Journal Article,

Origin of a signal intensity loss artifact in fat-saturation MR imaging
Axel L; Kolman L; Charafeddine R; Hwang SN; Stolpen AH
2000 Dec;217(3):911-915, Radiology
Artifactual water signal intensity loss can be observed on fat-saturation magnetic resonance (MR) images of inhomogeneous regions such as the thorax. Magnetic effects of air inclusions on fat-saturation pulses were investigated as the possible origin of this artifact. Computer simulation results agreed well with observed production of water saturation by means of nominal fat suppression in MR imaging of phantoms and a representative clinical example
— id: 43755, year: 2000, vol: 217, page: 911, stat: Journal Article,

Focal hypertrophic cardiomyopathy simulating a mass: MR tagging for correct diagnosis
Bergey PD; Axel L
2000 Jan;174(1):242-244, American journal of roentgenology
— id: 43760, year: 2000, vol: 174, page: 242, stat: Journal Article,

Dynamic cardiomyoplasty decreases myocardial workload as assessed by tissue tagged MRI
Blom AS; Pilla JJ; Pusca SV; Patel HJ; Dougherty L; Yuan Q; Ferrari VA; Axel L; Acker MA
2000 Sep-Oct;46(5):556-562, ASAIO journal
The effects of dynamic cardiomyoplasty (CMP) on global and regional left ventricular (LV) function in end-stage heart failure still remain unclear. MRI with tissue-tagging is a novel tool for studying intramyocardial motion and mechanics. To date, no studies have attempted to use MRI to simultaneously study global and regional cardiac function in a model of CMP. In this study, we used MRI with tissue-tagging and a custom designed MR compatible muscle stimulating/pressure monitoring system to assess long axis regional strain and displacement variations, as well as changes in global LV function in a model of dynamic cardiomyoplasty. Three dogs underwent rapid ventricular pacing (RVP; 215 BPM) for 10 weeks; after 4 weeks of RVP, a left posterior CMP was performed. After 1 year of dynamic muscle stimulation, the dogs were imaged in a 1.5 T clinical MR scanner. Unstimulated and muscle stimulated tagged long axis images were acquired. Quantitative 2-D regional image analysis was performed by dividing the hearts into three regions: apical, septal, and lateral. Maximum and minimum principal strains (lambda, and lambda2) and displacement (D) were determined and pooled for each region. MR LV pressure-volume (PV) loops were also generated. Muscle stimulation produced a leftward shift of the PV loops in two of the three dogs, and an increase in the peak LV pressure, while stroke volume remained unchanged. With stimulation, lambda1 decreased significantly (p<0.05) in the lateral region, whereas lambda2 increased significantly (p<0.05) in both the lateral and apical regions, indicating a decrease in strain resulting from stimulation. D only increased significantly (p<0.05) in the apical region. The decrease in strain between unassisted and assisted states indicates the heart is performing less work, while maintaining stroke volume and increasing peak LV pressure. These findings demonstrate that the muscle wrap functions as an active assist, decreasing the workload of the heart, while preserving total pump performance
— id: 43757, year: 2000, vol: 46, page: 556, stat: Journal Article,

Three-dimensional motion reconstruction and analysis of the right ventricle using tagged MRI
Haber I; Metaxas DN; Axel L
2000 Dec;4(4):335-355, Medical image analysis
Right ventricular (RV) dysfunction can serve as an indicator of heart and lung disease and can adversely affect the left ventricle. However, normal RV function must be characterized before abnormal states can be detected. We describe a method for reconstructing the 3D motion of the RV by fitting a deformable model to tag and contour data extracted from multiview tagged magnetic resonance images. The deformable model is a biventricular finite element mesh built directly from segmented contours. Our approach accommodates the geometrically complex RV by using the entire lengths of the tags, localized degrees of freedom, and finite elements for geometric modeling. Also, we outline methods for converting the 3D motion reconstruction results into potentially useful motion variables, such as strains and displacements. The technique was applied to synthetic data, two normal hearts, and two hearts with right ventricular hypertrophy (RVH). Noticeable differences were found between the motion variables calculated for normal volunteers and RVH patients
— id: 43754, year: 2000, vol: 4, page: 335, stat: Journal Article,

Assessment of synchronized direct mechanical ventricular actuation in a canine model of left ventricular dysfunction
Pusca SV; Pilla JJ; Blom AS; Patel HJ; Yuan Q; Ferrari VA; Prood C; Axel L; Acker MA
2000 Nov-Dec;46(6):756-760, ASAIO journal
Direct mechanical ventricular actuation (DMVA) is an experimental procedure that provides biventricular cardiac assistance by intracorporeal pneumatic compression of the heart. The advantages this technique has over other assist devices are biventricular assistance, no direct blood contact, pulsatile blood flow, and rapid, less complicated application. Prior studies of nonsynchronized DMVA support have demonstrated that a subject can be maintained for up to 7 days. The purpose of this study was to determine the acute hemodynamic effects of cardiac synchronized, partial DMVA support in a canine model (RVP) of left ventricular (LV) dysfunction. The study consisted of rapidly pacing seven dogs for 4 weeks to create LV dysfunction. At the conclusion of the pacing period, the DMVA device was positioned around the heart by means of a median sternotomy. The animals were then imaged in a 1.5 T whole body high speed clinical MR system, with simultaneous LV pressure recording. Left ventricular pressure-volume (PV) loops of the nonassisted and DMVA assisted heart were generated and demonstrated that DMVA assist shifted the loops leftward. In addition, assist significantly improved pressure dependent LV systolic parameters (left ventricular peak pressure and dp/dt max, p < 0.05), with no diastolic impairment. This study demonstrates that DMVA can provide synchronized partial assist, resulting in a decrease in the workload of the native heart, thus having a potential application for heart failure patients
— id: 43756, year: 2000, vol: 46, page: 756, stat: Journal Article,

Suppression of intravascular signal on fat-saturated contrast-enhanced thoracic MR arteriograms
Siegelman ES; Charafeddine R; Stolpen AH; Axel L
2000 Oct;217(1):115-118, Radiology
PURPOSE: To assess the prevalence of artifactual signal intensity loss within the aortic arch and proximal branch vessels on fat-saturated contrast material-enhanced magnetic resonance (MR) arteriograms of the thoracic aorta and to hypothesize about the cause of the loss of signal intensity. MATERIALS AND METHODS: Between January and June 1998, 105 consecutive MR arteriograms of the thoracic aorta were acquired in 103 patients at 1.5 T. Imaging included an arterial phase three-dimensional (3D) fat-saturated contrast-enhanced gradient-echo (GRE) sequence followed by a delayed two-dimensional (2D) transverse fat-saturated GRE sequence. All MR images were reviewed by two radiologists who were blinded to patient history and results of imaging studies and who evaluated the images for the presence of intraluminal loss of signal intensity in the aortic arch and the proximal branch vessels. RESULTS: Intravascular loss of signal intensity was present in at least one vessel on 23 of the 105 arterial phase 3D studies. Seventy-one of 91 left subclavian arterial segments had loss of signal intensity on the delayed 2D studies. CONCLUSION: Intravascular signal intensity loss can be present on contrast-enhanced fat-saturated images of the aortic arch and proximal branch vessels, particularly the left subclavian artery. This phenomenon, which is to the authors' knowledge previously unreported and which is hypothesized to result from undesired water saturation, should not be misinterpreted as stenotic or occlusive vascular disease
— id: 43758, year: 2000, vol: 217, page: 115, stat: Journal Article,

Cardiac-respiratory gating method for magnetic resonance imaging of the heart
Yuan Q; Axel L; Hernandez EH; Dougherty L; Pilla JJ; Scott CH; Ferrari VA; Blom AS
2000 Feb;43(2):314-318, Magnetic resonance in medicine
In studies of transmural myocardial function, acquisitions of high spatial and temporal resolution tagged cardiac images often exceed the practical time limit for breath-hold fast imaging techniques. Therefore, a dual cardiac-respiratory gating device has been constructed to acquire SPAMM-tagged cardiac MR images at or near end-expiration during spontaneous breathing, by providing an external trigger to a conventional MRI system. Combined cardiac and respiratory gating essentially eliminates the respiratory motion artifacts in tagged cardiac MR images. Compared to cardiac-gated images obtained during intermittent breath-holds, cardiac-respiratory gated images show improved tag-myocardium contrast due to magnetization recovery during inspiration
— id: 43759, year: 2000, vol: 43, page: 314, stat: Journal Article,

Fat suppression in MR imaging
Axel L
1999 Sep-Oct;19(5):1177-1177, Radiographics
— id: 43762, year: 1999, vol: 19, page: 1177, stat: Journal Article,

Validation of an optical flow method for tag displacement estimation
Dougherty L; Asmuth JC; Blom AS; Axel L; Kumar R
1999 Apr;18(4):359-363, IEEE Transactions on medical imaging
We present a validation study of an optical-flow method for the rapid estimation of myocardial displacement in magnetic resonance tagged cardiac images. This registration and change visualization (RCV) software uses a hierarchical estimation technique to compute the flow field that describes the warping of an image of one cardiac phase into alignment with the next. This method overcomes the requirement of constant pixel intensity in standard optical-flow methods by preprocessing the input images to reduce any intensity bias which results from the reduction in stripe contrast throughout the cardiac cycle. To validate the method, SPAMM-tagged images were acquired of a silicon gel phantom with simulated rotational motion. The pixel displacement was estimated with the RCV method and the error in pixel tracking was <4% 1000 ms after application of the tags, and after 30 degrees of rotation. An additional study was performed using a SPAMM-tagged multiphase slice of a canine left ventricle. The true displacement was determined using a previously validated active contour model (snakes). The error between methods was 6.7% at end systole. The RCV method has the advantage of tracking all pixels in the image in a substantially shorter period than the snakes method
— id: 43763, year: 1999, vol: 18, page: 359, stat: Journal Article,

Renal artery stenosis: evaluation with conventional angiography versus gadolinium-enhanced MR angiography
Gilfeather M; Yoon HC; Siegelman ES; Axel L; Stolpen AH; Shlansky-Goldberg RD; Baum RA; Soulen MC; Schnall MD
1999 Feb;210(2):367-372, Radiology
PURPOSE: To evaluate the interobserver and intermodality variability of conventional angiography and gadolinium-enhanced magnetic resonance (MR) angiography in the assessment of renal artery stenosis. MATERIALS AND METHODS: Fifty-four patients underwent conventional angiography and gadolinium-enhanced three-dimensional gradient-echo MR angiography. Three angiographers blinded to each other's interpretations and the MR angiographic findings assessed the conventional angiograms for renal artery stenosis. Similarly, three blinded MR imagers evaluated the MR angiograms. RESULTS: Interobserver variability for the degree of renal artery stenosis in the 107 kidneys evaluated was not significantly different between the two modalities. The mean SD of the degree of stenosis was 6.9% at MR angiography versus 7.5% at conventional angiography (alpha < or = .05, P > .05). In 70 kidneys (65%), the average degree of stenosis reported by the readers for the two modalities differed by 10% or less. In 22 cases (21%), the degree of stenosis was overestimated with MR angiography by more than 10% relative to the results of conventional angiography. In 15 cases (14%), the degree of stenosis was underestimated with MR angiography by more than 10%. CONCLUSION: Gadolinium-enhanced MR angiography permits evaluation of renal artery stenosis with an interobserver variability comparable with that of conventional angiography
— id: 43765, year: 1999, vol: 210, page: 367, stat: Journal Article,

Extrinsic compression of the left main coronary artery by the pulmonary artery in patients with long-standing pulmonary hypertension
Kawut SM; Silvestry FE; Ferrari VA; DeNofrio D; Axel L; Loh E; Palevsky HI
1999 Mar 15;83(6):984-6, A10, American journal of cardiology
Left main coronary artery compression by the pulmonary artery may be seen in patients with pulmonary hypertension who are undergoing cardiac catheterization. Cardiac magnetic resonance imaging is useful in these patients to document extrinsic compression, which might otherwise be mistaken for intrinsic atherosclerotic disease
— id: 43766, year: 1999, vol: 83, page: 984, stat: Journal Article,

Cascaded MRI-SPAMM for LV motion analysis during a whole cardiac cycle
Park J; Metaxas DN; Axel L; Yuan Q; Blom AS
1999 Aug;55(2):117-126, International journal of medical informatics
We present a new paradigm which incorporates multiple sets of tagged MRI data (MRI-SPAMM) acquired in a cascaded fashion in order to estimate the full 3-D motion of the left ventricle (LV) during its entire cardiac cycle. Our technique is based on an extension of our volumetric physics-based deformable models, whose parameters are functions. Using these parameters, we can characterize the local shape variation of an object with a small number of intuitive parameters. By integrating a cascaded sequence of SPAMM data sets into our modeling technique, we have extended the capability of the MRI-SPAMM technique and have provided an accurate representation of the LV motion during the full cardiac cycle (from end-diastole to end-diastole) to better understand cardiac mechanics
— id: 43761, year: 1999, vol: 55, page: 117, stat: Journal Article,

Effect of dobutamine on regional left ventricular function measured by tagged magnetic resonance imaging in normal subjects
Scott CH; Sutton MS; Gusani N; Fayad Z; Kraitchman D; Keane MG; Axel L; Ferrari VA
1999 Feb 1;83(3):412-417, American journal of cardiology
The effect of inotropic stimulation on the pattern and magnitude of regional left ventricular contraction was studied using tagged magnetic resonance imaging to assess whether dobutamine exacerbates variation in regional contraction at rest. Dobutamine stress testing defines a normal response as a homogeneous increase in regional wall motion. In 8 normal subjects, 4 equally spaced left ventricular short-axis levels were imaged through systole using tagged magnetic resonance imaging. The baseline imaging sequence was repeated with 5-, 10-, 15-, and 20-microg/kg/min dobutamine infusion. Regional myocardial displacement, radial thickening, and circumferential shortening were measured. The left ventricle was analyzed by level (base to apex) and wall (septum, inferior, lateral, anterior). Dobutamine did not alter baseline regional functional heterogeneity. Dobutamine infusion resulted in a uniform increase in displacement, radial thickening, and circumferential shortening from baseline to 10-microg/kg/min infusion without additional increases at higher doses
— id: 43767, year: 1999, vol: 83, page: 412, stat: Journal Article,

Physics and technology of cardiovascular MR imaging
Axel L
1998 May;16(2):125-133, Cardiology clinics
MR imaging has made rapid progress and promises to be of great utility in the evaluation of the cardiovascular system. Some of the features that make it so promising are its safety (with appropriate guidelines); its ability to produce high-quality tomographic images in arbitrary orientations; and the possibility to obtain unique data, such as on regional myocardial function and metabolism. Ongoing technical developments in such areas as more rapid imaging and newer contrast agents should continue to increase the usefulness of cardiovascular MR imaging
— id: 43772, year: 1998, vol: 16, page: 125, stat: Journal Article,

Right ventricular regional function using MR tagging: normals versus chronic pulmonary hypertension
Fayad ZA; Ferrari VA; Kraitchman DL; Young AA; Palevsky HI; Bloomgarden DC; Axel L
1998 Jan;39(1):116-123, Magnetic resonance in medicine
Right ventricular (RV) regional function, in both normal and diseased states, is not well characterized. Using 1D MR myocardial tagging, RV and septal intramyocardial segmental shortening was noninvasively measured in ten healthy subjects and in seven patients with chronic pulmonary hypertension. The normal RV free wall regional shortening was not uniform. A pattern of increasing RV free wall short-axis shortening was found from the RV outflow tract to the RV apex, and a more complex pattern of RV free wall long-axis shortening was observed. Both regional short- and long-axis shortening were globally reduced in pulmonary hypertension patients, with the greatest decreases in the RV outflow tract and in the basal septal wall region. Regional RV function can be quantitatively evaluated using MR tagging to determine the impact of chronic pulmonary hypertension on RV performance
— id: 43774, year: 1998, vol: 39, page: 116, stat: Journal Article,

Images in Cardiovascular Medicine. Scimitar syndrome
Ferrari VA; Reilly MP; Axel L; Sutton MG
1998 Oct 13;98(15):1583-1584, Circulation
— id: 43770, year: 1998, vol: 98, page: 1583, stat: Journal Article,

Prostatic abscess due to Aspergillus fumigatus: TRUS and MR imaging findings
Fisher ME; Nisenbaum HL; Axel L; Broderick GA
1998 Mar;17(3):181-184, Journal of ultrasound in medicine
— id: 43773, year: 1998, vol: 17, page: 181, stat: Journal Article,

Integrated MRI assessment of regional function and perfusion in canine myocardial infarction
Kraitchman DL; Young AA; Bloomgarden DC; Fayad ZA; Dougherty L; Ferrari VA; Boston RC; Axel L
1998 Aug;40(2):311-326, Magnetic resonance in medicine
A single integrated examination using regional measurements of perfusion from contrast-enhanced MRI and three-dimensional (3D) strain from tissue-tagged MRI was developed to differentiate infarcted myocardium from adjacent tissue with functional abnormalities. Ten dogs were studied at baseline and 10 days after a 2-hour occlusion of the left anterior descending coronary artery (LAD). Strain was determined using a 3D finite element model. Two-dimensional measurements of hypoenhancing regions were highly correlated with myocardial viability (r = 0.96). Signal intensity versus time curves obtained from contrast-enhanced MRI were used for quantitative perfusion analysis. The remote and adjacent noninfarcted tissue of the dogs with LAD occlusion, as well as the infarcted tissue, exhibited abnormal deformation patterns as compared to normal dogs (positive predictive value (PPV) of strain determination of infarction = 66%). Integration of contrast-enhanced MRI results with 3D strain analysis enabled the delineation of the myocardial infarction (PPV = 100%) from functionally compromised myocardium. This integrated cardiac examination shows promise for noninvasive serial assessment of potentially jeopardized noninfarcted myocardium to study the process of infarct remodeling and expansion
— id: 43771, year: 1998, vol: 40, page: 311, stat: Journal Article,

Complete left ventricular wall motion estimation from cascaded MRI-SPAMM data
Park J; Metaxas DN; Axel L
1998 ;9 Pt 2(4):1063-1065, Medinfo
We present a new paradigm which incorporates multiple sets of tagged MRI data (MRI-SPAMM) acquired in a cascaded fashion in order to estimate the full 3-D motion of the left ventricle (LV) during its entire cardiac cycle. Our technique is based on the extension of the volumetric physics-based deformable models, whose parameters are functions, which can capture the local shape variation of an object with a small number of intuitive parameters. By integrating a cascaded sequence of SPAMM data sets into our modeling technique, we have extended the capability of MRI-SPAMM and have provided an accurate representation of the LV motion from end-diastole to end-diastole to better understand cardiac mechanics
— id: 43764, year: 1998, vol: 9 Pt 2, page: 1063, stat: Journal Article,

Determination of global function and regional mechanics of dynamic cardiomyoplasty using magnetic resonance imaging
Pusca SV; Pilla JJ; Blom AS; Patel HJ; Dougherty L; Yuan Q; Ferrari VA; Axel L; Acker MA
1998 Sep-Oct;44(5):M491-M495, ASAIO journal
This study used tissue tagged magnetic resonance (MR) to assess regional strain and generate pressure-volume (PV) loops in a canine model of cardiomyoplasty (CMP). Three dogs with rapid ventricular pacing induced heart failure underwent dynamic CMP chronic cardiac assistance for 1 year. At the end of the study period, we performed a MR study with the myostimulator 'on' and 'off' and recording of left ventricular (LV) pressure. We determined the short axis displacement (D) and maximal and minimal principal strains (lambda1 and lambda2) by quantitative two-dimensional regional spatial modulation of magnetization visualization utility image analysis. LV PV loops were generated by combining the LV volume data from the MR images with the LV pressure recorded during imaging. Muscle stimulation produced a leftward shift of the LV PV loops in two of the three dogs, and an increase in LV peak pressure and dp/dt max. In contrast, short axis lambda1 and lambda2 did not change significantly (p = NS). D increased significantly in the anterolateral, posterolateral, and posteroseptal regions (p < 0.05) but did not change for the septal region (p = NS). Flap stimulation augments LV function in the absence of short axis strain change; this suggests that dynamic CMP exerts its main action along the long axis of the heart
— id: 43769, year: 1998, vol: 44, page: M491, stat: Journal Article,

Elimination of Nyquist ghosts in MRI by using fast linogram imaging
Gai N; Axel L
1997 Nov-Dec;7(6):1166-1169, Journal of magnetic resonance imaging
Timing inaccuracies between the even and odd echoes lead to the formation of Nyquist ghosts in conventional (blipped) echo-planar imaging (EPI). A fast radial scanning method based on the linogram sampling geometry was designed and implemented. No ghosting effects are seen with this scheme, and correction for timing inaccuracies is performed using simple postprocessing steps before reconstruction
— id: 43776, year: 1997, vol: 7, page: 1166, stat: Journal Article,

Analysis of left ventricular wall motion based on volumetric deformable models and MRI-SPAMM
Park J; Metaxas D; Axel L
1996 Mar;1(1):53-71, Medical image analysis
We present a new approach for the analysis of the left ventricular shape and motion based on the development of a new class of volumetric deformable models. We estimate the deformation and complex motion of the left ventricle (LV) in terms of a few parameters that are functions and whose values vary locally across the LV. These parameters capture the radial and longitudinal contraction, the axial twisting, and the long-axis deformation. Using Lagrangian dynamics and finite-element theory, we convert these volumetric primitives into dynamic models that deform due to forces exerted by the datapoints. We present experiments where we used magnetic tagging (MRI-SPAMM) to acquire datapoints from the LV during systole. By applying our method to MRI-SPAMM datapoints, we were able to characterize the 3-D shape and motion of the LV both locally and globally, in a clinically useful way. In addition, based on the model parameters we were able to extract quantitative differences between normal and abnormal hearts and visualize them in a way that is useful to physicians
— id: 43768, year: 1996, vol: 1, page: 53, stat: Journal Article,

Imaging of the heart
Axel L
1995 Sep;2 Suppl 2(1):S150-S151, Academic radiology
— id: 43775, year: 1995, vol: 2 Suppl 2, page: S150, stat: Journal Article,

[Quantitative analysis of heart motions using MRI tagging]
Imai H; Masuda Y; Axel L
1994 Jul;52 Suppl(Pt 1):505-511, Nippon rinsho. Japanese journal of clinical medicine
— id: 43748, year: 1994, vol: 52 Suppl, page: 505, stat: Journal Article,

Glossary of MR terms
Axel, Leon
Reston VA : American College of Radiology, 1991,
— id: 2068, year: 1991, vol: , page: , stat: ,

Orbital lesions: proton spectroscopic phase-dependent contrast MR imaging
Atlas SW; Grossman RI; Axel L; Hackney DB; Bilaniuk LT; Goldberg HI; Zimmerman RA
1987 Aug;164(2):510-514, Radiology
Thirteen orbital lesions in 12 patients were evaluated with both conventional spin-echo magnetic resonance (MR) imaging and phase-dependent proton spectroscopic imaging. This technique, which makes use of small differences in the resonant frequencies of water and fat protons, provides excellent high-resolution images with simultaneous chemical shift information. In this method, there is 180 degrees opposition of phase between fat protons and water protons at the time of the gradient echo, resulting in signal cancellation in voxels containing equal signals from fat and water. In this preliminary series, advantages of spectroscopic images in orbital lesions included better lesion delineation, with superior anatomic definition of orbital apex involvement; more specific characterization of high-intensity hemorrhage with a single pulse sequence; elimination of potential confusion from chemical shift misregistration artifact; further clarification of possible intravascular flow abnormalities; and improved apparent intralesional contrast
— id: 44097, year: 1987, vol: 164, page: 510, stat: Journal Article,

Glossary of NMR terms
Axel, Leon
Chicago IL : American College of Radiology, 1983,
— id: 2067, year: 1983, vol: , page: , stat: ,