Eric E. Sigmund, Ph.D.

Comparison of biexponential and monoexponential model of diffusion weighted imaging in evaluation of renal lesions: preliminary experience
Chandarana, Hersh; Lee, Vivian S; Hecht, Elizabeth; Taouli, Bachir; Sigmund, Eric E
2011 May;46(5):285-291, Investigative radiology
OBJECTIVES: : To obtain intravoxel incoherent motion (IVIM) parameters with biexponential analysis of multiple b-value diffusion-weighted imaging (DWI) and compare these parameters to apparent diffusion coefficient (ADC) obtained with monoexponential modeling in their ability to discriminate enhancing from nonenhancing renal lesions. MATERIALS AND METHODS: : Twenty-eight patients were imaged at 1.5 T utilizing contrast-enhanced (CE) magnetic resonance imaging (MRI) and breath-hold DWI using 8 b values (range: 0-800 s/mm). Perfusion fraction (fp), tissue diffusivity (Dt), and pseudo-diffusion coefficient (Dp) were calculated using segmented biexponential analysis. ADCtotal and ADC0-400-800 were calculated with monoexponential fitting of the DWI data. fp, Dt, Dp, ADCtotal, and ADC0-400-800 were compared between enhancing and nonenhancing renal lesions. Receiver operating characteristic analysis was performed for all DWI parameters. fp was correlated with percent enhancement. RESULTS: : There were a total of 31 renal lesions (15 enhancing and 16 nonenhancing) in 28 patients on CE-MRI. fp of enhancing masses was significantly higher (27.9 vs. 6.1) and Dt was significantly lower (1.47 vs. 2.40 x10 mm/s). IVIM parameters fp and Dt demonstrated higher accuracy in differentiating enhancing from nonenhancing renal lesions compared with monoexponential parameters ADC0-400-800 and ADCtotal, with area under the curve of 0.946, 0.896, 0.854, and 0.675, respectively. There was a good correlation between fp and percent enhancement (r = 0.7; P < 0.001). CONCLUSION: : IVIM parameters fp and Dt obtained with biexponential fitting of multi-b value DWI have higher accuracy compared with ADC (obtained with monoexponential fit) in discriminating enhancing from nonenhancing renal lesions. Furthermore, fp demonstrates good correlation with percent enhancement and can provide information regarding lesion vascularity without the use of exogenous contrast agent
— id: 130291, year: 2011, vol: 46, page: 285, stat: Journal Article,

A versatile flow phantom for intravoxel incoherent motion MRI
Cho GY; Kim S; Jensen JH; Storey P; Sodickson DK; Sigmund EE
2011 Nov 23;:?-?, Magnetic resonance in medicine
Although there have been many advancements in cancer research, much is still unknown about the heterogeneous tumor microenvironment. Diffusion-weighted MRI has proven to be a viable and versatile microstructural probe. Diffusion-weighted sequences specifically sensitive to intravoxel incoherent motion (IVIM) have seen a recent resurgence of interest as they promise to provide a valuable window on the vascular microenvironment. To understand, test, and optimize IVIM-sensitive approaches, a complex flow phantom was constructed to mimic certain characteristics of the tumor microenvironment such as tortuous microvasculature, heterogeneous vascular permeability, and interstitial fluid pressure buildup. Results using this phantom on a clinical scanner platform confirmed IVIM sensitivity to microscopic flow effects. Biexponential fitting of signal decay curves enabled quantitative extraction of perfusion fraction, IVIM-related pseudodiffusivity, and tissue diffusivity. Parametric maps were also generated, illustrating the potential utility of IVIM-sensitive imaging in clinical settings. The flow phantom proved to be an effective test-bed for validating and optimizing the IVIM-MRI technique to provide surrogate markers for microvascular properties. Magn Reson Med, 2011. (c) 2011 Wiley Periodicals, Inc
— id: 149836, year: 2011, vol: , page: ?, stat: Journal Article,

Magnetic resonance imaging of mixed ground glass nodules
Koo C.W.; Chen Q.C.; Sigmund E.E.; Mcgorty K.; Mason D.M.; Naidich D.P.
2011 ;26(3):W111-W111, Journal of thoracic imaging
Purpose: To evaluate mixed ground glass nodules (GGNs) utilizing 3 Tesla (T) MRI and 32-channel torso-array-coil and to correlate non-echo planar diffusion weighted imaging (DWI) and T2^* measurements with pathologic findings. Materials and Methods: Twelve patients with 13 GGNs >1cm in diameter detected on computed tomography were prospectively recruited for this Institutional Review Board approved study. T1-weighted 2D gradient echo (GRE), T2-weighted 2D turbo spin echo with fat saturation, T2^*-weighted multiple GRE, and diffusion weighted single shot twice-refocused spin echo axial images of the GGNs were acquired at end inspiration without intravenous contrast. Apparent diffusion coefficient (ADC) and T2^* values were determined and correlated to pathology. Results: All GGNs were visualized with the T2-weighted 2D TSE sequence providing the best morphologic delineation. Pathology was available for 9 of 13 lesions. ADC ranged from 1.19 to 1.78 mum²/ms (mean 1.45+/-0.19) and T2^* ranged from 6.78 to 27.81 mum²/ms (median 16.13, mean 16.68+/- 7.19) for the 7 malignant lesions. ADC was 1.59 and 1.42 and T2^* was 6.78 and 20.24 for the 2 malignant lesions with positive epidermal growth factor receptors. ADC ranged from 0.9 to 1.47 mum²/ms (mean 1.18 +/-0.4) and T2^* ranged from 6.87 to 10.93 (mean 8.9 +/-2.87) for the 2 benign lesions. Conclusion: 3T MRI with a 32-channel torso-array-coil provides a radiation free means of GGN evaluation. The T2-weighted 2D TSE with fat saturation sequence yields the best lesion visibility. DWI and T2^* measurements may provide quantitative measures for distinguishing malignant from benign nodules
— id: 136977, year: 2011, vol: 26, page: W111, stat: Journal Article,

Intravoxel incoherent motion imaging of tumor microenvironment in locally advanced breast cancer
Sigmund, E E; Cho, G Y; Kim, S; Finn, M; Moccaldi, M; Jensen, J H; Sodickson, D K; Goldberg, J D; Formenti, S; Moy, L
2011 May;65(5):1437-1447, Magnetic resonance in medicine
Diffusion-weighted imaging plays important roles in cancer diagnosis, monitoring, and treatment. Although most applications measure restricted diffusion by tumor cellularity, diffusion-weighted imaging is also sensitive to vascularity through the intravoxel incoherent motion effect. Hypervascularity can confound apparent diffusion coefficient measurements in breast cancer. We acquired multiple b-value diffusion-weighted imaging at 3 T in a cohort of breast cancer patients and performed biexponential intravoxel incoherent motion analysis to extract tissue diffusivity (D(t) ), perfusion fraction (f(p) ), and pseudodiffusivity (D(p) ). Results indicated significant differences between normal fibroglandular tissue and malignant lesions in apparent diffusion coefficient mean (+/-standard deviation) values (2.44 +/- 0.30 vs. 1.34 +/- 0.39 mum(2) /msec, P < 0.01) and D(t) (2.36 +/- 0.38 vs. 1.15 +/- 0.35 mum(2) /msec, P < 0.01). Lesion diffusion-weighted imaging signals demonstrated biexponential character in comparison to monoexponential normal tissue. There is some differentiation of lesion subtypes (invasive ductal carcinoma vs. other malignant lesions) with f(p) (10.5 +/- 5.0% vs. 6.9 +/- 2.9%, P = 0.06), but less so with D(t) (1.14 +/- 0.32 mum(2) /msec vs. 1.18 +/- 0.52 mum(2) /msec, P = 0.88) and D(p) (14.9 +/- 11.4 mum(2) /msec vs. 16.1 +/- 5.7 mum(2) /msec, P = 0.75). Comparison of intravoxel incoherent motion biomarkers with contrast enhancement suggests moderate correlations. These results suggest the potential of intravoxel incoherent motion vascular and cellular biomarkers for initial grading, progression monitoring, or treatment assessment of breast tumors. Magn Reson Med, 2011. (c) 2011 Wiley-Liss, Inc
— id: 131795, year: 2011, vol: 65, page: 1437, stat: Journal Article,

Diffusion-weighted imaging of the brain at 7 T with echo-planar and turbo spin echo sequences: preliminary results
Sigmund, Eric E; Gutman, David
2011 Jul;29(6):752-765, Magnetic resonance imaging
Ultra-high-field clinical MRI scanners (e.g., 7 T and above) are becoming increasingly prevalent and can potentially enhance diagnostic ability through higher contrast, resolution and/or sensitivity. Diffusion-weighted MRI is a highly valued component in today's radiological exam and may benefit from the enhanced signal-to-noise ratio provided by high field with the appropriate imaging strategy. The most common diffusion pulse sequence readout (echo-planar imaging (EPI)) has been widely employed for in vivo human 7 T diffusion tensor imaging (DTI). In this article, we present results of brain DTI at 7 T with two diffusion-weighted imaging pulse sequence readouts: echo-planar imaging (EPI-DTI) and turbo spin echo (TSE-DTI). Results indicate that analogous coverage, quality and resolution typical of lower field (2 mm) can be obtained by properly processed EPI-DTI at 7 T, and, with some reduction in efficiency and sharpness, TSE-DTI at 7 T. Furthermore, 7 T TSE-DTI shows promise in obtaining higher-resolution results in targeted acquisitions of specific brain areas
— id: 135530, year: 2011, vol: 29, page: 752, stat: Journal Article,

Optimization of b-value sampling for diffusion-weighted imaging of the kidney
Zhang JL; Sigmund EE; Rusinek H; Chandarana H; Storey P; Chen Q; Lee VS
2011 Jan;67(1):89-97 L, Magnetic resonance in medicine
Diffusion-weighted imaging (DWI) involves data acquisitions at multiple b values. In this paper, we presented a method of selecting the b values that maximize estimation precision of the biexponential analysis of renal DWI data. We developed an error propagation factor for the biexponential model, and proposed to optimize the b-value samplings by minimizing the error propagation factor. A prospective study of four healthy human subjects (eight kidneys) was done to verify the feasibility of the proposed protocol and to assess the validity of predicted precision for DWI measures, followed by Monte Carlo simulations of DWI signals based on acquired data from renal lesions of 16 subjects. In healthy subjects, the proposed methods improved precision (P = 0.003) and accuracy (P < 0.001) significantly in region-of-interest based biexponential analysis. In Monte Carlo simulation of renal lesions, the b-sampling optimization lowered estimation error by at least 20-30% compared with uniformly distributed b values, and improved the differentiation between malignant and benign lesions significantly. In conclusion, the proposed method has the potential of maximizing the precision and accuracy of the biexponential analysis of renal DWI. Magn Reson Med, 2011. (c) 2011 Wiley-Liss, Inc
— id: 135366, year: 2011, vol: 67, page: 89, stat: Journal Article,

[Functional MRI of the kidney]
Mannelli, Lorenzo; Valentino, Massimo; Laffi, Giacomo; Lomas, David J; Sigmund, Eric E; Raz, Eytan; Chandarana, Hersh
2010 Nov-Dec;27(6):599-608, Giornale italiano di nefrologia
Functional MRI is a new and exciting tool enabling non-invasive assessment of renal function. Diffusion-weighted imaging (DWI), diffusion tensor imaging (DTI), blood oxygen level-dependent (BOLD) MRI, and magnetic resonance elastography (MRE) are some of the techniques under investigation. In this article we review the basic principles of these techniques, their possible applications, and their limitations
— id: 119231, year: 2010, vol: 27, page: 599, stat: Journal Article,

Diagnosis of cirrhosis with intravoxel incoherent motion diffusion MRI and dynamic contrast-enhanced MRI alone and in combination: Preliminary experience
Patel, Jignesh; Sigmund, Eric E; Rusinek, Henry; Oei, Marcel; Babb, James S; Taouli, Bachir
2010 Mar;31(3):589-600, Journal of magnetic resonance imaging
PURPOSE:: To report our preliminary experience with the use of intravoxel incoherent motion (IVIM) diffusion-weighted magnetic resonance imaging (DW-MRI) and dynamic contrast-enhanced (DCE)-MRI alone and in combination for the diagnosis of liver cirrhosis. MATERIALS AND METHODS:: Thirty subjects (16 with noncirrhotic liver, 14 with cirrhosis) were prospectively assessed with IVIM DW-MRI (n = 27) and DCE-MRI (n = 20). IVIM parameters included perfusion fraction (PF), pseudodiffusion coefficient (D*), true diffusion coefficient (D), and apparent diffusion coefficient (ADC). Model-free DCE-MR parameters included time to peak (TTP), upslope, and initial area under the curve at 60 seconds (IAUC60). A dual input single compartmental perfusion model yielded arterial flow (Fa), portal venous flow (Fp), arterial fraction (ART), mean transit time (MTT), and distribution volume (DV). The diagnostic performances for diagnosis of cirrhosis were evaluated for each modality alone and in combination using logistic regression and receiver operating characteristic analyses. IVIM and DCE-MR parameters were compared using a generalized estimating equations model. RESULTS:: PF, D*, D, and ADC values were significantly lower in cirrhosis (P = 0.0056-0.0377), whereas TTP, DV, and MTT were significantly increased in cirrhosis (P = 0.0006-0.0154). There was no correlation between IVIM- and DCE-MRI parameters. The highest Az (areas under the curves) values were observed for ADC (0.808) and TTP-DV (0.952 for each). The combination of ADC with DV and TTP provided 84.6% sensitivity and 100% specificity for diagnosis of cirrhosis. CONCLUSION:: The combination of DW-MRI and DCE-MRI provides an accurate diagnosis of cirrhosis. J. Magn. Reson. Imaging 2010;31:589-600. (c) 2010 Wiley-Liss, Inc
— id: 107780, year: 2010, vol: 31, page: 589, stat: Journal Article,

Variability of renal apparent diffusion coefficients: limitations of the monoexponential model for diffusion quantification
Zhang, Jeff L; Sigmund, Eric E; Chandarana, Hersh; Rusinek, Henry; Chen, Qun; Vivier, Pierre-Hugues; Taouli, Bachir; Lee, Vivian S
2010 Mar;254(3):783-792, Radiology
Purpose: To investigate whether variability in reported renal apparent diffusion coefficient (ADC) values in literature can be explained by the use of different diffusion weightings (b values) and the use of a monoexponential model to calculate ADC. Materials and Methods: This prospective study was approved by institutional review board and was HIPAA-compliant, and all subjects gave written informed consent. Diffusion-weighted (DW) imaging of the kidneys was performed in three healthy volunteers to generate reference diffusion decay curves. In a literature meta-analysis, the authors resampled the reference curves at the various b values used in 19 published studies of normal kidneys (reported ADC = [2.0-4.1] x 10(-3) mm(2) / sec for cortex and [1.9-5.1] x 10(-3) mm(2) / sec for medulla) and then fitted the resampled signals by monoexponential model to produce 'predicted' ADC. Correlation plots were used to compare the predicted ADC values with the published values obtained with the same b values. Results: Significant correlation was found between the reported and predicted ADC values for whole renal parenchyma (R(2) = 0.50, P = .002), cortex (R(2) = 0.87, P = .0002), and medulla (R(2) = 0.61, P = .0129), indicating that most of the variability in reported ADC values arises from limitations of a monoexponential model and use of different b values. Conclusion: The use of a monoexponential function for DW imaging analysis and variably sampled diffusion weighting plays a substantial role in causing the variability in ADC of healthy kidneys. For maximum reliability in renal apparent diffusion coefficient quantification, data for monoexponential analysis should be acquired at a fixed set of b values or a biexponential model should be used. (c) RSNA, 2010
— id: 111628, year: 2010, vol: 254, page: 783, stat: Journal Article,

T1 hyperintense renal lesions: characterization with diffusion-weighted mr imaging versus contrast-enhanced MR imaging
Kim, Sooah; Jain, Monica; Harris, Andrew B; Lee, Vivian S; Babb, James S; Sigmund, Eric E; Rueff, Laura E; Taouli, Bachir
2009 Jun;251(3):796-807, Radiology
PURPOSE: To compare the performance of apparent diffusion coefficient (ADC) measurement obtained with diffusion-weighted (DW) magnetic resonance (MR) imaging in the characterization of non-fat-containing T1 hyperintense renal lesions with that of contrast material-enhanced MR imaging, with histopathologic analysis and follow-up imaging as the reference standards. MATERIALS AND METHODS: Institutional review board approval was obtained for this HIPAA-compliant retrospective study, and the informed consent requirement was waived. Two independent observers retrospectively assessed MR images obtained in 41 patients with non-fat-containing T1 hyperintense renal lesions. The MR examination included acquisition of DW and contrast-enhanced T1-weighted images. For each index lesion, the observers assessed the (a) mean (+/- standard deviation) of ADC, (b) enhancement ratio, and (c) subtracted images for the presence of enhancement (confidence score, 1-5). Histopathologic analysis of renal cell carcinomas (RCCs) and follow-up imaging for benign lesions were the reference standards. ADCs of benign lesions and RCCs were compared. Receiver operating characteristic (ROC) curve analysis was performed to assess the accuracy of DW imaging, enhancement ratio, and subtraction for the diagnosis of RCC. Results: A total of 64 lesions (mean diameter, 3.9 cm), including 38 benign T1 hyperintense cysts and 26 RCCs, were assessed. Mean ADCs of RCCs were significantly lower than those of benign cysts ([1.75 +/- 0.57] x 10(-3) mm(2)/sec vs [2.50 +/- 0.53] x 10(-3) mm(2)/sec, P < .0001). ADCs of solid and cystic portions of complex cystic RCCs were significantly different ([1.37 +/- 0.55] x 10(-3) mm(2)/sec vs [2.45 +/- 0.63] x 10(-3) mm(2)/sec, P < .0001). When data from both observers were pooled, area under the ROC curve, sensitivity, and specificity were 0.846, 71%, and 91%, respectively, for DW imaging; 0.865, 65%, and 96%, respectively, for enhancement ratio (at the excretory phase); and 0.861, 83%, and 89%, respectively, for subtraction (P = .48 and P = .85, respectively). The combination of DW imaging and subtraction resulted in area under the ROC curve, sensitivity, and specificity of 0.893, 87%, and 92%, respectively, with significantly improved reader confidence compared with subtraction alone (P = .041). CONCLUSION: The performance of DW imaging was equivalent to that of enhancement ratio in the characterization of T1 hyperintense renal lesions, with both methods having lower sensitivity than image subtraction without reaching significance
— id: 99211, year: 2009, vol: 251, page: 796, stat: Journal Article,

High-resolution MRI of internal field diffusion-weighting in trabecular bone
Sigmund, E E; Cho, H; Song, Y-Q
2009 May;22(4):436-448, NMR in biomedicine
Trabecular bone structure is known to play a crucial role in the overall strength, and thus fracture risk, of such areas of the skeleton as the vertebrae, spine, femur, tibiae, or radius. Several MR methods devoted to probing this structure depend upon the susceptibility difference between the solid bone matrix and the intervening fluid/marrow/fat, usually in the context of a linewidth (1/T(2)') measurement or mapping technique. A recently demonstrated new approach to this system involves using internal gradients to encode diffusion weighting, and extracting structural information (e.g., surface-to-volume ratio) from the resulting signal decay. This contrast method has been demonstrated in bulk measurements on cleaned, water-saturated bovine trabecular bone samples. In the present work, microscopic imaging (0.156 mm in-plane resolution) is performed in order to spatially resolve this contrast on the trabecular level, and confirm its interpretation for the bulk measurements. It is found that the local rate of decay due to diffusion in the internal field (DDIF) is maximal close to the trabecular surfaces. The overall decay rate in a lower resolution scan probes the abundance of these surfaces, and provides contrast beyond that found in conventional proton density weighted or T(1)-weighted imaging. Furthermore, a microscopic calculation of internal field distributions shows a qualitative distinction between the structural sensitivities of DDIF and T(2)'. DDIF contrast is highly localized around trabecular walls than is the internal field itself, making it a less sensitive but more specific measure of such important properties as trabecular number
— id: 111667, year: 2009, vol: 22, page: 436, stat: Journal Article,

Diffusion-weighted MR imaging of the kidneys and the urinary tract
Kim, Sooah; Naik, Mohit; Sigmund, Eric; Taouli, Bachir
2008 Nov;16(4):585-96, vii, Magnetic resonance imaging clinics of North America
There is currently a growing interest in applications of diffusion-weighted imaging (DWI) in the abdomen and pelvis. DWI provides original functional information where the signal and contrast are determined by the microscopic mobility of water. DWI can provide additional information over conventional MR sequences, and could potentially be used as an alternative to contrast-enhanced sequences in patients with chronic renal insufficiency at risk of nephrogenic systemic fibrosis. We provide an overview on basic physics background on DWI applied to the kidneys, and we summarize the current available data, including our recent experience
— id: 91449, year: 2008, vol: 16, page: 585, stat: Journal Article,

Diffusion-based MR methods for bone structure and evolution
Sigmund, E E; Cho, H; Chen, P; Byrnes, S; Song, Y-Q; Guo, X E; Brown, T R
2008 Jan;59(1):28-39, Magnetic resonance in medicine
A new approach to MR trabecular bone characterization is presented. This method probes the diffusion of spins through internal magnetic field gradients due to the susceptibility contrast between the bone and water (or marrow) phases. The resulting spin magnetization decay encodes properties of the underlying structure. This method, termed decay due to diffusion in the internal field (DDIF), is well established as a probe of pore size and structure. In the present work its application is shown for in vitro experiments on excised bovine tibiae samples. A comparison with pulsed field gradient (PFG) measurement of restricted diffusion shows a strong correlation of DDIF with the surface-to-volume ratio (SVR) of bones. Calculation of the internal magnetic field within the bone structure also supports this interpretation. These NMR measurements compare well with the image analysis from microscopic computed tomography (muCT). The SVR is not accessible in the clinically standard densitometry measurements, and provides vital information on bone strength and therefore on its fracture risk. The DDIF and PFG methods derive this information from a straightforward pulse sequence that does not employ either high applied field gradients or microimaging, and thus may have clinical potential. Magn Reson Med 59:28-39, 2008. (c) 2007 Wiley-Liss, Inc
— id: 75489, year: 2008, vol: 59, page: 28, stat: Journal Article,

A single-scan method for measuring flow along an arbitrary direction
Cho, H; Ren, X-H; Sigmund, E E; Song, Y-Q
2007 May;186(1):11-16, Journal of magnetic resonance
In this article, we demonstrate a single-scan method to measure an average flow velocity vector along an arbitrary direction. This method is based on the MMME sequence and utilizes static and pulsed magnetic field gradients along multiple directions for the optimal determination of flow velocity components in three-dimensional space. Experimentally measured average flow velocities from the flow induced phase shift with a single-scan MMME sequence show excellent agreements with the known flow rate, and the signal decay of each echo due to a velocity distribution is also quantitatively verified with known laminar flow patterns
— id: 74006, year: 2007, vol: 186, page: 11, stat: Journal Article,

Rapid measurement of three-dimensional diffusion tensor
Cho, H; Ren, X-H; Sigmund, E E; Song, Y-Q
2007 Apr 21;126(15):154501-154501, Journal of chemical physics
In this article, the authors demonstrate a rapid NMR method to measure a full three-dimensional diffusion tensor. This method is based on a multiple modulation multiple echo sequence and utilizes static and pulsed magnetic field gradients to measure diffusion along multiple directions simultaneously. The pulse sequence was optimized using a well-known linear inversion metric (condition number) and successfully tested on both isotropic (water) and anisotropic (asparagus) diffusion systems
— id: 74005, year: 2007, vol: 126, page: 154501, stat: Journal Article,

Spatial heterogeneity length scales in carbonate rocks
Pomerantz, AE; Sigmund, EE; Song, YQ
2007 NOV ;32(1-2):221-231, Applied magnetic resonance
Spatially resolved distributions of T-2 relaxation times in carbonate rocks are measured with slice-selective multiple spin echo magnetic resonance imaging to study the length scales of heterogeneity in these samples. Single-voxel Carr-Pureell-Mciboom-Gill decays are fit to double exponential functions, and the results of those fits are combined into a histogram. We describe a novel qualitative method of assessing the importance of different length scales of heterogeneity, involving comparing various aspects of these histograms to the full-core T2 distributions. Using this technique, it is found that almost all individual voxels relax not only with more than one time constant but indeed with a range of relaxation times that approximates the full breadth of relaxation times for the entire core, indicating significant subvoxel heterogeneity. In addition, different voxcls are found to exhibit relaxation times that differ by orders of magnitude, indicating significant heterogeneity between the scale of a voxel (1 min) and that of the entire core (several centimeters). These results reflect the importance of a broad range of length scales of heterogeneity in these carbonate rocks
— id: 75491, year: 2007, vol: 32, page: 221, stat: Journal Article,

Multiple-modulation-multiple-echo magnetic resonance
Sigmund, EE; Cho, H; Song, YQ
2007 NOV ;30A(6):358-377, Concepts in magnetic resonance. Pt. A. Bridging education & research
We describe several applications of a versatile pulse sequence family employing multiple spin echoes within one acquisition to accelerate multidimensional experiments. The core sequence, called multiple modulation multiple echo, measures the maximal set of spin echoes generated from a set of RF pulses with unequal time spacings. These echoes can be modulated individually to exhibit different encoding. As a result, one scan of the sequence determines a series of data points as a function of the specific encoding mechanism. The variety of realizations of this sequence includes single shot measurements of diffusion or flow in ID, 2D, and single-scan 2D slice-selective imaging. The essential spin dynamics of such sequences is introduced and their applications are reviewed. (C) 2007 Wiley Periodicals, Inc
— id: 75490, year: 2007, vol: 30A, page: 358, stat: Journal Article,

Anisotropy and penetration depth of MgB2 from B-11 NMR
Chen, B; Sengupta, P; Halperin, WP; Sigmund, EE; Mitrovic, VF; Lee, MH; Kang, KH; Mean, BJ; Kim, JY; Cho, BK
2006 NOV 16 ;8(1-2):221-231, New journal of physics
The B-11 NMR spectra in polycrystalline MgB2 were measured for several magnetic fields (1.97 and 3.15 T) as a function of temperature from 5 to 40 K. The composite spectra in the superconducting state can be understood in terms of anisotropy of the upper critical field, gamma(H), which is determined to be 5.4 at low temperature. Using Brandt's algorithm (Brandt 1997 Phys. Rev. Lett. 78 2208) the full spectrum, including satellites, was simulated for the temperature 8 K and a magnetic field of 1.97 T. The penetration depth. was determined to be 1152 +/- 50 angstrom, and the anisotropy of the penetration depth, gamma(lambda), was estimated to be close to one at low temperature. Therefore, our findings establish that there are two different anisotropies for upper critical field and penetration depth at low temperatures
— id: 75492, year: 2006, vol: 8, page: 221, stat: Journal Article,

Stokes-Einstein relation in supercooled aqueous solutions of glycerol
Chen, Bo; Sigmund, E E; Halperin, W P
2006 Apr 14;96(14):145502-145502, Physical review letters
The diffusion of glycerol molecules decreases with decreasing temperature as its viscosity increases in a manner simply described by the Stokes-Einstein relation. Approaching the glass transition, this relation breaks down as it does with a number of other pure liquid glass formers. We have measured the diffusion coefficient for binary mixtures of glycerol and water and find that the Stokes-Einstein relation is restored with increasing water concentration. Our comparison with theory suggests that adding water postpones the formation of frustration domains
— id: 66477, year: 2006, vol: 96, page: 145502, stat: Journal Article,

Fast imaging with the MMME sequence
Cho, H; Chavez, L; Sigmund, E E; Madio, D P; Song, Y-Q
2006 May;180(1):18-28, Journal of magnetic resonance
The multiple-modulation-multiple-echo sequence, previously used for rapid measurement of diffusion, is extended to a method for single shot imaging. Removing the gradient switching requirement during the application of RF pulses by a constant frequency encoding gradient can shorten experiment time for ultrafast imaging. However, having the gradient on during the pulses gives rise to echo shape variations from off-resonance effects, which make the image reconstruction difficult. In this paper, we propose a simple method to deconvolve the echo shape variation from the true one-dimensional image. This method is extended to two-dimensional imaging by adding phase encoding gradients between echoes during the acquisition period to phase encode each echo separately. Slice selection is achieved by a frequency selective pulse at the beginning of the sequence. Imaging speed is mainly limited by the phase encoding gradients' switching times and echo overlap when echo spacing is very short. This technique can produce a single-shot image of sub-millimeter resolution in 5 ms
— id: 66478, year: 2006, vol: 180, page: 18, stat: Journal Article,

Rapid T1 measurement via decay-recovery decomposition: applications in fringe field and distributed relaxation experiments
Sigmund, Eric E; Caudal, Nicolas; Song, Yi-Qiao
2006 Feb;29(1-3):232-241, Solid state nuclear magnetic resonance
Spin-lattice relaxation time (T(1)) measurements are often time-consuming due to the need to measure the full equilibrium magnetization with a long wait time. However, any magnetization recovery can be decomposed into pure recovery and pure decay components, the latter of which lends itself to a much simpler and faster extraction of T(1). We demonstrate several pulse sequences that accomplish this decomposition experimentally and illustrate its applications in a steady magnetic field gradient, and in materials possessing a broad distribution of T(1)
— id: 66045, year: 2006, vol: 29, page: 232, stat: Journal Article,

Multiple echo diffusion tensor acquisition technique
Sigmund, Eric E; Song, Yi-Qiao
2006 Jan;24(1):7-18, Magnetic resonance imaging
The standard method of diffusion tensor imaging (DTI) involves one diffusion-sensitizing gradient direction per acquired signal. This paper describes an alternative method in which the entire direction set required for calculating the diffusion tensor is captured in a few scans. In this method, a series of radiofrequency (RF) pulses are applied, resulting in a train of spin echoes. A pattern of applied magnetic field gradients between the RF pulses generates a different diffusion weighting in both magnitude and direction for each echo, resulting in a dataset sufficient to determine the tensor. This significantly reduces the time required for a full DTI scan and potentially allows a tradeoff of this time for image quality. In the present work, this method is demonstrated in an anisotropic diffusion phantom (asparagus)
— id: 66052, year: 2006, vol: 24, page: 7, stat: Journal Article,

NMR pore size measurements using an internal field in porous media
Song YQ; Sigmund EE; Lisitza NV
NMR imaging in chemical engineering Weinheim : Wiley-VCH, 2006,
— id: 4026, year: 2006, vol: , page: ?, stat: Chapter,

Simultaneous measurement of diffusion along multiple directions
Tang, Xiao-Ping; Sigmund, Eric E; Song, Yi-Qiao
2004 Dec 22;126(50):16336-16337, Journal of the American Chemical Society
— id: 66022, year: 2004, vol: 126, page: 16336, stat: Journal Article,

Alkali ion-cryptand interactions and their effects on electrolyte conductivity
Ding ZN; Ellis DE; Sigmund EE; Halperin WP; Shriver DF
2003 ;5:2072-2081, Physical chemistry chemical physics : PCCP
— id: 66486, year: 2003, vol: 5, page: 2072, stat: Journal Article,

Antiferromagnetism in the vortex cores of YBa2Cu307-delta
Mitrovic VF; Sigmund EE; Halperin WP; Reyes AP; Kuhns PL; Moulton WG
2003 ;67:220503-220503, Physical review. B. Condensed matter
— id: 66483, year: 2003, vol: 67, page: 220503, stat: Journal Article,

High field-gradient translational diffusion measurements in a bitter magnet
Sigmund EE; Halperin WP; Reyes AP; Kuhns PL; Moulton WG
2003 ;10(1):10-11, National High Magnetic Field Laboratory reports
— id: 66482, year: 2003, vol: 10, page: 10, stat: Journal Article,

Hole-burning diffusion measurements in high magnetic field gradients
Sigmund, E E; Halperin, W P
2003 Jul;163(1):99-104, Journal of magnetic resonance
We describe methods for the measurement of translational diffusion in very large static magnetic field gradients by NMR. The techniques use a 'hole-burning' sequence that, with the use of fringe field gradients of 42 T/m, can image diffusion along one dimension on a submicron scale. Two varieties of this method are demonstrated, including a particularly efficient mode called the 'hole-comb,' in which multiple diffusion times comprising an entire diffusive evolution can be measured within the span of a single detected slice. The advantages and disadvantages of these methods are discussed, as well as their potential for addressing non-Fickian diffusion, diffusion in restricted media, and spatially inhomogeneous diffusion
— id: 66479, year: 2003, vol: 163, page: 99, stat: Journal Article,

Inductive shielding of NMR phase noise
Sigmund EE; Mitrovic VF; Calder ES; Thomas GW; Bachman HN; Halperin WP; Kuhns PL; Reyes AP
2002 ;159:190-194, Journal of magnetic resonance
— id: 66487, year: 2002, vol: 159, page: 190, stat: Journal Article,

Nuclear magnetic resonance study of ultraslow diffusion in electrolytes and glass-forming liquids
Sigmund, Eric E
[S.l. : s.n.], 2002,
Thesis (Ph.D., Physics and Astronomy) -- Northwestern University, 2002
— id: 1935, year: 2002, vol: , page: , stat: ,

Polar signal averaging
Thomas GW; Bachman HN; Sigmund EE; Mitrovic VF; Calder ES; Halperin WP
2002 ;14:359-364, Concepts in magnetic resonance. Pt. A. Bridging education & research
— id: 66488, year: 2002, vol: 14, page: 359, stat: Journal Article,

Spatially resolved electronic structure inside and outside the vortex cores of a high-temperature superconductor
Mitrovic VF; Sigmund EE; Eschrig M; Bachman HN; Halperin WP; Reyes AP; Kuhns P; Moulton WG
2001 Oct 4;413(6855):501-504, Nature
Puzzling aspects of high-transition-temperature (high-Tc) superconductors include the prevalence of magnetism in the normal state and the persistence of superconductivity in high magnetic fields. Superconductivity and magnetism generally are thought to be incompatible, based on what is known about conventional superconductors. Recent results, however, indicate that antiferromagnetism can appear in the superconducting state of a high-Tc superconductor in the presence of an applied magnetic field. Magnetic fields penetrate a superconductor in the form of quantized flux lines, each of which represents a vortex of supercurrents. Superconductivity is suppressed in the core of the vortex and it has been suggested that antiferromagnetism might develop there. Here we report the results of a high-field nuclear-magnetic-resonance (NMR) imaging experiment in which we spatially resolve the electronic structure of near-optimally doped YBa2Cu3O7-delta inside and outside vortex cores. Outside the cores, we find strong antiferromagnetic fluctuations, whereas inside we detect electronic states that are rather different from those found in conventional superconductors
— id: 66480, year: 2001, vol: 413, page: 501, stat: Journal Article,

Progressive saturation NMR relaxation
Mitrovic VF; Sigmund EE; Halperin WP
2001 ;64:024520-024520, Physical review. B. Condensed matter
— id: 66485, year: 2001, vol: 64, page: 024520, stat: Journal Article,

NMR phase noise in bitter magnets
Sigmund EE; Calder ES; Thomas GW; Mitrovic VF; Bachman HN; Halperin WP; Kuhns PL; Reyes AP
2001 Feb;148(2):309-313, Journal of magnetic resonance
We have studied the temporal instability of a high field resistive Bitter magnet through nuclear magnetic resonance (NMR). This instability leads to transverse spin decoherence in repeated and accumulated NMR experiments as is normally performed during signal averaging. We demonstrate this effect via Hahn echo and Carr--Purcell--Meiboom--Gill (CPMG) transverse relaxation experiments in a 23-T resistive magnet. Quantitative analysis was found to be consistent with separate measurements of the magnetic field frequency fluctuation spectrum, as well as with independent NMR experiments performed in a magnetic field with a controlled instability. Finally, the CPMG sequence with short pulse delays is shown to be successful in recovering the intrinsic spin--spin relaxation even in the presence of magnetic field temporal instability
— id: 66481, year: 2001, vol: 148, page: 309, stat: Journal Article,

Lithium transport in a macrocyclic electrolyte
Sigmund EE; Halperin WP; Dillon REA; Shriver DF
2001 ;64:214201-214201, Physical review. B. Condensed matter
— id: 66484, year: 2001, vol: 64, page: 214201, stat: Journal Article,