Ravinder R Regatte, Ph.D.

Comparison of a 28-channel receive array coil and quadrature volume coil for morphologic imaging and T2 mapping of knee cartilage at 7T
Chang, Gregory; Wiggins, Graham C; Xia, Ding; Lattanzi, Riccardo; Madelin, Guillaume; Raya, Jose G; Finnerty, Matthew; Fujita, Hiroyuki; Recht, Michael P; Regatte, Ravinder R
2012 Feb;35(2):441-448, Journal of magnetic resonance imaging
PURPOSE: To compare a new birdcage-transmit, 28-channel receive array (28-Ch) coil and a quadrature volume coil for 7T morphologic MRI and T2 mapping of knee cartilage. MATERIALS AND METHODS: The right knees of 10 healthy subjects were imaged on a 7T whole body magnetic resonance (MR) scanner using both coils. 3D fast low-angle shot (3D-FLASH) and multiecho spin-echo (MESE) sequences were implemented. Cartilage signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), thickness, and T2 values were assessed. RESULTS: SNR/CNR was 17%-400% greater for the 28-Ch compared to the quadrature coil (P </= 0.005). Bland-Altman plots show mean differences between measurements of tibial/femoral cartilage thickness and T2 values obtained with each coil to be small (-0.002 +/- 0.009 cm / 0.003 +/- 0.011 cm) and large (-6.8 +/- 6.7 msec/-8.2 +/- 9.7 msec), respectively. For the 28-Ch coil, when parallel imaging with acceleration factors (AF) 2, 3, and 4 was performed SNR retained was: 62%-69%, 51%-55%, and 39%-45%. CONCLUSION: A 28-Ch knee coil provides increased SNR/CNR for 7T cartilage morphologic imaging and T2 mapping. Coils should be switched with caution during clinical studies because T2 values may differ. The greater SNR of the 28-Ch coil could be used to perform parallel imaging with AF2 and obtain similar SNR as the quadrature coil. J. Magn. Reson. Imaging 2012;441-448. (c) 2011 Wiley Periodicals, Inc
— id: 150560, year: 2012, vol: 35, page: 441, stat: Journal Article,

Compressed sensing sodium MRI of cartilage at 7T: Preliminary study
Madelin, Guillaume; Chang, Gregory; Otazo, Ricardo; Jerschow, Alexej; Regatte, Ravinder R
2012 Jan;214(1):360-365, Journal of magnetic resonance
Sodium MRI has been shown to be highly specific for glycosaminoglycan (GAG) content in articular cartilage, the loss of which is an early sign of osteoarthritis (OA). Quantitative sodium MRI techniques are therefore under development in order to detect and assess early biochemical degradation of cartilage, but due to low sodium NMR sensitivity and its low concentration, sodium images need long acquisition times (15-25min) even at high magnetic fields and are typically of low resolution. In this preliminary study, we show that compressed sensing can be applied to reduce the acquisition time by a factor of 2 at 7T without losing sodium quantification accuracy. Alternatively, the nonlinear reconstruction technique can be used to denoise fully-sampled images. We expect to even further reduce this acquisition time by using parallel imaging techniques combined with SNR-improved 3D sequences at 3T and 7T
— id: 149806, year: 2012, vol: 214, page: 360, stat: Journal Article,

Reproducibility of subregional trabecular bone micro-architectural measures derived from 7-Tesla magnetic resonance images
Chang G; Wang L; Liang G; Babb JS; Saha PK; Regatte RR
2011 Jun;24(3):121-125, MAGMA (European Society for Magnetic Resonance in Medicine & Biology)
High-resolution magnetic resonance imaging (MRI) of trabecular bone combined with quantitative image analysis represents a powerful technique to gain insight into trabecular bone micro-architectural derangements in osteoporosis and osteoarthritis. The increased signal-to-noise ratio of ultra high-field MR (>/=7 Tesla) permits images to be obtained with higher resolution and/or decreased scan time compared to scanning at 1.5/3T. In this small feasibility study, we show high measurement precision for subregional trabecular bone micro-architectural analysis performed on 7T knee MR images. The results provide further support for the use of trabecular bone measures as biomarkers in clinical studies of bone disorders
— id: 120831, year: 2011, vol: 24, page: 121, stat: Journal Article,

Quantitative assessment of trabecular bone micro-architecture of the wrist via 7 Tesla MRI: preliminary results
Chang G; Wang L; Liang G; Babb JS; Wiggins GC; Saha PK; Regatte RR
2011 Aug;24(4):191-199, MAGMA (European Society for Magnetic Resonance in Medicine & Biology)
OBJECT: The goal of this study was to determine the feasibility of performing quantitative 7 T magnetic resonance imaging (MRI) assessment of trabecular bone micro-architecture of the wrist, a common fracture site. MATERIALS AND METHODS: The wrists of 4 healthy subjects (1 woman, 3 men, 28+/-8.9 years) were scanned on a 7 T whole body MR scanner using a 3D fast low-angle shot (FLASH) sequence (TR/TE = 20/4.5 m s, 0.169x0.169x0.5 mm). Trabecular bone was segmented and divided into 4 or 8 angular subregions. Total bone volume (TBV), bone volume fraction (BVF), surface-curve ratio (SC), and erosion index (EI) were computed. Subjects were scanned twice to assess measurement reproducibility. RESULTS: Group mean subregional values for TBV, BVF, SC, and EI (8 subregion analysis) were as follows: 8489 +/- 3686, 0.27 +/- 0.045, 9.61 +/- 6.52; and 1.43 +/- 1.25. Within each individual, there was subregional variation in TBV, SC, and EI (>5%), but not BVF (<5%). Intersubject variation (>/=12%) existed for all parameters. Within-subject coefficients of variation were </=10%. CONCLUSION: This is the first study to perform quantitative 7T MRI assessment of trabecular bone micro-architecture of the wrist. This method could be utilized to study perturbations in bone structure in subjects with osteoporosis or other bone disorders
— id: 132301, year: 2011, vol: 24, page: 191, stat: Journal Article,

MR Imaging Assessment of Articular Cartilage Repair Procedures
Chang, Gregory; Sherman, Orrin; Madelin, Guillaume; Recht, Michael; Regatte, Ravinder
2011 May;19(2):323-337, Magnetic resonance imaging clinics of North America
Because articular cartilage is avascular and has no intrinsic capacity to heal itself, physical damage to cartilage poses a serious clinical problem for orthopedic surgeons and rheumatologists. No medication exists to treat or reconstitute physical defects in articular cartilage, and pharmacotherapy is limited to pain control. Developments in the field of articular cartilage repair include microfracture, osteochondral autografting, osteochondral allografting, repair with synthetic resorbable plugs, and autologous chondrocyte implantation. MR imaging techniques have the potential to allow in vivo monitoring of the collagen and proteoglycan content of cartilage repair tissue and may provide useful additional metrics of cartilage repair tissue quality
— id: 134459, year: 2011, vol: 19, page: 323, stat: Journal Article,

Quantitative magnetic resonance imaging evidence of synovial proliferation is associated with radiographic severity of knee osteoarthritis
Krasnokutsky, Svetlana; Belitskaya-Levy, Ilana; Bencardino, Jenny; Samuels, Jonathan; Attur, Mukundan; Regatte, Ravinder; Rosenthal, Pamela; Greenberg, Jeffrey; Schweitzer, Mark; Abramson, Steven B; Rybak, Leon
2011 Oct;63(10):2983-2991, Arthritis & rheumatism
OBJECTIVE: To evaluate the relationships between both quantitative and semiquantitative assessments of the degree of knee synovitis on 3T magnetic resonance imaging (MRI) and the severity of knee osteoarthritis (OA) on radiography. METHODS: Fifty-eight patients with knee OA underwent nonfluoroscopic fixed-flexion knee radiography. In addition, dynamic contrast-enhanced 3T MRI of the knees was performed, before and after gadolinium administration, to quantify synovial membrane volume (SV) as a measure of synovial proliferation (expressed as the quantitative SV), and semiquantitative measures of synovitis were also applied using both contrast-enhanced and unenhanced images. Two radiologists scored the knee radiographs using the Osteoarthritis Research Society International atlas; interreader agreement was assessed using kappa statistics and concordance correlation coefficients. Multiple linear and logistic regression analyses were used to assess associations among variables, while controlling for the effects of age, body mass index, sex, and meniscal extrusion. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated for measures of disease activity. RESULTS: The Kellgren/Lawrence (K/L) grade of radiographic knee OA severity (beta = 0.78), the diseased compartment joint space width (dcJSW) (beta = -0.22), and the diseased compartment joint space narrowing (dcJSN) score (beta = 0.53) were each significantly associated with the quantitative SV (P = 0.0001, P = 0.0003, and P = 0.0001, respectively). Furthermore, the quantitative SV strongly correlated with the total volume of subchondral bone marrow lesions (BMLs) (beta = 0.22, P = 0.0003). The K/L grade, dcJSW, and dcJSN score were each significantly associated with the semiquantitative Boston Leeds Osteoarthritis Knee Score (BLOKS) for the extent of infrapatellar synovitis (OR 9.05 [95% CI 1.94, 42.3] for K/L grade; OR 0.75 [95% CI 0.54, 1.03] for dcJSW; and OR 2.22 [95% CI 1.15, 4.31] for dcJSN score) and extent of joint effusion (OR 5.75 [95% CI 1.23, 26.8] for K/L grade; OR 0.70 [95% CI 0.50, 0.98] for dcJSW; and OR 1.96 [95% CI 1.02, 3.74] for dcJSN score). In addition, the semiquantitative synovitis grade on contrast-enhanced MRI was significantly associated with the K/L grade (beta = 0.036, P = 0.0040) and dcJSN score (beta = 0.015, P = 0.0266), and also significantly associated with the BLOKS synovitis score. CONCLUSION: Synovitis is a characteristic feature of advancing knee OA and is significantly associated with the K/L grade, JSW, JSN score, and total volume of BMLs on radiographs. Furthermore, BLOKS scoring of synovitis on unenhanced MRI is associated with measurements of synovitis on contrast-enhanced MRI
— id: 137878, year: 2011, vol: 63, page: 2983, stat: Journal Article,

Uniform saturation of a strongly coupled spin system by two-frequency irradiation
Lee, Jae-Seung; Khitrin, Anatoly K; Regatte, Ravinder R; Jerschow, Alexej
2011 Jun 21;134(23):234504-234504, Journal of chemical physics
The theoretical basis of two-frequency saturation is given here in the framework of Provotorov theory. The parameters influencing the saturation efficiency are discussed and studied experimentally using a liquid-crystalline test system. It is shown that double-frequency irradiation can be extremely efficient when the irradiation frequencies are placed at opposite sides of the characteristic frequency of the spin system, and that the frequency separation in the double-frequency irradiation can be varied over a large range. Provotorov theory is also shown to provide good insights into the experimental findings, which would otherwise be difficult to obtain from simulations
— id: 134734, year: 2011, vol: 134, page: 234504, stat: Journal Article,

T1rho MRI of menisci and cartilage in patients with osteoarthritis at 3T
Wang L; Chang G; Xu J; Vieira RL; Krasnokutsky S; Abramson S; Regatte RR
2011 Sep 9;:?-? #, European journal of radiology
OBJECTIVE: To assess and compare subregional and whole T1rho values (median+/-interquartile range) of femorotibial cartilage and menisci in patients with doubtful (Kellgren-Lawrence (KL) grade 1) to severe (KL4) osteoarthritis (OA) at 3T. MATERIALS AND METHODS: 30 subjects with varying degrees of OA (KL1-4, 13 females, 17 males, mean age+/-SD=63.9+/-13.1 years) were evaluated on a 3T MR scanner using a spin-lock-based 3D GRE sequence for T1rho mapping. Clinical proton density (PD)-weighted fast spin echo (FSE) images in sagittal (without fat saturation), axial, and coronal (fat-saturated) planes were acquired for cartilage and meniscus Whole-organ MR imaging score (WORMS) grading. Wilcoxon rank sum test was performed to determine whether there were any statistically significant differences between subregional and whole T1rho values of femorotibial cartilage and menisci in subjects with doubtful to severe OA. RESULTS: Lateral (72+/-10ms, median+/-interquartile range) and medial (65+/-10ms) femoral anterior cartilage subregions in moderate-severe OA subjects had significantly higher T1rho values (P<0.05) than cartilage subregions and whole femorotibial cartilage in doubtful-minimal OA subjects. There were statistically significant differences in meniscus T1rho values of the medial posterior subregion of subjects with moderate-severe OA and T1rho values of all subregions and the whole meniscus in subjects with doubtful-minimal OA. When evaluated based on WORMS, statistically significant differences were identified in T1rho values between the lateral femoral anterior cartilage subregion in patients with WORMS5-6 (advanced degeneration) and whole femorotibial cartilage and all cartilage subregions in patients with WORMS0-1 (normal). CONCLUSION: T1rho values are higher in specific meniscus and femorotibial cartilage subregions. These findings suggest that regional damage of both femorotibial hyaline cartilage and menisci may be associated with osteoarthritis
— id: 139810, year: 2011, vol: , page: ?, stat: Journal Article,

Assessment of subchondral bone marrow lipids in healthy controls and mild osteoarthritis patients at 3T
Wang L; Salibi N; Chang G; Vieira RL; Babb JS; Krasnokutsky S; Abramson S; Regatte RR
2011 Aug 18;:?-?, NMR in biomedicine
The compartment-specific lipid changes in femoral-tibial bone of healthy controls and mild osteoarthritis (OA) patients were quantified at 3.0 T. Healthy volunteers [Kellgren-Lawrence (KL) grade = 0; n = 15, 4 females, 11 males, mean age 39 +/- 16 years, age range = 24-78 years] and mild OA patients (KL = 1, 2; n = 26, 12 females, 14 males, mean age 61 +/- 14 years, age range = 27-80 years) were scanned on a 3 T scanner. Clinical proton density (PD)-weighted fast spin echo (FSE) images in the sagittal (without fat-saturation), axial and coronal (fat-saturation) planes were acquired for cartilage Whole-Organ MR Imaging Score (WORMS) grading. A voxel of 10 x 10 x 10 mm(3) was positioned in the medial and lateral compartments of the tibia [medial tibial (MT) and lateral tibial (LT)] and femur [medial femoral (MF) and lateral femoral (LF)] for MRS measurements using the single voxel-stimulated echo acquisition mode (STEAM) pulse sequence. All MRS data were processed with Java-based Magnetic Resonance User Interface (JMRUI). Wilcoxon's rank sum test and mixed model two-way analysis of variance (anova) were performed to determine significant differences between different compartments as well as examine the effect of OA grade and compartment, and their interactions. Generally, the MF compartment index of unsaturation was increased in healthy subjects compared with OA subjects (whether graded by KL or WORMS score). Differences between MF at KL0 and all other compartments at KL1 except LF approached statistical significance (p < 0.05). Differences in saturated lipids signals could be observed predominantly in the 2.03 p.p.m. frequency shift. Healthy controls in the MF compartment had the lowest saturated lipid signals, and mild OA patients with KL2 and WORMS5-6 in the MF compartment had the highest saturated lipid signals compared with other compartments at 2.03 p.p.m. (p < 0.05).
— id: 139811, year: 2011, vol: , page: ?, stat: Journal Article,

MRI of the wrist at 7 tesla using an eight-channel array coil combined with parallel imaging: Preliminary results
Chang, Gregory; Friedrich, Klaus M; Wang, Ligong; Vieira, Renata L R; Schweitzer, Mark E; Recht, Michael P; Wiggins, Graham C; Regatte, Ravinder R
2010 Mar;31(3):740-746, Journal of magnetic resonance imaging
PURPOSE:: To determine the feasibility of performing MRI of the wrist at 7 Tesla (T) with parallel imaging and to evaluate how acceleration factors (AF) affect signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and image quality. MATERIALS AND METHODS:: This study had institutional review board approval. A four-transmit eight-receive channel array coil was constructed in-house. Nine healthy subjects were scanned on a 7T whole-body MR scanner. Coronal and axial images of cartilage and trabecular bone micro-architecture (3D-Fast Low Angle Shot (FLASH) with and without fat suppression, repetition time/echo time = 20 ms/4.5 ms, flip angle = 10 degrees , 0.169-0.195 x 0.169-0.195 mm, 0.5-1 mm slice thickness) were obtained with AF 1, 2, 3, 4. T1-weighted fast spin-echo (FSE), proton density-weighted FSE, and multiple-echo data image combination (MEDIC) sequences were also performed. SNR and CNR were measured. Three musculoskeletal radiologists rated image quality. Linear correlation analysis and paired t-tests were performed. RESULTS:: At higher AF, SNR and CNR decreased linearly for cartilage, muscle, and trabecular bone (r < -0.98). At AF 4, reductions in SNR/CNR were:52%/60% (cartilage), 72%/63% (muscle), 45%/50% (trabecular bone). Radiologists scored images with AF 1 and 2 as near-excellent, AF 3 as good-to-excellent (P = 0.075), and AF 4 as average-to-good (P = 0.11). CONCLUSION:: It is feasible to perform high resolution 7T MRI of the wrist with parallel imaging. SNR and CNR decrease with higher AF, but image quality remains above-average. J. Magn. Reson. Imaging 2010;31:740-746. (c) 2010 Wiley-Liss, Inc
— id: 107782, year: 2010, vol: 31, page: 740, stat: Journal Article,

Biochemical and physiological MR imaging of skeletal muscle at 7 tesla and above
Chang, Gregory; Wang, Ligong; Cardenas-Blanco, Arturo; Schweitzer, Mark E; Recht, Michael P; Regatte, Ravinder R
2010 Jun;14(2):269-278, Seminars in musculoskeletal radiology
Ultra-high field (UHF; >or=7 T) magnetic resonance imaging (MRI), with its greater signal-to-noise ratio, offers the potential for increased spatial resolution, faster scanning, and, above all, improved biochemical and physiological imaging of skeletal muscle. The increased spectral resolution and greater sensitivity to low-gamma nuclei available at UHF should allow techniques such as (1)H MR spectroscopy (MRS), (31)P MRS, and (23)Na MRI to be more easily implemented. Numerous technical challenges exist in the performance of UHF MRI, including changes in relaxation values, increased chemical shift and susceptibility artifact, radiofrequency (RF) coil design/B (1)(+) field inhomogeneity, and greater RF energy deposition. Nevertheless, the possibility of improved functional and metabolic imaging at UHF will likely drive research efforts in the near future to overcome these challenges and allow studies of human skeletal muscle physiology and pathophysiology to be possible at >or=7 T
— id: 109796, year: 2010, vol: 14, page: 269, stat: Journal Article,

3D (23)Na MRI of human skeletal muscle at 7 Tesla: initial experience
Chang, Gregory; Wang, Ligong; Schweitzer, Mark E; Regatte, Ravinder R
2010 Aug;20(8):2039-2046, European radiology
OBJECTIVE: To evaluate healthy skeletal muscle pre- and post-exercise via 7 T (23)Na MRI and muscle proton T(2) mapping, and to evaluate diabetic muscle pre- and post-exercise via 7 T (23)Na MRI. METHODS: The calves of seven healthy subjects underwent imaging pre- and post-exercise via 7 T (23)Na MRI (3D fast low angle shot, TR/TE = 80 ms/0.160 ms, 4 mm x 4 mm x 4 mm) and 1 week later by (1)H MRI (multiple spin-echo sequence, TR/TE = 3,000 ms/15-90 ms). Four type 2 diabetics also participated in the (23)Na MRI protocol. Pre- and post-exercise sodium signal intensity (SI) and proton T(2) relaxation values were measured/calculated for soleus (S), gastrocnemius (G), and a control, tibialis anterior (TA). Two-tailed t tests were performed. RESULTS: In S/G in healthy subjects post-exercise, sodium SI increased 8-13% (p < 0.03), then decreased (t (1/2) = 22 min), and (1)H T(2) values increased 12-17% (p < 0.03), then decreased (t (1/2 )= 12-15 min). In TA, no significant changes in sodium SI or (1)H T(2) values were seen (-2.4 to 1%, p > 0.17). In S/G in diabetics, sodium SI increased 10-11% (p < 0.04), then decreased (t (1/2) = 27-37 min) without significant change in the TA SI (-3.6%, p = 0.066). CONCLUSION: It is feasible to evaluate skeletal muscle via 3D (23)Na MRI at 7 T. Post-exercise muscle (1)H T(2) values return to baseline more rapidly than sodium SI. Diabetics may demonstrate delayed muscle sodium SI recovery compared with healthy subjects
— id: 110682, year: 2010, vol: 20, page: 2039, stat: Journal Article,

Does joint alignment affect the T2 values of cartilage in patients with knee osteoarthritis?
Friedrich, Klaus M; Shepard, Timothy; Chang, Gregory; Wang, Ligong; Babb, James S; Schweitzer, Mark; Regatte, Ravinder
2010 Jun;20(6):1532-1538, European radiology
OBJECTIVE: To assess the relationship between T2 values of femorotibial cartilage and knee alignment in patients with clinical symptoms of medial osteoarthritis (OA). METHODS: Twenty-four patients (mean age +/- standard deviation, 62.5 +/- 9.9 years) with clinical symptoms of medial knee OA, 12 with varus and 12 with valgus alignment of the femorotibial joint, were investigated on 3T MR using a 2D multi-echo spin echo (MESE) sequence for T2 mapping. Analysis of covariance, Spearman correlation coefficients, exact Mann-Whitney tests, and Fisher's exact tests were used for statistical analysis. RESULTS: Overall the T2 values of cartilage in the medial compartment (median +/- interquartile-range, 49.44 +/- 6.58) were significantly higher (P = 0.0043) than those in the lateral compartment (47.15 +/- 6.87). Patients with varus alignment (50.83 +/- 6.30 ms) had significantly higher T2 values of cartilage (P < 0.0001) than patients with valgus alignment (46.20 +/- 6.00 ms). No statistically significant association between the T2 values of cartilage (in either location) and the Kellgren Lawrence score was found in the varus or in the valgus group. CONCLUSION: T2 measurements were increased in medial knee OA patients with varus alignment, adding support to the theory of an association of OA and joint alignment
— id: 111559, year: 2010, vol: 20, page: 1532, stat: Journal Article,

Radiographic severity of knee osteoarthritis predicts quantitative Bone Marrow Lesions on MRI
Krasnokutsky S.; Regatte R.; Bencardino J.; Rybak L.; Belitskaya-Levy I.; Samuels J.; Attur M.
2010 ;62:137-137, Arthritis & rheumatism
Objective: To evaluate the relationship of quantitative assessment of Bone Marrow Lesions (BML) with knee OA severity by radiographic findings. Methods: 58 OA patients (mean age 62+/-10, mean BMI 27+/-3, 59% female) underwent standardized nonfluoroscopic fixed-flexion knee radiographs. Two radiologists read the X-rays for KL grade, joint space width (JSW), and, using the OARSI atlas, joint space narrowing (JSN) and osteophytes; interreader agreement was assessed using Kappas and concordance correlation coefficients. Linear and logistic regression analysis was performed to assess associations while controlling the effects of age, sex and BMI. 3T-MRI included sagittal T2-weighted fat saturated spin-echo images (TR/TE=4000ms/75ms, FOV=15cm, matrix=256x128, slice thickness=3.0mm, receiver bandwidth 130Hz/pixel) and in/out of phase of FLASH images. Compartment-wise (medial tibial, lateral tibial, medial femur, lateral femur) BML volumes were quantified with T2-weighted fat saturated images and in/out of phase images respectively. BML volumes were dichotomized for statistical analysis. Results: KL score was a significant predictor of total BML volume (OR = 8.41, p = 0.0235). Medial tibial JSW, OARSI medial JSN, and medial tibial plateau osteophytes approached significance as predictors of BML volume at the medial tibia (OR = 0.71, p = 0.0551; OR = 2.16, p = 0.0597; and OR = 2.68, p = 0.0875, respectively). OARSI lateral JSN was a significant predictor of BML volume at the lateral tibia (OR = 3.62, p = 0.0169). Lateral tibial plateau osteophytes were predictors of total BML volume (OR = 4.58, p = 0.0299) and of BML volume at the lateral tibia (OR = 2.31, p = 0.0685). Lateral femoral condyle osteophytes approached significance as a predictor for BML at the lateral femur (OR = 2.25, p = 0.0651). Furthermore, quantitative BML volume strongly correlated with total quantitative synovial volume measured on MRI (beta= 0.22, p = 0.0003). Conclusions: Our data indicate that BML volume on MRI is a characteristic feature of progressive stages of OA, which not only correlates with JSN and osteophytes, but does so in a compartment-specific way. The data suggest that the altered mechanical forces that promote compartmental disease in OA lead to BML, JSN and osteophyte formation. Whether BML further contribute to cartilage loss, and are therefore targets of therapeutic intervention, remains to be determined
— id: 130946, year: 2010, vol: 62, page: 137, stat: Journal Article,

Optimal control NMR differentiation between fast and slow sodium
Lee, JS; Regatte, RR; Jerschow, A
2010 JUL 19 ;494(4-6):331-336, Chemical physics letters
Sodium ions in tissues and organs may experience motion on a variety of timescales, leading to NMR relaxation effects with quadrupolar coupling as the primary mechanism. The various effects that this fluctuating interaction has on spin dynamics can be exploited for distinguishing slow sodium ions from fast ones. Techniques such as triple-quantum filtering have been used for this purpose in the past. In this work we present optimal pulses which significantly improve the selectivity towards slow-tumbling sodium. These pulses can also be modified for robustness against magnetic field inhomogeneities, and could hence also become useful as MRI contrast methods. (C) 2010 Elsevier B. V. All rights reserved
— id: 111398, year: 2010, vol: 494, page: 331, stat: Journal Article,

Sodium inversion recovery MRI of the knee joint in vivo at 7T
Madelin, Guillaume; Lee, Jae-Seung; Inati, Souheil; Jerschow, Alexej; Regatte, Ravinder R
2010 Nov;207(1):42-52, Journal of magnetic resonance
The loss of proteoglycans (PG) in the articular cartilage is an early signature of osteoarthritis (OA). The ensuing changes in the fixed charge density in the cartilage can be directly linked to sodium concentration via charge balance. Sodium ions in the knee joint appear in two pools: in the synovial fluids or joint effusion where the ions are in free motion and bound within the cartilage tissue where the Na(+) ions have a restricted motion. The ions in these two compartments have therefore different T and T relaxation times. The purpose of this study is to demonstrate the feasibility of a fluid-suppressed 3D ultrashort TE radial sodium sequence by implementing an inversion recovery (IR) preparation of the magnetization at 7T. This method could allow a more accurate and more sensitive quantification of loss of PG in patients with OA. It is shown that adiabatic pulses offer significantly improved performance in terms of robustness to B and B inhomogeneities when compared to the hard pulse sequence. Power deposition considerations further pose a limit to the RF inversion power, and we demonstrate in simulations and experiments how a practical compromise can be struck between clean suppression of fluid signals and power deposition levels. Two IR sequences with different types of inversion pulses (a rectangular pulse and an adiabatic pulse) were tested on a liquid phantom, ex vivo on a human knee cadaver and then in vivo on five healthy volunteers, with a (Nyquist) resolution of approximately 3.6 mm and a signal-to-noise ratio of approximately 30 in cartilage without IR and approximately 20 with IR. Due to specific absorption rate limitations, the total acquisition time was approximately 17 min for the 3D radial sequence without inversion or with the rectangular IR, and 24:30 min for the adiabatic IR sequence. It is shown that the adiabatic IR sequence generates a more uniform fluid suppression over the whole sample than the rectangular IR sequence
— id: 113946, year: 2010, vol: 207, page: 42, stat: Journal Article,

Olympic fencers: adaptations in cortical and trabecular bone determined by quantitative computed tomography
Chang, G; Regatte, R R; Schweitzer, M E
2009 May;20(5):779-785, Osteoporosis international
We investigated how cortical bone, trabecular bone, and muscle adapt in US Olympic Fencing Team members. These athletes demonstrate femoral cortical bone expansion, greater distal femoral trabecular bone density, and greater muscle mass compared to controls. This is the first study to investigate musculoskeletal adaptations in Olympic fencers. PURPOSE: Wolff's law states that bone remodels according to mechanical forces placed upon it. Our goal was to determine how cortical and trabecular bone adapt in Olympic athletes who perform intermittent high-impact activity. MATERIALS AND METHODS: Nine males from the 2004 US Olympic Fencing Team and nine matched controls were evaluated by quantitative computed tomography. Femurs were scanned at 50% and 75% along the shaft. We evaluated cortical thickness (C.Th), cortical (C.Ar), trabecular (Tb.Ar), and total bone areas (Tot.Ar), proportions of C.Ar and Tb.Ar to Tot.Ar, cortical (C.BMD.), trabecular (Tb.MBD), and total bone densities (Tot.BMD), muscle (M.Ar), and thigh areas (Th.Ar). RESULTS: Fencers had greater C.Th (+24.5 to 38.8%), C.Ar (+16.9 to 19.6%), C.Ar/Tot.Ar (+6.3 to 16.3%), and lower Tb.Ar/Tot.Ar (-23.5% to -23.8%; p<0.05). Fencers demonstrated a positive difference in C.Th in the dominant vs. nondominant thigh at 50% (+5.4%, p = 0.040) and at 75% (+13.8%, p = 0.048 by analysis of covariance). Fencers had 54% greater Tb.BMD at 75% (p = 0.025), but not at 50% (p = 0.63). There was no difference between groups for C.BMD (p = .66 at 50%, p = 0.88 at 75%). Fencers had greater M.Ar (+30%) and asymmetrically greater M.Ar (+12.2%) in the dominant thigh (p < 0.004). CONCLUSION: In world-class athletes who perform intermittent, high-impact activity, cortical bone expands, trabecular bone density is greater, and muscle mass is greater. This is the first study to examine musculoskeletal adaptations in Olympic fencers
— id: 105913, year: 2009, vol: 20, page: 779, stat: Journal Article,

In vivo 7.0-tesla magnetic resonance imaging of the wrist and hand: technical aspects and applications
Friedrich, Klaus M; Chang, Gregory; Vieira, Renata L R; Wang, Ligong; Wiggins, Graham C; Schweitzer, Mark E; Regatte, Ravinder R
2009 Mar;13(1):74-84, Seminars in musculoskeletal radiology
Magnetic resonance imaging (MRI) at 7.0 T has the potential for higher signal-to-noise ratio (SNR), improved spectral resolution, and faster imaging compared with 1.5-T and 3.0-T MR systems. This is especially interesting for challenging imaging regions like the wrist and the hand because of the small size of the visualized anatomical structures; the increase in SNR could then be directly converted into higher spatial resolution of the images. Practically, imaging at 7.0 T poses a variety of technical challenges such as static (B (0)) and radiofrequency (B (1)) homogeneities, shimming, chemical shift artifacts, susceptibility artifacts, alterations in tissue contrast, specific absorption rate limitations, coil construction, and pulse sequence tuning. Despite these limitations, this first experience in anatomical imaging of the wrist and the hand at 7.0 T is very promising. Functional imaging techniques will gain importance at ultra-high-field MRI and need to be assessed in detail in the future
— id: 94396, year: 2009, vol: 13, page: 74, stat: Journal Article,

T2 measurements of cartilage in osteoarthritis patients with meniscal tears
Friedrich, Klaus M; Shepard, Timothy; de Oliveira, Valesca Sarkis; Wang, Ligong; Babb, James S; Schweitzer, Mark; Regatte, Ravinder
2009 Nov;193(5):W411-W415, American journal of roentgenology
OBJECTIVE: The objective of this study was to quantitatively assess cartilage degeneration via T2 mapping to compare patients with and those without meniscal tears. SUBJECTS AND METHODS: Thirty-seven patients (18 men, mean age +/- SD, 65.7 +/- 7.8 years; 19 women, mean age, 63.8 +/- 12.0 years) with clinical symptoms of osteoarthritis were studied on 3-T MRI using a 2D multiecho spin-echo sequence for T2 mapping. Meniscal signal and morphology were qualitatively graded and correlated to the T2 values of cartilage. Analysis of covariance, Bonferroni multiple comparison correction, and Spearman's correlation coefficients were used for statistical analysis. RESULTS: Patients with meniscal tears (median +/- interquartile range, 50.1 +/- 6.1 milliseconds) had significantly (p = 0.021) higher T2 values of cartilage than those without meniscal tears (45.7 +/- 4.8 milliseconds). T2 values of cartilage were significantly higher in the medial compartment than in the lateral compartment in patients with medial meniscal tears (p = 0.018). CONCLUSION: T2 measurements are increased in patients with meniscal tears; this finding adds support to the theory of an association of osteoarthritis with damage to both the menisci and hyaline cartilage
— id: 104734, year: 2009, vol: 193, page: W411, stat: Journal Article,

Optimal excitation of (23)Na nuclear spins in the presence of residual quadrupolar coupling and quadrupolar relaxation
Lee, Jae-Seung; Regatte, Ravinder R; Jerschow, Alexej
2009 Nov 7;131(17):174501-174501, Journal of chemical physics
Optimal control theory is applied for designing pulse sequences to optimally excite a spin-3/2 system with residual quadrupolar coupling in the presence of quadrupolar relaxation. A homogeneous form of the master equation is constructed to simulate the dynamics of the spin system, and a general optimization procedure with a homogeneous form of the equation of motion is described. The optimized pulses are tested with (23)Na NMR, and their performance is compared with that of pulses optimized in the absence of relaxation
— id: 105227, year: 2009, vol: 131, page: 174501, stat: Journal Article,

Selective detection of ordered sodium signals by a jump-and-return pulse sequence
Lee, Jae-Seung; Regatte, Ravinder R; Jerschow, Alexej
2009 Sep;200(1):126-129, Journal of magnetic resonance
A simple pulse sequence, derived from the shaped pulse optimally exciting the central transition of a spin 3/2, can be used to selectively detect ordered sodium with a given quadrupolar coupling. The pulse sequence consists of two pulses with opposite phases and separated by a delay, called a quadrupolar jump-and-return (QJR) sequence. This QJR sequence is tested with a phantom made of sodium ions in bacteriophage and in aqueous solution and its feasibility for contrast modification based on the quadrupolar coupling is demonstrated
— id: 101906, year: 2009, vol: 200, page: 126, stat: Journal Article,

Relaxation times of skeletal muscle metabolites at 7T
Wang, Ligong; Salibi, Nouha; Wu, Yan; Schweitzer, Mark E; Regatte, Ravinder R
2009 Jun;29(6):1457-1464, Journal of magnetic resonance imaging
PURPOSE: To demonstrate the feasibility of quantitatively evaluating and measuring T(1) and T(2) relaxation times of human tibialis anterior (TA) muscles metabolites in vivo at 7T and to compare these results with those of 3T. MATERIALS AND METHODS: A model lipid phantom (corn oil) and healthy volunteers (n = 4, mean +/- SD age 35.6 +/- 5.6 years) were scanned on 3T and 7T whole-body MR scanners. A voxel of 10 x 10 x 10 mm(3) was positioned on the lipid phantom and right calf TA muscles using the single-voxel stimulated echo acquisition mode (STEAM) pulse sequence. All magnetic resonance spectroscopy (MRS) data were processed with Java-based Magnetic Resonance User Interface (JMRUI) using Hankel Lanczos Singular Value Decomposition (HLSVD) filtering to remove the residual water signal. RESULTS: T(1) shows a steady increase while T(2) shows a slight decrease with B(0) and the spectra show larger spectral resolution at 7T than at 3T in the lipid phantom. T(1) values of all the metabolites are higher, while T(2) values are slightly lower at 7T than those of 3T compared to reported results in TA. The maximum percentage of increase in T(1) is about approximately 488%, the maximum percentage of decrease in T(2) is about approximately 65%. CONCLUSION: The preliminary results can potentially be used for calculating relaxation correction factors required for absolute quantitation of skeletal muscle metabolite concentrations and for further protocol and sequence optimization. J. Magn. Reson. Imaging 2009;29:1457-1464. (c) 2009 Wiley-Liss, Inc
— id: 99239, year: 2009, vol: 29, page: 1457, stat: Journal Article,

Rapid isotropic 3D-sodium MRI of the knee joint in vivo at 7T
Wang, Ligong; Wu, Yan; Chang, Gregory; Oesingmann, Niels; Schweitzer, Mark E; Jerschow, Alexej; Regatte, Ravinder R
2009 Sep;30(3):606-614, Journal of magnetic resonance imaging
PURPOSE: To demonstrate the feasibility of acquiring high-resolution, isotropic 3D-sodium magnetic resonance (MR) images of the whole knee joint in vivo at ultrahigh field strength (7.0T) via a 3D-radial acquisition with ultrashort echo times and clinically acceptable acquisition times. MATERIALS AND METHODS: Five healthy controls (four males, one female; mean +/- standard deviation [SD] age 28.7 +/- 4.8 years) and five patients with osteoarthritis (OA) (three males, two females; mean +/- SD age 52.4 +/- 5.6 years) underwent (23)Na MRI on a 7T, multinuclei equipped whole-body scanner. A quadrature (23)Na knee coil and a 3D-gradient echo (GRE) imaging sequence with a radial acquisition were utilized. Cartilage sodium concentration was measured and compared between the healthy controls and OA patients. RESULTS: The average signal-to-noise ratio (SNR) for different spatial resolutions (1.2-4 mm) varied from approximately 14-120, respectively. The mean sodium concentration of healthy subjects ranged from approximately 240 +/- 28 mM/L to 280 +/- 22 mM/L. However, in OA patients the sodium concentrations were reduced significantly by approximately 30%-60%, depending on the degree of cartilage degeneration. CONCLUSION: The preliminary results suggest that sodium imaging at 7T may be a feasible potential alternative for physiologic OA imaging and clinical diagnosis. J. Magn. Reson. Imaging 2009;30:606-614. (c) 2009 Wiley-Liss, Inc
— id: 101905, year: 2009, vol: 30, page: 606, stat: Journal Article,

Adaptations in trabecular bone microarchitecture in Olympic athletes determined by 7T MRI
Chang, Gregory; Pakin, S Kubilay; Schweitzer, Mark E; Saha, Punam K; Regatte, Ravinder R
2008 May;27(5):1089-1095, Journal of magnetic resonance imaging
PURPOSE: To produce in vivo high-resolution images of the knee and to determine the feasibility of using 7T MR to detect changes in trabecular bone microarchitecture in elite athletes (Olympic fencers) who undergo high impact activity. MATERIALS AND METHODS: The dominant knees of four males from the U.S. Olympic Fencing Team and three matched healthy male controls were scanned in a 7T whole-body scanner using a quadrature knee coil with three-dimensional (3D) fast low angle shot (FLASH): 50 axial images at the distal femur (0.156 mm x 0.156 mm) and 80 axial images at the knee joint (0.195 mm x 0.195 mm). Bone volume fraction (BVF) and marrow volume fraction (MVF) images were computed and fuzzy distance transform (FDT) and digital topological analysis (DTA) were applied to determine: trabecular number (Tb.N), trabecular thickness (Tb.Th), and trabecular separation (Tb.Sp); BVF (BV/TV); trabecular and marrow space surface-to-curve ratio (SC, marker of plate to rod ratio); and trabecular and marrow space erosion index (EI, inverse marker for network connectivity). Quadriceps muscle volume (MV) was calculated as well. We calculated group means and performed two-tailed t-tests to determine statistical significance. RESULTS: Compared to controls, fencers had: decreased Tb.Sp (P = 0.0082 at femur, P = 0.051 at joint); increased Tb.N (P < 0.05 at both femur and joint) and BV/TV (P < 0.001 at both femur and joint); increased trabecular SC and decreased marrow space SC (P < 0.01 at both femur and joint); decreased trabecular EI and increased marrow space EI (P < 0.01 at both femur and joint); and increased MV (P = 0.038). There was no difference in Tb.Th at the distal femur (P = 0.92) or joint (P = 0.71) between groups. CONCLUSION: To our knowledge, this is the first study to perform 7T MRI of the knee in vivo. Elite athletes who undergo high impact activity have increased MV and improved trabecular bone structure compared to controls
— id: 81572, year: 2008, vol: 27, page: 1089, stat: Journal Article,

PHYS 281-23Na and CEST MRI for assessing osteoarthritis and disc disorders
Jerschow, A; Ling, W; Navon, G; Regatte, RR
2008 AUG 17 ;236(2):94-94, Abstracts of papers (American Chemical Society)
— id: 106241, year: 2008, vol: 236, page: 94, stat: Journal Article,

PHYS 281-23Na and CEST MRI for assessing osteoarthritis and disc disorders
Jerschow, A; Ling, W; Navon, G; Regatte, RR
2008 AUG 17 ;236(2):108-108, Abstracts of papers (American Chemical Society)
— id: 106242, year: 2008, vol: 236, page: 108, stat: Journal Article,

Synovial but not cartilage volumes on MRI predict radiographic severity of knee Osteoarthritis (OA)
Krasnokutsky, S; Samuels, J; Attur, M; Regatte, R; Belitskaya-Levy, I; Babb, J; Rosenthal, P; Al-Mussawir, H; Abellana, V; Greenberg, J; Schweitzer, M; Abramson, SB
2008 SEP ;58(9):S889-S890, Arthritis & rheumatism
— id: 88577, year: 2008, vol: 58, page: S889, stat: Journal Article,

Optimal nuclear magnetic resonance excitation schemes for the central transition of a spin 3/2 in the presence of residual quadrupolar coupling
Lee, Jae-Seung; Regatte, Ravinder R; Jerschow, Alexej
2008 Dec 14;129(22):224510-224510, Journal of chemical physics
Optimal control theory is applied for enhancing the intensity of the central peak of a spin 3/2 signal in the presence of a residual quadrupolar coupling. While a maximum enhancement is always possible in the regime omega(rf) << omega(Q) via the use of modulated and shaped pulses, the intermediate rf-power regime omega(rf)-omega(Q) does not admit simple solutions based on intuition. In this work we present optimized shaped pulses that have been derived using an optimization algorithm based on optimal control and test these with (23)Na NMR in this regime. In addition to enhancing the intensity of the central transition signal, the satellite peaks can be effectively suppressed, which is a useful feature for the implementation in (23)Na imaging sequences
— id: 94397, year: 2008, vol: 129, page: 224510, stat: Journal Article,

Assessment of glycosaminoglycan concentration in vivo by chemical exchange-dependent saturation transfer (gagCEST)
Ling, Wen; Regatte, Ravinder R; Navon, Gil; Jerschow, Alexej
2008 Feb 19;105(7):2266-2270, Proceedings of the National Academy of Sciences of the United States of America
Glycosaminogycans (GAGs) are involved in numerous vital functions in the human body. Mapping the GAG concentration in vivo is desirable for the diagnosis and monitoring of a number of diseases such as osteoarthritis, which affects millions of individuals. GAG loss in cartilage is typically an initiating event in osteoarthritis. Another widespread pathology related to GAG is intervertebral disk degeneration. Currently existing techniques for GAG monitoring, such as delayed gadolinium-enhanced MRI contrast (dGEMRIC), T(1)(rho), and (23)Na MRI, have some practical limitations. We show that by exploiting the exchangeable protons of GAG one may directly measure the localized GAG concentration in vivo with high sensitivity and therefore obtain a powerful diagnostic MRI method
— id: 76129, year: 2008, vol: 105, page: 2266, stat: Journal Article,

Characterization of bovine patellar cartilage by NMR
Ling, Wen; Regatte, Ravinder R; Schweitzer, Mark E; Jerschow, Alexej
2008 Apr;21(3):289-295 6, NMR in biomedicine
Metabolic and structural changes in cartilage tissue are thought to be at the root of degenerative joint disease. We identify here the NMR resonances in bovine patellar cartilage tissue by static and high-resolution magic angle spinning (HRMAS) NMR spectroscopy, (1)H-(13)C heteronuclear single-quantum correlation (HSQC) spectroscopy, total correlation spectroscopy (TOCSY), and saturation transfer experiments. Some differences between the patellar cartilage samples studied here and earlier nasal cartilage and intervertebrate disc studies were found. In addition, we show assignments downfield of the water signal, which also includes the assignment of amide and hydroxy protons on the basis of their exchangeability with water. These results will allow an identification of spectroscopic markers of cartilage degradation using techniques such as chemical exchange saturation transfer imaging.
— id: 73798, year: 2008, vol: 21, page: 289, stat: Journal Article,

Novel contrast mechanisms at 3 Tesla and 7 Tesla
Regatte, Ravinder R; Schweitzer, Mark E
2008 Sep;12(3):266-280, Seminars in musculoskeletal radiology
Osteoarthritis (OA) is the most common musculoskeletal degenerative disease, affecting millions of people. Although OA has been considered primarily a cartilage disorder associated with focal cartilage degeneration, it is accompanied by well-known changes in subchondral and trabecular bone, including sclerosis and osteophyte formation. The exact cause of OA initiation and progression remains under debate, but OA typically first affects weightbearing joints such as the knee. Magnetic resonance imaging (MRI) has been recognized as a potential tool for quantitative assessment of cartilage abnormalities due to its excellent soft tissue contrast. Over the last two decades, several new MR biochemical imaging methods have been developed to characterize the disease process and possibly predict the progression of knee OA. These new MR biochemical methods play an important role not only for diagnosis of disease at an early stage, but also for their potential use in monitoring outcome of various drug therapies (success or failure). Recent advances in multicoil radiofrequency technology and high field systems (3 T and above) significantly improve the sensitivity and specificity of imaging studies for the diagnosis of musculoskeletal disorders. The current state-of-the-art MR imaging methods are briefly reviewed for the quantitative biochemical and functional imaging assessment of musculoskeletal systems
— id: 91448, year: 2008, vol: 12, page: 266, stat: Journal Article,

Clean demarcation of cartilage tissue 23Na by inversion recovery
Rong, Peng; Regatte, Ravinder R; Jerschow, Alexej
2008 Aug;193(2):207-209, Journal of magnetic resonance
Monitoring the sodium concentration in vivo using 23Na MRI can be an important tool for assessing the onset of tissue disorders. Practical clinical 23Na MRI methods furthermore often do not allow one to use sufficiently small voxel sizes such that only the tissue of interest is seen, but a large signal contamination can arise from sodium in synovial fluid. Here we demonstrate that applying an inversion recovery (IR) technique allows one to distinctly select either the cartilage-bound or the free sodium for visualization in an image. The results are validated both ex vivo and in vivo
— id: 94398, year: 2008, vol: 193, page: 207, stat: Journal Article,

Rapid 3D-T(1) mapping of cartilage with variable flip angle and parallel imaging at 3.0T
Wang, Ligong; Schweitzer, Mark E; Padua, Abraham; Regatte, Ravinder R
2008 Jan;27(1):154-161, Journal of magnetic resonance imaging
PURPOSE: To rapidly acquire T(1)-weighted images using a three-dimensional fast low angle shot (3D FLASH) sequence in combination with generalized autocalibrating partially parallel acquisitions (GRAPPA) and variable flip angle (VFA) method at 3.0T. MATERIALS AND METHODS: 3D T(1) maps of model systems (gadolinium [Gd] and agarose phantoms), bovine cartilage, and human subjects were constructed on a 3.0T clinical whole-body MR scanner. The T(1) values of model systems measured using the 2D inversion-recovery fast-spin-echo (IR-FSE) sequence were considered as a reference method to validate the rapid 3D method for comparison. RESULTS: The root mean square coefficient of variation percentage (RMS-CV%) of the median T(1) of agarose phantom across different acquisition methods was approximately 6.2%. The RMS-CV% of the median T(1) of bovine cartilage across different acquisition methods was approximately 4.1%. The RMS-CV% of median T(1) of the cartilages among the subjects was between approximately 7.3% to 11.1%. In our study, rapid 3D-T(1) mapping with VFA and parallel imaging with different acceleration factors (AFs) (AF = 1, 2, 3, and 4) seems to have no obvious influence on the T(1) mapping (before and after contrast agent administration). CONCLUSION: The preliminary results demonstrate that it is possible to quantify 3D-T(1) mapping of the whole knee joint (with 0.7 mm(3) isotropic resolution) under approximately five minutes with excellent in vivo reproducibility at 3.0T
— id: 76456, year: 2008, vol: 27, page: 154, stat: Journal Article,

Three-dimensional spin-lock magnetic resonance imaging of the shoulder joint at 3 T: initial experience
La Rocca Vieira, Renata; Pakin, Sait Kubilay; de Albuquerque Cavalcanti, Conrado Furtado; Schweitzer, Mark; Regatte, Ravinder
2007 Dec;36(12):1171-1175, Skeletal radiology
OBJECTIVES: This was a pilot study which aimed to assess the feasibility of 3D-spin-lock (3D-T(1rho)) MRI of the shoulder joint and to establish baseline values of healthy humeral and glenoid cartilages in vivo. MATERIAL AND METHODS: Four asymptomatic volunteers [mean age 31 years (range 29-36 years)] were recruited. A 3.0 T scanner, employing a four-channel, phased-array, shoulder, radio-frequency (RF) coil was used. Three-dimensional T(1rho)-weighted images were acquired with a 3D gradient-echo (GRE) sequence with T(1rho) magnetization preparation. In order to a construct T(1rho) map, we acquired four 3D-T(1rho)-weighted images with spin-locking length (TSL) values of 2 ms, 10 ms, 20 ms, and 30 ms. The glenoid and humeral cartilage were segmented manually at each slice of the 3D images. We performed additional regional analysis by dividing the cartilage into anterior/posterior and superior/inferior regions. RESULTS: The global average T(1rho) value of the shoulder cartilages varied from 37.9 ms to 48.5 ms and from 32.4 ms to 36.9 ms for humeral and glenoid cartilages, respectively. In the humeral cartilage, the average regional T(1rho) values varied from 35.9 ms to 52.2 ms; 54.4 ms to 69.0 ms; 39.1 ms to 49.3 ms and 34.6 ms to 57.2 ms for the anterior-superior, anterior-inferior , posterior-superior and posterior-inferior regions, respectively. In the glenoid cartilage, the values varied from 31.3 ms to 40.8 ms; 34.1 ms to 35.3 ms; 26.7 ms to 37.2 ms and 32.8 ms to 35.7 ms for the same regions, respectively. CONCLUSION: We demonstrated that 3D-T(1rho) MRI of the shoulder can be performed on a 3 T clinical scanner within specific absorption rate (SAR) limits, and we present baseline values for healthy patients which may be useful for quantitative comparison with diseased shoulders
— id: 76331, year: 2007, vol: 36, page: 1171, stat: Journal Article,

Bone marrow changes (edema and fatty infiltration) on MRI predict radiographic severity of knee OA
Regatte R; Krasnokutsky S; Samuels J; Rosenthal P; Abellana V; Greenberg J; Babb J; Schweitzer M; Attur M; Abramson SB
2007 ;15:C180-C180, Osteoarthritis & cartilage
— id: 86572, year: 2007, vol: 15, page: C180, stat: Journal Article,

Ultra-high-field MRI of the musculoskeletal system at 7.0T
Regatte, Ravinder R; Schweitzer, Mark E
2007 Feb;25(2):262-269, Journal of magnetic resonance imaging
High-field (3T) and ultra-high-field (UHF, 7T and above) systems are increasingly being used to explore potential musculoskeletal applications because they provide a high intrinsic signal-to-noise ratio (SNR), potentially higher resolution (spatial and temporal), and improved contrast. However, imaging at 7T and above presents certain challenges, such as homogeneous radiofrequency (RF) coil design, increased chemical shift artifacts, susceptibility artifacts, RF energy deposition, and changes in relaxation times compared to more typical clinical scanners (1.5 and 3T). Despite these issues, MRI at 7T likely will provide some excellent opportunities for high-resolution morphologic imaging and forays into functional imaging of musculoskeletal systems. In this review we address some of these issues and also demonstrate the feasibility of acquiring high-resolution in vivo images of the musculoskeletal system in healthy human volunteers at 7.0T
— id: 71207, year: 2007, vol: 25, page: 262, stat: Journal Article,

Magic sandwich echo relaxation mapping of anisotropic systems
Regatte, Ravinder R; Schweitzer, Mark E; Jerschow, Alexej; Reddy, Ravinder
2007 Apr;25(3):433-438, Magnetic resonance imaging
The main objective of this article was (i) to refocus the residual dipolar and quadrupolar interactions in anisotropic tissues employing magic sandwich echo (MSE) imaging and to compare the results with that of conventional spin-echo (SE) imaging, and (ii) to quantify MSE relaxation and dispersion characteristics in bovine Achilles tendon and compare with spin-lattice relaxation time constant in the rotating frame (T(1rho)). Magic sandwich echo weighted images are approximately 75-100% higher in signal-to-noise ratio than the corresponding T(2)-weighted images. Magic sandwich echo relaxation times varied from 13+/-2 to 19+/-3 ms (mean+/-S.D.), depending upon the structural location of tendon. T(2) relaxation times only varied from 4+/-1 to 10+/-3 ms (mean+/-S.D.) on the same corresponding locations. Magic sandwich echo provides approximately 100% enhancement in relaxation times compared to T(2). Preliminary results based on bovine Achilles tendon and cartilage specimens suggest that the MSE technique has potential for refocusing residual dipolar as well as quadrupolar interactions in anisotropic systems and yields higher intensities than conventional SE imaging as well as T(1rho)-encoded imaging, especially at low-burst pulse amplitudes (250 and 500 Hz).
— id: 72730, year: 2007, vol: 25, page: 433, stat: Journal Article,

Behavior of ordered sodium in enzymatically depleted cartilage tissue
Ling, Wen; Regatte, Ravinder R; Schweitzer, Mark E; Jerschow, Alexej
2006 Nov;56(5):1151-1155, Magnetic resonance in medicine
The onset of cartilage tissue disorders can be characterized by a loss of proteoglycans (PGs) and diagnosed by contrast-enhanced proton ((1)H) MRI techniques, as well as sodium MRI. The behavior of sodium located in anisotropic environments, is examined as a function of cartilage degeneration. PGs are proteolytically depleted from the cartilage samples, which gives rise to a decrease of the ordered sodium content. More surprisingly, however, the residual quadrupolar couplings are shown to increase with increasing depletion levels. Since the residual quadrupolar couplings are intimately related to local order and anisotropic motion, measuring their distribution in cartilage may provide insight into the structural changes that occur within the tissue upon degradation. In this study relatively mild orientational dependence of the couplings was found. Little or no free sodium was observed in the cartilage specimens under study
— id: 73797, year: 2006, vol: 56, page: 1151, stat: Journal Article,

Ultra-high-field MRI of knee joint at 7.0T: preliminary experience
Pakin, S Kubilay; Cavalcanti, Conrado; La Rocca, Renata; Schweitzer, Mark E; Regatte, Ravinder R
2006 Sep;13(9):1135-1142, Academic radiology
RATIONALE AND OBJECTIVES: To measure signal-to-noise ratio (SNR), contrast, and relaxation times (T1 and T2) in human knee joint at 7.0T whole-body scanner. MATERIALS AND METHODS: MRI experiments were performed on a 7.0T Siemens whole-body scanner using an 18-cm diameter transmit/receive knee coil. Normalized SNR and relaxation times (T1 and T2) were computed on all volunteers (healthy, n=5) for femoral, tibial, and patellar cartilage. RESULTS: Average T1 values of femoral, tibial, and patellar cartilages were found as 1.55, 1.76, and 1.62 seconds, respectively. Average T2 values of femoral, tibial, and patellar cartilages were found as 51.3, 43.9, and 39.7 milliseconds, respectively. No statistically significant differences were observed between T1 and T2 values of different cartilage tissues (P>.08 for all comparisons). Compared with previously reported relaxation times of cartilage tissue at 3.0T, an approximately 35% increase was observed in T1 values, whereas no significant change was observed in T2. Regional analysis was also performed to investigate the change in relaxation parameters for weight-bearing vs. non-weight-bearing areas. A statistically significant difference was observed in T2 of tibial cartilage (P=.009). The rest of the comparisons yielded insignificant differences (P>.32). CONCLUSION: Our preliminary results demonstrate the feasibility of acquiring high resolution three-dimensional images of knee joint (with and without fat suppression) at 7.0T whole-body scanner
— id: 79456, year: 2006, vol: 13, page: 1135, stat: Journal Article,

3D-T1rho quantitation of patellar cartilage at 3.0T
Pakin, S Kubilay; Schweitzer, Mark E; Regatte, Ravinder R
2006 Dec;24(6):1357-1363, Journal of magnetic resonance imaging
PURPOSE: To demonstrate the feasibility of three-dimensional (3D) T(1rho)-weighted imaging of human knee joint at 3.0T without exceeding the specific absorption rate (SAR) limits and the measurement of the baseline T(1rho) values of patellar cartilage and several muscles at the knee joint. MATERIALS AND METHODS: 3D gradient-echo sequence with a self-compensating spin-lock pulse cluster of 250 Hz power was used to acquire 3D-T(1rho)-weighted images of the knee joint of five healthy subjects. Global and regional analysis of patellar cartilage T(1rho) were performed. Furthermore, T(1rho) of several periarticular muscles were analyzed. RESULTS: The global average T(1rho) value of the patellar cartilage varied from 39 to 43 msec. The regional average T(1rho) values varied from 38 to 42 msec, and from 42 to 44 msec for medial and lateral facets, respectively. In vivo reproducibility of average T(1rho) of patellar cartilage was found to be 5% (coefficient of variation). Similarly, the global average T(1rho) values for biceps femoris, lateral gastrocnemius, medial gastrocnemius, and sartorius varied between 31-46, 29-49, 35-48, and 32-50 msec, respectively. CONCLUSION: We demonstrated the feasibility of 3D-T(1rho)-weighted imaging of the knee joint at 3.0T without exceeding SAR limits
— id: 94399, year: 2006, vol: 24, page: 1357, stat: Journal Article,

Rapid 3D-T1rho mapping of the knee joint at 3.0T with parallel imaging
Pakin, S Kubilay; Xu, Jian; Schweitzer, Mark E; Regatte, Ravinder R
2006 Sep;56(3):563-571, Magnetic resonance in medicine
Three-dimensional spin-lattice relaxation time in the rotating frame (3D-T1rho) with parallel imaging at 3.0T was implemented on a whole-body clinical scanner. A 3D gradient-echo sequence with a self-compensating spin-lock pulse cluster was combined with generalized autocalibrating partially parallel acquisitions (GRAPPA) to acquire T1rho-weighted images. 3D-T1rho maps of an agarose phantom and three healthy subjects were constructed using an eight-channel phased-array coil without parallel imaging and with parallel imaging acceleration factors of 2 and 3, in order to assess the reproducibility of the method. The coefficient of variation (CV) of the median T1rho of the agarose phantom was 0.44%, which shows excellent reproducibility. The reproducibility of in vivo 3D-T1rho maps was also investigated in three healthy subjects. The CV of the median T1rho of the patellar cartilage varied between approximately 1.1% and 4.3%. Similarly, the CV varied between approximately 2.1-5.8%, approximately 1.4-8.7%, and approximately 1.5-4.1% for the biceps femoris and lateral and medial gastrocnemius muscles, respectively. The preliminary results demonstrate that 3D-T1rho maps can be constructed with good reproducibility using parallel imaging. 3D-T1rho with parallel imaging capability is an important clinical tool for reducing both the total acquisition time and RF energy deposition at 3T
— id: 69581, year: 2006, vol: 56, page: 563, stat: Journal Article,

T1rho relaxation mapping in human osteoarthritis (OA) cartilage: comparison of T1rho with T2
Regatte, Ravinder R; Akella, Sarma V S; Lonner, J H; Kneeland, J B; Reddy, Ravinder
2006 Apr;23(4):547-553, Journal of magnetic resonance imaging
PURPOSE: To quantify the spin-lattice relaxation time in the rotating frame (T1rho) in various clinical grades of human osteoarthritis (OA) cartilage specimens obtained from total knee replacement surgery, and to correlate the T1rho with OA disease progression and compare it with the transverse relaxation time (T2). MATERIALS AND METHODS: Human cartilage specimens were obtained from consenting patients (N = 8) who underwent total replacement of the knee joint at the Pennsylvania Hospital, Philadelphia, PA, USA. T2- and T1rho-weighted images were obtained on a 4.0 Tesla whole-body GE Signa scanner (GEMS, Milwaukee, WI, USA). A 7-cm diameter transmit/receive quadrature birdcage coil tuned to 170 MHz was employed. RESULTS: All of the surgical knee replacement OA cartilage specimens showed elevated relaxation times (T2 and T1rho) compared to healthy cartilage tissue. In various grades of OA specimens, the T1rho relaxation times varied from 62 +/- 5 msec to 100 +/- 8 msec (mean +/- SEM) depending on the degree of cartilage degeneration. However, T2 relaxation times varied only from 32 +/- 2 msec to 45 +/- 4 msec (mean +/- SEM) on the same cartilage specimens. The increase in T2 and T1rho in various clinical grades of OA specimens were approximately 5-50% and 30-120%, respectively, compared to healthy specimens. The degenerative status of the cartilage specimens was also confirmed by histological evaluation. CONCLUSION: Preliminary results from a limited number of knee specimens (N = 8) suggest that T1rho relaxation mapping is a sensitive noninvasive marker for quantitatively predicting and monitoring the status of macromolecules in early OA. Furthermore, T1rho has a higher dynamic range (>100%) for detecting early pathology compared to T2. This higher dynamic range can be exploited to measure even small macromolecular changes with greater accuracy compared to T2. Because of these advantages, T1rho relaxation mapping may be useful for evaluating early OA therapy
— id: 66998, year: 2006, vol: 23, page: 547, stat: Journal Article,

Depth-dependent proton magnetization transfer in articular cartilage
Regatte, Ravinder R; Akella, Sarma V S; Reddy, Ravinder
2005 Aug;22(2):318-323, Journal of magnetic resonance imaging
PURPOSE: To measure the proton magnetization transfer ratio (MTR) maps in control and collagen-depleted bovine patellar cartilage specimens as a function of cartilage depth during mechanical compression. MATERIALS AND METHODS: One-dimensional proton projection MR images employing a spin-echo imaging sequence were obtained on a custom-built NMR spectrometer interfaced to an Oxford magnet operating at 2T. The mechanical compressions were performed with a custom-built MR-compatible pressure cell and evaluated dynamically via one-dimensional projection. High-spatial-resolution two-dimensional MT images were obtained using a fast spin-echo (FSE) sequence on a 4T whole-body GE Signa scanner (GEMS, Milwaukee, WI, USA) to quantify the MTR maps of normal and collagen-depleted bovine patellae. RESULTS: All of the cartilage plugs from the bovine patellae showed that the MTR value increases continuously as a function of cartilage depth. Although the overall MTR trend as a function of depth is the same in both control and collagen-depleted cartilage, the magnitude of the MTR value differs between the two. The MTR value is decreased with collagen depletion and increased with mechanical compression. The increase in MTR value during compression may be due to a decrease in free water content and volume, resulting in an increase in collagen concentration. CONCLUSION: We demonstrated that the MTR in bovine patellar cartilage is depth-dependent and is relatively higher in the radial zone compared to the superficial zone. The high MTR in the radial zone not only depends on collagen content, it may also reflect a number of other parameters, such as the arrangement of macromolecules, high solid content, bound water fraction attached to macromolecules, radial orientation, etc
— id: 94400, year: 2005, vol: 22, page: 318, stat: Journal Article,

Reduction of residual dipolar interaction in cartilage by spin-lock technique
Akella, Sarma V S; Regatte, Ravinder R; Wheaton, Andrew J; Borthakur, Arijitt; Reddy, Ravinder
2004 Nov;52(5):1103-1109, Magnetic resonance in medicine
The influence of radiofrequency (RF) spin-lock pulse on the laminar appearance of articular cartilage in MR images was investigated. Spin-lock MRI experiments were performed on bovine cartilage plugs on a 4.7 Tesla small-bore MRI scanner, and on human knee cartilage in vivo on a 1.5 Tesla clinical scanner. When the normal to the surface of cartilage was parallel to B0, a typical laminar appearance was exhibited in T2-weighted images of cartilage plugs, but was absent in T1rho-weighted images of the same plugs. At the 'magic angle' orientation (when the normal to the surface of cartilage was 54.7 degrees with respect to B0), neither the T2 nor the T1rho images demonstrated laminae. At the same time, T1rho values were greater than T2 at both orientations throughout the cartilage. T1rho dispersion (i.e., the dependence of the relaxation rate on the spin-lock frequency omega1) was observed, which reached a steady-state value of close to 2 kHz in both parallel and magic-angle orientations. These results suggest that residual dipolar interaction from motionally-restricted water and relaxation processes, such as chemical exchange, contribute to T1rho dispersion in cartilage. Further, one can reduce the laminar appearance in human articular cartilage by applying spin-lock RF pulses, which may lead to a more accurate diagnosis of degenerative changes in cartilage
— id: 49171, year: 2004, vol: 52, page: 1103, stat: Journal Article,

In vivo measurement of T1rho dispersion in the human brain at 1.5 tesla
Borthakur, Arijitt; Wheaton, Andrew J; Gougoutas, Alexander J; Akella, Sarma V S; Regatte, Ravinder R; Charagundla, Sridhar R; Reddy, Ravinder
2004 Apr;19(4):403-409, Journal of magnetic resonance imaging
PURPOSE: To measure T1rho relaxation times and T1rho dispersion in the human brain in vivo. MATERIALS AND METHODS: Magnetic resonance imaging (MRI) was performed on a 1.5-T GE Signa clinical scanner using the standard GE head coil. A fast spin-echo (FSE)-based T1rho-weighted MR pulse sequence was employed to obtain images from five healthy male volunteers. Optimal imaging parameters were determined while considering both the objective of the study and the guarantee that radio-frequency (RF) power deposition during MR did not exceed Food and Drug Administration (FDA)-mandated safety levels. RESULTS: T1rho-weighted MR images showed excellent contrast between different brain tissues. These images were less blurred than corresponding T2-weighted images obtained with similar contrast, especially in regions between brain parenchyma and cerebrospinal fluid (CSF). Average T1rho values for white matter (WM), gray matter (GM), and CSF were 85 +/- 3, 99 +/- 1, and 637 +/- 78 msec, respectively, at a spin-locking field of 500 Hz. T1rho is 30% higher in the parenchyma and 78% higher in CSF compared to the corresponding T2 values. T1rho dispersion was observed between spin-locking frequencies 0 and 500 Hz. CONCLUSION: T1rho-weighted MRI provides images of the brain with superb contrast and detail. T1rho values measured in the different brain tissues will serve as useful baseline values for analysis of T1rho changes associated with pathology
— id: 49175, year: 2004, vol: 19, page: 403, stat: Journal Article,

3D-T1rho-relaxation mapping of articular cartilage: in vivo assessment of early degenerative changes in symptomatic osteoarthritic subjects
Regatte, Ravinder Reddy; Akella, Sarma V S; Wheaton, Andrew J; Lech, Gwen; Borthakur, Arijitt; Kneeland, J Bruce; Reddy, Ravinder
2004 Jul;11(7):741-749, Academic radiology
RATIONALE AND OBJECTIVES: To determine the in vivo feasibility of quantifying early degenerative changes in patellofemoral joint of symptomatic human knee using spin-lattice relaxation time in the rotating frame (T(1rho)) magnetic resonance imaging (MRI). MATERIALS AND METHODS: All the MRI experiments were performed on a 1.5 T whole-body GE Signa clinical scanner using a custom built 15-cm diameter transmit-receive quadrature birdcage radiofrequency coil. The T(1rho)-prepared magnetization was imaged with a three-dimensional gradient-echo pulse sequence pre-encoded with a three-pulse cluster consisting of two hard 90 degrees pulses and a low power spin-lock pulse. Quantitative T(1rho) relaxation maps of asymptomatic (n = 8 males), and six symptomatic human volunteers (four men, two women) were computed using a appropriate signal expression. RESULTS: All six symptomatic volunteers showed elevation in T(1rho) relaxation times when compared with asymptomatic subjects. In symptomatic population, the T(1rho) relaxation times varied from 63 +/- 4 ms to 95 +/- 12 ms (mean +/- standard deviation) depending on the degree of cartilage degeneration. The increase in T(1rho) of symptomatic population was statistically significant (n = 6, P <.002) when compared with corresponding asymptomatic population. However, in asymptomatic population the relaxation times varied only from approximately 45 to 55 ms (n = 8, age range 22-45 years). CONCLUSION: Preliminary results demonstrated the in vivo feasibility of quantifying early biochemical changes in symptomatic osteoarthritis subjects employing T(1rho)-weighted MRI on a 1.5 T clinical scanner. This study on limited number of symptomatic population shows that T(1rho)-weighted MRI provides a noninvasive marker for quantitation of early degenerative changes of cartilage in vivo. However, further studies are needed to correlate early osteoarthritis determined from arthroscopy with T(1rho) in a large symptomatic population
— id: 49172, year: 2004, vol: 11, page: 741, stat: Journal Article,

Proton MRI of metabolically produced H2 17O using an efficient 17O2 delivery system
Tailor, Dharmesh R; Baumgardner, James E; Regatte, Ravinder R; Leigh, John S; Reddy, Ravinder
2004 Jun;22(2):611-618, Neuroimage
In vivo detection of H(2)(17)O produced via metabolic reduction of inhaled (17)O-enriched gas is demonstrated using proton magnetic resonance imaging (MRI). Specifically, (1)H T(1rho)-weighted MRI, which may be readily implemented on any MRI scanner, is applied as an indirect (17)O imaging method to quantitatively monitor the distribution of metabolically produced (17)O water (mpH(2)(17)O) in the rat brain. The delivery of (17)O(2) to rats is conducted via a specially designed closed respiration circuit that conserves the expensive gas. Quantitative mapping of H(2)(17)O performed via (1)H T(1rho)-weighted MRI is validated by direct (17)O-magnetic resonance spectroscopy. The MRI data show that a steady-state H(2)(17)O concentration of 25.7 +/- 1.66 mM (n = 4) is achieved in the rat brain within approximately 30 min under the (17)O inhalation paradigm used. From the first minute of the mpH(2)(17)O time courses, cerebral metabolic rate of oxygen (CMRO(2)) is estimated to be 2.10 +/- 0.44 micromol g(-1) min(-1) (n = 4), a value that is consistent with the literature
— id: 49173, year: 2004, vol: 22, page: 611, stat: Journal Article,

In vivo quantification of T1rho using a multislice spin-lock pulse sequence
Wheaton, Andrew J; Borthakur, Arijitt; Kneeland, J Bruce; Regatte, Ravinder R; Akella, Sarma V S; Reddy, Ravinder
2004 Dec;52(6):1453-1458, Magnetic resonance in medicine
A multislice spin-lock (MS-SL) pulse sequence is implemented on a clinical scanner to acquire multiple images with spin-lock-generated contrast of the knee joints of six healthy human subjects. The MS-SL sequence produces images with T1rho contrast with an additional factor of intrinsic T2rho weighting, which hinders direct measurement of T1rho. A method is presented to compensate the MS-SL-generated data with regard to T2rho in an effort to accurately calculate multislice T1rho maps in a feasible experimental time. The T2rho-compensated multislice T1rho maps produced errors in the measurement of T1rho in healthy patellar cartilage of approximately 5% compared to the gold standard measurement of T1rho acquired with single-slice spin-lock pulse sequence. The MS-SL sequence has potential as an important clinical tool for the acquisition of multislice T1rho-weighted images and/or quantitative multislice T1rho maps
— id: 49170, year: 2004, vol: 52, page: 1453, stat: Journal Article,

Proteoglycan loss in human knee cartilage: quantitation with sodium MR imaging--feasibility study
Wheaton, Andrew J; Borthakur, Arijitt; Shapiro, Erik M; Regatte, Ravinder R; Akella, Sarma V S; Kneeland, J Bruce; Reddy, Ravinder
2004 Jun;231(3):900-905, Radiology
The feasibility of using sodium magnetic resonance (MR) imaging to detect proteoglycan loss in early-stage osteoarthritis is evaluated. Fixed charge density (FCD) maps were calculated from sodium MR imaging data collected in nine healthy volunteers and three individuals with symptoms of early-stage osteoarthritis by using a 4.0-T clinical MR imaging unit. Data from the healthy individuals revealed a mean FCD of -182 mmol/L +/- 9. Data from the symptomatic subjects revealed focal regions of decreased FCD, with mean values ranging from -108 to -144 mmol/L, indicating proteoglycan loss from the cartilage matrix. The data suggest that sodium MR imaging has potential for use as a quantitative diagnostic tool to measure changes in proteoglycan content in early-stage osteoarthritis
— id: 49174, year: 2004, vol: 231, page: 900, stat: Journal Article,

T1rho MR imaging of the human wrist in vivo
Akella, Sarma V S; Regatte, Ravinder R; Borthakur, Arijitt; Kneeland, J Bruce; Leigh, John S; Reddy, Ravinder
2003 Jun;10(6):614-619, Academic radiology
RATIONALE AND OBJECTIVES: The purpose of this study was (a) to demonstrate the feasibility of computing T1rho maps of, and T1rho dispersion in, human wrist cartilage at MR imaging in vivo and (b) to compare T1rho and T2 weighting in terms of magnitude of relaxation times and signal intensity contrast. MATERIALS AND METHODS: T2 and T1rho magnetic resonance images of wrist joints in healthy volunteers (n = 5) were obtained with a spin-echo sequence and a fast spin-echo sequence pre-encoded with a spin-lock pulse cluster. A 1.5-T clinical imager was used (Signa; GE Medical Systems, Milwaukee, Wis) with a 9.5-cm-diameter transmit-receive quadrature birdcage coil tuned to 63.75 MHz. RESULTS: T1rho relaxation times at a spin-lock frequency of 500 Hz vary from 40.5 msec +/- 0.85 to 56.6 msec +/- 4.83, and T2 relaxation times vary from 28.1 msec +/- 1.88 to 34.5 msec +/- 2.63 (mean +/- standard error of the mean, n = 5, P < .016) in various regions of the wrist. T1rho dispersion was observed in the range of spin-lock frequencies studied. T1rho-weighted images not only have higher signal-to-noise ratios but also show better fluid and fat signal suppression than T2-weighted images. CONCLUSION: It was possible to perform T2- and T1rho-weighted MR imaging of human wrist cartilage in vivo with standard clinical imagers. The higher signal-to-noise ratio and improved contrast between cartilage and surrounding fat achieved with T1rho imaging may provide better definition of lesions and accurate quantitation of small changes in cartilage degeneration
— id: 49178, year: 2003, vol: 10, page: 614, stat: Journal Article,

Three-dimensional T1rho-weighted MRI at 1.5 Tesla
Borthakur, Arijitt; Wheaton, Andrew; Charagundla, Sridhar R; Shapiro, Erik M; Regatte, Ravinder R; Akella, Sarma V S; Kneeland, J Bruce; Reddy, Ravinder
2003 Jun;17(6):730-736, Journal of magnetic resonance imaging
PURPOSE: To design and implement a magnetic resonance imaging (MRI) pulse sequence capable of performing three-dimensional T(1rho)-weighted MRI on a 1.5-T clinical scanner, and determine the optimal sequence parameters, both theoretically and experimentally, so that the energy deposition by the radiofrequency pulses in the sequence, measured as the specific absorption rate (SAR), does not exceed safety guidelines for imaging human subjects. MATERIALS AND METHODS: A three-pulse cluster was pre-encoded to a three-dimensional gradient-echo imaging sequence to create a three-dimensional, T(1rho)-weighted MRI pulse sequence. Imaging experiments were performed on a GE clinical scanner with a custom-built knee-coil. We validated the performance of this sequence by imaging articular cartilage of a bovine patella and comparing T(1rho) values measured by this sequence to those obtained with a previously tested two-dimensional imaging sequence. Using a previously developed model for SAR calculation, the imaging parameters were adjusted such that the energy deposition by the radiofrequency pulses in the sequence did not exceed safety guidelines for imaging human subjects. The actual temperature increase due to the sequence was measured in a phantom by a MRI-based temperature mapping technique. Following these experiments, the performance of this sequence was demonstrated in vivo by obtaining T(1rho)-weighted images of the knee joint of a healthy individual. RESULTS: Calculated T(1rho) of articular cartilage in the specimen was similar for both and three-dimensional and two-dimensional methods (84 +/- 2 msec and 80 +/- 3 msec, respectively). The temperature increase in the phantom resulting from the sequence was 0.015 degrees C, which is well below the established safety guidelines. Images of the human knee joint in vivo demonstrate a clear delineation of cartilage from surrounding tissues. CONCLUSION: We developed and implemented a three-dimensional T(1rho)-weighted pulse sequence on a 1.5-T clinical scanner
— id: 49179, year: 2003, vol: 17, page: 730, stat: Journal Article,

Probing rat brain oxygenation with near-infrared spectroscopy (NIRS) and magnetic resonance imaging (MRI)
Chen, Yu; Intes, Xavier; Tailor, Dharmesh R; Regatte, Ravinder R; Ma, HongYan; Ntziachristos, Vasilis; Leigh, John S; Reddy, Ravinder; Chance, Britton
2003 ;510:199-204, Advances in experimental medicine & biology
— id: 49181, year: 2003, vol: 510, page: 199, stat: Journal Article,

In vivo proton MR three-dimensional T1rho mapping of human articular cartilage: initial experience
Regatte, Ravinder Reddy; Akella, Sarma V S; Borthakur, Arijitt; Kneeland, J Bruce; Reddy, Ravinder
2003 Oct;229(1):269-274, Radiology
The purpose of this study was to demonstrate the feasibility of computing three-dimensional relaxation maps of spin-lattice relaxation time in the rotating frame (T1rho) from in vivo magnetic resonance (MR) images of the human patellofemoral joint. T1rho was measured by applying a three-dimensional gradient-echo pulse sequence in six healthy subjects and one symptomatic subject by using a 1.5-T MR imager and a 15-cm-diameter transmit-receive quadrature birdcage radiofrequency coil. Average T1rho measured in healthy patellar cartilage was 49.7 msec +/- 3.2 (mean +/- SD). Two-dimensional T1rho-weighted images were obtained with a fast spin-echo pulse sequence for comparison. There was good correlation between two-dimensional and three-dimensional T1rho values for the six healthy subjects (R2 = 0.88, slope = 1.16)
— id: 49176, year: 2003, vol: 229, page: 269, stat: Journal Article,

Proton spin-lock ratio imaging for quantitation of glycosaminoglycans in articular cartilage
Regatte, Ravinder Reddy; Akella, Sarma V S; Borthakur, Arijitt; Reddy, Ravinder
2003 Jan;17(1):114-121, Journal of magnetic resonance imaging
PURPOSE: To quantify glycosaminoglycans (GAG) in intact bovine patellar cartilage using the proton spin-lock ratio imaging method. This approach exploits spin-lattice relaxation time in the rotating frame (T(1rho)) imaging and T(1rho) relaxivity (R(1rho)). MATERIALS AND METHODS: All the magnetic resonance imaging (MRI) experiments were performed on a 4-T whole-body GE Signa scanner (GEMS, Milwaukee, WI), and spectroscopy experiments of chondroitin sulfate (CS) phantoms were done on a 2-T custom-built spectrometer. A custom-built 11-cm-diameter transmit-receive birdcage coil, which was tuned to a proton frequency of 170 MHz, was employed for the imaging experiments. T(1rho) measurements were made using a fast spin echo (FSE) sequence pre-encoded with a three-pulse cluster consisting of two 90 degrees hard pulses separated by a low-power rectangle pulse for spin-locking. RESULTS: The methodology is first validated on CS phantoms and then used to quantify GAG content in intact bovine cartilage (N = 5). There is a good agreement between the GAG map calculated from the T(1rho) ratio imaging method (71 +/- 4%) and GAG measured from spectrophotometric assay (75 +/- 5%) in intact bovine tissue. CONCLUSION: We have demonstrated a proton spin-lock ratio imaging method to quantify absolute GAG distribution in the cartilage in a noninvasive and nondestructive manner
— id: 49183, year: 2003, vol: 17, page: 114, stat: Journal Article,

T 1 rho-relaxation mapping of human femoral-tibial cartilage in vivo
Regatte, Ravinder Reddy; Akella, Sarma V S; Wheaton, Andrew J; Borthakur, Arijitt; Kneeland, J Bruce; Reddy, Ravinder
2003 Sep;18(3):336-341, Journal of magnetic resonance imaging
PURPOSE: To demonstrate the in vivo feasibility of measuring spin-lattice relaxation time in the rotating frame (T(1rho)); and T(1rho)-dispersion in human femoral cartilage. Furthermore, we aimed to compute the baseline T(1rho)-relaxation times and spin-lock contrast (SLC) maps on healthy volunteers, and compare relaxation times and signal-to-noise ratio (SNR) with corresponding T(2)-weighted images. MATERIALS AND METHODS: All MR imaging experiments were performed on a 1.5 T GE Signa scanner (GEMS, Milwaukee, WI) using a custom built 15-cm transmit-receive quadrature birdcage radio-frequency (RF) coil. The T(1rho)-prepared magnetization was imaged with a single-slice two-dimensional fast spin-echo (FSE) pulse sequence preencoded with a three-pulse cluster consisting of two hard 90 degrees pulses and a low power spin-lock pulse. T(1rho)-dispersion imaging was performed by varying the spin-lock frequency from 100 to 500 Hz in five steps in addition to varying the length of the spin-lock pulse. RESULTS: The average T(1rho)-relaxation times in the weight-bearing (WB) and nonweight-bearing (NWB) regions of the femoral condyle were 42.2 +/- 3.6 msec and 55.7 +/- 2.3 msec (mean +/- SD, N = 5, P < 0.0001), respectively. In the same regions, the corresponding T(2)-relaxation times were 31.8 +/- 1.5 msec and 37.6 +/- 3.6 msec (mean +/- SD, N = 5, P < 0.0099). T(1rho)-weighted images have approximately 20%-30% higher SNR than the corresponding T(2)-weighted images for similar echo time. The average SLC in the WB region of femoral cartilage was 30 +/-4.0%. Furthermore, SLC maps provide better contrast between fluid and articular surface of femoral-tibial joint than T(1rho)-maps. The T(1rho)-relaxation times varied from 32 msec to 42 msec ( approximately 31%) in the WB and 37 msec to 56 msec ( approximately 51%) in NWB regions of femoral condyle, respectively, in the frequency range 0-500 Hz (T(1rho)-dispersion). CONCLUSION: The feasibility of performing in vivo T(1rho) relaxation mapping in femoral cartilage at 1.5T clinical scanner without exceeding Food and Drug Administration (FDA) limits on specific absorption rate (SAR) of RF energy was demonstrated
— id: 49177, year: 2003, vol: 18, page: 336, stat: Journal Article,

Indirect 17(O)-magnetic resonance imaging of cerebral blood flow in the rat
Tailor, Dharmesh R; Roy, Arijit; Regatte, Ravinder R; Charagundla, Sridhar R; McLaughlin, Alan C; Leigh, John S; Reddy, Ravinder
2003 Mar;49(3):479-487, Magnetic resonance in medicine
Proton T(1rho)-dispersion MRI is demonstrated for indirect, in vivo detection of (17)O in the brain. This technique, which may be readily implemented on any clinical MRI scanner, is applied towards high-resolution, quantitative mapping of cerebral blood flow (CBF) in the rat by monitoring the clearance of (17)O-enriched water. Strategies are derived and employed for 1) quantitation of absolute H(2) (17)O tracer concentration from a ratio of high- and low-frequency spin-locked T(1rho) images, and 2) mapping CBF without having to transform the T(1rho) signal to H(2) (17)O tracer concentration. Absolute regional blood flow was mapped in a single 3-mm brain slice at an in-plane resolution of 0.4 x 0.8 mm within a 5-min tracer washout time; these data are consistent with the less localized CBF measurements reported in the literature. T(1rho)-weighted imaging yields excellent signal-to-noise ratios, spatiotemporal resolution, and anatomical contrast for mapping CBF
— id: 49180, year: 2003, vol: 49, page: 479, stat: Journal Article,

Proteoglycan depletion-induced changes in transverse relaxation maps of cartilage: comparison of T2 and T1rho
Regatte, Ravinder Reddy; Akella, Sarma V S; Borthakur, Arijitt; Kneeland, J Bruce; Reddy, Ravinder
2002 Dec;9(12):1388-1394, Academic radiology
RATIONALE AND OBJECTIVES: The authors performed this study to (a) measure changes in T2 relaxation rates, signal-to-noise ratio (SNR), and contrast with sequential depletion of proteoglycan in cartilage; (b) determine whether there is a relationship between the T2 relaxation rate and proteoglycan in cartilage; and (c) compare the T2 mapping method with the spin-lattice relaxation time in the rotating frame (T1rho) mapping method in the quantification of proteoglycan-induced changes. MATERIALS AND METHODS: T2- and T1rho-weighted magnetic resonance (MR) images were obtained in five bovine patellae. All images were obtained with a 4-T whole-body MR unit and a 10-cm-diameter transmit-receive quadrature birdcage coil tuned to 170 MHz. T2 and T1rho maps were computed. RESULTS: The SNR and contrast on the T2-weighted images were, on average, about 43% lower than those on the corresponding T1rho-weighted images. The T2 relaxation rates varied randomly without any particular trend, which yielded a poor correlation with sequential depletion of proteoglycan (R2 = 0.008, P < .70). There was excellent linear correlation between the percentage of proteoglycan in the tissue and the T1rho relaxation rate (R2 = 0.85, P < .0001). CONCLUSION: T2-weighted imaging neither yields quantitative information about the changes in proteoglycan distribution in cartilage nor can be used for longitudinal studies to quantify proteoglycan-induced changes. T1rho-weighted imaging, however, is sensitive to sequential depletion of proteoglycan in bovine cartilage and can be used to quantify proteoglycan-induced changes
— id: 49182, year: 2002, vol: 9, page: 1388, stat: Journal Article,

Proteoglycan-induced changes in T1rho-relaxation of articular cartilage at 4T
Akella SV; Regatte RR; Gougoutas AJ; Borthakur A; Shapiro EM; Kneeland JB; Leigh JS; Reddy R
2001 Sep;46(3):419-423, Magnetic resonance in medicine
Proteoglycan (PG) depletion-induced changes in T1rho (spin-lattice relaxation in rotating frame) relaxation and dispersion in articular cartilage were studied at 4T. Using a spin-lock cluster pre-encoded fast spin echo sequence, T1rho maps of healthy bovine specimens and specimens that were subjected to PG depletion were computed at varying spin-lock frequencies. Sequential PG depletion was induced by trypsinization of cartilage for varying amounts of time. Results demonstrated that over 50% depletion of PG from bovine articular cartilage resulted in average T1rho increases from 110-170 ms. Regression analysis of the data showed a strong correlation (R2 = 0.987) between changes in PG and T1rho. T1rho values were highest at the superficial zone and decreased gradually in the middle zone and again showed an increasing trend in the region near the subchondral bone. The potentials of this method in detecting early degenerative changes of cartilage are discussed. Also, T(1rho)-dispersion changes as a function of PG depletion are described
— id: 49184, year: 2001, vol: 46, page: 419, stat: Journal Article,

A novel approach to observing articular cartilage deformation in vitro via magnetic resonance imaging
Kaufman JH; Regatte RR; Bolinger L; Kneeland JB; Reddy R; Leigh JS
1999 May;9(5):653-662, Journal of magnetic resonance imaging
The design of a pressure cell that compresses a cartilage specimen in one dimension within an imaging magnet is presented. One-dimensional projection images in a direction perpendicular to the articular surface of the cartilage specimen were used to generate a uniaxial confined deformation creep curve for normal and trypsin-degraded cartilage specimens during a continuous 0.690 MPa (100 psi) pressure application. The resulting curves are shown to fit a two time constant viscoelastic model well and also indicate that the elastic modulus of cartilage decreases and the deformation rate increases upon trypsin proteolysis. Furthermore, cartilage permeability is shown as a function of cartilage strain for both the normal and trypsin-degraded case. Several two-dimensional slice-selective images were collected both before and after 80 minutes of continuous compression. These images were used to evaluate the relative changes in the spin-lattice, T1, and spin-spin, T2, relaxation time constant maps for both normal and degraded cartilage specimens in response to compression. The results of this study demonstrate the utility of a novel, non-magnetic, cartilage compression device and also support the validity of a simple two-component rheological model of articular cartilage
— id: 49186, year: 1999, vol: 9, page: 653, stat: Journal Article,

Sodium and proton MR properties of cartilage during compression
Regatte RR; Kaufman JH; Noyszewski EA; Reddy R
1999 Dec;10(6):961-967, Journal of magnetic resonance imaging
Proton and sodium MR relaxation times of bovine articular cartilage specimens were measured as a function of proteoglycan (PG) depletion and as a function of mechanical compression. Proton and sodium relaxation times of normal cartilage were compared with relaxation times of PG-depleted cartilage to evaluate the significance of PG depletion-induced changes in MR relaxation parameters. These comparisons were conducted for both uncompressed and mechanically compressed states. The mechanical compressions were performed with an MR-compatible pressure cell and evaluated dynamically via interleaved one-dimensional proton and sodium MR projection imaging. The comparisons indicate that sodium relaxation parameters are sensitive to PG depletion when cartilage is in a mechanically compressed state or an uncompressed state. In contrast, proton relaxation parameters do not change significantly with PG depletion when cartilage is in an uncompressed state. However, during mechanical compression, proton T2 becomes sensitive to PG depletion. These results support the potential of sodium magnetic resonance imaging (MRI) as a possible modality for obtaining imaging contrast related to PG depletion. The results also indicate the potential of proton MRI to provide such contrast if the image acquisition is conducted in conjunction with a mechanical compression via physical exercise.J. Magn. Reson Imaging 10:961-967, 1999
— id: 49185, year: 1999, vol: 10, page: 961, stat: Journal Article,