Faculty Bibliography

OBJECTIVE: The objective of the study was to investigate the feasibility of 7-T shoulder magnetic resonance imaging by developing transmit and receive radiofrequency (RF) coil arrays and exploring RF shim methods. MATERIALS AND METHODS: A mechanically flexible 8-channel transmit array and an anatomically conformable 10-channel receive array were designed and implemented. The transmit performance of various RF shim methods was assessed through local flip angle measurements in the right and left shoulders of 6 subjects. The receive performance was assessed through signal-to-noise ratio measurements using the developed 7-T coil and a baseline commercial 3-T coil. RESULTS: The 7-T transmit array driven with phase-coherent RF shim weights provided adequate B1 efficiency and uniformity for turbo spin echo shoulder imaging. B1 twisting that is characteristic of high-field loop coils necessitates distinct RF shim weights in the right and left shoulders. The 7-T receive array provided a 2-fold signal-to-noise ratio improvement over the 3-T array in the deep articular shoulder cartilage. CONCLUSIONS: Shoulder imaging at 7-T is feasible with a custom transmit/receive array either in a single-channel transmit mode with a fixed RF shim or in a parallel transmit mode with a subject-specific RF shim.

PURPOSE: To demonstrate the feasibility of performing bone microarchitecture, high-resolution cartilage, and clinical imaging of the hip at 7T. MATERIALS AND METHODS: This study had Institutional Review Board approval. Using an 8-channel coil constructed in-house, we imaged the hips of 15 subjects on a 7T magnetic resonance imaging (MRI) scanner. We applied: 1) a T1-weighted 3D fast low angle shot (3D FLASH) sequence (0.23 x 0.23 x 1-1.5 mm3 ) for bone microarchitecture imaging; 2) T1-weighted 3D FLASH (water excitation) and volumetric interpolated breath-hold examination (VIBE) sequences (0.23 x 0.23 x 1.5 mm3 ) with saturation or inversion recovery-based fat suppression for cartilage imaging; 3) 2D intermediate-weighted fast spin-echo (FSE) sequences without and with fat saturation (0.27 x 0.27 x 2 mm) for clinical imaging. RESULTS: Bone microarchitecture images allowed visualization of individual trabeculae within the proximal femur. Cartilage was well visualized and fat was well suppressed on FLASH and VIBE sequences. FSE sequences allowed visualization of cartilage, the labrum (including cartilage and labral pathology), joint capsule, and tendons. CONCLUSION: This is the first study to demonstrate the feasibility of performing a clinically comprehensive hip MRI protocol at 7T, including high-resolution imaging of bone microarchitecture and cartilage, as well as clinical imaging. J. Magn. Reson. Imaging 2013;. (c) 2013 Wiley Periodicals, Inc.

We aimed to determine whether a unique, ultra-high-field 7 T magnetic resonance imaging (MRI) scanner could detect occult cartilage and meniscal injuries in asymptomatic female dancers. This study had Institutional Review Board approval. We recruited eight pre-professional female dancers and nine non-athletic, female controls. We scanned the dominant knee on a 7 T MRI scanner using a three-dimensional fast low-angle shot sequence and a proton density, fast spin-echo sequence to evaluate cartilage and menisci, respectively. Two radiologists scored cartilage (International Cartilage Repair Society classification) and meniscal (Stoller classification) lesions. We applied two-tailed z- and t-tests to determine statistical significance. There were no cartilage lesions in dancers or controls. For the medial meniscus, the dancers demonstrated higher mean MRI score (2.38 +/- 0.61 vs 1.0 +/- 0.97, P < 0.0001) and higher frequency of mean grade 2 lesions (88% vs 11%, P < 0.01) compared with the controls. For the lateral meniscus, there was no difference in score (0.5 +/- 0.81 vs 0.5 +/- 0.78, P = 0.78) in dancers compared with the control groups. Asymptomatic dancers demonstrate occult medial meniscal lesions. Because this has been described in early osteoarthritis, close surveillance of dancers' knee symptoms and function with appropriate activity modification may help maintain their long-term knee health.

The clinical diagnosis of osteoporosis has evolved over the past 20 years to emphasize the relationship between compromised bone strength and fracture susceptibility. The goal of treatment of osteoporosis is fracture prevention. The aging of the American population will place additional burdens on our healthcare system among which will be the need to treat and prevent the estimated increase in fracture rates projected over the next 10 years. There is a significant number of currently available bone strengthening medications used in the treatment of osteoporosis, and this report highlights the effects of these drugs on bone mineral density values and on the relative rates of fragility fractures when these drugs are compared to placebo in clinical trials of subjects with osteoporosis. Identifying those individuals most in need of immediate treatment to prevent fractures remains a challenge despite the use of fracture risk assessment tools, which assess bone mineral density and clinical parameters in order to define an individual's risk of fracture over a finite period of time. Newer tools that may help better define bone strength (resistance to fracture) include high resolution MRI and finite element analysis of the MRI generated images, and this technology and our experience with it is briefly reviewed in this report. There are a number of new classes of drugs in development for the treatment of osteoporosis, and the clinician is likely to have additional antiresorptive and anabolic agents as treatment options for this condition over the next few years.

Purpose:To assess the potential use of sodium magnetic resonance (MR) imaging of cartilage, with and without fluid suppression by using an adiabatic pulse, for classifying subjects with versus subjects without osteoarthritis at 7.0 T.Materials and Methods:The study was approved by the institutional review board and was compliant with HIPAA. The knee cartilage of 19 asymptomatic (control subjects) and 28 symptomatic (osteoarthritis patients) subjects underwent 7.0-T sodium MR imaging with use of two different sequences: one without fluid suppression (radial three-dimensional sequence) and one with fluid suppression (inversion recovery [IR] wideband uniform rate and smooth truncation [WURST]). Fluid suppression was obtained by using IR with an adiabatic inversion pulse (WURST pulse). Mean sodium concentrations and their standard deviations were measured in the patellar, femorotibial medial, and lateral cartilage regions over four consecutive sections for each subject. The minimum, maximum, median, and average means and standard deviations were calculated over all measurements for each subject. The utility of these measures in the detection of osteoarthritis was evaluated by using logistic regression and the area under the receiver operating characteristic curve (AUC). Bonferroni correction was applied to the P values obtained with logistic regression.Results:Measurements from IR WURST were found to be significant predicators of all osteoarthritis (Kellgren-Lawrence score of 1-4) and early osteoarthritis (Kellgren-Lawrence score of 1 or 2). The minimum standard deviation provided the highest AUC (0.83) with the highest accuracy (>78%), sensitivity (>82%), and specificity (>74%) for both all osteoarthritis and early osteoarthritis groups.Conclusion:Quantitative sodium MR imaging at 7.0 T with fluid suppression by using adiabatic IR is a potential biomarker for osteoarthritis.(c) RSNA, 2013.

Phosphorus ((31) P) magnetization transfer (MT) techniques enable the non-invasive measurement of metabolic turnover rates of important enzyme-catalyzed reactions, such as the creatine kinase reaction (CK), a major transducing reaction involving adenosine triphosphate and phosphocreatine. Alteration in the kinetics of the CK reaction rate appears to play a central role in many disease states. In this study, we developed and implemented at ultra-high field (7T) a novel three-dimensional (31) P-MT imaging sequence that maps the kinetics of CK in the entire volume of the lower leg at relatively high resolution (0.52 mL voxel size), and within acquisition times that can be tolerated by patients (below 60 min). We tested the sequence on five healthy and two clinically diagnosed type 2 diabetic subjects. Overall, we obtained measurements that are in close agreement with measurements reported previously using spectroscopic methods. Importantly, our spatially resolved method allowed us to measure local CK reaction rate constants and metabolic fluxes in individual muscles in a non-invasive manner. Furthermore, it allowed us to detect variations of the CK rates of different muscles, which would not have been possible using unlocalized MRS methods. The results of this work suggest that 3D mapping of the CK reaction rates and metabolic fluxes can be achieved in the skeletal muscle in vivo at relatively high spatial resolution and with acquisition times well tolerated by patients. The ability to measure bioenergetics simultaneously in large areas of muscles will bring new insights into possible heterogeneous patterns of muscle metabolism associated with several diseases and serve as a valuable tool for monitoring the efficacy of interventions

OBJECTIVE: To assess the relationship between knee alignment and subregional T1rho values of the femorotibial cartilage and menisci in patients with mild (Kellgren-Lawrence grade 1) to moderate (KL3) osteoarthritis (OA) at 3T. MATERIALS AND METHODS: 26 subjects with a clinical diagnosis of KL1-3 OA were included and subdivided into three subgroups: varus, valgus, and neutral. All subjects were evaluated on a 3T MR scanner. Mann-Whitney and Wilcoxon signed rank tests were performed to determine any statistically significant differences in subregional T1rho values of femorotibial cartilage and menisci among the three subgroups of KL1-3 OA patients. RESULTS: Medial femoral anterior cartilage subregion in varus group had significantly higher (p<0.05) T1rho values than all cartilage subregions in valgus group. Medial tibial central cartilage subregion had significantly higher T1rho values (p<0.05) than lateral tibial central cartilage subregion in varus group. The posterior horn of the medial meniscus in neutral group had significantly higher T1rho values (p<0.0029) than all meniscus subregions in valgus group. CONCLUSION: There exists some degree of association between knee alignment and subregional T1rho values of femorotibial cartilage and menisci in patients with clinical OA.

OBJECT: Our objective was to use 7 T MRI to compare cartilage morphology (thickness) and collagen composition (T2 values) in cartilage repair patients and healthy controls. MATERIALS AND METHODS: We scanned the knees of 11 cartilage repair patients and 11 controls on a 7 T MRI scanner using a high-resolution, gradient-echo sequence to measure cartilage thickness and a multi-echo spin-echo sequence to measure cartilage T2 values. We used two-tailed t tests to compare cartilage thickness and T2 values in: repair tissue (RT) versus adjacent cartilage (AC); RT versus healthy control cartilage (HC); AC versus HC. RESULTS: Mean thickness in RT, AC, HC were: 2.2 +/- 1.4, 3.6 +/- 1.1, 3.3 +/- 0.7 mm. Differences in thickness between RT-AC (p = 0.01) and RT-HC (p = 0.02) were significant, but not AC-HC (p = 0.45). Mean T2 values in RT, AC, HC were: 51.6 +/- 7.6, 40.0 +/- 4.7, 45.9 +/- 3.7 ms. Differences in T2 values between RT-AC (p = 0.0005), RT-HC (p = 0.04), and AC-HC (p = 0.004) were significant. CONCLUSION: 7 T MRI allows detection of differences in morphology and collagen architecture in: (1) cartilage repair tissue compared to adjacent cartilage and (2) cartilage repair tissue compared to cartilage from healthy controls. Although cartilage adjacent to repair tissue may be normal in thickness, it can demonstrate altered collagen composition.

PURPOSE: The development and implementation of a spectrally selective 3D-Turbo Spin Echo sequence for quantitative mapping of phosphocreatine (PCr) concentration in different muscles of the lower leg of healthy volunteers both at 3 T and 7 T. METHODS: Nine healthy volunteers were recruited, all of whom where scanned at 3 T and 7 T. Three dimensional PCr concentration maps were obtained after images were corrected for B(1) inhomogeneities, T(1) relaxation weighting, and partial volume of fatty tissue in the muscles. Two volunteers performed plantar flexions inside the magnet, and the oxidative capacity of their muscles was estimated. RESULTS: Three dimensional PCr concentration maps were obtained, with full muscle coverage and nominal voxel size of 0.52 mL at both fields. At 7 T a 2.7-fold increase of signal-to-noise ratio was achieved compared to 3 T. CONCLUSION: Imaging (31) P metabolites at 7 T allowed for significant increase in signal to noise ratio compared to imaging at 3 T, while quantification of the PCr concentration remained unaffected. The importance of such an increase in signal-to-noise ratio is 2-fold, first higher resolution images with reduced partial volume effects can be acquired, and second multiple measurements such as dynamic imaging of PCr post-exercise, (31) P magnetization transfer, or other (1) H measurements, can be acquired in a single imaging session. Magn Reson Med, 2013. (c) 2013 Wiley Periodicals, Inc.

The rate of phosphocreatine (PCr) resynthesis after physical exercise has been extensively studied with phosphorus ((31) P)-MRS. Previous studies have used small surface coils that were limited to measuring one superficial muscle per experiment. This study focuses on the development and implementation of a spectrally selective three-dimensional turbo spin echo (3D-TSE) sequence at 3T and 7T with temporal resolution of 24 s, using two geometrically identical volume coils. We acquired imaging data of PCr recovery from four healthy volunteers and one diabetic patient, who performed plantar flexions using resistance bands. We segmented the anatomical regions of six different muscles from the lower leg, namely the gastrocnemius [lateral (GL) and medial (GM)], the tibialis [anterior (TA) and posterior (TP)], the soleus (S) and the peroneus (P) and measured the local PCr resynthesis rate constants. During the same examination, we also acquired unlocalized (31) P-MRS data at a temporal resolution of 6 s. At 3T, the PCr resynthesis rate constants were measured at 25.4 +/- 3.7 s [n = 4, mean +/- standard deviation (SD)] using the MRS method and 25.6 +/- 4.4 s using the MRI method. At 7T, the measured rates were 26.4 +/- 3.2 s and 26.2 +/- 4.7 s for MRS and MRI. Using our imaging method, we measured the local PCr resynthesis rate constants in six individual muscles of the lower leg (min/max 20.2/31.7 s). The recovery rate constants measured for the diabetic patient were 55.5 s (MRS) and 52.7 s (MRI). The successful implementation of our 3D-method suggests that imaging is possible at both fields with a relatively high spatial resolution (voxel size: 4.2 mL at 3T and 1.6 mL at 7T) using volume coils and that local PCr resynthesis rates can be obtained in a single measurement. The advantage of the imaging method is that it can highlight differences in PCr resynthesis rates between different muscles in a single measurement in order to study spatial gradients of metabolic properties of diseased states for which very little is currently known