Suchandrima Banerjee

Relationship between trabecular bone structure and articular cartilage morphology and relaxation times in early OA of the knee joint using parallel MRI at 3 T.

OBJECTIVE To evaluate trabecular bone structure in relationship with cartilage parameters in distal femur and proximal tibia of the human knee at 3Tesla (3T) using high-resolution magnetic resonance imaging (MRI) with parallel imaging. METHOD Sixteen healthy controls and 16 patients with mild osteoarthritis (OA) were studied using a 3T magnetic resonance (MR) scanner and an eight-channel phased-array knee coil. Axial 3D GeneRalized Autocalibrating Partially Parallel Acquisition (GRAPPA)-based phase cycled Fast Imaging Employing Steady State Acquisition (FIESTA-c) images were acquired in order to quantify the trabecular bone structure. For assessing cartilage morphology (thickness, volume), sagittal high-resolution 3D spoiled gradient echo (SPGR) images were acquired. In a subset of the subjects, sagittal images were acquired for measuring T1rho and T2 relaxation times, using 3D T1rho and T2 mapping techniques. RESULTS Good measurement reproducibility was observed for bone parameters, the coefficients of variations (CVs) ranging from 1.8% for trabecular number (app. Tb.N) to 5.5% for trabecular separation (app. Tb.Sp). Significant differences between control and OA groups were found for bone volume fraction bone volume over total volume (app. BV/TV) and app. Tb.Sp in all compartments. Significantly increased values in T1rho and T2 were demonstrated in OA patients compared with controls at the femur, but not at the tibia. T1rho was negatively correlated with app. BV/TV, app. Tb.N and app. Tb.Sp both at the medial femoral condyle (MFC) and lateral tibia (LT), while T2 was only correlated at the LT. Also, medial tibia (MT) T1rho was negatively correlated with app. BV/TV (R(2)=-0.49, P<0.05) and app. Tb.N (R(2)=-0.42, P<0.05) from the opposite side of lateral femoral condyle (LFC). Significant correlations were found between trabecular bone parameters and cartilage thickness and normalized volume, mainly at LT, tibia (T) and femur (F). CONCLUSION At this early stage of OA, an overall decrease in bone structure parameters and an increase in cartilage parameters (T1rho, T2) were noticed in patients. Trabecular bone structure correlated with articular cartilage parameters suggesting that loss of mineralized bone is associated with cartilage degeneration.

In vivo bone and cartilage MRI using fully-balanced steady-state free-precession at 7 tesla

The purpose of this work was to investigated the feasibility of fully‐balanced steady‐state free‐precession (bSSFP) pulse sequence for trabecular bone and knee cartilage imaging in vivo using ultra‐high‐field (UHF) MRI at 7T in comparison with pulse sequences previously used at 3T. We showed that bSSFP and spin‐echo imaging is possible at higher field strengths within 3.2 W/kg specific absorption rate (SAR) constraints. All pulse sequences were numerically optimized based on measured tissue relaxation parameters from six healthy volunteers (T1 = 820 ± 128 ms, T2 = 43.5 ± 3 ms for bone marrow and T1 = 1745 ± 104 ms and T2 = 30 ± 4 ms for cartilage). From simulations of the Bloch equation, a signal‐to‐noise ratio (SNR) increase of more than 1.9 was predicted. Cartilage SNR of bSSFP was 2.4 times higher at 7T (51.3 ± 4.3) compared with 3T (21.3 ± 3.3). Bone SNR increased from 11.8 ± 2.0 to 13.2 ± 2.5 at the higher field strength. We concluded that there is SNR benefit and great potential for bone and cartilage imaging at higher field strength. Magn Reson Med, 2007.

7T Human Spine Imaging Arrays With Adjustable Inductive Decoupling

Ultrahigh-field human spine RF transceiver coil arrays face daunting technical challenges in achieving large imaging coverage with sufficient B1 penetration and sensitivity, and in attaining robust decoupling among coil elements. In this paper, human spine coil arrays for ultrahigh field were built and studied. Transceiver arrays with loop-shaped microstrip transmission line were designed, fabricated, and tested for 7-tesla (7T) MRI. With the proposed adjustable inductive decoupling technique, the isolation between adjacent coil elements is easily addressed. Preliminary results of human spine images acquired using the transceiver arrays demonstrate the feasibility of the design for ultrahigh-field MR applications and its robust performance for parallel imaging.

In vivo ultra-high-field magnetic resonance imaging of trabecular bone microarchitecture at 7 T

To investigate the feasibility of 7T magnetic resonance imaging (MRI) to visualize and quantify trabecular bone structure in vivo by comparison with 3T MRI and in vivo three‐dimensional (3D) high‐resolution peripheral quantitative computed tomography (HR‐pQCT).

Application of refocused steady-state free-precession methods at 1.5 and 3 T to in vivo high-resolution MRI of trabecular bone: simulations and experiments.

To evaluate the potential of fully‐balanced steady‐state free‐precession (SSFP) sequences in in vivo high‐resolution (HR) MRI of trabecular bone at field strengths of 1.5 and 3 T by simulation and experimental methods.

Rapid in vivo musculoskeletal MR with parallel imaging at 7T

The purpose of this work was to implement autocalibrating GRAPPA‐based parallel imaging (PI) for in vivo high‐resolution (HR) MRI of cartilage and trabecular bone micro‐architecture at 7T and to evaluate its performance based on comparison of MR‐derived morphology metrics between accelerated and conventional images and comparison of geometry factor measures between 3T and 7T. Using an eight channel coil array for trabecular MRI at the ankle, a higher maximum feasible acceleration (R) = 6 and lower geometry factor values than that at 3T were observed. The advantages of two‐dimensional acceleration were also demonstrated. In knee cartilage and bone acquisitions, feasibility of PI with a dual‐channel quadrature coil was investigated. Robust quantification of bone and cartilage metrics could be derived from accelerated ankle and knee acquisitions. PI can enhance the clinical feasibility of in vivo bone and cartilage HR‐MRI for osteoporosis and osteoarthritis at 7T. Magn Reson Med, 2008.

Parallel imaging of knee cartilage at 3 Tesla

To evaluate the feasibility and reproducibility of quantitative cartilage imaging with parallel imaging at 3T and to determine the impact of the acceleration factor (AF) on morphological and relaxation measurements.

Reduced-FOV excitation decreases susceptibility artifact in diffusion-weighted MRI with endorectal coil for prostate cancer detection

The purposes of this study were to determine if image distortion is less in prostate MR apparent diffusion coefficient (ADC) maps generated from a reduced-field-of-view (rFOV) diffusion-weighted-imaging (DWI) technique than from a conventional DWI sequence (CONV), and to determine if the rFOV ADC tumor contrast is as high as or better than that of the CONV sequence. Fifty patients underwent a 3T MRI exam. CONV and rFOV (utilizing a 2D, echo-planar, rectangularly-selective RF pulse) sequences were acquired using b=600, 0s/mm(2). Distortion was visually scored 0-4 by three independent observers and quantitatively measured using the difference in rectal wall curvature between the ADC maps and T2-weighted images. Distortion scores were lower with the rFOV sequence (p<0.012, Wilcoxon Signed-Rank Test, n=50), and difference in distortion scores did not differ significantly among observers (p=0.99, Kruskal-Wallis Rank Sum Test). The difference in rectal curvature was less with rFOV ADC maps (26%±10%) than CONV ADC maps (34%±13%) (p<0.011, Students t-test). In seventeen patients with untreated, biopsy confirmed prostate cancer, the rFOV sequence afforded significantly higher ADC tumor contrast (44.0%) than the CONV sequence (35.9%), (p<0.0012, Students t-test). The rFOV sequence yielded significantly decreased susceptibility artifact and significantly higher contrast between tumor and healthy tissue.

Blood oxygen level-dependent (BOLD) MRI of diabetic nephropathy: Preliminary experience

To evaluate the blood oxygen level‐dependent (BOLD) magnetic resonance imaging (MRI) findings in kidneys of patients with diabetic nephropathy.

GRAPPA-based susceptibility-weighted imaging of normal volunteers and patients with brain tumor at 7 T

Susceptibility-weighted imaging (SWI) is a valuable technique for high-resolution imaging of brain vasculature that greatly benefits from the emergence of higher field strength MR scanners. Autocalibrating partially parallel imaging techniques can be employed to reduce lengthy acquisition times as long as the decrease in signal-to-noise ratio does not significantly affect the contrast between vessels and brain parenchyma. This study assessed the feasibility of a Generalized Autocalibrating Partially Parallel Acquisition (GRAPPA)-based SWI technique at 7 T in both healthy volunteers and brain tumor patients. GRAPPA-based SWI allowed a twofold or more reduction in scan time without compromising vessel contrast and small vessel detection. Postprocessing parameters for the SWI needed to be modified for patients where the tumor causes high-frequency phase wrap artifacts but did not adversely affect vessel contrast. GRAPPA-based SWI at 7 T revealed regions of microvascularity, hemorrhage and calcification within heterogeneous brain tumors that may aid in characterizing active or necrotic tumor and monitoring treatment effects.