Diffusion tensor magnetic resonance imaging of the human calf - Comparison between 1.5 T and 3.0 T - Preliminary results

Objectives: To compare diffusion tensor-magnetic resonance imaging (DT-MRI) of human calf muscles at 1.5 T and 3.0 T, and to measure a number of quantitative parameters to characterize diffusion anisotropy in organized muscle tissue using similar imaging parameters. Methods and Materials: After Institutional Review Board approval and informed consent, five healthy volunteers were studied. Imaging was performed on both 1.5 T and 3.0 T MR systems using the similar imaging protocol. Diffusion-sensitized single-shot spinecho echo planar imaging pulse sequences were used to collect 2-dimensional images through the calf Imaging was performed using b-values of 0, 300, 500, and 700 s/mm(2). Image analyses and tensor calculations were performed offline using DT imaging studio (Johns Hopkins University, Baltimore, MD). The eigenvalues (lambda(1), lambda(2), lambda(3)), trace of the diffusion tensor (Tr < D >), fractional anisotropy: relative anisotropy, and volume ratio were calculated in 3 different calf muscles (medial and lateral gastrocnemius and soleus). Signal-to-noise ratios (SNRs) were compared for both field strengths (1.5 T and 3.0 T), the different muscles and all b-values. A regression analysis was performed to look at within-subject effects (linear mixed effect model). Results: No significant differences were found between all quantitative measured DT-MRI parameters, b-values, and muscle groups at 3.0 T and 1.5 T (P = 0.105; P = 0.719). The mean of SNR on the 2 different field strengths (3.0:1.5 T) was 1.64, which was significantly different (P < 0.0001). Significant differences in SNR in all 3 muscles were found between sequences using b = 300 s/mm(2) and 700 s/mm(2) (p < 0.001; p = 0.006) and between sequences using b = 300 s/mm(2) and 500 s/mm(2) (p < 0.001; p = 0.03), and 500 s/mm(2) and 700 s/mm(2) (p = 0.005; P = 0.03), respectively, for medial gastrocnemius and soleus muscle. Conclusions: This study demonstrates useful parameters to perform DT-MRI at 1.5 T and 3.0 T. DT-MRI at 1.5 T and 3.0 T provide in vivo validation of quantitative structural analysis of human skleletal muscle.