Diffusion tensor imaging of normal prostate at 3 T: effect of number of diffusion-encoding directions on quantitation and image quality

OBJECTIVE: The purpose of this study was to prospectively investigate differences of diffusion tensor imaging (DTI) using a different number of diffusion-encoding directions and to evaluate the feasibility of tractography in healthy prostate at 3 T. METHOD: 12 healthy volunteers underwent DTI with single-shot echo-planar imaging at 3 T using a phased-array coil. Diffusion gradients of each DTI were applied in 6 (Group 1), 15 (Group 2) and 32 (Group 3) non-collinear directions. For each group, the mean apparent diffusion coefficient (ADC), fractional anisotrophy (FA) and signal-to-noise ratio (SNR) were measured in the peripheral zone (PZ) and central gland (CG). The quality of diffusion-weighted and tractographic images were also evaluated. RESULTS: In all three groups, the mean ADC value of the CG was statistically lower than that of the PZ (p<0.01) and the mean FA value of the CG was statistically greater than that of the PZ (p<0.01). For the mean FA value of the CG, no statistical difference was seen among the three groups (p=0.052). However, the mean FA value of the PZ showed a statistical difference among the three groups (p=0.035). No significant difference in SNR values was seen among the three groups (p>0.05). Imaging quality of diffusion-weighted tractographic images was rated as satisfactory or better in all three groups and was similar among the three groups. CONCLUSION: In conclusion, prostate DTI at 3 T was feasible with different numbers of diffusion-encoding directions. The number of diffusion-encoding directions did not have a significant effect on imaging quality.