High b Value (2,000 s/mm(2)) Diffusion-Weighted Magnetic Resonance Imaging in Prostate Cancer at 3 Tesla: Comparison with 1,000 s/mm(2) for Tumor Conspicuity and Discrimination of Aggressiveness

OBJECTIVE: The objective of our study was to investigate tumor conspicuity and the discrimination potential for tumor aggressiveness on diffusion-weighted magnetic resonance imaging (DW-MRI) with high b value at 3-T. MATERIALS AND METHODS: The institutional review board approved this study and waived the requirement for informed consent. A total of 50 patients with prostate cancer (69 cancer foci; 48 in the PZ, 20 in the TZ, and one in whole prostate) who underwent multiparametric prostate MRI including DW-MRI (b values: 0, 1000 s/mm(2) and 0, 2000 s/mm(2)) on a 3-T system were included. Lesion conspicuity score (LCS) using visual assessment (1 = invisible for surrounding normal site; 2 = slightly high intensity; 3 = moderately high; and 4 = very high) and tumor-normal signal intensity ratio (TNR) were assessed, and apparent diffusion coefficient (ADC, ×10(−3) mm(2)/s) of the tumor regions and normal regions were measured. RESULTS: Mean LCS and TNR at 0, 2000 s/mm(2) was significantly higher than those at 0, 1000 s/mm(2) (p<0.001 for both). In addition, ADC at both 0, 1000 and 0, 2000 s/mm(2) was found to distinguish intermediate or high risk cancer with Gleason score ≥7 from low risk cancer with Gleason score ≤6 (p<0.001 for both). Furthermore, ADC of tumor regions correlated with Gleason score at both 0, 1000 s/mm(2) (ρ = −0.602; p<0.001) and 0, 2000 s/mm(2) (ρ = −0.645; p<0.001). CONCLUSIONS: For tumor conspicuity and characterization of prostate cancer on DW-MRI of 3-T MRI, b = 0, 2000 s/mm(2) is more useful than b = 0, 1000 s/mm(2).