What is the optimal b value in diffusion-weighted MR imaging to depict prostate cancer at 3T?

Objective To determine an optimal b value to visualise prostate cancer using diffusion-weighted magnetic resonance imaging at 3 T. Methods Forty one patients with biopsy proven prostate cancer underwent 3 T diffusion-weighted MRI performed with 5 b values (0, 1,000, 1,500, 2,000, 2,500 s/mm(2)) using a 16-channel coil. Best lesion visibility, the central gland-lesion (CG-L) and the peripheral zone-lesion (PZ-L) contrast-to-noise ratio (CNR) were compared between different b value images, apparent diffusion coefficient (ADC) were measured. In a subset of 29 patients a high resolution b1,500 s/mm(2)diffusion-weighted sequence was additionally assessed. Results The b = 1,500 s/mm(2) and b = 2,000 s/mm(2) images provided the best lesion visibility respectively in 27/41 and in 10/41patients. The highest CG-L and PZ-L CNR were obtained with b = 1,500 s/mm(2) (P < 0.0001). The mean ADC value calculated from 0 to 1,500 s/mm(2) b values in cancer lesions (ADC = 736 +/- 173 10(-6) mm(2)/s) was statistically significantly lower than in the peripheral zone (ADC = 1,338 +/- 256 10(-6) mm(2)/s, P < 0.0001) and in the central gland (ADC = 1,270 +/- 239 10(-6) mm(2)/s, P < 0.0001). The high resolution diffusion sequence was judged of better lesion visibility than (17/29) or equivalent to (6/29) the best images from the 5b sequence. Conclusion At 3 T, prostate cancer lesions are best depicted with b = 1,500 s/mm(2) and b = 2,000 s/mm(2) images, b = 1,500 s/mm(2) high-resolution diffusion images improve the image quality and contrast.