Diffusion-Weighted Magnetic Resonance Imaging for the Evaluation of Prostate Cancer: Optimal B Value at 3T

Objective: To retrospectively determine the optimal b value of diffusion-weighted imaging (DWI) for predicting the presence of localized prostate cancer, and to evaluate the utility of DWI under different b values in differentiating between cancers and benign prostatic tissues. Materials and Methods: Eighty patients with suspected prostate cancer underwent MRI including DWI at 3T, followed by radical prostatectomy. DWI was examined under different b values. Apparent diffusion coefficient (ADC) maps were generated by using b = 0, and other b values of 300, 700, 1000 or 2000 $s/mm^2$. For predicting the presence of cancers, four different ADC maps were analyzed independently by two blinded readers. ADCs were measured in benign and malignant tissues. Results: For predicting the presence of 110 prostate cancers, the sensitivity and area under the curve (AUC) for an experienced reader was significantly greater at b = 1000 (85% and 0.91) than b = 300, 700 or 2000 $s/mm^2$ (p < 0.01). For a less-experienced reader, the AUC was significantly greater at b = 700, 1000 or 2000 than b = 300 $s/mm^2$ (p < 0.01). Mean ADCs of the cancers in sequence from b = 300 to 2000 $s/mm^2$ were 1.33, 1.03, 0.88 and $0.68{\times}10^{-3}mm^2/s$, which were significantly lower than those of benign tissues (p < 0.001). Conclusion: The optimal b value for 3T DWI for predicting the presence of prostate cancer may be 1000 $s/mm^2$.