Prostate cancer is the second most common cancer among men worldwide; moreover, the incidence of prostate cancer is rising in Asia and Eastern Europe. The accurate assessment of prostate cancer aggressiveness is important for deciding the most appropriate initial treatment strategy. The Gleason score is an important preoperative predictor of response to treatment and patient outcomes. However, biopsy determination of the Gleason grade is invasive and often does not accurately reflect the final Gleason score. Recently, functional MRI sequences such as DWI and dynamic contrast-enhanced (DCE) imaging have been shown to provide information about tumor aggressiveness. The apparent diffusion coefficient (ADC) is negatively correlated with the Gleason score for prostate cancer. Specifically, patients with high Gleason scores have tumors with lower ADCs. This relationship is likely because tumors with high Gleason scores exhibit increased cellularity.Intravoxel incoherent motion (IVIM) MR imaging quantitatively assesses the microscopic translational motion that occurs in each image voxel on MR imaging scans. Both pure molecular diffusion (D) and microcirculation-related diffusion, otherwise known as pseudodiffusion (D*), can be distinguished using IVIM MR imaging, as can the blood flow fraction (f). Recent studies with IVIM imaging showed that reduced ADCs for prostate cancer are due to decreased molecular diffusion and to a decreased perfusion fraction. However, studies on the relationship between IVIM parameters and Gleason scores are rare. Therefore, this study evaluated the potential of IVIM imaging to predict histological and prognostic parameters by investigating whether IVIM parameters correlated with Gleason score.

The Institutional Review Board approved this retrospective study and informed consent was waived. A total of 41 patients with histologically proven prostate cancer who underwent prostate MR imaging using a 3T MRI machine were included. For 8 DWI b-values (0, 10, 20, 50, 100, 200, 500, and 800 sec/mm2), a spin-echo echo-planar imaging (EPI) sequence was performed. D, f, D*, and ADCfit values were compared among three groups of patients with prostate cancer: Gleason score 6 (n = 9), 7 (n = 16), or 8 or higher (n = 16). Receiver operating characteristic (ROC) curves were generated for D, f, D*, and ADCfit to assess the ability of each parameter to distinguish cancers with low Gleason scores from cancers with intermediate or high Gleason scores.Pearson’s coefficient analysis revealed significant negative correlations between Gleason score and ADCfit (r = -0.490, P = 0.001) and Gleason score and D values (r = -0.514, P = 0.001). Gleason score was poorly correlated with f (r = 0.168, P = 0.292) and D* values (r = -0.108, P = 0.500). The ADCfit and D values of prostate cancers with Gleason scores 7 or 8 were significantly lower than values for prostate cancers with Gleason score 6 (P < 0.05). ROC curves were constructed to assess the ability of IVIM parameters to discriminate prostate cancers with Gleason score 6 from cancers with Gleason scores 7 or 8. Areas under the curve were 0.671 to 0.974. ADCfit and D yielded the highest Az value (0.960–0.956), whereas f yielded the lowest Az value (0.633).To optimize the diagnostic accuracy of each parameter, cutoff values of ADCfit < 1.29 x 10-3 mm2/s, D < 1.18 x 10-3 mm2/s, D* < 27.97 x 10-3 mm2/s, and f < 18.42% were used. ADCfit and D strongly correlated with Gleason scores for prostate cancer. The best IVIM parameter for discriminating prostate cancers with low Gleason scores from cancers with intermediate or high Gleason scores was D, which expresses pure molecular diffusion.