Material and Method: Thirty-nine patients with prostate cancer who underwent pre-operative endorectal Diffusion-Weighted (DW) magnetic resonance (MR) imaging between March 2006 and March 2010 were included. Regions of interest (ROIs) were drawn on ADC maps at sites of visible tumor on DW images and ADC maps comparison to histopathology. Differentiation between ADC values of tumor and non-tumor areas were analyzed by using paired t-test and sign-test and between tumors grading were analyzed by using Wilcoxon rank-sum (Mann-Whitney) test and Kruskal-Wallis equality-of population rank test.

Results: The mean ADC of tumor is lower than non-tumor areas at all b-values. There is negative correlation between ADC value and tumor grading with statistical significance at b = 1,000 sec/mm2, between tumor grade I (1.95x10-3 mm2/sec, SD = 0.33) and tumor grade II (1.16x10-3 mm2/sec, SD = 0.27) (p = 0.03) and between tumor grade I and tumor grade III (1.10x10-3 mm2/sec, SD = 0.36) (p = 0.002) and at b = 2,000 sec/mm2, between tumor grade I (2.21x10-3 mm2/sec, SD = 0.08) and tumor grade II (1.22x10-3 mm2/sec, SD = 0.38) (p = 0.01), and between tumor grade I and tumor grade III (1.32x10-3 mm2/sec, SD = 0.49) (p = 0.04). There is no statistical significance difference between tumor grade II and grade III.

Conclusion: Tumor shows restricted diffusion with ADC value lower than non-tumor areas. There is a significant negative correlation between ADCs and tumor grading between low and intermediate grades and between low and high grades tumor at the b = 1,000 and 2,000 sec/mm2. ADC maps may be a useful tool for non-invasive assessment of the aggressiveness of prostate cancers that are visible on MR images.

Keywords: Endorectal diffusion-weighted-MRI, ADC values, Prostate cancer, Gleason score