Diffusion-weighted imaging with relative signal intensity statistical thresholding for delineating prostate cancer tumors.

PURPOSE We assessed the utility of diffusion-weighted imaging (DWI) with relative signal intensity (rSI) statistical thresholding for delineating prostate cancer tumors. MATERIALS AND METHODS Seventeen patients with prostate cancer underwent DWI before total prostatectomy. We measured standard deviation (SD) of the signal intensity (SI) of the lesser pelvic space at DWI, created rSI maps, displaying signal intensities with SDs of only > +3, > +3.5, > +4, or > +5, and assessed correlation between the proportion of cancerous area on the 4 different rSI maps and that on pathological slices. RESULTS We could detect prostate cancer on rSI maps for all cases with SD > +3, but not 2 cases with SD > +3.5, five with SD > +4, and eight with SD > +5. The correlation coefficients (R) between the proportion of cancerous area on pathological examination and rSI maps were 0.7464 for SD > +3 (P = 0.0006); 0.6469 for SD > +3.5 (P = 0.0050); 0.6459 for SD > +4 (P = 0.0051), and 0.4540 for SD > +5 (P = 0.0671). CONCLUSION DWI-based rSI mapping may be used to delineate the extent of prostate cancer. We achieved best correlation between ratio of cancerous area of the lesser pelvic space on pathological examination and on rSI map using a threshold with SD > +3 of the SI.