In this work we aim to show the clinical feasibility of quantitative 3D T2 mapping for tissue characterization and with the potential for prostate cancer detection. We implemented a 3D T2-prepared multi-shot gradient echo sequence and a dictionary matching approach for quantitative T2 analysis. We tested it in three biopsy-proven prostate cancer patients who underwent a simultaneous 18F-Choline PET/MR scan. Quantitative T2 matched literature values and we observed reduced T2 in lesions compared to normal peripheral zone tissue even in only moderately differentiated cancers (Gleason 3+4). Lesion location matched uptake of simultaneously acquired 18F-Choline PET.