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Objective:
Management of Prostate Imaging-Reporting & Data System(PI-RADS) 3 lesions is controversial. 4-32% of these lesions can be clinically significant prostate cancers (CS PCa). Hybrid Multidimensional-MRI (HM-MRI) is a quantitative microstructural imaging method that detects prostate cancer (PCa) based on estimated tissue changes in tissue composition associated with cancer. The purpose of this study was to investigate whether additional review of the HM-MRI cancer maps together with multiparametric MRI (mp-MRI) may be helpful to stratify PI-RADS 3 lesions into CS PCa and clinically insignificant cancers/benign lesions.

Materials and Methods:
This retrospective, Health Insurance Portability and Accountability Act (HIPAA)-compliant, Institutional Review Board (IRB)-approved, single-institutional study of 61 patients with known or suspected PCa who underwent 3T MRI with a combination of mp-MRI (T2-weighted (T2W), diffusion weighted imaging (DWI) and dynamic contrast enhanced (DCE) and HM-MRI (with multiple combinations of TE = 57,70,100,150 ms and b-values of 0, 150, 750, 1500 s/mm²). Stromal, epithelial and luminal volumes were calculated by fitting the HM-MRI data to a three-compartment signal model with paired attenuation diffusion coefficient (ADC) and T2 values associated with each compartment. Cancer was predicted in regions with fractional volumes of epithelium >40%, lumen <20% and >25 mm². Three readers (R1 - R3) with 1 - 20 years’ prostate MRI experience retrospectively blindly reviewed the mp-MRI of 61 patients and scored PI-RADS 3 - 5 lesions and locations according to PI-RADS version (v) 2.1 and then rescored the PI-RADS 3 - 5 lesion and location after reviewing the HM-MRI map. Scored lesions were correlated with pathology results from 12-core MRI-Transrectal ultrasound (TRUS) biopsy or prostatectomy whole-mount slices for CS PCa (Gleason grade >/= 3+4). Accuracy, negative predictive value (NPV), and positive predictive value (PPV) for predicting CS PCa were calculated for mp-MRI and HM-MRI + mp-MRI PI-RADS 3 lesions for each observer.

Results:
PI-RADS 3 accuracy for reader R1, R2, and R3 improved after additional review of HM-MRI compared to only mp-MRI (from 24.5%, 18.9%, and 31.4% to 36.7%, 45.8%, and 47.1%; <em>p</em> = .025, .018, and .126). PI-RADS 3 PPV of R1, R2, R3 improved, but not significantly for R2 (from 23.9%, 9.5%, 4.5% to 29.5%, 13.8%, 16.3%; <em>p</em> = .042, .335, .038). PI-RADS 3 NPV of R1, R2, R3 improved with HM-MRI (from 33.3%, 83.3%, and 76.9% to 100%, 94.7%, and 96.3%; <em>p</em> = .031, .52, and .034).

Conclusion:
Additional review of the HM-MRI map to mp-MRI images increased PI-RADS 3 accuracy, PPV and NPV of the expert and less-experienced readers. The HM-MRI map may help in the management of PI-RADS 3 lesions.