Multiparametric Magnetic Resonance Imaging for the Detection of Clinically Significant Prostate Cancer: What Urologists Need to Know. Part 2: Interpretation.

BACKGROUND: There is large variability among radiologists in their detection of clinically significant (cs) prostate cancer (PCa) on multiparametric magnetic resonance imaging (mpMRI). OBJECTIVE: To reduce the interpretation variability and achieve optimal accuracy in assessing prostate mpMRI. DESIGN, SETTING, AND PARTICIPANTS: How the interpretation of mpMRI can be optimized is demonstrated here. Whereas part 1 of the "surgery-in-motion" paper focused on acquisition, this paper shows the correlation between (ab)normal prostate anatomical structures and image characteristics on mpMRI, and how standardized interpretation according to Prostate Imaging Reporting and Data System version 2 (PI-RADS v2) should be performed. This will be shown in individual patients. SURGICAL PROCEDURE: To detect csPCa, three mpMRI "components" are used: "anatomic" T2-weighted imaging, "cellular-density" diffusion-weighted imaging, and "vascularity" dynamic contrast-enhanced MRI. MEASUREMENTS: Based on PI-RADS v2, the accompanying video shows how mpMRI interpretation is performed. Finally, the role of mpMRI in detecting csPCa is briefly discussed and the main features of the recently introduced PI-RADS v2.1 are evaluated. RESULTS AND LIMITATIONS: With PI-RADS v2, it is possible to quantify normal and abnormal anatomical structures within the prostate based on its imaging features of the three mpMRI "components." With this knowledge, a more objective evaluation of the presence of a csPCa can be performed. However, there still remains quite some space to reduce interobserver variability. CONCLUSIONS: For understanding the interpretation of mpMRI according to PI-RADS v2, knowledge of the correlation between imaging and (ab)normal anatomical structures on the three mpMRI components is needed. PATIENT SUMMARY: This second surgery-in-motion contribution shows what structures can be recognized on prostate magnetic resonance imaging (MRI). How a radiologist performs his reading according to the so-called Prostate Imaging Reporting and Data System criteria is shown here. The main features of these criteria are summarized, and the role of prostate MRI in detecting clinically significant prostate cancer is discussed briefly.