PI-RADS version 2: evaluation of diffusion-weighted imaging interpretation between b = 1000 and b = 1500 s mm– 2

Objective: To investigate the variability of diffusion-weighted imaging (DWI) interpretation of Prostate Imaging Reporting and Data System (PI-RADS) version 2 (v2) in evaluating prostate cancer (PCa). Methods: 154 patients with PCa underwent multiparametric 3T MRI, followed by radical prostatectomy. DWI with different b values (b = 0, 100, 1000 and 1500 s mm− 2) was obtained. Using the PI-RADS v2, two radiologists independently scored suspicious lesions in each patient and compared DWI of b = 1000 (DWI1000) with 1500 (DWI1500) s mm− 2 . Results: On DWI1000 and DWI1500, the intermethod and interobserver agreements of DWI scores were excellent in all patients (κ ≥ 0.873). In each peripheral zone and transition zone DWI scores, both observers showed excellent intermethod agreement between DWI1000 and DWI1500 (κ ≥ 0.897), and interobserver agreement for DWI1000 and DWI1500 was good to excellent (κ ≥ 0.796). For estimating clinically significant cancer, the area under receiver operating characteristics curves of DWI1000 and DWI1500 were 0.710 and 0.724 for observer 1 (p = 0.11), and 0.649 and 0.656 for observer 2 (p = 0.12), respectively. Conclusion: The PI-RADS v2 scoring at 3T shows excellent agreement between DWI1000 and DWI1500 in evaluating PCa, with excellent inter-observer agreement. Advance in knowledge: DWI using b = 1000 s mm−2 instead of b = 1500 s mm−2 reduces examination time or image distortion, with improved the signal-to-noise ratio.