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

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).

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.

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.

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.