Abstract Background Multiparametric MRI is useful for early detection of clinically significant prostate cancer (csPCa), but its standard apparent diffusion coefficient (ADC) has limited utility as a quantitative metric for automated, patient‐level detection of csPCa. Restriction spectrum imaging (RSI), an advanced diffusion technique, yields a quantitative biomarker (RSIrs) that improves csPCa detection. RSIrs is typically calculated from a dedicated multi‐ b ‐value acquisition. RSIrs estimated from conventional MRI has not been studied. Purpose To evaluate the accuracy and validity of RSI metrics estimated post hoc from conventional diffusion‐weighted imaging (DWI) to serve as a viable surrogate for a dedicated RSI acquisition. Materials and Methods We conducted a retrospective, multicenter study of patients with both a dedicated RSI acquisition and conventional DWI. We compared three different RSI restriction score (RSIrs) calculation methods: from the dedicated acquisition (RSIrs dedicated ), from conventional DWI alone (RSIrs post‐hoc ), and from a combination of conventional DWI with only the high b ‐values from the RSI acquisition (RSIrs combo ). We compared these methods for quantitative agreement and csPCa detection performance (area under the receiver operating characteristic AUC, 95% confidence interval) of maximum RSIrs (RSIrs max ) in the prostate compared to that of minimum ADC (ADC). Results Data from n = 1095 patients (16 centers) were analyzed. Post hoc RSIrs max differed systematically from RSIrs dedicated by a median of +156 (RSIrs post‐hoc ) and −59 (RSIrs combo ), respectively. AUCs for csPCa detection were 0.51 0.47,0.54, 0.60 0.57,0.64, 0.70 0.67,0.74, and 0.77 0.74,0.80 for ADC, RSIrs post‐hoc , RSIrs combo , and RSIrs dedicated , respectively. Conclusion Even when estimated using conventional DWI, RSIrs is a superior quantitative biomarker to ADC for automated, patient‐level detection of csPCa. A dedicated RSI acquisition gives the best performance. A compromise would be to acquire high b‐ values (1500 and 2500 s/mm 2 ) to complement low b‐ values (<1000 s/mm 2 ) from conventional DWI.
Do et al. (Sun,) studied this question.