Post-hoc Estimation of a Quantitative Restriction Spectrum Imaging Biomarker for Prostate Cancer Detection Using Conventional MRI
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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, multi-center 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 s/mm 2 , 2500 s/mm 2 ) to complement low b- values (<1000 s/mm 2 ) from conventional DWI.
