Performance of apparent diffusion coefficient values and ratios for the prediction of prostate cancer aggressiveness across differentMRI acquisition settings

PURPOSE In this study, we assessed the performance of apparent diffusion coefficient (ADC) and diffusion-weighted imaging (DWI) metrics and their ratios across different magnetic resonance imaging (MRI) acquisition settings, with or without an endorectal coil (ERC), for the evaluation of prostate cancer (PCa) aggressiveness using whole-mount specimens as a reference. METHODS We retrospectively reviewed the data of pCa patients with a Gleason score (GS) of 3 + 4 or higher who underwent prostate MRI using a 3T unit at our institution. They were divided into two groups based on the use of ERC forMRI acquisition, and patients who underwent prostate MRI with an ERC constituted the ERC ( n = 55) data set, while the remaining patients accounted for the non-ERC data set (n = 41). DWI was performed with b-values of 50, 500, 1000, and 1400 s/mm(2), and ADCmaps were automatically calculated. Additionally, computed DWI (cDWI) was performed with a b-value of 2000 s/mm(2). Six ADC and two cDWI parameters were evaluated. In the ERC data set, receiver operating characteristic curves were plotted for each metric to determine the best cutoff threshold values for differentiating GS 3 + 4 PCa from that with a higher GS. The performance of these cutoff values was assessed in non-ERC data set. The diagnostic accuracies and area under the curves (AUCs) of the metrics were compared using Fisher exact test and De Long method, respectively. RESULTS Among all metrics, the mean ADC ratio of the tumor to normal prostate (ADC(mean-ratio)) yielded the highest AUC, 0.84, for differentiating GS 3 + 4 PCa from that with a higher GS. The best threshold cutoff values of ADC(mean-ratio) (<= 0.51) for discriminating GS 3 + 4 PCa from that with a higher GS correctly classified 48 of 55 patients with an accuracy of 87.27%. However, there was no significant difference between the metrics in terms of accuracy and AUC (P =.163 and P =.214). Similarly, in the non-ERC data set, the ADC(mean-ratio) provided the highest diagnostic accuracy (82.92%) by classifying 34 of 41 patients. However, Fisher exact test yielded no significant difference between DWI and ADC metrics in terms of diagnostic accuracy in non-ERC data (P =.561). CONCLUSION The mean ADC ratio of the tumor to normal prostate showed the highest accuracy and AUC in differentiating GS 3 + 4 PCa and PCa with a higher GS across different MRI acquisition settings; however, the performance of different ADC and DWI metrics did not differ significantly.