Apparent Diffusion Coefficient (ADC) Ratio Versus Conventional ADC for Detecting Clinically Significant Prostate Cancer With 3-T MRI.

The purpose of this study is to evaluate the performance of the apparent diffusion coefficient ratio (ADC; the ADC of the suspected prostate cancer [PCa] focus on MRI divided by the ADC in a noncancerous reference area) with that of conventional ADC for detection of high-grade PCa (Gleason score [GS] ≥ 3 + 4) versus low-grade PCa (GS = 3 + 3) with whole-mount (WM) histopathologic analysis used as a reference. The cohort of this retrospective study included 218 men with 240 unilateral PCa lesions assessed by both 3-T multiparametric MRI and whole-mount histopathologic analysis. ROIs were placed on individual lesions verified by WM histopathologic analysis, to calculate the mean ADC (ADC) and lowest ADC within each lesion (ADC), and within non-tumor-containing regions of the same tumor zone but on the contralateral side (ADC), to calculate the background ADC. The ADC (the ADC divided by the ADC) was calculated. The performance of individual ADC and ADC values in discriminating PCa with a GS of 3 + 3 from PCa with a GS of 3 + 4 or greater was assessed using the AUC value. The ADC had a higher AUC value for discriminating PCa lesions with a GS of 3 + 3 from those with a GS of 3 + 4 or greater (the AUC value increased from 0.70 using the ADC and 0.67 using the ADC [the minimum ADC of the PCa lesion] to 0.80 for the ADC and 0.72 for the ADC [the ADC divided by the ADC]; = 0.043). When stratified by PCa zonal location, the ADC had significantly more robust accuracy in the transition zone (the AUC value increased from 0.63 for ADC to 0.87 for ADC; = 0.019) compared with the peripheral zone (the AUC value increased from 0.74 for ADC to 0.78 for ADC; = 0.44). When analyzed on the basis of endorectal coil use, the ADC performed nonsignificantly better in both the endorectal coil and non-endorectal coil subcohorts, although it performed better in the former. As an intrapatient-normalized diagnostic tool, the ADC ratio provided the best AUC value for discrimination of low-grade from high-grade PCa on 3-T MRI.