Short-term repeatability of monoexponential apparent diffusion coefficient in prostate cancer: dependence on b-value, tumor grade, lesion size, and lesion location.

BackgroundDiffusion-weighted magnetic resonance imaging (DWI) of prostate cancer (PCa) is commonly quantified using monoexponential apparent diffusion coefficient (ADCm) values. However, repeatability of ADCm as qualitative biomarker for PCa is not well established.PurposeTo evaluate repeatability of prostate ADCm.Material and MethodsA total of 112 patients with PCa who underwent two repeated prostate DWI scans (12 b-values, 0-2000 s/mm2) on the same day before prostatectomy. ADCm values were analyzed across different b-value combinations and PCa lesion sizes. Bland-Altman plots, Spearman rank correlation, within-subject standard deviation (wSD), and coefficient of variation (wCV) were calculated.ResultsBland-Altman plots demonstrated no observable trend differences across ADCm intensity ranges. The results indicate correlation of ADCm repeatability with PCa aggressiveness, expressed as Gleason Grade Group (GGG). Specifically, wCV decreased towards higher GGG compared with GGG=1, wCV was <0.07 with b-value pairs from 0, 700 to 0, 1300 s/mm2. Majority of evaluated lesions that had high wSD up to 0.2 × 10-3 mm2/s were found in lower GGGs. Different b-value combinations demonstrated varying effects on ADCm performance. The lowest repeatability was observed with the lesion size <5 mL while for the lesion size ≥5 mL wSD was <0.1 × 10-3 mm2/s.ConclusionOur study demonstrated repeatability of ADCm mean values as quantitative imaging biomarkers for PCa detection and characterization.