Repeatability of diffusion-weighted MRI of the prostate using whole lesion ADC values, skew and histogram analysis

Purpose: To investigate the repeatability of diffusion-weighted imaging parameter including ADC-derived histogram values in prostate cancer. Methods: 10 patients with prostate cancer were prospectively recruited to a retest cohort. 3 T diffusion-weighted MRI of the prostate was acquired consecutively with patient getting off the scanner between studies. Prostatectomy-histopathology defined tumour regions-of-interest were outlined on ADC maps and diffusion-weighted metrics including histograms were calculated. The coefficient of reproducibility (CoR) and Bland-Altman plots were used to assess repeatability. Results: 10th centile, 90th centile, and median ADC showed good repeatability with mean difference ranging from -0.005 to -0.025 x 10(3) mm(2)s(-1), and CoR ranging from 0.271-0.294 x 10(3) mm(2)s(-1) of scan 1 mean). Two measures of heterogeneity and simplified texture, IQR and mean local range, had only moderate repeatability. IQR had a mean difference of -0.032 x 10(3) mm(2)s(-1) between scans with CoR 0.181 x 10(3) mm(2)s(-1) (56% of scan 1 mean). Mean local range had a mean difference -0.008 x 10(3) mm(2)s(-1) between scans (37% of scan 1 mean). Bland-Altman plots showed good repeatability for test and re-test analysis for median, percentile and mean range values. All ADC values had good reliability regardless of whether the tumour border was included in quantitative analysis. ADC histogram skew had poor repeatability, CoR 0.78 x 10(3) mm(2)s(-1) (373% of scan 1 mean). Conclusion: 10th and 90th centile ADC demonstrated sufficient repeatability for clinical use. However, more advanced measures of heterogeneity such as histogram skew, IQR, or mean local range may be limited by their repeatability.