S-PI-RADS and PI-RRADS for Biparametric MRI in the Detection of Prostate Cancer and Post-treatment Local Recurrence

Grayscale ADC map for quantitative analysis of the signal intensity (SI) of suspicious areas in S-PI-RADS and PI-RRADS. The apparent diffusion coefficient (ADC) scale measures the SI values of normal tissue and cell density of prostate cancer that increase with a decrease in ADC values. Three sub-parameters are identified: ADC minimum or ADC_min, ADC mean, and ADC maximum or ADC_max. ADC_max value is the water or urine (white) with high signal intensity value and is obtained from average of three circular regions-of-interest (ROIs) placed within the bladder; ADC_max value varies on the same MRI scanner and between different MRI scanners [for example on our 3T MRI unit (Achieva, Philips Medical Systems, Healthcare, Eindhoven, the Netherlands)] equipped with a phased array body coil, the ADC_max value on the ADC map generated using b-values of 0, 500, 1000 and 1500 s/mm² can reach an average value of 4000]. ADC_min value is the bone (black) equal to 0 and is obtained from a circular ROI placed within the femur head; ADC_min value does not vary on the same MRI scanner nor between different MRI scanners. ADCmean is obtained from the formula: ADC_mean=(ADC_max + ADC_min)/2. On grayscale ADC map, measurable and homogeneous areas with ADC values ≥ ADCmean can be considered as moderately hypointense SI areas on ADC map, while those with ADC values < ADCmean are considered as markedly hypointense SI areas on the ADC map.