Colorectal hepatic metastases: quantitative measurements using single-shot echo-planar diffusion-weighted MR imaging

The purpose of this study was to obtain quantitative measurements of the apparent diffusion coefficient (ADC1), flow insensitive apparent diffusion coefficient (ADC2) and perfusion fraction (F) of colorectal hepatic metastases using DWI and to compare these measurements with those obtained in liver parenchyma. Forty patients with 66 hepatic metastases from colorectal carcinoma were prospectively evaluated using DWI with three b values. Quantitative maps of the ADC1 (using b=0, 150, 500 s/mm²images), ADC2 (using b=150, 500 s/mm² images) and fractional variation (F) between ADC1 and ADC2, which reflects perfusion fraction, were calculated. The ADC1, ADC2 and F derived from metastases and liver parenchyma were compared. The mean ADC1 values of liver parenchyma and metastases were significantly higher than the mean ADC2 values (P<0.0001, paired t-test). Colorectal metastases were found to have higher mean ADC1 and ADC2 values compared with liver (P<0.0001, Mann-Whitney test). However, the estimated F was found to be lower in metastases compared to liver (P=0.03, Mann-Whitney test). Colorectal hepatic metastases were characterised by higher ADC1 and ADC2 values, but lower F values compared to liver.