Quantitative Apparent Diffusion Coefficient measurements are a more repeatable measure of sacroiliitis than visual scoring

Introduction Visual scoring of short tau inversion recovery (STIR) magnetic resonance images (MRI) is widely used for assessing sacroiliitis1. However, current scoring systems contain a number of subjective elements including assessment of depth and brightness of inflammation, and the number of inflamed joint quadrants. Furthermore, observers can only make binary choices for each joint quadrant. Quantitative apparent diffusion coefficient (ADC) measurements2 are based on pixel values in the image itself and are therefore intrinsically objective. This study aims to compare the repeatability3 of visual STIR scoring and quantitative ADC measurements.