Muscular weakness is associated with fatty infiltration and changes to muscle fibre structure. Quantitative magnetic resonance imaging (MRI) may be able to detect subtle muscle changes in rheumatoid arthritis (RA) patients. Before this method is used, variability of MRI measurements involving regions of interest (ROI) must first be measured. Fat fraction, T2 measurement and diffusion tensor imaging was performed on 19 participants with RA. Intra-rater and inter-rater variability of MRI measurements for thigh muscle ROIs were assessed. Inter-rater and intra-rater variability scores were high, suggesting that these measurements are sufficiently precise to allow the study of subtle changes to muscle.