Water T2 mapping from low to high fat fraction values in lower limb skeletal muscles of different neuromuscular disorders

Motivation: Muscle water T2 is an interesting quantitative MRI biomarker in neuromuscular disorders but its interpretation is influenced by the presence of fat. Goal(s): We investigated how this water T2-fat relationship differed between nine different neuromuscular disorders. Approach: We looked at linear and 2nd degree polynomial fits, all obtained with the same 3-T system, sequence and post-processing pipeline. Results: Polynomial fitting describes the data better and the water T2-fat relationship needs to be interpreted in a disease-specific context, especially when there is a known inflammatory component and/or if water T2 is increased before the occurrence of any muscle fat replacement. Impact: The relationship between MRI biomarkers water T2, reflecting active muscle damage, and fat fraction, reflecting disease progression, should be interpreted in the context of the disease, whether or not there is inflammation or extensive active muscle damage.