Evaluating CMR

Measuring Ectopic Fat Using MRI

MRI can also be used to assess ectopic fat deposition within the muscle and liver (32, 33). The Dixon method is most commonly used to measure fatty infiltration by MRI. In essence, the protons in fat and water produce different signals, which means the fat signal intensity of a given region relative to its water signal intensity can be used as a marker of lipid infiltration. Using this method, MRI cannot separate the lipid into its intra- and extra-cellular lipid compartments. This is not a concern in the liver as lipid exists only within the cell. In muscle, however, lipid exists both inside and outside the cell. This may be important as lipid accumulation can have different metabolic consequences depending on whether it is inside or outside the muscle cell. Nevertheless, MRI measures of lipid accumulation within the muscle and liver closely match skeletal muscle and liver intracellular lipid measures using criterion methods such as biopsy (33) or magnetic resonance spectroscopy (34, 35).  

MRI is one of the criterion methods for measuring intra-abdominal fat and skeletal muscle mass. It can also be used to assess lipid infiltration in tissues such as muscle and the liver. However, assessing body composition using MRI is an expensive, time-consuming, and labour-intensive process. In addition, MRI’s limited availability hinders the routine use of this tool for assessing body composition and predicting obesity-related health risk in clinical practice.