Evaluating CMR

Measuring Ectopic Fat Using CT

The average HU or mean attenuation value of adipose tissue-free skeletal muscle voxels can also be used as an index of skeletal muscle lipid content (Figure 5) (39). As with the liver, the lower the skeletal muscle mean attenuation value or the greater the number of low-density skeletal muscle voxels (e.g., 0-30 HU), the higher the skeletal muscle lipid content. However, unlike the liver, fat is stored both inside and outside the muscle cell. As such, CT muscle attenuation values reflect both intra-myocellular (IMCL) and extra-myocellular (EMCL) lipid content. Although similar, they are not analogous to intra-myocellular lipid values obtained through skeletal muscle biopsy or proton magnetic resonance spectroscopy.

In summary, CT 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, CT is expensive and involves radiation exposure, which limits the routine use of this tool for assessing body composition and predicting obesity-related health risk in clinical practice.