Imaging techniques for the assessment of ectopic fat in liver and skeletal muscle

Abstract

The prevalence of obesity worldwide has prompted the development of noninvasive imaging techniques to monitor excessive accumulation of fat. Noninvasive methods to quantify liver and skeletal muscle fat may be used to assess efficacy and safety endpoints in drug development. Multiple imaging methods have been proposed to measure the amount fat in the liver. The leading methods for quantifying liver fat are magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS), as these techniques are capable of estimating the hepatic proton density fat fraction (PDFF), a generalizable, standardized measurement that is reproducible across sites and scanner manufacturers, models, and software. Other techniques, such as computed tomography, ultrasound, and MR techniques that measure uncorrected signal fat fraction rather than PDFF, are confounded by biological, physical, or technical factors. In muscle, the only noninvasive method to gain widespread acceptance is MRS as it is the only technique that can differentiate the fat that accumulates inside skeletal muscle cells (intramyocellular lipid (IMCL)) from the fat that accumulates between skeletal muscles and between skeletal muscle cells.