Adipose tissue and liver

Abstract

Adipose tissue and liver are central tissues in whole body energy metabolism. Their composition, structure, and function can be noninvasively imaged using a variety of measurement techniques that provide a safe alternative to an invasive biopsy. Imaging of adipose tissue is focused on quantitating the distribution of adipose tissue in subcutaneous and intra-abdominal (visceral) adipose tissue depots. Also, detailed subdivisions of adipose tissue can be distinguished with modern imaging techniques. Adipose tissue (or adipocyte) accumulation or infiltration of other organs can also be imaged, with intramuscular adipose tissue a common example. Although liver fat content is now accurately imaged using standard magnetic resonance imaging (MRI) techniques, inflammation and fibrosis are more difficult to determine noninvasively. Liver imaging efforts are therefore concerted on developing accurate imaging markers of liver fibrosis and inflammatory status. Magnetic resonance elastography (MRE) is presently the most reliable imaging technique for measuring liver fibrosis but requires an external device for introduction of shear waves to the liver. Methods using multiparametric diffusion, perfusion, relaxometry, and hepatocyte-specific MRI contrast agents may prove to be more easily implemented by clinicians, provided they reach similar accuracy as MRE. Adipose tissue imaging is experiencing a revolution with renewed interest in characterizing and identifying distinct adipose depots, among them brown adipose tissue. Magnetic resonance spectroscopy provides an interesting yet underutilized way of imaging adipose tissue metabolism through its fatty acid composition. Further studies may shed light on the role of fatty acid composition in different depots and why saturated fat in subcutaneous adipose tissue is a marker of high insulin sensitivity.