Computed tomography: What and how does it measure?

The current study provides a comprehensive review about the use and the clinical applications of computed tomography (CT) associated with the in vivo evaluation of the human body composition. The high-resolution CT images allow the accurate separation of the various body compartments at the tissue/organ level including adipose tissue, skeletal muscle, bones and organs. The further ability of the imaging modality to distinguish the cortical from the trabecular bone and the visceral from the susbcutaneous fat is of great value in clinical studies. CT may also give important information about the components of the subcutaneous adipose tissue and the muscle or liver fat infiltration. The efficient determination of the skeletal muscle attenuation and bone mineral density, that related with metabolic disorders, is feasible with the aid of CT data. The area and volume of each human body compartment may be estimated with high accuracy and reproducibility from CT scans. These estimations may be carried out using the methods of manual planimetry, semi-automatic segmentation of the tissue of interest, stereological point-counting approach and geometrical models based either on linear or area measurements. The advantages and disadvantages of the aforementioned methods for the quantification of the human body composition are presented and discussed.