Quantifying Body Composition from Chest CT Scans

The non-contrast–enhanced chest CT exams (acquired at suspended full inspiration using 64-slice multidetector row CT scanners, Siemens Medical Solutions, Erlangen, Germany or GE Healthcare, Waukesha, Wisconsin, USA) were used to measure the IMAT and SAT areas as well as the pectoralis muscles (PMs) density [19 (link),23 (link)]. The cross-sectional SAT area was measured as the area between the PM and skin surface in the slice just above the superior margin of the aortic arch [20 (link),24 (link)]. Density of the SAT area was analyzed to estimate an individualized attenuation threshold for the IMAT (i.e., the extramyocellular lipid content) [20 (link),25 (link)]. The cross-sectional areas within the PM with attenuation below the estimated threshold were measured as the IMAT (S3 Fig). The IMAT and SAT areas were corrected as IMAT and SAT indices (area by height squared, cm²/m²) to account for the anthropometric variations. Moreover, the mean density of the PM area (after excluding the IMAT area) was also measured as a surrogate measure of the intramyocellular lipid content, Hounsfield unit by area, HU/cm², S3 Fig).