CT-based Quantification of Body Composition

CT scan based densitometric quantification has been described in detail elsewhere [18 (link)]. Briefly, area-based quantification of adipose tissue compartments was performed on the L3/4 spinal level (volumetric quantification of selected slice, divided by slice thickness) using a semiautomatic software tool (Syngo Volume tool, Siemens Healthcare, Munich, Berlin, Germany). Specific regions of interest (ROI) were manually determined: total fat area (TFA) (whole abdominal circumference, Figure 1a) and VFA (by defining the fascial plane of the abdominal muscle wall, Figure 1b). The limits of measurement for selecting the specific fat area were −190 HU (Hounsfield units) to −30 HU. SFA was calculated by subtracting VFA from TFA. On the same image slice, at the L3/4 spinal level, an ROI determining the SMM (sum of M. psoas major, M. erector spinae, M. quadratus lumborum, M. latissimus dorsi, M. transversus abdominis, M. obliquus internus abdominis and externus abdominis, and M. rectus abdominis;Figure 1c) was measured by limiting the attenuation threshold between 40 HU and 100 HU (excluding muscle lipid content; thresholds were based on visual controls which were conducted as a plausibility test within our study cohort) and normalized for height squared (see Figure 1) [13 (link),18 (link)].