CT scans were processed using semi-automated algorithms programmed into MATLAB v13.0 (MathWorks; Natick, MA). After identifying individual vertebral levels on each patient’s CT scan, the deep fascia was traced at each level, as shown in Figure 1. Using automated methods, each pixel within the area encompassed by the fascia was sampled for its radiologic density (in Hounsfield Units [HU]). Those pixels which were sampled to be in the density range of fat were designated as abdominal visceral fat, and the sum of the pixels were termed the visceral fat area. The visceral fat area from T12 through L4 was averaged for each patient and served as the primary exposure variable for this study. Additionally, total psoas area (TPA) was measured as described in our previous work.(9 (link)–12 (link)) Briefly, the cross-sectional areas of the left and right psoas muscles at the level of L4 were measured.