The scans were then assessed by two radiologists, one of whom is a board certified sub-specialist gastrointestinal radiologist. Regions of interest were drawn around the psoas muscles bilaterally at the L3 vertebral body as per accepted validated methods. The sum of the psoas muscle area was subsequently divided by the square of the corresponding individual’s recorded height in metres in order to determine the psoas muscle index. Psoas muscle index cut-off values were sourced from a retrospective study which calculated optimal cut-off values by receiver operating characteristic analysis for survival[10 (link)].