FIGURE 5. Split CT protocol to optimize contrast enhancement in each body region. Desired contrast enhancement is arterial in thorax, portal–venous in upper abdomen, venous in pelvis, and late-venous in neck and head. To meet these requirements, PET/CT scanners need to allow whole-body acquisition starting with thorax (scanned in caudocranial direction), followed by abdomen and pelvis (craniocaudal direction), and by neck and head (caudocranial scanning).