[en] Conventionally, use of CT in PET-CT imaging was limited to attenuation correction and lesion localization. However, the need was felt to provide complete diagnostic CT information in a single PET-CT investigation and hence various contrast protocols used in CT Imaging have now been adopted in PET-CT Imaging. The modern nuclear medicine professional must be well conversant with the use of these contrast CT protocols. Single Phase Protocol: Acquisition of whole body contrast CT imaging is started at around 55-60 seconds post contrast injection. Multiple phase Protocol: Triple phase Liver Protocol Liver Arterial phase: 15-20 seconds post injection or immediately after bolus tracking. This is phase when the contrast is still in the arteries and has not enhanced the liver. Liver Portal Phase: 45-50 seconds post injection or 25-30 seconds after bolus tracking. This is the phase when portal vein enhancement is seen. Whole body Venous phase: 55-60 seconds post injection or 35-40 seconds after bolus tracking whole body CT is acquired. In this phase, the liver parenchyma enhances through blood supply by the portal vein. Dual Phase Pancreatic Protocol: Late Arterial phase: 35-40 seconds post injection. In this phase the normal pancreatic glandular tissue enhances optimally whereas a pancreatic malignancy does not. This phase gives good tumor to normal pancreatic parenchyma differentiation. Whole body Venous phase: 55-60 seconds post injection whole body CT is acquired. Dual Phase Organ-Specific Protocol: Similar to pancreatic protocol, any organ or lesion can be evaluated for late arterial and venous enhancement which gives a measure of the tissue vascularity. Thus, adoption of these contrast CT protocols helps us provide additional diagnostic CT information and reduces the need for patient to undergo separate multiphase or single phase contrast CT. (author)