renal cortex and the medulla are enhancing. the renal cell carcinoma in the left kidney is not as well defined when compared to the corticomedullary phase images, but is actually slightly more conspicuous. there is some contrast noted within the collecting system during this phase (7c). ct urography main article: ct urogram figure 8. selected images from a ct urography protocol ct. 8a is an axial ct image from the renal parenchymal phase. there is a mildly enhancing soft tissue mass in the left renal pelvis (arrow) consistent with a transitional cell carcinoma. figure 8b (coronal reformats) and 8c (left oblique coronal reformats) demonstrate the double bolus technique of ct urography. these images confirm soft tissue mass (arrows) in the renal pelvis with contrast excretion into the collecting system (arrowheads). ct urography (ctu) is commonly used in the evaluation of hematuria, and specifically tailored to image the renal collecting system, ureters and bladder in addition to the renal parenchyma. initial imaging includes a noncontrast phase to detect renal calculi as a source of hematuria. note that dual energy ct may eventually allow the noncontrast phase to be eliminated. contrast enhancement techniques for ctu vary from institution to institution. a common technique is a double bolus, single phase imaging algorithm. excretory phase imaging allows for not only evaluation of the ureteral lumen, but also periureteral abnormalities including external masses and lymphadenopathy. pancreatic masses figure 9. selected images from a pancreatic protocol. 9a is a noncontrast ct image demonstrating subtle fullness in the region of the pancreatic neck (arrow). 9b is a ct image performed during the early arterial phase during which there is opacification of the arterial structure with subtle fullness in the pancreatic neck (arrow). the pancreas is not enhancing during this phase. 9c was performed in a late arterial/pancreatic phase demonstrating normal enhancement of the pancreas (arrowhead) with a hypoenhancing mass (arrow) in the pancreatic neck. the pancreatic mass is more visible during this phase. pancreatic masses are often evaluated using both an early arterial (to evaluate for vascular involvement and thus resectability, figure 9a) and a later “pancreatic” phase (which optimizes pancreatic parenchymal enhancement and thus is best at differentiating pancreatic tumors from pancreatic parenchyma, figure 9b). pancreatic adenocarcinoma typically is hypoenhancing when compared to the surrounding parenchyma. most other common pancreatic tumors are hypervascular with avid enhancement (such as pancreatic neuroendocrine tumors) and appear brighter than the surrounding pancreatic parenchyma after the injection of intravenous contrast material. incidental findings ct imaging should be performed to evaluate the specific clinical question, however incidental findings are noted in approximately 5-16 % of patients scanned for an unrelated reasons. it is not acceptable practice to anticipate the possibility of incidental lesions given their low incidence and prospectively add additional phases to routine protocols. unfortunately, several recent surveys demonstrated that this practice is more common than might be anticipated, and contributes to unnecessary medical radiation exposure to a large population of patients. even more egregious is the fact that many of these findings could potentially be more accurately evaluated with other non-radiation imaging modalities such as mri or ultrasound. although the management of incidental findings is not the focus of this chapter, some of these findings will require complete characterization with further ct phases such as arterial phase (certain liver tumors) or delayed images (adrenal lesions). management of incidental findings has been controversial since they are relatively common, especially in the elderly, and more ct scanning may be required for further characterization of what is frequently a benign finding. in an effort to provide guidance on which incidental findings should be appropriately further evaluated and what the appropriate imaging modality should be, the acr published a white paper on management of incidental findings detected at ct of the abdomen in 2010. conclusion volume rendering of an abdominal ct. multiphase ct examinations are very important for the detection and characterization of certain clinical conditions, but should not be generalized for every patient undergoing ct of the abdomen and pelvis. a recent survey demonstrated that many physicians are routinely performing multiphase ct for the majority of patients in an attempt to prospectively characterize potential lesions detected during the scan. however, unindicated multiphase ct examinations are an important source of medical radiation that does not contribute to the care of patients. adherence to published standards such as the acr appropriateness criteria can both decrease medical radiation and optimize imaging for the specific clinical indication.