Computed tomography of the abdomen and pelvis

Renal stones, appendicitis, pancreatitis, diverticulitis, abdominal aortic aneurysm, and bowel obstruction are conditions that are readily diagnosed and assessed with CT. CT is also the first line for detecting solid organ injury after trauma.

Multidetector CT (MDCT) can clearly delineate anatomic structures in the abdomen, which is critical in the diagnosis of internal diaphragmatic and other nonpalpable or unsuspected hernias.

[citation needed] In cases of suspected bowel leak or perforation, gastrointestinal fistula, interloop abscess or other fluid collection, oncologic staging and surveillance, and CT colonography, oral positive contrast is useful in delineating the lesions.

[citation needed] The most common technique is to perform portal venous phase imaging in the abdomen and pelvis (approximately 60–90 seconds after contrast administration, figure 2).

CTA is commonly used in the head and chest in the evaluation of pulmonary emboli, aneurysms, vascular malformations, dissection, bleeding and ischemia.

Although a "hypervascular", biphasic evaluation would generally be used for these patients, note that a single phase is often adequate for follow up imaging.

[citation needed] Delayed phase imaging (figure 5) encompasses scanning at a variety of different times following contrast administration, and depends on the pathology in question.

In addition, if there is a need to definitively characterize a hepatic mass, MRI is generally more sensitive and specific, with no associated radiation dose.

[citation needed] Transient hepatic attenuation differences in the arterial phase may mimic diseases of the liver.

Following noncontrast scanning, intravenous contrast is injected and a corticomedullary phase is obtained at approximately 70 seconds (figure 7a, 7b).

Excretory phase imaging allows for not only evaluation of the ureteral lumen, but also periureteral abnormalities including external masses and lymphadenopathy.

[citation needed] 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.

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.

A CT scan image showing a ruptured abdominal aortic aneurysm .
CT Scan of 11 cm Wilms' tumor of right kidney in 13-month-old patient.
FIGURE 1. Non-contrast CT demonstrating multiple bilateral renal calculi (arrows), which can be obscured on contrast-enhanced images, particularly delayed images when there is excreted contrast in the renal collecting system; axial left, coronal reformat on right. [ citation needed ]
FIGURE 3. Axial (left) and coronal (right) CT angiography images of the abdominal aorta evaluating for aortic aneurysm. [ citation needed ]
FIGURE 4: Arterial and portal venous phase CT of cholangiocarcinoma. Selected images from a biphasic CT demonstrating early arterial enhancement of a posterior right hepatic lobe mass with mild wash out on delayed phase images in the setting of cirrhosis characteristic of hepatocellular carcinoma. [ citation needed ]
FIGURE 5. Selected images form CT performed using a Cholangiocarcinoma specific protocol. 5a is a portal venous phase image demonstrating a single low attenuation mass which does not appear to enhance. 5b is a 15 minute delayed image which demonstrates delayed enhancement of the liver mass (arrow) characteristic of Cholangiocarcinoma. Several other enhancing masses (arrowheads) are also seen which were not evident on the portal venous phase images. [ citation needed ]
FIGURE 6. Selected images from a biphasic CT of Focal Nodular Hyperplasia in the left hepatic lobe (arrow). These masses have characteristic early arterial enhancement (6a) with contrast wash out on the portal venous phase images (6b) from the mass making these lesions difficult to identify on portal venous phase images alone. [ citation needed ]
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). [ citation needed ]
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. [ citation needed ]
Volume rendering of an abdominal CT.