Phases of CECT Whole Abdomen

Standard Phase Timing and Utility

The American College of Radiology recommends a standard CECT whole abdomen protocol that includes four distinct phases: noncontrast, late arterial, portal venous, and delayed, with specific combinations tailored to the clinical indication 1, 2, 3
The noncontrast phase identifies high-attenuation ingested material and can be replaced with virtual noncontrast series on newer multienergy CT scanners, as suggested by the Radiology society 1, 2, 3
The late arterial phase provides arterial opacification, allows detection of contrast extravasation, and is critical for detecting hypervascular lesions and arterial bleeding, with a recommended timing of 35 seconds post-injection 1, 2, 3, 4
The portal venous phase provides optimal bowel wall enhancement, allows better evaluation of solid organs, improves detection of slow venous bleeding, and is most sensitive for hypovascular metastases with 85-91.5% sensitivity, at a recommended timing of 60-70 seconds post-injection 1, 2, 3, 4
The delayed phase allows improved detection of slow venous bleeding and enhances lesion characterization, with a recommended timing of 90+ seconds post-injection 1, 2, 3, 4

For suspected GI bleeding, the American College of Radiology recommends using a multiphase protocol with noncontrast, late arterial, and portal venous phases to confirm contrast extravasation and localize bleeding source, achieving 85-90% sensitivity and 92% specificity for detecting active hemorrhage 1, 2
For liver lesion evaluation, the Praxis Medical Insights guideline suggests including arterial, portal venous, and delayed phases, as hypervascular lesions require arterial phase imaging while hypovascular metastases are best detected on portal venous phase 4
For trauma evaluation, the Journal of the American College of Radiology recommends that the portal venous phase is the primary phase for solid organ injury detection, though dual-phase imaging including arterial phase significantly improves sensitivity and accuracy for splenic vascular injury 5
For CT enterography, the Radiology society suggests that a single enteric phase is adequate for detecting inflammatory conditions and masses, while multiphasic examinations improve detection and characterization of vascular lesions 6, 3

The Radiology society recommends avoiding oral contrast in suspected GI bleeding as it delays scanning and positive oral contrast can obscure bleeding 1, 2, 3
Neutral oral contrast is preferred for small bowel evaluation as it allows better visualization of enhancing lesions against hypointense background, as suggested by the Radiology society 6
ECG gating is particularly useful for ascending aorta evaluation where cardiac motion can create artifacts, though it adds complexity, according to the Journal of the American College of Radiology 7
A slice thickness of 2.5-5 mm is recommended, with thinner slices improving lesion detection, as suggested by the Praxis Medical Insights guideline 4

The Journal of the American College of Radiology recommends not performing noncontrast CT alone for abdominal evaluation as it has significantly lower sensitivity for detecting both visceral organ and vascular injuries compared to contrast-enhanced studies 5

The arterial phase in liver CECT begins 10–20 seconds after contrast injection and lasts 25–35 seconds, providing optimal arterial opacification for hepatic imaging. 8
During the arterial phase, hypervascular liver metastases demonstrate early strong enhancement, aiding their detection. 8
The portal‑venous phase extends from 30–45 seconds up to 120 seconds post‑injection, offering the most sensitive window for identifying hypovascular hepatic lesions. 8
The delayed (late) phase starts after 120 seconds and continues until contrast “bubbles” disappear (approximately 5 minutes), which is useful for lesion characterization on contrast‑enhanced ultrasound. 9
In the delayed phase, metastatic lesions typically appear hypoechoic relative to surrounding liver tissue, a characteristic feature for differentiation. 8

For comprehensive liver lesion evaluation, protocols should include arterial, portal‑venous, and delayed phases; arterial imaging is essential for hypervascular lesions, while portal‑venous imaging best reveals hypovascular metastases. 8
Rim enhancement observed on arterial and portal‑venous images is valuable for characterizing metastatic disease. 8

In CT enterography, contrast‑enhanced imaging is initiated 50–70 seconds after intravenous contrast injection, positioning the scan between the enteric and portal phases for optimal small‑bowel assessment. 10
The technique requires administration of ≈ 900 mL neutral or biphasic enteric contrast over 45–60 minutes prior to scanning to achieve adequate luminal distention. 10

A 20‑gauge intravenous catheter is recommended to minimize microbubble destruction and ensure consistent arterial enhancement. 8

When evaluating focal liver lesions, all vascular phases should be reviewed; relying solely on the delayed phase can lead to misinterpretation due to phase‑related artifacts. 8