Phases of CECT Whole Abdomen
A standard CECT whole abdomen protocol includes four distinct phases: noncontrast (or virtual noncontrast), late arterial (35 seconds), portal venous (60-70 seconds), and delayed (90+ seconds), with the specific combination tailored to the clinical indication. 1
Standard Phase Timing and Utility
The timing and purpose of each phase are precisely defined:
Noncontrast phase: Identifies high-attenuation ingested material that can mimic bleeding or hemorrhage; can be replaced with virtual noncontrast series on newer multienergy CT scanners 1
Late arterial phase (35 seconds post-injection): Provides arterial opacification, allows detection of contrast extravasation, and is critical for detecting hypervascular lesions and arterial bleeding 1, 2
Portal venous phase (60-70 seconds post-injection): Provides optimal bowel wall enhancement, allows better evaluation of solid organs, improves detection of slow venous bleeding, and is most sensitive for hypovascular metastases (85-91.5% sensitivity) 1, 2
Delayed phase (90+ seconds post-injection): Allows improved detection of slow venous bleeding and enhances lesion characterization 1, 2
Protocol Selection Based on Clinical Context
For Suspected GI Bleeding
Use multiphase protocol with noncontrast, late arterial, and portal venous phases to confirm contrast extravasation and localize bleeding source, as this combination achieves 85-90% sensitivity and 92% specificity for detecting active hemorrhage 1
For Liver Lesion Evaluation
Include arterial, portal venous, and delayed phases as hypervascular lesions (like HCC) require arterial phase imaging while hypovascular metastases are best detected on portal venous phase 2
For Trauma Evaluation
Portal venous phase (70 seconds) 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 compared to single-phase imaging (p=0.016 and p=0.029 respectively) 1, 3
For CT Enterography
Single enteric phase (50 seconds) is adequate for detecting inflammatory conditions and masses, while multiphasic examinations (arterial + enteric/portal venous ± delayed) improve detection and characterization of vascular lesions 1
Critical Technical Considerations
Oral contrast should be avoided in suspected GI bleeding as it delays scanning and positive oral contrast can obscure bleeding 1
Neutral oral contrast is preferred for small bowel evaluation as it allows better visualization of enhancing lesions against hypointense background 1
ECG gating is particularly useful for ascending aorta evaluation where cardiac motion can create artifacts, though it adds complexity 1
Slice thickness of 2.5-5 mm with thinner slices improving lesion detection 2
Common Pitfalls to Avoid
Do not perform 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 1
Avoid unnecessary triple-phase imaging when dual-phase (arterial + portal venous) provides equivalent diagnostic accuracy, as this reduces radiation exposure by approximately 25% 3, 4
Do not delay contrast-enhanced CT in patients with stable creatinine <1.5 mg/dL due to unfounded concerns about contrast-induced nephropathy, as the risk is negligible in patients with normal renal function and the diagnostic benefits are fundamental 5