CT Aortogram Contrast Requirement
Yes, a CT aortogram (CT angiography of the aorta) absolutely requires intravenous contrast administration. This is a defining characteristic that distinguishes CTA from standard CT imaging.
Why Contrast is Essential
Contrast enhancement is mandatory for CT aortography because visualization of the aortic lumen, wall characteristics, and vascular pathology cannot be adequately assessed without it. 1 The American College of Radiology explicitly defines CTA as requiring thin-section CT acquisition timed to coincide with peak arterial enhancement, along with multiplanar reformations and 3D renderings—all three elements are essential. 1
Critical Information Provided by Contrast
Luminal assessment: Contrast allows visualization of the true aortic lumen diameter, which is essential for accurate measurement and diagnosis. 2
Thrombus detection: Contrast-enhanced imaging distinguishes between patent lumen and mural thrombus, which non-contrast CT cannot reliably differentiate. 1
Branch vessel involvement: Contrast is necessary to evaluate involvement of branch vessels (celiac, mesenteric, renal arteries), which is critical for surgical or endovascular planning. 1
Dissection flap visualization: The intimal flap in aortic dissection requires contrast to be seen. 1
Vascular complications: Active extravasation, pseudoaneurysm, and other vascular complications require contrast for detection. 3
Technical Protocol Requirements
The contrast bolus must be timed to coincide with peak arterial enhancement, typically using bolus tracking or test bolus techniques. 1 Standard protocols include:
Arterial phase imaging: Acquisition during peak arterial enhancement (typically 60-90 seconds after injection). 4
Thin-section acquisition: Submillimeter isotropic datasets for multiplanar reconstruction. 1
3D rendering: Required element distinguishing CTA from standard contrast-enhanced CT. 1
ECG gating: Particularly valuable for ascending aorta to minimize cardiac motion artifacts. 1, 2
When Non-Contrast CT Has Limited Role
Non-contrast CT can detect the presence of an aortic aneurysm but cannot provide the comprehensive information needed for management decisions. 1
Non-contrast CT may be used for AAA screening when ultrasound is not suitable, as it can measure outer-to-outer aortic diameter. 1
Non-contrast imaging cannot assess for dissection, thrombus characteristics, or branch vessel involvement. 1, 3
In suspected contained rupture, a dual-phase protocol (non-contrast followed by contrast) may be performed, where the non-contrast phase helps identify the "crescent sign" of dissecting hematoma. 1
Common Pitfall to Avoid
Do not confuse standard "CT abdomen/pelvis with contrast" with "CTA abdomen/pelvis." 1 While both use intravenous contrast, only CTA includes:
- Arterial-phase bolus timing (not portal venous phase)
- Thin-section acquisition with isotropic voxels
- Mandatory 3D rendering and multiplanar reformations
Standard contrast-enhanced CT performed in portal venous phase will miss critical vascular detail and cannot substitute for CTA when aortic pathology is suspected. 1
Contrast Volume Considerations
Modern protocols allow for reduced contrast volumes while maintaining diagnostic quality:
Individualized protocols based on body habitus and tube voltage can reduce contrast volume by 55-63% compared to standard protocols. 5, 6
Low-volume protocols (38-50 mL) are feasible with third-generation dual-source CT scanners and appropriate technique. 7, 8
Despite volume reduction, diagnostic attenuation (typically 300-350 HU) must be maintained. 7, 5, 6
Alternative When Contrast is Contraindicated
If intravenous iodinated contrast is absolutely contraindicated (severe renal insufficiency, severe contrast allergy), MR angiography (MRA) is the alternative imaging modality, not non-contrast CT. 1, 2 MRA provides similar diagnostic information without requiring iodinated contrast or ionizing radiation. 1