Does CTA Include Arterial and Venous Phases?
CTA protocols can be timed to capture either arterial OR venous phases depending on the clinical indication, but for many vascular pathologies—particularly mesenteric ischemia and pulsatile tinnitus—both arterial and portal venous phases should be included as part of the complete protocol. 1
Understanding CTA Definition and Timing
The American College of Radiology defines CTA as using "thin-section CT acquisition that is timed to coincide with peak arterial or venous enhancement" with required 3D rendering and multiplanar reformations. 1 This definition indicates that CTA can be performed with either phase, but the specific protocol depends entirely on what you're trying to diagnose.
When Both Phases Are Mandatory
Mesenteric Ischemia
Both arterial and portal venous phases must be included in the protocol to assess both arterial and venous patency. 1 The arterial phase influenced clinical care in 19% of patients compared to portal venous phase alone, demonstrating that venous phase-only imaging leads to suboptimal evaluation of mesenteric arteries and diagnostic errors. 1
- The arterial phase detects arterial stenosis, embolism, thrombosis, and dissection 1
- The portal venous phase identifies mesenteric vein thrombosis and assesses bowel wall perfusion 1
- Dual-phase imaging achieves 93-100% sensitivity and specificity for acute mesenteric ischemia 1
Pulsatile Tinnitus
Modified CTA bolus timing allows for a "balanced phase" examination that facilitates detection of both arterial and venous etiologies of pulsatile tinnitus in the head and neck. 1 This approach captures both arterial pathologies (dAVFs, AVMs, fibromuscular dysplasia) and venous abnormalities (sigmoid sinus diverticulum, dehiscence, SSWAs) simultaneously. 1
Thoracic Aortic Pathology
CTA protocols for aortic pathology usually include both an arterial phase and a delayed contrast phase to comprehensively assess the vasculature. 1 This dual-phase approach is standard for pre-TEVAR planning and surveillance. 1
When Single Phase May Suffice
Extremity Trauma
For extremity trauma CTA, the arterial phase alone is typically sufficient. 2 Adding a venous phase increases detection of venous injuries but does not change surgical management or add significant clinical value (p > 0.125). 2
Standard Arterial Imaging
When evaluating arterial stenosis, aneurysms, or arterial anatomy alone, a single arterial phase with proper timing may be adequate depending on the clinical question. 3, 4
Critical Ordering Pitfall
Do not order "CT abdomen/pelvis with contrast" when you need vascular assessment—this typically defaults to venous phase only without arterial imaging or required 3D rendering. 5, 6 Specifically request "CTA abdomen/pelvis" and indicate if dual-phase imaging is needed for your clinical indication. 5
Standard CT with IV contrast performed during venous phase alone can assess major arterial lesions but leads to suboptimal evaluation of mesenteric arteries and diagnostic errors compared to proper dual-phase CTA. 1
Technical Considerations
- Dual-phase imaging during a single breath-hold is feasible with modern MDCT scanners, acquiring arterial and venous phases serially with 15-second intervals during a 31-second breath-hold. 3
- Virtual monoenergetic reconstruction from venous phase spectral CT can potentially create arterial-equivalent images at 40-50 keV, though this remains investigational. 7
- ECG gating is particularly important for ascending aorta imaging where cardiac motion creates artifacts, and is included in standard CTA codes without separate billing. 1, 8