What is CTA (Computed Tomography Angiography)?
CTA is a non-invasive imaging technique that uses intravenous contrast material combined with multidetector CT scanning to create detailed, three-dimensional images of blood vessels throughout the body. 1
Technical Overview
CTA works by acquiring thin-section CT images timed precisely to coincide with peak arterial enhancement after contrast injection. The volumetric dataset is then interpreted using:
- Primary transverse reconstructions
- Multiplanar reformations
- 3D renderings (a required element that distinguishes CTA from standard contrast CT) 2
The technique offers volumetric imaging rather than the planar images of traditional catheter angiography, enabling extensive post-processing including multiplanar reformatted and maximum-intensity projection images to create an arterial "road map." 1
Key Clinical Advantages
Superior Diagnostic Capabilities
- Sensitivity and specificity of 90-100% for detecting arterial stenoses >50% diameter compared to catheter angiography 1
- Shows collateral vessels and arteries distal to occlusions that may not appear on catheter angiography 1
- Detects non-vascular findings and vascular lesions (aneurysms, cystic adventitial disease) not visible with projectional catheter techniques 1
- Has replaced catheter angiography as the reference standard for aortic imaging 1
Practical Benefits Over Alternatives
Compared to MRA, CTA provides:
- Faster acquisition times 1
- Better safety in patients with pacemakers or defibrillators 1
- Less severe metal artifacts 1
- Minimal issues with claustrophobia 1
Compared to catheter angiography:
Major Clinical Applications
Stroke and Neurovascular Disease
- High accuracy for large-vessel occlusion detection with high interrater reliability 3
- Sensitivity 92-100% and specificity 82-100% for intracranial occlusions 4
- Covers extra- and intracranial vasculature in one sequence 3
- Radiation dose approximately 5-6 mSv for single-phase CTA 3
Peripheral Arterial Disease
- Enables rapid scanning of the entire arterial system from abdomen through lower extremities 1
- Excellent accuracy in bypass graft assessment 1
- More clinically useful than duplex ultrasound 1
Aortic Pathology
- First-line modality for aortic aneurysms, dissection, and acute aortic syndrome 2, 5
- Excellent for pre-operative planning and post-intervention surveillance 2
Important Limitations and Caveats
Heavy Calcification
Heavily calcified atherosclerotic disease limits image interpretation, particularly in tibial arteries. Patients who are poor candidates for tibial CTA include:
- Age >80 years
- Diabetics
- Dialysis patients 1
Dual-energy CTA can reduce blooming and beam-hardening artifacts from calcification and metallic stents 1
Contrast-Related Issues
- Requires iodinated contrast (risk of nephropathy, though considered negligible) 3
- Contraindicated in patients with severe contrast allergies
- Caution in renal dysfunction 4
Radiation Exposure
- Complete CT stroke protocol (NCCT + multiphase CTA): ~8.5 mSv
- Adding CT perfusion increases dose to 12-16 mSv 3
- Acceptable radiation dose of 3-5 mSv for standard protocols 3
Optimal Technique Considerations
Timing is critical: Optimized acquisition timing ensures visualization of collaterals and distal vessels 1. For suspected vessel occlusions, delayed or low-pitch CTA may be beneficial as it allows 9-12 intracranial circulation times versus the single circulation time of catheter angiography 6.
ECG-gating minimizes cardiac motion artifact and allows accurate measurement of the ascending thoracic aorta 2.