Digital subtraction angiography
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Digital subtraction angiography (DSA)
DSA is an invasive X-ray angiographic technique that produces a clear image of blood vessels after injection of iodinated contrast.
Principle
- A mask image is obtained before contrast injection.
- Contrast is injected through a catheter placed in an artery or vein.
- A second image is acquired when the vessel is opacified.
- The computer subtracts the mask from the contrast image, removing bone and soft-tissue background and leaving the contrast-filled vessels visible.
This improves vessel conspicuity and can reduce the amount of contrast needed. Patient motion can cause subtraction artifacts. Murray & Nadel's Textbook of Respiratory Medicine, p. 450.
Procedure
- Usually performed under local anesthesia.
- Vascular access is commonly through the femoral artery, sometimes radial or brachial access.
- A catheter is advanced under fluoroscopy to the vessel of interest.
- Iodinated contrast is injected and serial images are captured.
- It may include 2D imaging, biplane imaging, or 3D rotational angiography.
Main uses
DSA remains particularly useful when detailed vascular anatomy is needed or when treatment can be performed during the same session:
- Cerebral aneurysm, arteriovenous malformation (AVM), and dural arteriovenous fistula
- Subarachnoid hemorrhage with negative or equivocal CT angiography
- Carotid stenosis assessment before or during stenting
- Cerebral vasculitis when CTA or MRA is indeterminate
- Peripheral arterial disease and acute arterial occlusion
- Renal, visceral, pulmonary, and bronchial vascular imaging
- Endovascular procedures: angioplasty, stenting, embolization, thrombectomy, and coiling
CTA and MRA have reduced its role as a purely diagnostic test, but DSA remains important for uncertain noninvasive findings and for image-guided intervention. Grainger & Allison's Diagnostic Radiology, p. 1371.
Advantages
- High spatial and temporal resolution
- Dynamic evaluation of arterial, capillary, and venous phases
- Precise visualization of small vessels and collateral circulation
- Can directly guide treatment in the same procedure
Limitations and risks
Because it requires arterial catheterization, DSA is not usually used for screening. Risks include:
- Puncture-site bleeding or hematoma
- Arterial dissection, thrombosis, or embolization
- Stroke, particularly in cerebral angiography
- Iodinated contrast reaction or kidney injury
- Radiation exposure
- Infection, rarely
For carotid imaging, DSA is highly accurate but is generally reserved for therapeutic planning or intervention because of these procedural risks. Fuster and Hurst's The Heart, 15th ed., p. 768. A recent review also identifies cerebral infarction, contrast allergy, and access-site hematoma or infection as potential complications in DSA procedures (complications review).
DSA versus CTA and MRA
| Feature | DSA | CTA | MRA |
|---|---|---|---|
| Invasive | Yes | No | No |
| Radiation | Yes | Yes | No |
| Iodinated contrast | Yes | Usually | No, or gadolinium |
| Spatial/temporal resolution | Highest | High | Moderate to high |
| Enables intervention | Yes | No | No |
| Typical role | Problem-solving and treatment | Rapid diagnostic vascular imaging | Noninvasive vascular imaging |
Key point: DSA is often considered the reference standard for detailed vascular imaging, but its invasive nature means CTA or MRA is commonly used first.
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