1. What is digital subtraction angiography?
Digital subtraction angiography (DSA) is considered the "gold standard" for vascular imaging. However, DSA is an invasive procedure with a risk of complications, a 1% overall neurologic deficit rate, and a 0.5% rate of persistent deficits.
Diagnostic indications for DSA include evaluation of aneurysms in subarachnoid hemorrhage when CTA/MR is negative, accurate evaluation of arteriovenous malformations, and cerebral hemorrhage of unknown etiology.
Endovascular interneural procedures for DSA include acute stroke mechanical thrombectomy, aneurysm coiling, arteriovenous fistula/malformation embolization, intracranial/extracranial stent placement, preoperative embolization of vascular tumors, and vasospasm as a complication of subarachnoid hemorrhage endovascular treatment of disease.
Digital subtraction angiography has a wide range of clinical applications. It is suitable for clinical diagnosis and minimally invasive interventional therapy in various departments such as tumor, urology, respiratory tract, digestive tract, heart, brain, and peripheral.
2. How to implement digital subtraction angiography in brain imaging?
Most diagnostic cerebral angiograms are performed under local anesthesia. Cerebrovascular catheterization can be performed using a transfemoral vein or occasionally a transradial or transbrachial approach using the standard Seldinger technique.
Angiography is usually initiated from the internal carotid artery (ICA). The contrast medium can be injected manually or through a pump syringe. An automated pump can be used to inject 15 to 20 mL of contrast medium at a rate of 3 to 5 mL/s for 3D digital subtraction angiography, depending on the size and position of the catheter and the underlying anatomy.
Conventional cerebral angiography is performed at frame rates of two to three images per second, whereas for studies of AVM or fast-flow pathology, frame rates of 4 to 7 images per second or even higher are usually preferred.
Angiography machines equipped with planar detectors (FD) have become the standard for neuroangiographic imaging. Using this device, not only fast high-quality 3D vessel volumes (3D rotational angiography) but also CT-like images of the brain parenchyma (FD-CT) can be obtained, enabling the detection of intraparenchymal and subarachnoid hemorrhages.
Diagnostic DSA is less indicated due to the quality of CTA and MRA. DSA can be used to resolve discrepancies or inconclusive findings between other noninvasive methods and as an integral part of endovascular interventional procedures. Digital subtraction angiography may be a useful test to further investigate suspected vasculitis when noninvasive methods yield equivocal findings.
Almost all patients with spontaneous subarachnoid hemorrhage and negative CTA still require digital subtraction angiography to rule out occult aneurysms or small dural or small fistulas. In cases of intraparenchymal hemorrhage, DSA is often part of the diagnostic workup in younger patients to detect potential arteriovenous malformations (AVMs) and is critical for carotid interventions, particularly to facilitate recurrence of carotid stenting. Digital subtraction angiography also has an important role in preoperative angiography and is sometimes evaluated in jugular bulb tumors, meningiomas, or other potentially hypervascular tumors and is often used in conjunction with preoperative embolization (if indicated), to reduce subsequent intraoperative blood loss.
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