Digital subtraction angiography
Digital subtraction angiography is a fluoroscopy technique that is used in interventional radiology to clearly visualize blood vessels in a bony or dense soft tissue environment.
Some facts about Digital subtraction angiography:
- Contrast medium is used to produce image by subtracting a 'pre-contrast image' or mask from subsequent images, once the contrast medium has been introduced into a structure.
- Images of the blood vessels are produced without interfering shadows from overlapping tissues which provides a clear view of the vessels and allows for a lower dose of contrast medium
- The subtraction images appear noisier than the source images since image subtraction causes a decrease in signal-to-noise ratio
- This can be solved by increasing mA.
- Algorithms are also there in place for reducing scatter.
- Although DSA is primarily used to image blood vessels, it is also useful in the diagnosis and treatment of arterial and venous occlusions, including carotid artery stenosis, pulmonary embolisms, and acute limb ischaemia.
- It is used for arterial stenosis, which is particularly useful for potential kidney donors in detecting renal artery stenosis; cerebral aneurysms and arteriovenous malformations (AVM).
- IV-DSA is not suitable for patients with kidney failure or diabetes since the dye load is significantly higher than that used in arteriography
- An image of the blood vessels in the brain is provided in DSA to detect a problem with blood flow.
- A catheter (a small, thin tube) is inserted into an artery in the leg and passing it up to the blood vessels in the brain
- X-ray images are taken of the blood vessels after a contrast dye is injected through the catheter.
Preparation for Digital subtraction angiography:
Presence of atherosclerotic disease such as prior myocardial infarction, diabetes, renal function status, medications, allergies and previous exposure to iodinated contrast media, prior surgical procedures, especially vascular, reports from previously performed angiograms, if any and review of any relevant vascular imaging studies, such as preprocedural CT angiogram should be evaluated before the procedure.
Procedure for Digital subtraction angiography:
- The patient lies on the angiography table and local anesthesia is administered at the intended puncture site.
- General anesthesia is performed in certain procedures such as a child undergoing cerebral angiography.
- Seldinger technique is used to gain access to a blood vessel and often ultrasound is used for visualizing the vessel in real-time for puncturing.
- A straight 18 gauge needle and .035 inch guidewires is included in a standard access kit, on which the diagnostic and therapeutic catheters are threaded.
- A micro-introducer access kit is used for access in many cases, either for the entire procedure or to be replaced with the standard kit.
- The use of micro-introducer facilitates less traumatic entry and can be retrieved without massive bleeding should there be a need for re-puncturing
- Hemostasis is applied to the puncture site on procedure completion.
- Intravenous digital subtraction angiography (IV-DSA) is a form of angiography is a computer technique in which an X-ray image of a region of the body before and after radiopaque iodine based dye has been injected intravenously into the body is compared.
- Blood vessels and tissue on the first image are digitally subtracted from the second image, which provides a clear picture of the artery which can then be studied independently and in isolation from the rest of the body.
