Digital Subtraction Angiography (DSA) is a fluoroscopic technique that uses complex X-Ray machines to provide clear images of the inner surface of the blood vessels, also called lumen. This technique provides clear picture of the arteries, veins, as well as the four chambers of the heart. This technique is widely used in interventional radiology since it helps to eliminate radiopaque structures like bones and provide an accurate image of the blood vessels in question.
The procedure is performed by using a catheter – a small, flexible, narrow tube – which is inserted into an artery in the leg and allowed to flow to up to the blood vessels in the brain. Then a contrasting medium (typically a high density clear liquid) is injected into the catheter, to allow for clear picture of the blood vessels in legs, heart or other organs. A picture is taken before and after the contrast dye is injected; then the first image is ‘subtracted’ from the second image – to highlight the blood vessels. This is why the method is called Digital Subtraction Angiography (DSA).
Digital Subtraction Angiography is used to diagnose a variety of diseases related to the blood vessels. A person may be recommended to get a digital subtraction angiography done to check for any obstructive vascular diseases, which are a result of blockage or narrowing in the inner section of the arteries and veins. Moreover, the procedure can also be used to diagnose other conditions such as brain aneurysm, bleeding vessels, unusual links of arteries and veins, as well as analyse the blood vessels of a tumour.
That said, the technique is also helpful in various interventional procedures, since it helps provide enhanced visibility. Some conditions that the technique can effectively help in include:
- Endovascular aneurysm repair
- Arterial balloon angioplasty
- Arterial stent
- Endovascular embolisation
- Biliary procedures
Procedure of a Digital Subtraction Angiography
Before conducting a digital subtraction angiography, the doctor will examine the patient on a number of factors and conditions. Some evaluation parameters include, though are not limited to:
- Any atherosclerotic disease such as a myocardial infection
- Renal functionality
- Ongoing medicines
- Previous surgeries especially vascular ones
- Reports of past angiograms, if any
- Reports of vascular imaging studies relevant to the procedure
- Any other health condition that could potentially cause complications
Once the pre-evaluation is done properly, the patient is asked to lie down on an angiography table and is given local anaesthesia. In some cases, such as where the patient is a child, general anaesthesia may be used. Once done, a small incision is made in the leg to inset the catheter into the artery in the leg. Once placed, a contrast medium – a dye – is injected into the catheter to produce clear images of the blood vessels without any interfering overlapping tissues. Before the contrast medium is injected into the catheter, mask image of the area concerned is taken which typically only shows results like a normal X-Ray image. Once the contrasting medium is successfully inserted, contrast images are taken via complex X-Ray machines during the time the contrast medium is flowing into the artery. These images are then stored and worked upon digitally by subtracting the non-contrast (mask images) pixel by pixel from the contrast images to only show the filled vessels. These images can be viewed in real-time since they are displayed continuously on the monitor, while the examination is in progress.
Once the procedure is completed, haemostasis is done to the incision site and post-operative care is advised by the doctor, per case basis.
Complications of a Digital Subtraction Angiography
A DSA is relatively a safe procedure with very rare complications, such as:
- Drainage or bleeding from the site of the incision
- Formation of a pseudoaneurysm at the puncture site
- Harmful effect of the contrast medium on other organs such as Kidneys
- Hypersensitivity or allergy to the contrast medium
Broadly, a digital subtraction angiography is a safe, easy, fast, and cost-effective procedure which can also be performed on an out-patient basis to get information, which is otherwise not obtained from a conventional angiography. Moreover, with technological advancement, digital subtraction angiography provides greater contrast sensitivity and hence, makes for a very strong substitute for conventional angiography. The results of the procedure are immediately available and are also very accurate, adding more credibility to the method.