Digital Subtraction Angiography (DSA) is a medical imaging technique used to highlight blood vessels in areas with dense or bony tissue. The vessels can be hard to see with other anatomical structures in the way, so they are subtracted from the final image using a reference photograph taken at the start of the test. This allows medical providers to clearly see the involved vessels so they can identify malformations, occlusions, and other problems that might be difficult to spot. Testing can take place in a hospital or imaging clinic and may be an outpatient procedure.
Angiograms of the skull are common candidates for digital subtraction angiography because it can be difficult to see cerebral blood vessels with the bone in the way. The test starts with an image to capture all the structures in the area of interest before a technician injects a contrast dye. A series of images are snapped to follow the dye as it moves through the blood vessels. Digital processing with a computer can remove the bone and tissue in the background, leaving a crisp image of the blood vessels behind.
The level of clarity in the image can depend on the age of the equipment and the processing program. This is a form of fluoroscopy, real-time x-ray imaging, and the image quality may be highly variable. Properly maintained equipment operated by experienced technicians is more likely to yield clear, usable images, especially if the technician performs the test frequently.
This is only one option for looking at blood vessels, and may not be the first choice, depending on why the doctor wants an imaging study and the available technology. Digital subtraction angiography requires some basic equipment that may be available at many facilities, in contrast to more expensive imaging supplies that are only installed at large hospitals and imaging centers. Correct administration of the test also requires some training to position the patient correctly, select appropriate contrast agents, and monitor the procedure to make sure it is generating useful images.
When a medical provider recommends digital subtraction angiography, patients can ask for more information. They may want to know why the test is requested and what additional steps may be required. For example, if the digital subtraction angiography reveals a vascular malformation, the patient might need magnetic resonance imaging of the skull to provide more information. This could require a trip to another imaging center if a hospital doesn’t have the technology available.