Magnetic Resonance Angiography
This is a sophisticated non-invasive investigation that helps visualize the arterial and venous system. It relies on a large external magnetic field which magnetizes the charged particles within the body called protons. This in-turn can be manipulated and the vibrations from protons are tapped by sensitive receivers to process the final image of the arteries and veins. A special type of contrast or dye can also be used in MRI to better visualize the arteries and veins without exposing the patient to iodine based dye. Modern MR scanners provide high quality images without exposing the patient to radiation. It has now become the imaging technique of choice for the investigation of PAD in many centres.
Indications and contraindications
MRA is a sensitive investigation which is used to diagnose arterial abnormalities such as narrowing and blocks. It avoids the use of radiation and iodine based contrast agents or dye. Hence, it may be better suited than CTAngiography in some patients. However, it cannot be used in patients with Pacemaker or certain types of metallic implants like prosthetic heart valves, intracranial aneurysm clips or metallic intraocular foreign bodies. Patients on dialysis and kidney failure risk the complication of Nephrogenic Systemic Fibrosis (NSF) and MRA should be avoided in these patients.
It is important to inform the clinician if you any metallic implant and you are required to fill in a questionnaire to ensure that you comply with the safety requirements for an MRI. You will lie down on a table that slides into a large magnet shaped tube. It is important to lie as still as possible during the examination to obtain a clear image. You may have plastic coils placed over you during this test. The staff can communicate with you during the test through a microphone in the room. The test may take between 30 and 60 minutes to complete and you may also receive a dye through a cannula in your arm. It is normal to expect loud bangs during the test which are noises made by the MRI machine.