Cardiovascular, eurovascular and other vascular diseases are the leading causes of death. Imaging of blood vessels thus important in depiction of stenotic, occlusive, aneurismal, inflammatory or vascular malformations.Conventional x-ray angiography and digital subtraction angiography (DSA) are used to depict vascular lesions with high accuracy via intravascular administration of contrast (dye) material. It is the gold standard with a very high spatial resolution and temporal resolution with the possibility of multiple projections.
DSA is useful to detect several abnormalities such as arteriosclerosis, and arteriovenous occlusion or stenosis, cerebral aneurysms, and A.V.malformations.It is an x-ray-imaging test, which takes pictures of the blood vessels or arteries of the body. However, it requires arterial catheterisation, injection of contrast, and exposure to ionising radiation with their associated risks.
AdvertisementAnother method, doppler ultrasonography (US), though non-invasive and sensitive to flow, suffers from significant attenuation in bone, air and bowel gas, thereby limiting the regions in which it can be successfully applied. With the invention of non-invasie magnetic resonance imaging (MRI) technique, imaging of flow has blossomed into a powerful technique to visualise blood flow in vessel, called MR Angiography (MRA).
Blood vessels are rendered, not in the usual tomographic format of standard MR images, but as a projection over a large volume, similar to a conventional angiogram.It does not require the injection of an external contrast because MRA uses the natural magnetic properties of the hydrogen atoms present in our bodies to create (with the help of a computer) images of the blood vesels.
It is a special type of MRI study and often, the patient having a MRI scan can have MRA study as well at the same time. Whereas MRI looks at the organs and soft tissues of the human body, MRA looks specifically at the blood vessels. It enables the determination of flow velocity, direction, and even profiles within the vessel. It is painles and the study takes 30 to 60 minutes, whereas DSA sometimes takes several hours.
MRA is recommended for patients suspected to have narrowing or other abnormalities of arteries or veins in head, neck cardiovascular or in other parts of the body. MRA can also detect abnormal widening of the vessels called aneurysms of the arteries or veins. There are no known risks of MRA examination. Patients with heart pacemakers, brain aneurysm clips, inner ear implants or any other metal implants cannot have in MRA examination.
In summary, it is an excellent method of choice to evaluate the thoracic aorta, pulmonary arteires, abdominal aorta and its branches (renal and mesenteric arteries).MRA is also useful in patients for who surgery is anticipated and these conditions include, tumors, aneurysms, vascular malformations, and vascular occlusions or thromboses.
Furthermore, the combination of MRI and MRA within a single examination procedure will frequently avoid the need for multiple diagnostic imaging methods, such as DSA, CT, and US. Finally, the well-known advantages of MRA over other imaging methods, such as avoidance of ionising radiations, the lack of need for dye/contrast gents, and the wide field of view, may influence the spectrum of indications such that the focus is particularly on patients for whom these risk factors should be avoided.