Norm of Magnetic Resonance Angiography (MRA)
Anatomy of normal vessels are well visualized, and blood flow is unobstructed.
Usage of Magnetic Resonance Angiography (MRA)
Evaluate vascular structure; evaluate blood flow, especially in the venous system, for possible aneurysms, stenosis, thromboses, or blockages; determine tumor vascularity; assess for evidence of direct tumor involvement of vascular structures; evaluate clients with carotid stenosis preoperatively so that the carotid artery endarterectomy is performed with decreased complication; assist in diagnosis of cerebrovascular disease, cardiovascular disease, cerebral arteriovenous malformations, congenital heart disease, renal or hepatic vasculature disorder, trigeminal neuralgia; assess effectiveness of various therapeutic interventions related to vascular structure and blood flow.
Description of Magnetic Resonance Angiography (MRA)
Magnetic resonance angiography (MRA) is a noninvasive vascular imaging technique. This procedure is performed by use of the magnetic resonance imaging (MRI) scanner equipment, and MRA may be performed with MRI. MRA provides structural evaluation of arteries and veins and the image of blood flow. The two types of MRA are time of fight (TOF) and phase contrast (PC). TOF angiography uses a process described as “flow-related enhancement,” which relies on the inflow of fully magnetized blood into the imaging plane. PC angiography directly measures flow by generating vascular images. These images detect changes in the phase of the blood's transverse magnetization as it moves along a magnetic field gradient. Therefore it relies on alterations in spin phase for image contrast. Both of these methods emphasize the signals in the structures, which contain blood flow, and reconstruct only those structures with flow. The computer subtracts images of other structures, which are of lesser interest, from the image. Both of these methods can obtain two- or three-dimensional images. MRA can be performed without injection of contrast medium or radiation exposure. However, some radiologists prefer using a contrast, such as gadolinium chelate or gadolinium-DTPA, to enhance the visualization of venous flow.
Professional Considerations of Magnetic Resonance Angiography (MRA)
Consent form IS required.
- See Preparation, Magnetic resonance imaging.
- See Procedure, Magnetic resonance imaging.
- If the client has been sedated for the procedure, make certain that he or she is fully awake before ambulating, and follow institutional protocol for postsedation monitoring.
Client and Family Teaching
- This procedure may take 15–30 minutes to perform.
- See Client and Family Teaching, Magnetic resonance imaging.
Factors That Affect Results
- See Factors That Affect Results, Magnetic resonance imaging.
- False-positive and false-negative results in cerebral aneurysm evaluation can be caused by vessel tortuosity and susceptibility artifacts (which occur at the interfaces of structures with different magnetic susceptibilities).
- The same MRI scanner equipment, with different software and pulse sequences, is used to perform MRA.
- The results of MRA are beginning to guide medical management and determine the extent of surgical intervention.
- The use of MRA versus conventional angiography remains controversial. Gadolinium-enhanced MRA is more sensitive and specific, as well as less risky, than conventional arteriography for detection of renal artery stenosis. Risk for false results with MRA exists with cerebral aneurysms. MRA has been found to be as accurate as arteriography for carotid artery stenosis in large vessels, but not in smaller vessels such as the terminal carotid branch.