Theory, Technique, and Practice of Magnetic Resonance Angiography

Abstract

Magnetic resonance angiography (MRA) is now a widely accepted technique used to characterize vascular pathology such as stenosis, dissection, fistula, and aneurysms. Magnetic resonance techniques are increasingly driving clinical decision making by vascular physicians. The physics behind MRA can contribute to the general understanding and interpretation of the anatomic images. We seek to provide a window into how magnetic resonance images are generated, which techniques may be employed, and the potential advantages and limitations of various techniques and to discuss the future role MRA may have for the vascular physician.

The morphology of the human cerebrovascular system

“…To measure the flow, the signal in the slice below the one that is imaged is saturated with rapid RF pulses which suppress background or stationary tissues, whereas fresh-moving blood entering the slice after the RF pulse will retain its signal intensity and create contrast between blood and background tissue, highlighting arterial vessels with a contrast that decreases with the flow (Muhs et al, 2007). ToF-MRA (with venous saturation) is based on the flow and movement of protons in the blood through the imaging plane.…”

Getting ahead with CTA & MRA

“…Magnetic resonance works by manipulating hydrogen, the most common element in human tissue. 2 An MRA can evaluate for intracranial or extracranial atherosclerosis, arteriovenous malformation (AVM), intact aneurysms, or other cerebrovascular disease. MRI uses this principle to evaluate cerebral structures.…”

“…Hydrogen creates a radiofrequency signal when exposed to a magnetic field. 2 To prepare your patient, focus on education. Because radiofrequency signals differ from structure to structure based on how much hydrogen they have, a computer can assemble the radiofrequency signals into a readable picture.…”

“…1 Be alert that most magnetic resonance scanners have a weight limit. 2 If you administered sedation, continue to monitor the patient's cardiopulmonary status. Although MRA doesn't use radiation, and no adverse effect to the fetus from magnetic resonance or gadolinium have been documented, this doesn't mean adverse effects do not exist.…”

“…1,2 Another advantage is that CTA and MRA typically take less time to perform than conventional angiography. The primary advantage is the less invasive nature of both imaging studies compared with conventional angiography.…”