Peripheral Vascular MRA

# Introduction
Magnetic resonance angiography (MRA) is a non-invasive technique to image the lumen of blood vessels within the cardiovascular tree. While the gold standard remains intra-arterial contrast angiography, MRA has become a reliable tool with a diagnostic accuracy rivaling that of the invasive approach without the associated risks. It is increasingly being utilized for the diagnosis and pre-operative planning of vascular stenoses and other structural lesions.

# Techniques
- Spin echo (black blood sequences) are used to evaluate the vessel wall
- 3D time-of-flight (bright blood sequences) are used for angiography
- Phase contrast velocity mapping directly measures flow and is helpful in evaluating stenoses
- Contrast enhancement (CE) with gadolinium improves the identification of blood and reduces artifacts
Novel contrast media for molecular imaging are being developed (see Molecular imaging and related novel technologies)
- Novel contrast media for molecular imaging are being developed (see Molecular imaging and related novel technologies)

# Clinical applications

## Carotid arteries
- Identification of:
Stenosis
Turbulent flow
Arterial thrombus
- Stenosis
- Turbulent flow
- Arterial thrombus
Fig. Carotid stenosis

## Aorta
- Identification of:
Aneurysms (complex, false, dissection flaps)
Flow velocity in true and false lumen
Involvement of branch arteries
Abscesses
Arch abnormalities
Coarctation
Supravalvular stenosis
- Aneurysms (complex, false, dissection flaps)
Flow velocity in true and false lumen
Involvement of branch arteries
- Flow velocity in true and false lumen
- Involvement of branch arteries
- Abscesses
- Arch abnormalities
- Coarctation
- Supravalvular stenosis
Fig. Aortic dissection
Fig. Abdominal aortic aneurysm

## Mesenteric arteries
- Anatomy: celiac, superior mesenteric, and inferior mesenteric arteries
Fig. Mesenteric stenosis

## Renal arteries
Fig. Renal artery stenosis

## Peripheral arteries
- Anatomy: iliac and infrainguinal arteries
Fig. Peripheral arterial lesion

## Atherosclerotic plaque
- Vessel wall imaging with MR plaque sequences characterizes the biological components of atherosclerotic lesions (lipid-rich/necrotic core, fibrous cap, hemorrhage, calcification, inflammation) and aides in the identification of vulnerable plaques prone to rupture (see Atherosclerosis/Plaque Imaging with CMR).

# Validation

## Carotid stenosis
- MRA vs. cerebral angiography - 2006 meta-analysis 
Traditional TOF
70-99% stenosis: sensitivity 88% and specificity 84%
100% stenosis (complete occlusion): sensitivity 98% and specificity 100%
- Traditional TOF
70-99% stenosis: sensitivity 88% and specificity 84%
100% stenosis (complete occlusion): sensitivity 98% and specificity 100%
- 70-99% stenosis: sensitivity 88% and specificity 84%
- 100% stenosis (complete occlusion): sensitivity 98% and specificity 100%
- CE improves detection
70-99% stenosis: sensitivity 94% and specificity 93%
- 70-99% stenosis: sensitivity 94% and specificity 93%

## Aortic dissection

## Abdominal aortic aneurysm

## Mesenteric stenosis
- CE-MRA vs. angiography of the celiac and superior mesenteric arteries 
Sensitivity 94% and specificity 100%
- Sensitivity 94% and specificity 100%

## Renal artery stenosis
- CE-MRA vs. angiography 
Sensitivity 95% and specificity 92%
- Sensitivity 95% and specificity 92%

## Peripheral arterial disease
- CE-MRA vs. angiography 
Sensitivity 93% and specificity 98%
- Sensitivity 93% and specificity 98%

# Further online resources
- Patient information about MRA from the American College of Radiology.