Magnetic Resonance Angiography (MRA)

1. Aetna considers magnetic resonance angiography (MRA) medically necessary according to the selection criteria outlined below.  MRA is considered appropriate when it can replace a more invasive test (e.g., contrast angiography) and reduce risk for members.  While MRA is a rapidly evolving technology, its clinical safety and effectiveness for all anatomical regions have not been established by the peer- reviewed medical literature.

   Head and Neck

   MRA of the head and neck is considered medically necessary for any of the following conditions:

   1. As a follow-up study for a known arterio-venous malformation (AVM), and for a known non-ruptured intra-cranial aneurysm (ICA) that is greater than 3 mm in size; or
   2. To definitively establish presence of stenoses or other abnormalities of the vertebrobasilar system in members with symptoms highly suggestive of vertebrobasilar syndrome (binocular vision loss, diplopia, dysarthria, dysphagia, positional vertigo); or
   3. To evaluate members with signs/symptoms highly suggestive of leaking/ruptured ICA or AVM (i.e., blood in the cerebral spinal fluid, stiff neck, sudden explosive headache); or
   4. To evaluate pulsatile tinnitus in members with signs or symptoms suggestive of a vascular lesion; or
   5. To rule out ICA, including aneurysms of the circle of Willis, in members who are thought to be at higher risk (e.g., history of ICA in a first-degree relative or presence of polycystic kidney disease); or
   6. To evaluate conditions of the carotid arteries such as:  
       
      
      1. Aneurysm tumor
      2. Cervicocranial arterial dissection in members with suggestive signs or symptoms (e.g., amaurosis fugax, oculo-sympathetic palsy, symptoms of focal brain ischemia, and unilateral headache)
      3. Injury to the carotid artery
      4. Stenotic/occlusive disease in asymptomatic members who are candidates for carotid endarterectomy surgery (CEA) when a Duplex Doppler scan is abnormal
      5. Stenotic/occlusive disease in symptomatic members (e.g., cerebro-vascular disease or transient ischemic attack).

   Note: As MRA is considered an alternative to angiography for evaluation of the carotids, a subsequent angiography would only be considered medically necessary if there was a significant discrepancy between the findings of Duplex ultrasonography and MRA that would impact on surgical planning.

   Chest

   MRA of the chest is considered medically necessary for any of the following indications:

   1. For diagnosis, treatment planning, and post-operative follow-up for conditions of the thoracic aorta such as aneurysm (true or pseudoaneurysm), dissection, or stenotic/occlusive vascular disease; or
   2. For diagnosis, treatment planning, and post-operative surgical shunt evaluation in members with congenital heart disease (CHD) or developmental anomalies of the thoracic vasculature (e.g., atresia or hypoplasia of the pulmonary arteries, coarctation of the aorta, double aortic arch, interrupted inferior vena cava, partial anomalous venous connection, persistent left superior vena cava, right-sided aortic arch, total anomalous pulmonary venous connection, and truncus arteriosus); or
   3. For diagnosing a suspected pulmonary embolism when the use of intravascular iodinated contrast material is contraindicated, or as a substitute for pulmonary angiography when a ventilation/perfusion (V/Q) scan does not provide sufficient information for treatment decisions; or
   4. For pulmonary venous and left atrial evaluation, pre- and post-radiofrequency ablation for atrial fibrillation.

   Spine

   MRA of the spinal canal is considered medically necessary for individuals with known cases of spinal cord arterio-venous fistula and arterio-venous malformation.  MRA of the spinal canal is considered experimental and investigational for all other indications.

   Abdomen

   MRA of the abdomen is considered medically necessary for any of the following indications:

   1. To assess of the main renal arteries for the evaluation of renal artery stenosis in persons with refractory uncontrolled hypertension* not due to pheochromocytoma; or
   2. To assess persons with sickle cell disease; or
   3. To assess pelvic (e.g., aorto-iliac) arteries for stenoses in members with peripheral vascular disease; or
   4. To evaluate hepatic vasculature prior to transjugular intrahepatic portosystemic shunt (TIPS); or
   5. To determine the extent of an abdominal aortic aneurysm and associated occlusive disease in members undergoing elective repair; or
   6. To evaluate for chronic mesenteric ischemia.

      * Refractory hypertension is defined as diastolic blood pressure consistently greater than 100 mm Hg on 3 or more blood pressure medications.

   Lower Extremity

   MRA of the lower extremities is considered medically necessary as an initial test for diagnosis and surgical planning in the treatment of peripheral arterial disease of the lower extremity.  A subsequent angiography study is only required if the inflow vessel is not identified on the MRA.  If conventional catheter angiography is performed first, doing a subsequent MRA may be indicated if a distal run-off vessel is not identified.  Both tests should not be routinely performed.

   Allergy, etc.

   The use of MRA is considered medically necessary in members with documented allergy to iodinated contrast material, and in members who have accelerating hypertension and/or accelerating renal insufficiency. 

2. Aetna considers the use of gadofosveset trisodium (Ablavar, previously marketed as Vasovist injection) an appropriate agent for medically necessary contrast-enhanced MRA of blood vessels in the abdomen and lower extremities in adults.

3. Aetna considers MRA to be experimental and investigational for all other indications because its effectiveness for indications other than the ones listed above has not been established, including any of the following:
   
   
   1. Cardiac MRI for velocity flow mapping; or
   2. Evaluating accessory renal arteries in prospective renal donors, including potential living kidney donors; or
   3. Evaluating members with symptoms suggestive of dural, sagittal or cavernous sinus thrombosis/occlusion; or
   4. Ruling out ICA in members who have vague central nervous system symptoms (e.g., dizziness, headache, non-specific sensory loss, or vertigo); or
   5. Evaluating premature ventricular contraction; or
   6. Evaluating recurrent cystic hygroma of the axilla; or
   7. Screening for renovascular hypertension; or
   8. Screening of the general population for ICAs.

Magnetic Resonance Venography (MRV)

1. Aetna considers MRV medically necessary for any of the following indications:

   1. For evaluation of thrombosis or compression by tumor of the cerebral venous sinus in members who are at risk (e.g., hyper-coagulable disorders, meningitis, oral contraceptive use, otitis media, sinusitis, underlying malignant process) or have signs or symptoms (e.g., drowsiness and confusion accompanying a headache, focal motor or sensory deficits, papilledema, or seizures); or
   2. For evaluation of venous thrombosis or occlusion in the large systemic veins (e.g., superior vena cava, subclavian, or other deep veins in the chest); or
   3. For evaluation of venous thrombosis or occlusion in the portal and/or hepatic venous system (e.g., Budd-Chiari syndrome).
       
2. Aetna considers MRV experimental and investigational for diagnosis of deep vein thrombosis in the arms or legs because the peer-reviewed medical literature has not established MRV to be superior to Duplex ultrasonography for this purpose.  MRV is considered experimental and investigational for all other indications (e.g., diagnosis of chronic cerebrospinal venous insufficiency) because its effectiveness for indications other than the ones listed above has not been established.

Magnetic resonance angiography (MRA) is an application of magnetic resonance imaging (MRI) that provides visualization of blood flow, as well as images of normal and diseased blood vessels.  While MRA appears to be a rapidly developing technology, the clinical safety and effectiveness of this procedure for all anatomical regions has not been proven.

The use of MRA in evaluating flow in the carotid arteries, the circle of Willis, the anterior, middle or posterior cerebral arteries, the vertebral or basilar arteries, or the venous sinuses have been the most well researched applications.  Numerous articles have demonstrated that MRA can image the vessels with a high degree of sensitivity and specificity.  However, the appropriate use of MRA in this setting must be coordinated with the use of the competing technologies, Duplex ultrasonography and angiography.  There is no mention in the literature that all 3 technologies should be used routinely in the work-up of carotid artery disease.  In terms of screening patients with symptoms suggestive of disease, duplex ultrasonography has been shown to be equivalent to MRA, and thus this test is recommended as the initial diagnostic test.  In terms of surgical planning, MRA has been shown to be competitive with angiography, therefore this test can be the second definitive test used for surgical planning.  In this scenario, an angiography would only be considered medically necessary if the ultrasonography and MRA showed major discrepancies.  Finally, in a more limited role, MRA has been suggested as an alternative to angiography in those patients unable to undergo an angiogram due to allergy to contrast material.

Patients with transient ischemic attacks or strokes typically undergo MRI as part of the initial work-up to identify infarcted areas in the brain.  An intra-cranial MRA can be easily appended to the MRI and for that reason has been frequently ordered.  However, an intra-cranial MRA is considered not medically necessary.  MRI can adequately image any infarcted areas, and in the case of transient ischemic attacks, by definition, one would not expect to see any vascular abnormalities.  The use of MRA in the work-up of patients with the vertebrobasilar syndrome must be considered on a case-by-case basis.  The MRA may be appropriate in patients when other sources of emboli have been ruled out, and the MRA is considered as an alternative to an angiogram in order to establish the diagnosis of vertebral artery disease.

Although MRA provides additional imaging capabilities for intra-cranial aneurysms (ICAs) and vascular lesions, it is not clear from the literature how this information will impact on patient management.  In particular, patients who present subacutely with symptoms consistent with aneurysm or vascular malformations will probably undergo a conventional spin-echo MRI followed by angiography, if indicated.  It is unclear from the literature how MRA would alter this imaging hierarchy.  Several authors commented that the anatomic detail provided by MRA is not sufficient to replace an angiogram.  Magnetic resonance angiography has also been suggested as a novel screening technique for patients at high risk for aneurysm; however, its clinical relevance is unknown because of a lack of understanding of the natural history of aneurysms and which aneurysms represent a high risk of rupture.  Due to its low diagnostic yield, MRA is considered not medically necessary for the routine work-up of patients with non-specific, non-focal symptoms, such as headache or dizziness.

Magnetic resonance angiography is an effective non-invasive technique for establishing a diagnosis and evaluating the extent and severity of nearly all diseases of the thoracic aorta.  Studies have shown that MRA of the chest has a high level of diagnostic accuracy for pre-operative and post-operative evaluation of aortic dissection of aneurysm.  Depending on the clinical presentation, MRA may be used as an alternative to other non-invasive imaging technologies (e.g.,  trans-esophageal echocardiography and CT).

Saremi and Tafti (2009) noted that cardiac ablation procedures have become the standard of therapy for various arrhythmias including atrial fibrillation (AF).  Understanding the morphological characteristics of the left atrium (LA) and pulmonary vein (PV) in detail and identification of its anatomic variants is crucial to perform a successful ablation procedure and minimize complications.  The current techniques for radiofrequency ablation of AF include targeting the PVs or the tissue in the antrum of the LA.  Localization of the anatomic structures within the LA is performed by using fluoroscopy, electro-anatomic mapping, and intra-cardiac echocardiography. Multi-dimensional CT and MRA are invaluable techniques for better visualization of the anatomic landmarks that are essential for cardiac ablation procedures as well as prompt diagnosis and, in selected cases, prevention of procedure-related complications.  Some of the complications of ablation procedures may include cardiac tamponade, PV stenosis, as well as esophageal and phrenic nerve injuries.

Holmes et al (2009) stated that ablation procedures for AF are being performed with increasing frequency.  One of the most serious complications is the development of pulmonary vein stenosis, which occurs in 1 % to 3 % of current series.  The presentation of pulmonary vein stenosis varies widely.  The majority of patients are symptomatic although specific referral bias patterns can affect this.  Symptoms may include dyspnea or hemoptysis or may be consistent with bronchitis.  These symptoms are affected by the number of stenotic veins as well as the severity of the stenosis.  The more severe the stenosis and the greater number of stenosed veins result in more symptoms.  Because of the variability in symptoms, clinicians must have heightened sensitivity to the presence of the condition.  Diagnostic tests of value include MRA and computed tomography.  Although echocardiography has been used, it does not usually provide adequate assessment.  Progression of stenosis is unpredictable and may be rapid.  The specific anatomy of the stenosis varies widely and affects management.  Because of the presence of antral fusion of the origin of the left superior and left inferior pulmonary vein, a stenosis involving 1 or the other can impinge and affect outcome.  In this setting, bifurcation techniques familiar to interventional cardiology are very helpful.  Controversy currently exists about the optimal treatment approach.  The use of balloons and larger stents (approximately 10 mm) results in more optimal results than just balloon angioplasty alone; however, even with stent implantation, recurrent re-stenosis may occur in 30 % to 50 % of patients.  Follow-up of these patients typically involves computed tomography imaging to document re-stenosis.  If significant re-stenosis is identified, it should be treated promptly because of the potential for progression to total occlusion.

Furthermore, a CMS decision memo (2010) noted that it has received a position statement in the form of a combined comment from the American College of Cardiology (ACC), American College of Radiology (ACR), American Society of Neuroradiology (ASNR), North American Society for Cardiovascular Imaging (NASCI), and the Society for Cardiovascular Magnetic Resonance (SCMR).  They were in favor of combining the currently separate NCDs, allowing local Medicare contractor discretion to cover use of MRA for additional indications which are currently non-covered, and they recommended national coverage for MRA of the pulmonary veins before and after radiofrequency ablation for AF.  http://www.cmms.hhs.gov/medicare-coverage-database/details/nca-decision-memo.aspx?NCAId=236&ver=11&NcaName=Magnetic+Resonance+Angiography+(MRA)&NCDId=177&ncdver=3&IsPopup=y&bc=AAAAAAAAEAAA&.

Current scientific data shows that diagnostic pulmonary MRAs are improving due to recent developments such as faster imaging capabilities and gadolinium-enhancement.  However, these advances in MRA are not significant enough to warrant replacement of pulmonary angiography in the diagnosis of pulmonary embolism for patients who have no contraindication to receiving intravenous iodinated contrast material.  The tortuous pulsatile nature of the coronary arteries presents an imposing technical challenge to MRA.  The application of MRA for this purpose is still in its infancy.

Studies have proven that MRA is considered a reliable diagnostic tool for the pre-operative evaluation of patients who will undergo elective abdominal aortic aneurysm (AAA) repair.  In addition, scientific data has revealed that MRA is considered comparable to conventional angiography in determining the extent of the AAA, as well as evaluation of aorto-illiac occlusion disease and renal artery pathology that may be necessary in the surgical planning for AAA repair.  If pre-operative angiography is not necessary, then patients are not exposed to the risks associated with invasive contrast procedures, namely allergic reactions, end-organ damage or arterial injury.  Magnetic resonance angiography has also become accepted as a method to detect suspected stenosis in the main renal arteries; its inability to image distal lesions and accessory arteries limits its diagnostic abilities.

Although MRA assessment for the evaluation of renal artery stenosis is acceptable, the accuracy of MRA as a screening method for renovascular hypertension is unproven, and MRA is inadequate in the identification of accessory renal arteries because it has not achieved the level of accuracy needed to replace conventional angiography in the evaluation of potential living renal donors.

Surgical planning for peripheral arterial occlusive disease in the lower extremities depends on identification of adequate inflow and distal run off vessels.  Magnetic resonance angiography has been shown to be a superior technique in identifying distal run-off vessels and is competitive with angiography in identifying appropriate inflow vessels.  Therefore, MRA can be used as an initial test for surgical planning, with a subsequent angiography only if the inflow vessel is not identified.  If angiography is performed first, an MRA may be appropriate if a distal run-off vessel is not identified because MRA is capable of detecting a viable run-off vessel for bypass not seen on traditional angiography, especially when exploratory surgery is not believed to be a reasonable medical course of action for the patient.

On December 24, 2008, the United States Food and Drug Administration (FDA) approved Vasovist injection (gadofosveset trisodium, now marketed as Ablavar), the first contrast imaging agent for use in patients undergoing MRA.  Gadofosveset reversibly binds to albumin providing extended intravascular enhancement compared with existing extracellular magnetic resonance contrast agents.  Administration of gadofosveset provides a clearer image in patients who are suspected of having blockages or other problems with the blood vessels in their abdomen or extremities.  The safety and effectiveness of Vasovist was established in 2 clinical trials of patients with known or suspected aorto-iliac disease.  In the studies, patients underwent MRA with and without Vasovist and their scans were compared to standard X-ray pictures using contrast.  Magnetic resonance angiography with Vasovist detected more arterial disease than MRA performed without Vasovist and the pictures were of improved technical quality.

Bosch et al (2008) evaluated the safety and effectiveness of gadofosveset in patients with pedal arterial disease.  A total of 185 adult patients with known or suspected pedal arterial disease were randomized in a group receiving 0.03 mmol/kg and a group receiving 0.05 mmol/kg of gadofosveset for MRA of the pedal arteries.  Gadofosveset-enhanced and unenhanced time-of-flight MR angiograms were compared with conventional angiograms for the presence of vascular stenosis.  All patients underwent drug safety analysis.  For each of 3 blinded readers, the specificity (21 to 35 %) of gadofosveset-enhanced MRA was a statistically significant (p < 0.010) improvement over that of unenhanced MRA in the detection of clinically significant (greater than 50 %) stenosis.  The sensitivities of the 2 techniques were similar.  For all blinded readers of MR angiograms, sensitivity, specificity, and accuracy were higher with use of the 0.03-mmol/kg dose of gadofosveset than with the 0.05-mmol/kg dose.  In the 0.03-mmol/kg group, 28 % of patients reported a total of 50 adverse events, 96 % of which were reported as mild or moderate.  In the 0.05-mmol/kg group, 28 % of patients reported a total of 55 adverse events, 98 % of which were reported as mild or moderate.  No patients died; 1 patient left the study because of myocardial infarction considered unrelated to the study drug.  The authors concluded that because of markedly better efficacy than no contrast agent and a minimal and transient side-effect profile, 0.03 mmol/kg of gadofosveset was found safe and effective for MRA of patients with pedal arterial disease.

In a multi-center, comparative, phase III single-dose clinical study, McGregor et al (2008) examined the effectiveness of gadofosveset-enhanced MRA for evaluation of renal artery disease.  Gadofosveset (0.03 mmol/kg) was administered to adult patients with known or suspected renal arterial disease; the drug allows collection of images in the first-pass and steady-state phases.  The combination of these images was compared to non-contrast MRA, using catheter X-ray angiography (XRA) as the standard of reference.  All MRA images were collected at 1.5 T in 1 imaging session for direct comparison, and XRA within 30 days.  Sensitivity, specificity, and accuracy for diagnosing significant disease (stenosis greater than or equal to 50 %) were calculated for MRA using 3 independent blinded readers.  Patient safety was monitored for 72 to 96 hours.  A total of 145 patients were enrolled and received gadofosveset; the 127 with complete efficacy data entered the primary efficacy analysis.  Gadofosveset-enhanced MRA led to significant improvement (p < 0.01) in sensitivity (+25 %, +26 %, +42 %), specificity (+23 %, +25 %, +29 %), and accuracy (+23 %, +28 %, +29 %) over non-enhanced MRA for the 3 readers.  The rate of uninterpretable examinations decreased from 30 % to less than 2 %.  There were no serious adverse events, and the most common adverse events were nausea, pruritis, and headache (8 % each).  No significant trends in clinical chemistry parameters, nor significant changes in serum creatinine, were found following administration of gadofosveset.  The authors concluded that in patients with known or suspected renal arterial disease, gadofosveset-enhanced MRA significantly improves sensitivity, specificity, and accuracy versus non-enhanced MRA.  Gadofosveset was safe and well-tolerated in this patient population.

There is evidence that MRA, as an adjunct to conventional MRI, is useful in the evaluation of the of spinal cord.  Farb et al (2002) described the cases of 9 patients with initial MRI and clinical findings suggestive of spinal dural arterio-venous fistula (AVF) who underwent spinal MRA with an auto-triggered elliptic centric ordered three-dimensional (3-D) gadolinium-enhanced technique (hereafter, this MRA technique) before conventional intra-arterial angiography.  In all 9 patients, findings with this MRA technique correctly and precisely localized the spinal dural AVF.  Observer error resulted in 1 case in which the site of the fistula was not prospectively reported, but was easily identified retrospectively on the spinal MR angiogram.

Saraf-Lavi E et al (2002) studied the sensitivity, specificity, and accuracy of MRI alone compared with MRI plus MRA in determining whether dural AVF are present and established the accuracy of MRA in predicting fistula level.  A total of 20 patients with surgically proven dural AVF (diagnosed with radiographic digital subtraction angiography) and 11 control patients who had normal digital subtraction angiography findings underwent routine MRI plus 3-D contrast-enhanced MRA of the spine.  Images were reviewed in 2 stages (stage I, MRI only; stage II, MRI plus MRA) by 3 neuroradiologists who were blinded to the final diagnoses.  The sensitivity, specificity, and accuracy of the 3 reviewers in detecting the presence of fistulae ranged from 85 % to 90 %, from 82 % to 100 %, and from 87 % to 90 %, respectively, for stage I, compared with values of 80 % to 100 %, 82 %, and 81 % to 94 %, respectively, for stage II.  For each reviewer, there were no significant differences between the values for stage I and stage II; however, among the reviewers, one of the more experienced neuroradiologists had significantly greater sensitivity than a less experienced neuroradiologist for stage II.  On average, the percentage of true positive results for which the correct fistula level was predicted increased from 15 % for stage I to 50 % for stage II, and the correct level +/- one level was predicted in 73 % for stage II.  MR evidence of increased intra-dural vascularity was significantly greater in patients with dural AVF.  The authors concluded that the addition of MRA to standard MRI of the spine may improve sensitivity in the detection of spinal dural fistulae.  The principal benefit of MRA is in the improved localization of the vertebral level of the fistula, which potentially expedites the subsequent digital subtraction angiography study.

Luetmer et al (2005) tested the hypothesis that elliptic centric contrast-enhanced MRA can be used to detect spinal dural AVFs, predict the level of fistulas, and reduce the radiation dose and volume of iodinated contrast material associated with conventional angiography.  These researchers examined 31 patients who presented with suspected spinal dural AVF.  All patients underwent MRA and conventional angiography.  The effect of MRA on subsequent conventional angiography was assessed by analyzing total fluoroscopy time and volume of iodinated contrast material used.  At angiography, spinal dural AVFs were diagnosed in 22 of 31 patients, and MRA depicted an AVF in 20 of the 22 patients.  Magnectic resonance angiographic findings correctly predicted a negative angiogram in 7 of 9 cases.  Of the 20 true-positive MRA results, the level of the fistula was included in the imaging volume in 14.  In 13 of these 14 cases, MRA results correctly predicted the side and the level of the fistula to within 1 vertebral level.  Fluoroscopy time and the volume of contrast agent was reduced by more than 50 % in the 13 patients with a spinal dural AVF in whom MRA prospectively indicated the correct level.  The authors concluded that contrast-enhanced MRA can be used to detect spinal dural AVFs, predict the level of fistulas, and substantially reduce the radiation dose and volume of contrast agent associated with catheter spinal angiography.

Meckel et al (2007) stated that digital subtraction angiography (DSA) is the method of reference for imaging of dural AVF (DAVF).  The goal of this study was to analyze the value of different MR images including 3-D contrast-enhanced MRA with a high temporal resolution in diagnostic and follow-up imaging of DAVFs.  A total of 18 MR/MRA examinations from 14 patients with untreated (n = 9) and/or treated (n = 9) DAVFs were evaluated.  Two observers assessed all MR and MRA investigations for signs indicating the presence of a DAVF, for fistula characteristics such as fistula grading, location of fistulous point, and fistula obliteration after treatment.  All results were compared with DSA findings.  On time-resolved 3-D contrast-enhanced (TR 3-D) MRA, the side and presence of all patent fistulas (n = 13) were correctly indicated, and no false-positive findings were observed in occluded DAVFs (n = 5).  Grading of fistulas with this imaging technique was correct in 77 % and 85 % of patent fistulas for both readers, respectively.  On T2-weighted images, signs indicative of a DAVF were encountered only in fistulas with cortical venous reflux (56 %), whereas on 3-D time-of-flight (TOF) MRA, most fistulas (88 %) were correctly detected.  In complete fistula occlusion, false-positive findings were encountered on both T2-weighted images and on TOF MRA images.  The authors concluded that TR 3-D MRA proved reliable in detecting DAVFs and suitable for follow-up imaging.  The technique allowed -- within limitations -- to grade DAVFs.  Although 3-D TOF MRA can depict signs of DAVFs, its value for follow-up imaging is limited.

Mull et al (2007) examined the validity of MRA for identification of spinal arterio-venous (AV) abnormalities.  A total of 34 consecutive patients with suspicion of spinal vascular abnormalities underwent digital subtraction angiography (DSA) after MRA.  The level and side of the suspected spinal DAVF (SDAVF) and the feeding arteries in spinal AV malformations (SAVMs) were determined from MRA and compared with DSA.  DSA revealed SDAVF in 20 abnormalities of which 19 were spinal and 1 was tentorial with spinal drainage, as well as SAVM in 11 patients.  In 3 patients, MRA and DSA were both normal.  For detection of spinal AV abnormalities, neither false-positive nor false-negative MRA result was obtained.  The MRA-derived level of the feeding artery in SDAVF agreed with DSA in 14 of 19 cases.  In 5 cases, a mis-match of 1 vertebral level (not side) was noted for the feeding artery.  For the tentorial AVF, only the spinal drainage was depicted; the feeding artery was outside the MRA field of view.  In intra-dural SAVM, the main feeding artery was identified by MRA in 10 of 11 patients.  Magnetic resonance angiography could differentiate between glomerular and fistulous SAVM in 4 of 6 cases and between sacral SDAVF and filum terminale SAVM in 2 of 5 cases.  The authors concluded that MRA reliably detects or excludes various types of spinal AV abnormalities and localizes the (predominant) arterial feeder of most spinal AV shunts.  Although classification of the subtype of SAVMs remains difficult, with MRA it greatly helps to focus subsequent DSA.

Sharma and Westesson (2008) noted that contrast-enhanced MRA has been increasingly used in the evaluation of spinal vascular malformations.  Furthermore, in a review on advances in spinal cord MRA, Backes and Nijenhuis (2008) noted that current fast contrast-enhanced MR techniques are able to (i) visualize vessels supplying or draining the spinal cord and (ii) differentiate spinal cord arteries from veins.  The localization of the Adamkiewicz artery, the largest artery supplying the thoraco-lumbar spinal cord, has become possible in a reproducible and reliable manner.  Knowledge of the anatomic location of this artery and its arterial supplier may be of benefit in the work-up for aortic aneurysm surgery to reduce incidences of ischemic injury.  Spinal cord MRA is ready to become a diagnostic tool that can compete with catheter angiography for detecting and localizing arterial feeders of vascular lesions and is strongly advised for use prior to invasive catheter angiography.

The use of an MRA/MRV as part of the work-up of a patient with suspected cerebral thrombosis (i.e., dural sagittal or cavernous sinus thrombosis) must be considered on a case by case basis.  Magnetic resonance imaging is considered the imaging method of choice for establishing the diagnosis, but MRA/MRV may be useful in following the course of the disease.

Magnetic resonance venography (MRV) is now very effective for the evaluation of diseases of larger veins.  The specific indications for using MRV for evaluating the vena cavae are diagnosis of vena caval thrombus, differentiation of tumor thrombus and blood clot of the vena cava, diagnosis of superior vena caval syndrome, identification of superior vena caval invasion or encasement by lung or mediastinal tumors, diagnosis of the Budd-Chiari syndrome, diagnosis of caval anomalies such as persistent left superior vena cava and interrupted inferior vena cava, and identification of the presence and cause of obstruction or occlusion of the brachiocephalic, subclavian, and jugular veins.

Duplex ultrasonography is the typical initial diagnostic test for deep vein thrombosis (DVT).  Magnetic resonance venography has not been shown to be superior to ultrasonography, except in imaging the deep femoral and hypogastric vessels.  However, information about these vessels is frequently not needed to make patient management decisions, except perhaps in patients with pulmonary emboli where the source of the emboli has not been identified by ultrasonography.  McRae and Ginsberg (2004) MRV has the potential to be used as a stand-alone test for DVT but requires further evaluation.  Moreover, in a retrospective study (n = 973), Borer et al (2005) found that discontinuation of screening by means of ultrasound and MRV for the diagnosis of DVT did not change the rate of pulmonary embolism in patients with closed fractures of the pelvis or acetabulum.

Bates et al (2012) stated that objective testing for DVT is crucial because clinical assessment alone is unreliable and the consequences of misdiagnosis are serious.  This guideline focused on the identification of optimal strategies for the diagnosis of DVT in ambulatory adults.  The methods of this guideline followed those described in Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines.  These investigators suggested that clinical assessment of pre-test probability of DVT, rather than performing the same tests in all patients, should guide the diagnostic process for a first lower extremity DVT (Grade 2B).  In patients with a low pre-test probability of first lower extremity DVT, these researchers recommended initial testing with D-dimer or ultrasound (US) of the proximal veins over no diagnostic testing (Grade 1B), venography (Grade 1B), or whole-leg US (Grade 2B).  In patients with moderate pre-test probability, they recommended initial testing with a highly sensitive D-dimer, proximal compression US, or whole-leg US rather than no testing (Grade 1B) or venography (Grade 1B).  In patients with a high pre-test probability, they recommended proximal compression or whole-leg US over no testing (Grade 1B) or venography (Grade 1B).  The authors concluded that favored strategies for diagnosis of first DVT combined use of pre-test probability assessment, D-dimer, and US.  There is lower-quality evidence available to guide diagnosis of recurrent DVT, upper extremity DVT, and DVT during pregnancy.

The role of chronic cerebrospinal venous insufficiency (CCSVI) in the pathogenesis of multiple sclerosis (MS) is a matter of debate.  Chronic cerebrospinal venous insufficiency was first diagnosed using specialized trans-cranial and extra-cranial Doppler ultrasonography.  Some have advocated the use of MRV in place of trans-cranial Doppler because the results of MRV are less operator dependent.  However, there are limited data to support the use of MRV in diagnosis of CCSVI. I n a pilot study, Hojnacki et al (2010) the value of neck MRV for the diagnosis of CCSVI compared to Doppler sonography (DS) and selective venography (SV) in patients with MS and in healthy controls (HC).  A total of 10 MS patients and 7 HC underwent DS, 2D-Time-Of-Flight (TOF) venography and 3D-Time Resolved Imaging of Contrast Kinetics angiography (TRICKS). Patients with MS also underwent SV.  The internal jugular veins (IJVs) and the vertebral veins (VVs) were assessed by both MRV sequences, and the findings were validated against SV and DS; SV has been considered the diagnostic gold standard for MS patients.  All MS patients and none of the HC presented CCSVI, according to the DS criteria.  This was confirmed by SV.  For CCSVI diagnosis, DS showed sensitivity, specificity, accuracy, positive-predictive value (PPV) and negative-predictive value (NPV) of 100 %, whereas the figures were 40 %, 85 %, 58 %, 80 % and 50 % for 3D-TRICKS, and 30 %, 85 %, 52 %, 75 % and 46 % for 2D-TOF in the IJVs.  In MS patients, compared to SV, DS showed sensitivity, specificity, accuracy, PPV and NPV of 100 %, 75 %, 95 %, 94 % and 100 %, whereas the figures were 31 %, 100 %, 45 %, 100 % and 26 % for 3D-TRICKS and 25 %, 100 %, 40 %, 100 % and 25 % for 2D-TOF in the IJVs.  The authors concluded that the use of MRV for diagnosis of CCSVI in MS patients has limited value, and the findings should be interpreted with caution and confirmed by other imaging techniques such as DS and SV.

An UpToDate review on "Prevalence and evaluation of ventricular premature beats" (Podrid, 2012) does not mention the use of magnetic resonance angiography.