Evaluation of Susceptibility-weighted Magnetic Resonance Imaging and 4d-time-resolved Magnetic Resonance Angiography in Brain Arteriovenous Malformations
Evaluation of Susceptibility-weighted Magnetic Resonance Imaging and 4d-time-resolved Magnetic Resonance Angiography in Brain Arteriovenous Malformations
Brain arteriovenous malformations are abnormal communications between brain arteries and
 veins with an intervening tangle of abnormal arteries (nidus). Brain AVMs may be asymptomatic
 or symptomatic, presenting with acute hemorrhage or neurological symptoms. Brain AVMs that
 have not bled carry a yearly risk of intracranial hemorrhage of approximately 4% (Ondra et
 al.).

 The management is multidisciplinary involving neurosurgeons, interventional
 neuroradiologists, radiation physicians, neurologists and allied health care personnel.
 Patients may be treated with open neurosurgery, endovascular embolization, radiation therapy
 or any combination of these treatments. The goal of the treatment is to eliminate the brain
 AVM while preserving normal flow to the surrounding normal arteries. This involves
 obliteration of the shunting of blood via the AVM arteries to veins by a variety of
 treatments. The treatment regimen is individualized dependent on natural history, the
 angioarchitecture, location, risk of treatment(s) and patient wishes.
Why is MRI important in the management of brain AVMs i.e. over conventional catheter
 angiography? The "gold standard" for evaluation of brain AVMs is catheter angiography.
 However, the procedure is invasive, involves ionizing radiation, exposure to contrast media
 with potential for nephrotoxicity or allergy and carries a 1% risk of morbidity including
 stroke. In contrast, MRI is a non-invasive method to evaluate brain AVMs and has the added
 advantage over catheter angiography of depicting the anatomical localization of the AVM
 within the brain tissue. However, currently MRI is limited by lack of ability to demonstrate
 shunting of blood through the AVM, an important indicator that the brain AVM is still present
 after treatment.

 Susceptibility-weighted imaging (SWI) is a promising new MRI technology which indirectly
 evaluates the amount of oxygen within blood vessels. Small case series exploring the utility
 of SWI in brain AVMs has been reported suggesting the venous drainage of brain AVMs is often
 abnormally hyperintense because of abnormal shunting of oxygenated blood from AVM arteries to
 the draining vein(Bharathi D et al.). Typically in normal tissues, oxygenated blood on SWI
 images is hyperintense while deoxygenated blood in normal veins is hypointense. Developmental
 venous anomalies demonstrating enlarged draining veins are normal variants that must be
 distinguished from true AVMs . However, this capability has not been prospectively evaluated
 in a systematic fashion.

 Our current standard for contrast-enhanced evaluation of brain AVMs is to perform a
 contrast-enhanced MRA (CEMRA) followed by a post-contrast T1 volumetric whole brain sequence.
 The CEMRA allows depiction of contrast at its maximal intensity passing through the brain on
 its first pass. The post contrast T1 scan only demonstrates static contrast pooling within
 the brain AVM. However, neither CEMRA nor the post contrast scan provides information about
 the speed at which contrast is moving through a brain AVM ie. shunting. Evaluation of the
 temporal passage of contrast brain AVM would require a dynamic time-resolved technique with
 adequate temporal resolution to distinguish early vs late vs no shunting within a brain AVM.

 What is the current technology for MRI of brain AVMs? Susceptibility-weighted angiography
 (SWAN) imaging on the GE 3 T has been attempted but the preliminary evidence suggest that the
 images are of low resolution and difficult to interpret. In addition, our literature review
 found a paucity of studies evaluating staged treatment of brain AVMs with SWAN imaging. In
 our institution, brain AVMs may have staged treatment consistent of endovascular embolization
 and/or radiosurgery. After each treatment patients are followed with serial imaging MRI and
 Digital Subtraction Angiography (DSA). This provides an important opportunity to investigate
 the utility of non-invasive MRI to detect residual AVM after treatment.

 Thus, there is a significant opportunity to evaluate the value of SWAN and Time Resolved
 Magnetic Resonance Angiography (TRMRA) assessment of progressive obliteration of the AVM
 nidus. Specifically, this is attractive for brain AVMs that are treated with radiosurgery as
 MRI and DSA are required for clinical grounds for treatment planning purposes.
Inclusion Criteria:

 1. Informed consent

 2. Brain AVMs previously diagnosed with either CT Angiography, MRI or catheter
 angiography.

 3. Undergoing cerebral catheter angiography for clinical evaluation of the brain AVM.
 Patients with brain AVMs scheduled for catheter cerebral angiography will undergo MRI
 (GE 3T) within 3 months.

 4. Age > 18 years.

 5. mRS <=2

 6. Brain AVM visible on MRI, i.e. nidus > 1 cm

 Exclusion Criteria:

 1. Contraindication to MRI eg. Non-MRI compatible implant, severe claustrophobia

 2. Contraindication for contrast: GFR < 60 ml/min, allergy to contrast