Arteriovenous malformation (AVM) and dural arteriovenous fistula (AVF) are vascular malformations with direct arteriovenous (AV) connections. Intracranial hemorrhage is the presenting event in 40-70% of patients, causing significant morbidity and mortality. Current noninvasive imaging methods like MR and CT angiography are inadequate for comprehensive evaluation of the complex vascular architecture and hemodynamics of these lesions, including effects on cerebral blood flow (CBF). Even digital subtraction angiography (DSA, the gold standard) is not capable of providing accurate quantitative assessment of blood flow or degree of shunt. In arterial spin labeled (ASL) perfusion MRI of the brain, magnetically labeled arterial blood water is used as a diffusible tracer. In preliminary studies, it was observed that labeled blood no longer behaves as a diffusible tracer in vessels associated with untreated AVMs, but as an intravascular tracer since it bypasses the capillaries. The effect is that not only are AVM and draining vessels conspicuously demonstrated, but also that measurement of label with rapid transit allows potential quantification of AV shunt. The goal of this proposal is to test the hypothesis that ASL can be used as a novel method to detect and quantify AV shunting in AVM or AVF, while simultaneously evaluating effects on brain perfusion. The first part of the proposal focuses on further development and optimization of the ASL perfusion MRI technique for use in this setting. In the second part of the proposal, patients with suspected AVM or AVF who are undergoing DSA will also be studied using the optimized ASL perfusion MRI technique in a pilot study to assess its accuracy. In the third part of the proposal, the information obtained in the pilot study will be further analyzed to determine whether AV shunting can be quantified, whether alterations in CBF related to an AVM or AVF can be detected, and whether changes in AV shunt or CBF can be detected in those patients undergoing surgical excision or embolization.
An arteriovenous malformation (AVM) is a vascular malformation in the brain with direct connections between arteries and veins such that blood bypasses brain tissue. A patient with an AVM may not be aware of it until the AVM causes hemorrhage into the brain, which is the first presentation in as many as 40-70% of patients and may lead to permanent injury or death. Current imaging methods are inadequate for comprehensive evaluation of these lesions, so the goal of this proposal is to test a new method called arterial spin labeled (ASL) perfusion MRI to improve detection and evaluation of AVMs as well as to assess effects on nearby brain tissue.
