Diagnosis of Subclavian Steal Syndrome using a Novel Time-Resolved Magnetic Resonance Angiographic Technique

Introduction: The term Subclavian steal refers to reversal of normal direction of flow in the vertebral artery ipsilateral to severe stenosis/occlusion occurring between aortic arch and vertebral artery origin. The diagnosis of subclavian steal syndrome can be suggested by many techniques which include invasive angiography, noninvasive continuous wave Doppler ultrasonography of neck, multi-slice CT angiography, phase-contrast MR imaging and conventional contrast enhanced MRA. Since its introduction in the early 1990s contrast-enhanced MR angiography (CE-MRA), has revolutionized the diagnosis of vascular disease and has become the firstline tool for evaluating vascular disease in many centers. The advantages of CE-MRA over DSA and CTA include, no exposure to ionizing radiation and no risk of nephrotoxic iodinated contrast, as CE-MRA uses Gadolinium. The most common implementation of CE-MRA produces a detailed static image of vascular structures, similar to CTA with no temporal information about vascular dynamics. In recent years, a number of imaging techniques that increase the frame rate of MRA have been developed such as: SMASH, SENSE and TRICKS (2). All these acceleration strategies intentionally undersample MRI imaging data and synthesize missing data to create high frame rate 3D MR angiograms. When used in combination, they can produce up to a six fold increase in imaging speed and significantly improve temporal resolution while maintaining spatial resolution. With these advances 3D MRA images can now provide the dynamic information that is inherent in DSA exams, It allows vasculature to be visualized over time, capturing various phases of circulation while providing snapshots of vessels in a manner similar to that of DSA, but with more informative images that can be manipulated in three dimensions. In addition, time-resolved MR angiography permits specific vessel flow quantification.