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Characterization Of Flow Through Symmetric Stenoses Using Magnetic Resonance Imaging

MRI has recently gained popularity for non-invasively detecting and measuring blood flow. This is largely attributable to the development of several new flow sensitive MRI techniques. All of these techniques take advantage of either time-of-flight flow effects or the dependence of the spin phase on motion. While these phenomena have been understood for several decades, conventional MR imaging techniques have ignored them and assumed that the volume being imaged remains stationary for the duration of the exam. Consequently, conventional MRI images often have signal artifacts from flowing spins. These artifacts typically appear in the images as bright or dark signal regions which may be repeated along the phase encoding direction. New MRI sequences have been developed which exploit the source of these artifacts to reveal information about the nature of flow ranging from the anatomical mapping of vessels (MR angiography) to a quantitative analysis of velocity and higher order motion components. Unfortunately, the myriad of parameters of the imaging sequence (slice thickness, resolution, magnetic field gradient strength and duration, TR, TE) along with physical parameters of the image volume and its flow (relaxation times, distribution and direction of flow, velocity, acceleration, pulsatility) make the accurate measurement of flow a difficult task.