Evaluation of flow through simulated vascular stenoses with gradient echo magnetic resonance imaging

Magnetic resonance imaging using gradient echo sequences can quickly generate dynamic images of the cardiovascular system. We used a gradient echo sequence (repetition time = 21 milliseconds, echo time = 12 milliseconds, flip angle = 30 degrees) to evaluate how a simulated vascular stenoses affects the signal intensity of flowing fluid. Axial slices were obtained at regular intervals along a plastic tube containing a circular constriction (25%, 51%, or 73% reduction of cross-sectional area). Image data collected at each slice level were used to reconstruct 32 images evenly spaced in time over one cycle of pulsatile flow. Contrast ratios were calculated between signal intensities from tube lumen and surrounding stationary water jacket. Upstream from each stenosis, signal intensity increased during systole and decreased during diastole, paralleling the changes in velocity we measured with a flow probe. However, within the 51% and 73% stenoses and just beyond them, there were consistent decreases in systolic signal intensity. Flow through the 25% constriction had little effect on the signal intensity pattern. These results suggest that the gradient echo pulse sequence may be useful in evaluating disturbed flow associated with vascular stenoses.