Aortic pulse wave velocity estimation via cross correlation of blood velocity waveforms at multiple locations
Investigators: Sam Fielden, Arthur Stillman, John Oshinski
The primary goal of this project is to develop an investigational tool for the reliable estimation of pulse wave velocity in the aorta. This tool will be used in an ongoing patient study to examine the effect of valsartan on aortic stiffness.
Aortic stiffness has been shown to be a strong index of cardiovascular health; however, stiffness is difficult to determine directly. The pulse wave velocity (PWV) is a reliable proxy of stiffness; a stiffer vessel results in the pressure (or flow) wave being transmitted faster. Measuring aortic PWV has been done in the past through the use of phase-contrast MRI, a method by which the velocity of flowing fluid is mapped to a phase shift in the MR signal.
To determine PWV, we obtain phase-contrast MRI images of the ascending and descending aorta over the cardiac cycle. The movie below shows blood velocity in the ascending and descending aorta of a young, healthy male. Velocity directed toward the head is displayed as white, toward the foot as black.
From these images, we can display the velocity waves at multiple locations down the length of the aorta as a meshplot.
The delay time between the wave at each location and the first location is then calculated by cross correlating the two waves. The PWV is the slope of a line fitted to the plot of delay time vs. location. In the plot below, ascending data points are the set clustered on the left.
