Pulse wave velocity (PWV) is a commonly used measure of arterial stiffness that increases in conditions leading to cardiovascular disease, such as hypertension, diabetes mellitus, glucose intolerance, and metabolic syndrome. PWV has been shown to be an independent predictor of cardiovascular mortality and stroke. Reliable measurement of PWV is of particular interest for monitoring the progression or regression of vessel compliance during therapy. PWV can be measured invasively with intravascular pressure catheters placed at different locations in the vasculature. Because this requires an invasive procedure to be performed, non-invasive methods, including ultrasound and magnetic resonance imaging (MRI), have been investigated. Previously, one-dimensional (1D) and two-dimensional (2D) phase contrast (PC) MRI has been used to measure PWV. There is uncertainty regarding the optimal MRI sequence and post-processing algorithms to use for determining PWV in large vessels. For PWV estimation, typically transit-time (TT) methods are employed to estimate temporal differences of specific features of blood flow waveforms, e.g. time from foot-to-foot or peak-to-peak, between two locations of the vessel with known distance. However, the precision of this method greatly depends on the exact calculation of flow difference and distance between only two measuring points. Methodological improvements include a more continuous evaluation along a vessel center line and cross correlation (XCor) analysis for the estimation of waveform delays. These techniques have improved the accuracy of PWV estimation but relied on 2D PC acquisitions in sagittal oblique slices exactly transecting the thoracic aorta. With the introduction of flow-sensitive four-dimensional (4D) MRI techniques, information on multidirectional in vivo blood flow with full volumetric coverage of the vessel of interest is now available. This can possibly be exploited for PWV calculation. However, the accuracy of 4D PC for PWV calculation and the appropriate 4D PC sequence to use for PWV calculation has yet to be explored. Therefore, the primary aim of this study is to evaluate 2D and novel 4D PC techniques for calculation of PWV in the aorta in vivo.
April 2010 to September 2010
This project led by: Christopher J François, MD