Nontriggered MRI quantification of aortic pulse-wave velocity.

Pulse-wave velocity is an index of arterial stiffness, which is a strong indicator of cardiovascular risk. We present a high-speed technique that generates time-resolved complex difference signal intensity simultaneously in the ascending and descending aorta from velocity-encoded projections without gating, allowing quantification of pulse-wave velocity. The velocity-time curve was approximated with a time-resolved complex difference signal intensity to estimate the propagation time of the pulse wave in the aortic arch. The path length of the pulse wave is measured from an oblique sagittal image in a plane encompassing thoracic ascending and descending aorta, and pulse-wave velocity is computed from the ratio between the path length and pulse-wave propagation time. The method was implemented at 1.5 T and 3 T, and pulse-wave velocity was quantified in healthy subjects (ages 20-70 years, N=23) without symptoms or prior history of cardiovascular events. In addition, the method was compared against retrospectively EKG-gated PC-MRI. The overall results were found to be in good agreement with literature data showing age-related increase in aortic stiffness. The RMS differences between the projection and gated PC-MRI methods were less than 4%. Key benefits of the proposed method are simplicity in both data acquisition and processing requiring only computation of the complex difference between the velocity-encoded projections rather than absolute velocity.