A one‐dimensional velocity technique for NMR measurement of aortic distensibility

A technique is presented for rapidly and noninvasively determining aortic distensibility, by NMR measurement of wave velocity in the aorta. A two–dimensional NMR selective‐excitation pulse is used to repeatedly excite a cylinder of magnetization in the aorta, with magnetization read out along the cylinder axis each time. A toggled bipolar flow‐encoding pulse is applied prior to readout, to produce a one‐dimensional phase‐contrast flow image. Cardiac gating and data interleaving are employed to improve the effective time resolution to 2 ms. Wave velocities are determined from the slope of the leading edge of flow measured on the resulting M‐mode velocity image. The technique is sensitive over a range of distensibilities from 10⁻⁸ to 10⁻³ m s²/kg. The average value in the descending thoracic aorta in seven normal subjects was found to be 4.8 × 10⁻⁵ m s²/kg, with a significant inverse correlation with age.