We have used magnetic resonance imaging with cine velocity mapping to measure flow wave velocity in the thoracic aorta of 20 healthy volunteers of different ages. We have also studied the relationship between propagation of flow wave velocity and regional aortic compliance. Aortic flow velocity increased linearly with age (r = 0.87), and there was a significant difference between the youngest decade [age 10-19, mean velocity 4.3 +/- 0.7 (SD) m/s] and the oldest decade studied (age 50-59, mean velocity 7.2 +/- 0.2 m/s). Flow wave velocity (m/s) was negatively correlated with ascending aortic compliance (microliter/mmHg) (r = -0.75). Magnetic resonance imaging is a noninvasive method for measurement of aortic flow wave velocity that is an important parameter in assessing arterial wall mechanics and blood flow dynamic.

In vivo MR peak jet velocity measurements agree well with those made by Doppler ultrasound. The technique, which is not subject to restricted windows of access and has potential for further refinements, could contribute to improved evaluation of stenoses, especially at locations where ultrasonic access is limited.

SUMMARY Magnetic resonance velocity mapping by the field even echo rephasing sequence was used to provide two dimensional velocity profiles in the ascending and the descending aorta. Flow patterns were studied in ten healthy volunteers by a display method that gave clear details of the profiles. Velocity profiles in the ascending aorta were skewed in systole with an axis of skew roughly symmetrical about the plane of the aortic arch. During diastole flow was reversed along the posterior left wall of the ascending aorta while it continued forwards at the anterior right wall. In the descending aorta plug flow occurred but with minimal skew. Flow along the right wall was reversed during diastole. Turbulent flow did not occur in the ascending or descending aorta of any healthy subject.Magnetic resonance velocity mapping is a very powerful tool for the study of cardiovascular physiology. Its non-invasiveness, its quantitative two-dimensional data, its accuracy, and its high spatial resolution make it suitable for clinical use.The complex phenomena of blood flow in the heart and blood vessels are worthy of study because they give an insight into the normal and pathological function of the cardiovascular system. Flow profiles are known to be modified in some diseases1 2

For measurement of poststenotic jet velocities with magnetic resonance (MR) imaging, the authors reduced the echo time (TE) of the field even-echo rephasing (FEER) velocity mapping sequence from 14.0 to 3.6 msec, so minimizing the problem of MR signal loss from turbulent fluid. In vitro use of rotating disk and stenotic flow phantoms confirmed that the 3.6-msec TE sequence enables accurate measurement of jet velocities of up to 6.0 m/sec (r = .996). Peak jet velocity measurements were made with MR imaging in 36 patients with stenosis of native heart valves (n = 9), conduits (n = 19), or Fontan connections (n = 2) or with aortic coarctation (n = 6). Peak velocity measurements made with MR imaging agreed well with measurements made with Doppler ultrasound (US), which were available in 18 cases (standard deviation = 0.2 m/sec). Velocity mapping with fast-echo MR imaging is likely to have considerable importance as a noninvasive means of locating and evaluating stenoses, particularly at sites inaccessible to US, but care must be taken to prevent errors caused by malalignment, signal loss, phase wrap, or partial-volume effects.

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