Volume MR angiography: methods to achieve very short echo times.

Angiographic displays of cerebral vessels can be generated with single-excitation three-dimensional magnetic resonance imaging. Differentiation of true stenosis from artifactual signal loss, due to dephasing effects from fast or nonconstant blood flow and field inhomogeneities, poses a significant clinical problem that can be largely resolved with the use of very short echo times (TEs). A three-dimensional imaging technique was developed that allows TEs of 3.1 msec without and 4.5 msec with first-order flow compensation gradients. The short TEs were achieved with short asymmetric radio-frequency pulses, gradients of minimal duration, and fractional echoes. Significantly improved images of normal tortuous vessels with fast flow were obtained. With this method, accuracy in depicting the vessel lumen and confidence in the findings were markedly increased.