A technique for velocity imaging using magnetic resonance imaging.

Magnetic resonance imaging (MRI) is becoming well established as a technique which both shows anatomy and allows tissue characterisation. A further development of the technique allows the imaging of regular movement such as blood flow and cardiac wall motion. In particular, much effort has been put into developing techniques for imaging flowing blood and deducing such parameters as velocity and acceleration. Early work by Singer (1959) described a technique of blood flow velocity measurement using a “time-of-flight” method. Velocity images have been obtained by this method using a modified version of a spin-echo pulse sequence (Feinberg et al, 1984). Normally, a slice is excited using a selective 90° radio-frequency (RF) pulse and an echo is produced at a later time by applying a selective 180° pulse to the same slice. If moving hydrogen nuclei have, in the meantime, moved out of the slice, no signal will be returned from them, resulting in a reduction in signal intensity from blood vessels in the image. ...