| 摘要 |
<p>To produce image information from an object it is subjected to a continuous static magnetic field along a Z axis and to sets of sequences of gradient Gx, Gy and Gz to the magnetic field. Spins in a selected plane (the X-Z plane) are excited by selective rf pulses of an associated Gy gradient and the selected spins are subjected to a reversed Gy gradient together with a Gx gradient. The Gy gradient is then switched off and the direction of the Gx gradient is then repeatedly reversed. During the action of reversal of the Gx gradient a small Gz gradient is provided. Each reversed Gx gradient is held constant for a sufficient time for a free induction decay signal to be generated thus providing a multiple echo of the spins in the selected plane. Alternate signals are time-reversed and then both the time-reversed and non time-reversed signals are subject to Fourier transformation. </p> |
