Katz J, Peshock R M, Malloy C R, Schaefer S, Parkey R W
Magn Reson Med. 1987 May;4(5):422-30. doi: 10.1002/mrm.1910040503.
It has been shown previously that for constant magnetic field gradients, constant velocity flow leads to even-echo rephasing for all echo delay times. We show that for flow which is not pluglike, even-echo rephasing also occurs for the pulsed readout gradients used in magnetic resonance imaging if and only if the gradients begin at the time the 90 degrees pulse is applied. We also show for these gradients that even-echo rephasing for all echo delay times in the case of nonpluglike flow implies a constant flow velocity at the point considered. Furthermore, it suffices to assume the vanishing of the spin-echo phase for any even echo, since the vanishing of any even echo for all echo delay times implies that all other even echoes also vanish identically. The odd echoes are then all equal to each other and proportional to the flow velocity. If acceleration is present, it may then be seen that for nonpluglike flow, even-echo rephasing may only be present for some but not all echo delay times. However, for the typical slice selection gradients used in magnetic resonance imaging or for usual readout gradients starting after the 90 degrees pulse is applied, it is shown that for constant velocity flow the even-echo phases do not vanish identically. Hence, rephasing cannot always occur for nonpluglike flow in either of these situations. Furthermore, the spin-echo phases are proportional to the flow velocity.(ABSTRACT TRUNCATED AT 250 WORDS)
先前已表明，对于恒定磁场梯度，恒定流速的流动在所有回波延迟时间都会导致偶回波重聚相。我们表明，对于非塞状流动，当且仅当梯度在90度脉冲施加时开始时，磁共振成像中使用的脉冲读出梯度也会出现偶回波重聚相。我们还表明，对于这些梯度，在非塞状流动情况下所有回波延迟时间的偶回波重聚相意味着在所考虑的点处流速恒定。此外，假设任何偶回波的自旋回波相位消失就足够了，因为所有回波延迟时间内任何偶回波的消失意味着所有其他偶回波也同样消失。然后奇回波都彼此相等且与流速成比例。如果存在加速度，那么可以看出，对于非塞状流动，偶回波重聚相可能仅在某些而非所有回波延迟时间出现。然而，对于磁共振成像中使用的典型切片选择梯度或在90度脉冲施加后开始的通常读出梯度，结果表明对于恒定流速流动，偶回波相位不会完全消失。因此，在这两种情况下，非塞状流动并不总是会发生重聚相。此外，自旋回波相位与流速成比例。（摘要截断于250字）
