MRI Division, Hitachi Medical Corporation, Kashiwa, Chiba, Japan.
Magn Reson Med. 2012 Feb;67(2):464-9. doi: 10.1002/mrm.23015. Epub 2011 Jun 1.
In higher-field magnetic resonance imaging scanners, a spectrally selective fat saturation radiofrequency (RF) pulse does not work well because B(1) inhomogeneity increases. An adiabatic 180° pulse is used to improve nonuniform fat suppression, but requires inversion recovery time. Therefore, a new RF pulse that achieves flip angles near 90° and is B(1) insensitive has been developed. The pulse consists of three sinc-shaped RF pulses with different flip angles and with different time intervals between each RF pulse. Using the Bloch equations, we analyzed the optimal combination of flip angles. Experimental results demonstrated that M(z) was maintained at less than 0.05 M(0) for a B(1) inhomogeneity of ±35%. The optimal net flip angles was adjusted to 95° by varying the time interval between RF pulses. The pulse duration was 77 ms, which is less than half of the 170-ms inversion recovery time required for the adiabatic pulse. We demonstrated excellent fat suppression for body imaging.
在高磁场磁共振成像扫描仪中，由于 B1 不均匀性增加，光谱选择性脂肪饱和射频（RF）脉冲效果不佳。使用绝热 180°脉冲可改善不均匀脂肪抑制，但需要反转恢复时间。因此，开发了一种新的 RF 脉冲，可实现接近 90°的翻转角且对 B1 不敏感。该脉冲由三个具有不同翻转角的 sinc 形 RF 脉冲组成，并且每个 RF 脉冲之间具有不同的时间间隔。使用布洛赫方程，我们分析了翻转角的最佳组合。实验结果表明，对于 ±35%的 B1 不均匀性，M(z)保持在小于 0.05 M(0)。通过改变 RF 脉冲之间的时间间隔，将最佳净翻转角调整为 95°。脉冲持续时间为 77ms，不到绝热脉冲所需的 170ms 反转恢复时间的一半。我们为身体成像演示了出色的脂肪抑制效果。
