Schepers Janneke, van Osch Matthias J P, Bartels Lambertus W, Heukels Sean N, Viergever Max A, Nicolay Klaas
Department of Experimental in Vivo NMR, Image Sciences Institute, University Medical Center Utrecht, 3584 CH Utrecht, The Netherlands.
Magn Reson Med. 2005 Jun;53(6):1355-62. doi: 10.1002/mrm.20480.
Perfusion imaging with pulsed arterial spin labeling techniques, like flow-sensitive alternating inversion recovery (FAIR), may suffer from inflow of fresh, i.e., unlabeled, spins. Inflow of fresh spins is caused by the arrival of unlabeled spins in the image slice and can lead to underestimation of the perfusion if not taken into account. In this study it was shown that a decrease in B(1) field strength toward the edge of the transmit coil and the consequent reduction in the inversion efficiency leads to a narrowing of the arterial delivery function and a reduction in FAIR signal. Increasing the B(1) amplitude of the adiabatic inversion pulse from 2.3 to 5.7 times its minimum amplitude requirement resulted in an observed increase of 40 to 80% in the rat brain FAIR signal at inflow times longer than 0.65 s. For coils with limited dimensions and significant B(1) inhomogeneity over the perfusion labeling slab, the application of an excessively large B(1) amplitude in combination with adiabatic inversion is recommended to optimize the FAIR perfusion contrast.
使用脉冲动脉自旋标记技术（如血流敏感交替反转恢复法（FAIR））进行灌注成像时，可能会受到新鲜（即未标记）自旋流入的影响。新鲜自旋的流入是由未标记自旋到达图像切片引起的，如果不加以考虑，可能会导致灌注估计值偏低。本研究表明，向发射线圈边缘方向B(1)场强降低以及随之而来的反转效率降低，会导致动脉输送函数变窄以及FAIR信号降低。将绝热反转脉冲的B(1)幅度从其最小幅度要求的2.3倍增加到5.7倍，结果显示在流入时间超过0.65秒时，大鼠脑FAIR信号增加了40%至80%。对于尺寸有限且在灌注标记平板上存在显著B(1)不均匀性的线圈，建议应用过大的B(1)幅度并结合绝热反转来优化FAIR灌注对比度。
