SIMULTANEOUS MAPPING OF B1 AND B0 FIELDS AT 7 TESLA

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 内源性MRI灌注方法，如ASL，需要准确校准传输的 射频磁场(B1)，以实现标记自旋的精确反转。这 在高主磁场(B0)强度时尤其必要，其中波长和 穿透效应产生了非均匀的B1场以及高的局部SAR效应。B1 高场下的非均质性由于B0不均质性的增加而进一步加剧，这可能 导致包括AFI在内的标准方法低估了传输B1场。当 与B1幅度相比，偏离共振的程度是明显的，然后是标称翻转 AFI方法测量的角度小于B1场产生的实际章动。在……里面 为了获得正确的B1场强，还必须测量B0场，并且 由Bloch方程描述的完整系统可以在实际的翻转角下求解，其中 才是B1场的真正量度。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Endogenous MRI perfusion methods such as ASL require accurate calibration of the transmitted radiofrequency magnetic field (B1) in order to achieve precise inversion of the labeled spins. This is especially necessary at high main magnetic field (B0) strengths, where wavelength and penetration effects create heterogeneous B1 fields as well as high local SAR effects. B1 heterogeneity at high field is further compounded by increased B0 inhomogeneity, which can result in underestimation of the transmit B1 field by standard methods, including AFI. When the degree of off-resonance is appreciable compared to the B1 amplitude, then the nominal flip angle measured by the AFI method is less than the actual nutation produced by the B1 field. In order to obtain the correct B1 field strength, the B0 field must also be measured, and the complete system described by the Bloch equations can be solved for the actual flip angle, which is the true measure of the B1 field.