SIMULTANEOUS MAPPING OF B1 AND B0 FIELDS AT 7 TESLA

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 诸如ASL的内源性MRI灌注方法需要对所传输的信号进行精确校准。 射频磁场（B1），以实现标记自旋的精确反转。这 在高主磁场（B 0）强度时尤其必要，其中波长和 穿透效应产生不均匀的B1场以及高局部SAR效应。B1 高场的非均匀性由于B 0非均匀性的增加而进一步加剧，B 0非均匀性可以 导致通过标准方法（包括AFI）低估发射B1场。当 与B1振幅相比，偏离共振的程度是明显的，然后标称翻转 由AFI方法测量的角小于由B1场产生的实际章动。在 为了获得正确的B1场强度，还必须测量B 0场， 由布洛赫方程描述的完整系统可以求解实际的翻转角， 是B1场的真实度量。

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.