低场永磁体磁共振射频场映像

射频场映像是通过一定算法对磁共振射频线圈的发射场进行重建的方法.高场下的射频场经过生物组织时会发生明显变化，在其基础上可以反演生物组织体内电特性，进而对癌症等疾病进行早期诊断，是对生物组织的磁共振结构成像的有力补充.目前为止，射频场映像和电特性研究都以高场鸟笼线圈为主，对低场下的相控阵研究较少.本文主要研究了低场永磁体磁共振射频场的均匀度.有限元仿真和实验验证了在17.8 MHz激励下，射频场在空载和负载下均匀度均发生较大变化.射频场均匀度在负载下的改变在一定程度上可以反映负载生物组织的电特性，对磁共振电特性实用化研究提供了一定的参考价值.

B1 Mapping on Low-Field Permanent Magnet MRI Scanner

Methods to map radiofrequency (RF) field generated by an RF coil/pulse have been developed. By measuring the changes of RF field in biological tissues when an RF pulse passing through, the electrical properties of the tissue could be retrieved and used for early diagnosis of diseases such as cancer. So far, RF field mapping is mainly done for birdcage coils at high fields. Less research has been performed on phased array coils at low fields. This work studied how loading would affect the distribution of RF field in low-field MRI with permanent magnet (i.e., 17.8 MHz). Both finite element simulation and experimental results demonstrated that coil loading changed the uniformity of RF field significantly, and the distortion of RF field under the loaded condition could reflect the electrical characteristics of the loaded biological tissues.