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.
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