Analysis of High Impedance Coils Both in Transmission and Reception Regimes

Theory of a high impedance coil (HIC) - a cable loop antenna with a modified shield - is comprehensively discussed for MRI application in both transmitting and receiving regimes. Understanding a weakness of the previously reported HIC in transmitting regime, we suggest another HIC which is advantageous in both transmitting and receiving regimes compared to a conventional loop antenna. In contrast with the claim of previous works that the reported HICs are advantageous in transmission regime, we show only this HIC is a practical transceiver HIC. Using the perturbation approach and adding gaps to both shield and inner wire of the cable, we tune the resonance frequency to be suitable for ultra-high field (UHF) magnetic resonance imaging (MRI). These gaps reduce the quality factor of the enhanced HIC which makes its resonant frequency more stable with respect to different loadings. Our theoretical model and applicability of our HIC for MRI applications are verified by simulations. Using the theoretical model, we have designed and fabricated an array of three HICs operating at 298 MHz. The operation of the array has been experimentally studied in the presence of different phantoms used in ultrahigh field MRI and the results compared with those obtained for a conventional array.