Abstract
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.
Highlights
Phased array antennas play a key role in modern magnetic resonance imaging (MRI) to increase spatial resolution and efficiency compared to conventional radio-frequency coils
MRI APPLICABILITY To check the applicability of our high impedance coil (HIC) to MRI application, we numerically studied performance of the transceiver HIC regarding MRI criteria
We have found that in the transmission regime these HICs are not advantageous
Summary
Phased array antennas play a key role in modern magnetic resonance imaging (MRI) to increase spatial resolution and efficiency compared to conventional radio-frequency coils. If ZR is very small, it shorts the capacitance 2CTL , the induced voltage is loaded by a small inductance Lshield +2LTL , the current flowing through Vemf is large and the HICs in the array are strongly coupled. It confirms what we have claimed above: when the port is open, the induced voltage is really connected to a series circuit and this harmful resonance occurs at the antenna operation frequency. These angles should be chosen such that our large HIC resonates at 298 MHz (Larmor frequency of hydrogen at 7T) with balanced electric and magnetic current modes. The main factor of decoupling stays the same – the high impedance seen by the induced voltage
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