Design of an Electrically Automated RF Transceiver Head Coil in MRI.

Magnetic resonance imaging (MRI) is a widely used nonionizing and noninvasive diagnostic instrument to produce detailed images of the human body. The radio-frequency (RF) coil is an essential part of MRI hardware as an RF front-end. RF coils transmit RF energy to the subject and receive the returning MR signal. This paper presents an MRI-compatible hardware design of the new automatic frequency tuning and impedance matching system. The system automatically corrects the detuned and mismatched condition that occurs due to loading effects caused by the variable subjects (i.e., different human heads or torsos). An eight-channel RF transceiver head coil with the automatic system has been fabricated and tested at 7 Tesla (T) MRI system. The automatic frequency tuning and impedance matching system uses digitally controlled capacitor arrays with real-time feedback control capability. The hardware design is not only compatible with current MRI scanners in all aspects but also it operates the tuning and matching function rapidly and accurately. The experimental results show that the automatic function increases return losses from 8.4 dB to 23.7 dB (maximum difference) and from 12.7 dB to 19.6 dB (minimum difference) among eight channels within 550 ms . The reflected RF power decrease from 23.1% to 1.5% (maximum difference) and from 5.3% to 1.1% (minimum difference). Therefore, these results improve signal-to-noise ratio (SNR) in MR images with phantoms.