Design of an Electrically Automated RF Transceiver Head Coil in MRI

Abstract

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.

New resonator geometries for ICE decoupling of loop arrays

“…This association is particularly strong when the decoupling loop resonates near the Larmor frequency. At high fields, the coils’ matching performance have large variations with different subjects, and may need to be re-adjusted manually or remotely [33]. Therefore the new geometries are advantageous in ICE-decoupled loop arrays since they have more robust decoupling performance (larger |ω d – ω 0 |) compared to the conventional ICE decoupling method.…”

Experimental implementation of array‐compressed parallel transmission at 7 tesla

“…While such a construction is feasible for a fixed network, subject-to-subject or scan-to-scan tuning of the array compression weights would require the ability to remotely adjust the weights electronically or mechanically. Previous work in MRI has demonstrated the potential for remote tuning of phase shifts for RF shimming using commercial motor-driven phase shifters [17], and remote tuning and matching of coils using PIN diode switching of capacitor banks [18], varactors [19], and piezoelectric actuators connected to variable capacitors [20]. Other electronic approaches to remotely adjust phase shifts include PIN diode-based switched-line shifters [21, 22] and varactor-terminated transmission lines [23].…”

ArduiTaM: accurate and inexpensive NMR auto tune and match system

“…In this paper, we report our findings, and present a compact low-cost accurate Arduino-based automatic tuning and matching system, abbreviated as ArduiTaM. Unlike commercial solutions and previously published reports Hwang (1998); Koczor (2015); Muftuler (2002); PerezdeAlejo (2004); Sohn (2015Sohn ( , 2013 that use either the MR spectrometer or a commercial network analyzer for frequency generation and signal processing, our system employs a single chip frequency source covering a useful range of 35 MHz to 4.4 GHz, as well as discrete signal processing electronics, rendering it a completely standalone system capable of tuning and matching almost any relevant NMR/MRI probe channel. The ArduiTaM is compatible with most NMR spectrometers, can readily be interfaced via a few TTL lines, and requires neither software addons (like Koczor's work Koczor (2015)) nor hardware alterations.…”