Perspectives in Wireless Radio Frequency Coil Development for Magnetic Resonance Imaging

Abstract

This paper addresses the scientific and technological challenges related to the development of wireless radio frequency (RF) coils for magnetic resonance imaging (MRI) based on published literature together with the authors' interpretation and further considerations. Key requirements and possible strategies for the wireless implementation of three important subsystems, namely the MR receive signal chain, control signaling, and on-coil power supply, are presented and discussed. For RF signals of modern MRI setups (e.g., 3 T, 64 RF receive channels), with on-coil digitization and advanced methods for dynamic range (DR ≥ 16-bit) and data rate compression, still data rates > 500 Mbps will be required. For wireless high-speed MR data transmission, 60 GHz WiGig and optical wireless communication appear to be suitable strategies; however, on-coil functionality during MRI scans remains to be verified. Besides RF signals, control signals for on-coil components, e.g., active detuning, synchronization to the MR system, and B 0 shimming, have to be managed. Wireless power supply becomes an important issue, especially with a large amount of additional on-coil components. Wireless power transfer systems (>10 W) seem to be an attractive solution compared to bulky MR-compatible batteries and energy harvesting with low power output. In our opinion, completely wireless RF coils will ultimately become feasible in the future by combining efficient available strategies from recent scientific advances and novel research. Besides ongoing improvement of all three subsystems, innovations are specifically required regarding wireless technologies, MR compatibility, and wireless power supply.

Recent Advances in Radio‐Frequency Coil Technologies: Flexible, Wireless, and Integrated Coil Arrays

“…The analog MRI RF signal acquired from the subject must first be sampled, digitized, and potentially compressed for large data sets (eg, from arrays with many coil elements) before it can be wirelessly transmitted. To this end, the analog RF signal can be sampled "on-coil" with high-speed, high-resolution, MR-compatible analog-to-digital converters (ADCs) using analog down conversion, 33 direct undersampling, 34,35 or baseband demodulation sampling techniques, 36 which can reduce the amount of data, and therefore the data rate, to be wirelessly transmitted. 37 For example, a modern 3T 64-channel RF coil array has been estimated to only require a minimum data rate of 512 Mbps, or 8 Mbps/coil element, using 16-bit ADCs and a demodulated baseband technique.…”

“…37 For example, a modern 3T 64-channel RF coil array has been estimated to only require a minimum data rate of 512 Mbps, or 8 Mbps/coil element, using 16-bit ADCs and a demodulated baseband technique. 33,38,39 Critically, the ADCs data acquisition clock must be wirelessly synchronized with the MRI scanner clock using additional software and in-bore hardware to avoid clock-jitter, which effectively reduces the number of ADC sampled bits and can result in image artifacts. 40,41 The clock synchronization is an active area of research in wireless MRI and is a major obstacle to the ubiquitous use of wireless MRI in a clinical setting.…”

“…All of these wireless technologies for RF coil arrays require alternative power sources for their on-board electronics (eg, processors, ADCs, and wireless transceivers), which can have power requirements between an estimated 10 and 100 W for high-density coil arrays. 33 Innovatively, the MRI scanner itself can be used to provide power to the electronics by using two or more additional coils in the scanner to harvest power from the scanner RF transmit pulses during imaging. Specifically, this wireless power transfer (WPT) system uses a secondary coil tuned to the Larmor frequency to gather energy from the high-power scanner RF transmit pulses (eg, 10-30 kW) and to inductively couple it to a primary coil, where it can then be rectified and used to power electronics [52][53][54][55] (Fig.…”

“…For more information, an extensive review of wireless RF coil array hardware is presented in Ref. 33.…”

The Core of Medical Imaging: State of the Art and Perspectives on the Detectors

“…In particular, optical fibers guarantee patient safety while reducing signal interferences, although problems related to placement and curvature of the fibers still limit the coils positioning and handling. Wireless coils seem to enable the building of "wearable" coil arrays, which improves patient comfort and supports the integration of different channels at the coil level: in this way, channel number is exclusively dependent on the coils and not on system ADC inputs number as for the standard scanner [79].…”