1068 IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 59, NO. 4, APRIL 2012 Electromechanical Design and Construction of a Rotating Radio-Frequency Coil System for Applications in Magnetic Resonance Adnan Trakic*, Ewald Weber, Bing Keong Li, Member, IEEE, Hua Wang, Member, IEEE, Feng Liu, Member, IEEE, Craig Engstrom, and Stuart Crozier, Member, IEEE Abstract—While recent studies have shown that rotating a single radio-frequency (RF) coil during the acquisition of magnetic res- onance (MR) images provides a number of hardware advantages (i.e., requires only one RF channel, avoids coil–coil coupling and facilitates large-scale multinuclear imaging), they did not describe in detail how to build a rotating RF coil system. This paper presents detailed engineering information on the electromechanical design and construction of a MR-compatible RRFC system for human head imaging at 2T. A custom-made (bladeless) pneumatic Tesla turbine was used to rotate the RF coil at a constant velocity, while an infrared optical encoder measured the selected frequency of rotation. Once the rotating structure was mechanically balanced and the compressed air supply suitably regulated, the maximum frequency of rotation measured ∼14.5 Hz with a 2.4% frequency variation over time. MR images of a water phantom and human head were obtained using the rotating RF head coil system. Index Terms—Coil coupling, rotating RF coil (RRFC), Tesla turbine. I. INTRODUCTION M AGNETIC resonance imaging (MRI) is a widely ac- cepted tool for clinical assessment and diagnosis of var- ious disease states due to its exceptional soft-tissue contrast and a wide application spectrum [1]. In MRI, the patient is placed in a very strong and uniform static magnetic field in which (hydrogen) nuclei resonate at a radio frequency (RF) that is pro- portional to the static field strength. Transmission and reception coils (i.e., antennas) operating at the same RF are placed near and around the patient to excite and receive the magnetic res- onance (MR) signals, respectively. These signals are spatially encoded by pulsed gradient coils and digitally processed to form MR images. Manuscript received June 6, 2011; revised November 3, 2011; accepted De- cember 29, 2011. Date of publication January 6, 2012; date of current version March 21, 2012. This work was supported by the Australian Research Council. Asterisk indicates corresponding author. *A. Trakic is with The School of Information Technology and Electrical Engineering, The University of Queensland, Qld. 4072, Australia (e-mail: trakic@itee.uq.edu.au). E. Weber, B. K. Li, H. Wang, F. Liu, and S. Crozier are with The School of Information Technology and Electrical Engineering, The University of Queens- land, Qld. 4072, Australia (e-mail: ewald@itee.uq.edu.au; joeli@itee.uq.edu.au; hwang@itee.uq.edu.au; feng@itee.uq.edu.au; stuart@itee.uq.edu.au). C. Engstrom is with the School of Human Movement Studies, The University of Queensland, Qld. 4072, Australia (e-mail: craig@hms.uq.edu.au). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TBME.2012.2182993 Recent developments involve phased array coils (PHAs) [2], where MR images are received simultaneously on multiple RF coils that provide independent signal pathways [2]–[5]. In the parallel array, each RF coil can see only part of the sample due to its’ spatially constrained electromagnetic field sensitivity. Com- bining individual sensitivity-weighted images from each coil in the array yields a full field-of-view (FOV) image. While in- creasing the number of coils in an array increases the signal to noise ratio (SNR), it invariably intensifies the electromagnetic coil coupling interactions, causing complex spatiotemporal RF field behaviors and problems with the image reconstruction pro- cess [6], [7]. In addition, as the number of signal channels in- creases, the complexity of the system increases and fabrication costs escalate. In practice, it can, therefore, be very difficult and costly to engineer very large RF coil arrays. Since increasing the number of RF coils to a very large num- ber (>32) is extremely difficult due to the intricate coil–coil cou- pling interactions and involved engineering complexity, in re- cent studies, we have investigated the generation of MR images by rapidly rotating a single RF transceiver coil (RRFC) [8]–[10]. The advantages of this approach are that it requires only one RF coil and channel, circumvents electromagnetic signal and noise coupling interactions, and provides a large number of time- multiplexed sensitivity profiles that have useful properties for scan time reduction. Although it was demonstrated that MR im- ages can be obtained in a short time frame, these studies did not describe in sufficient detail how to reproduce and build a RRFC system that is fully compatible with the MRI scanner. This pa- per provides the engineering details on the electromechanical design and implementation of the RRFC system for human head imaging at 2 T. II. METHODS A. General Description The RRFC system consisted of a single RF coil that was mechanically rotated by a pneumatic Tesla turbine (see Figs. 1– 3). Fig. 2 shows the open-loop RRFC system configuration, in which the velocity of the RF coil was constantly monitored with an infrared (IR) photointerrupter device. The velocity mea- surements can be used later to optimally reconstruct MR im- ages, full details of which are given in [10]. The entire system was constructed from nonmagnetic materials (mostly plastics) to be electromagnetically compatible with the MRI scanner. The RRFC system was electromagnetically shielded to increase 0018-9294/$31.00 © 2012 IEEE