Stretchable self-tuning MRI receive coils based on liquid metal technology (LiquiTune).

Magnetic resonance imaging systems rely on signal detection via radiofrequency coil arrays which, ideally, need to provide both bendability and form-fitting stretchability to conform to the imaging volume. However, most commercial coils are rigid and of fixed size with a substantial mean offset distance of the coil from the anatomy, which compromises the spatial resolution and diagnostic image quality as well as patient comfort. Here, we propose a soft and stretchable receive coil concept based on liquid metal and ultra-stretchable polymer that conforms closely to a desired anatomy. Moreover, its smart geometry provides a self-tuning mechanism to maintain a stable resonance frequency over a wide range of elongation levels. Theoretical analysis and numerical simulations were experimentally confirmed and demonstrated that the proposed coil withstood the unwanted frequency detuning typically observed with other stretchable coils (0.4% for the proposed coil as compared to 4% for a comparable control coil). Moreover, the signal-to-noise ratio of the proposed coil increased by more than 60% as compared to a typical, rigid, commercial coil.

Conductive Thread-Based Stretchable and Flexible Radiofrequency Coils for Magnetic Resonance Imaging.

OBJECTIVE: We propose a novel flexible and entirely stretchable radiofrequency coil for magnetic resonance imaging. This coil design aims at increasing patient comfort during imaging while maintaining or improving image quality. METHODS: Conductive silver-coated thread was zigzag stitched onto stretchable athletic fabric to create a single-loop receive coil. The stitched coil was mounted in draped and stretched fashions and compared to a coil fabricated on flexible printed circuit board. Match/tune circuits, detuning circuits, and baluns were incorporated into the final setup for bench measurements and imaging on a 3T MR scanner. A fast spin echo sequence was used to obtain images for comparison. RESULTS: The fabricated coil presents multi-directional stretchability and flexibility while maintaining conductivity and stitch integrity. SNR calculations show that this stretchable coil design is comparable to a flexible, standard PCB coil with a 13-30% decrease in SNR depending on stretch degree and direction. In vivo human wrist images were obtained using the stitched coil. CONCLUSION: Despite the reduction in SNR for this combination of materials, there is a reduced percentage of SNR drop as compared to existing stretch coil designs. These imaging results and calculations support further experimentation into more complex coil geometries. SIGNIFICANCE: This coil is uniquely stretchable in all directions, allowing for joint imaging at various degrees of flexion, while offering the closest proximity of placement to the skin. The materials provide a similar level of comfort to athletic wear and could be incorporated into coils for a variety of anatomies.

Stitching Stretchable Radiofrequency Coils for MRI: A Conductive Thread and Athletic Fabric Approach.

OBJECTIVE: We propose a novel flexible and entirely stretchable radiofrequency coil for magnetic resonance imaging. This coil design aims at increasing patient comfort during joint imaging while maintaining or improving image quality. METHODS: Conductive silver-coated thread was stitched in a zigzag pattern onto stretchable athletic fabric to create a single-loop receive coil. The stitched coil was mounted in a draped and stretched fashion and compared to a coil fabricated on flexible printed circuit board. Match/tune circuits, detuning circuits, and baluns were incorporated into the final setup for bench measurements and imaging on a 3T MR scanner. A fast spin echo sequence was used to obtain images for comparison. RESULTS: The fabricated coil presents multi-directional stretchability and flexibility while maintaining conductivity and stitch integrity. Quality factor measurements and SNR calculations show that this stretchable coil design is comparable to a flexible, standard PCB coil. Detailed human wrist images were successfully obtained in vivo using the stretched, stitched coil. CONCLUSION: The resulting MR images and SNR calculations support further experimentation into more complex coil geometries. SIGNIFICANCE: This coil is uniquely stretchable in all direction and allows for joint imaging at various degrees of flexion. Additionally, this coil offers the closest proximity of placement to the skin with materials that provide a similar level of comfort to that of athletic wear and compression sleeves. This stitched design could be incorporated into coils for a variety of anatomies.

Dual-Tuned Removable Common-Mode Current Trap for Magnetic Resonance Imaging and Spectroscopy.

Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) are preferred methods of gathering structural and metabolic information from the body due to their non-invasive approach to obtaining a diagnosis. Dual-tuned radiofrequency (RF) coils can detect signals produced by both hydrogen and a second atomic nuclei of interest. However, undesired electromagnetic coupling often confounds both the design and utilization of RF coils. Coaxial shield currents, also known as common-mode currents, can be induced during MR scans and cause image distortion and reduction in signal-to-noise ratio (SNR); furthermore, the energy dissipated from the cabling can create heat that poses a risk of patient burns if the routed too closely. Thus, common-mode currents must be suppressed in RF coils by employing non-magnetic current traps. In this paper, we present a novel dual-tuned current trap that is fully removable and does not require soldering directly to the cable. The design was manufactured with 3D printing to support rapid fabrication and distribution. Bench measurements at the 3T Larmor frequencies for hydrogen and phosphorous-31 demonstrate common-mode attenuation of -18 dB and -8.4 dB respectively.