Abstract Purpose Wearable coils fabricated using conductive threads have high resistance that limits SNR. The purpose of this work is to demonstrate the utility of conductive fabric as a coil conductor that can be fabricated using a cutting plotter. Methods A single-channel coil was developed by feeding a conductive fabric sheet into an automatic cutting plotter. The fabric coil was loaded on a spherical phantom to evaluate SNR and B1+ homogeneity and compared with a single-channel conductive thread coil and a rigid printed circuit board (PCB) coil. A 14-channel wearable neck array was developed for structural imaging of the cervical spine and 4D flow MRI of the carotid arteries. The SNR from structural images and velocity-to-noise ratio (VNR) from flow images were compared with a 16-channel commercial coil. Results The single-channel conductive fabric coil provided 6.7% and 125.9% SNR increase when compared to the rigid PCB and conductive thread coils across 10 scan repetitions. The B1+ field homogeneity was 96.4%, 1% higher than the rigid PCB and conductive thread coils. The wearable neck array demonstrated a 51.1% average SNR increase from the cervical spine images across three volunteers and a 12.0% VNR increase from the postprocessed 4D flow data when compared with the commercial 16-channel array. Conclusion The possibility of developing wearable coils using conductive fabric to enhance SNR in structural images and VNR in 4D flow images is demonstrated. The conductive fabric technique enables fabrication on commercial garments resulting in form-fitting wearable coils.
Resonance Frequency Retuning System for Flexible MRI Coils
Radiofrequency coils are utilized during transmit and receive of MRI signals. Cable traps remove common-mode current from the coaxial cable shield, which helps improve the image quality and reduces risks of burns to the patient. Traditional cable traps use wounded coaxial cables that limit the flexibility in the design process. Floating cable traps were introduced which eliminated any physical connection between the trap and coaxial cable, allowing complete flexibility in design and placement. However, the design process of floating cable traps is iterative and may take several rounds of 3D modeling. This work seeks to optimize the design process through the use of parametric design methodologies. The proposed methodology allows for 3D printing the floating cable trap after inputting the design parameters. The cable trap was able to attenuate currents in the coaxial shields to −48 dB, highlighting its performance and design robustness.
Receive coils used in small animal MRI are rigid, inflexible surface loops that do not conform to the anatomy being imaged. The recent trend toward design of stretchable coils that are tailored to fit any anatomical curvature has been focused on human imaging. This work demonstrates the application of stretchable coils for small animal imaging at 7T. A stretchable coil measuring 3.5 × 3.5 cm was developed for acquisition of rat brain and spine images. The SNR maps of the stretchable coil were compared with those of a traditional flexible PCB coil and a commercial surface coil. Stretch and conformance testing of the coil was performed. Ex vivo images of rat brain and spine from the stretchable a coil was acquired using T1 FLASH and T2 Turbo RARE sequences. The axial phantom SNR maps showed that the stretchable coil provided 48.5% and 42.8% higher SNR than the commercial coil for T1-w and T2-w images within the defined ROI. A 33% increase in average penetration depth was observed within the ROI using the stretchable coil when compared to the commercial coil. The ex-vivo rat brain and spine images showed distinguishable anatomical details. Stretching the coil reduced the resonant frequency with reduction in SNR, while the conformance to varying sample volumes increased the resonant frequency with decreased SNR. This study also features an open-source plug-and-play system with preamplifiers that can be used to interface surface coils with the 7T Bruker scanner.