A 20‐gauge active needle design with thin‐film printed circuitry for interventional MRI at 0.55T

Abstract

Purpose This work aims to fabricate RF antenna components on metallic needle surfaces using biocompatible polyester tubing and conductive ink to develop an active interventional MRI needle for clinical use at 0.55 Tesla. Methods A custom computer numeric control‐based conductive ink printing method was developed. Based on electromagnetic simulation results, thin‐film RF antennas were printed with conductive ink and used to fabricate a medical grade, 20‐gauge (0.87 mm outer diameter), 90‐mm long active interventional MRI needle. The MRI visibility performance of the active needle prototype was tested in vitro in 1 gel phantom and in vivo in 1 swine. A nearly identical active needle constructed using a 44 American Wire Gauge insulated copper wire‐wound RF receiver antenna was a comparator. The RF‐induced heating risk was evaluated in a gel phantom per American Society for Testing and Materials (ASTM) 2182‐19. Results The active needle prototype with printed RF antenna was clearly visible both in vitro and in vivo under MRI. The maximum RF‐induced temperature rise of prototypes with printed RF antenna and insulated copper wire antenna after a 3.96 W/kg, 15 min. long scan were 1.64°C and 8.21°C, respectively. The increase in needle diameter was 98 µm and 264 µm for prototypes with printed RF antenna and copper wire‐wound antenna, respectively. Conclusion The active needle prototype with conductive ink printed antenna provides distinct device visibility under MRI. Variations on the needle surface are mitigated compared to use of a 44 American Wire Gauge copper wire. RF‐induced heating tests support device RF safety under MRI. The proposed method enables fabrication of small diameter active interventional MRI devices having complex geometries, something previously difficult using conventional methods.

Minimal artifact actively shimmed metallic needles in MRI

“…The void in the FSE images approaches the true width of the 4 mm needle after shimming could be conceived that leave the central working channel open. 52 Alternatively, shim inserts that are retractable can be designed. The shim insert in this work did not exhibit noticeable torque when operated in the scanner's bore.…”

“…One design challenge in this technique is the space inside a needle and whether shim conductors might be incorporated with minimal compromise on the core function of the device. For probes with working central channels, shim inserts with flexible printed coils mounted on thin wall hollow tubes could be conceived that leave the central working channel open 52 . Alternatively, shim inserts that are retractable can be designed.…”

An interventional MRI guidewire combining profile and tip conspicuity for catheterization at 0.55T

“…On the other hand, the recent introduction of high‐performance, low‐field MRI allows a∼9‐fold reduction in specific absorption rate (SAR) for approximately equal B 1rms , 31,32 and an increased electrical wavelength 14,22 compared to 1.5T systems, for a given imaging sequence, enabling safe‐by‐design iMRI devices 12,33 …”

“…On the other hand, the recent introduction of high-performance, low-field MRI allows a∼9-fold reduction in specific absorption rate (SAR) for approximately equal B 1rms , 31,32 and an increased electrical wavelength 14,22 compared to 1.5T systems, for a given imaging sequence, enabling safe-by-design iMRI devices. 12,33 In this study, we introduce a novel, 0.89 mm (0.035 ′′ ) outer diameter (OD) actively visualized, monopole antenna-based metallic guidewire design for human interventional catheterization procedures at 0.55T. Distinguishing from the previous studies, the proposed design here incorporates a clinically required, non-traumatizing curved tip geometry, a unique combination of continuous tip and full shaft visibility, clinically acceptable mechanical characteristics and a detachable RF connector which allows catheter delivery and exchange over the active guidewire.…”

“…Active devices incorporate RF antennas and electronic components embedded into the device body, and their signal is directly carried to the MR scanner, providing high SNR device visibility, significantly superior to that achievable in passive devices. 11,12 Their signal can be separated from other receive channels during image processing and can be colorized and overlaid onto the anatomical image for augmented conspicuity. 13 However, long metallic components used in active iMRI device designs are prone to RF-induced heating during real-time MRI.…”