Preclinical robotic device for magnetic resonance imaging guided focussed ultrasound

Abstract

Background: A robotic device featuring three motion axes was manufactured for preclinical research on focussed ultrasound (FUS). The device comprises a 2.75 MHz single element ultrasonic transducer and is guided by Magnetic Resonance Imaging (MRI). Methods:The compatibility of the device with the MRI was evaluated by estimating the influence on the signal-to-noise ratio (SNR). The efficacy of the transducer in generating ablative temperatures was evaluated in phantoms and excised porcine tissue.Results: System's activation in the MRI scanner reduced the SNR to an acceptable level without compromising the image quality. The transducer demonstrated efficient heating ability as proved by MR thermometry. Discrete and overlapping thermal lesions were inflicted in excised tissue. Conclusions:The FUS system was proven effective for FUS thermal applications in the MRI setting. It can thus be used for multiple preclinical applications of the emerging MRI-guided FUS technology. The device can be scaled-up for human use with minor modifications.

Robotic system for magnetic resonance imaging‐guided focused ultrasound treatment of thyroid nodules

“…MRI-compatible piezoelectric ultrasonic motors were utilised for actuating motion in the two mechanical positioning stages of the robot, following their vast employment in other preclinical MRIcompatible robotic devices for HIFU treatment. [70][71][72][73][74][75][76][77][78] The linear motion in the X and Z axes was achieved using simple plastic jackscrews with mounted plate mechanisms, following the vast experience of our group in the design of MRgFUS positioning devices using piezoelectric motors. [70][71][72][73][74][75][76][77][78] It is noted that all materials employed in the Although the composite agar-based thyroid model phantom exhibited tissue-like appearance on MR imaging and successfully validated the thermal heating performance of the system for the intended application, future improvements could be potentially performed, resulting in a phantom that more realistically mimics the human properties of the thyroid.…”

“…[70][71][72][73][74][75][76][77][78] The linear motion in the X and Z axes was achieved using simple plastic jackscrews with mounted plate mechanisms, following the vast experience of our group in the design of MRgFUS positioning devices using piezoelectric motors. [70][71][72][73][74][75][76][77][78] It is noted that all materials employed in the Although the composite agar-based thyroid model phantom exhibited tissue-like appearance on MR imaging and successfully validated the thermal heating performance of the system for the intended application, future improvements could be potentially performed, resulting in a phantom that more realistically mimics the human properties of the thyroid. Both the thyroid model and surrounding neck tissue phantoms were developed with an agar-base that is known to mechanically resemble human soft tissue.…”

“…Although the simple design of the device is based on previously proposed systems developed by our group, 71,74,[76][77][78]80 with one such recent system offering the potential for top to bottom MRgFUS therapy of thyroid tumours, 76 the herein system offers advanced characteristics. The current prototype has been designed for use on thyroid tumours and not on multiple, potentially deeper, targets as the previously developed system.…”

“…MRI‐compatible piezoelectric ultrasonic motors were utilised for actuating motion in the two mechanical positioning stages of the robot, following their vast employment in other preclinical MRI‐compatible robotic devices for HIFU treatment 70–78 . The linear motion in the X and Z axes was achieved using simple plastic jackscrews with mounted plate mechanisms, following the vast experience of our group in the design of MRgFUS positioning devices using piezoelectric motors 70–78 . It is noted that all materials employed in the development of the robotic system are non‐magnetic to allow proper functioning within the MRI environment.…”

“…Considering the thickness and depth of the thyroid gland, the robotic system, with the appropriate application of power, can controllably ablate thyroid nodules without affecting nearby organs. Moreover, due to the thin nature of the gland, a Y-axis for adjusting the focusing height of the transducer and providing motion along the Y imaging plane of the MRI, as previously employed in other MRgFUS robotic systems,71,74,[76][77][78]80 was not required herein. Additionally, the formed lesions provided a visual representation of the accuracy of robotic motion through the formation of almost square overlapping lesions as well as uniformly distant discrete lesions.F I G U R E 1 1 (A) Axial thermal maps acquired at different timepoints during sonications at an acoustic power of 45 W for a sonication time of 60 s at 30 mm focal depth as overlayed on the magnitude images of the agar-based thyroid phantom, and (B) Timeseries temperature increase recorded in the focal spot within the agar-based thyroid phantom during sonications.…”