工程科学与技术 (May 2025)
MRI Compatibility Research of Ultrasonic Motor and Material for DBS Surgical Robot
Abstract
ObjectiveDeep brain stimulation (DBS) surgery, a typical treatment targeting sub-millimeter anatomical points, requires highly precise surgical assistance devices and related technologies for electrode implantation. Magnetic Resonance Imaging (MRI) technology, known for its non-invasiveness, high spatial resolution, and good soft tissue contrast, is extensively used in pre-operative diagnosis, surgical planning, and postoperative follow-up of DBS. The integration of robotic assistance systems with MRI in DBS surgeries is a growing trend. However, since most existing robots are incompatible with MRI, their use in assisting DBS surgeries necessitates moving patients between the MRI scanning room and the operating room. This process is time-consuming and laborious and introduces issues such as contamination of the surgical area, surgery interruption, and re-registration of positioning. Developing a novel MRI-compatible surgical robot system for precise electrode implantation in DBS surgeries is of significant clinical importance and promising application prospects. This research primarily focuses on the ultrasonic motors and materials used in constructing the robot body, evaluating their compatibility in an MRI environment through theoretical analysis and experimental validation. The evaluation includes assessing their interference with MRI scanning to prevent potential safety and imaging issues. The goal is to provide substantial support for developing and applying DBS surgical robot systems by investigating and verifying these critical factors. In addition, these findings are intended to serve as a reference for future research and technological enhancements.MethodsIt is essential to ensure that the selected devices remain unaffected by the MRI environment and operate normally. This can be assessed by comparing their performance in both MRI and standard environments. In addition, the operation of these devices should not significantly impact the imaging quality, particularly concerning clinical quality metrics. Therefore, evaluating the effect of these devices on MRI image quality is necessary. MRI image quality can be assessed through control experiments using a standard object (typically a copper sulfate water phantom) with and without external device interference. Generally, MRI image quality is subjectively evaluated by visually identifying noise and assessing image quality. For DBS surgery, where precision and safety are paramount, any significant artifacts or noise can indicate MRI incompatibility. Another method involves quantitatively and objectively evaluating the signal-to-noise ratio (SNR) in the MRI image's area of interest. This study employs the American College of Radiology's single-image SNR measurement method and related formula for SNR value assessment and analysis. The experimental testing system involves placing the water phantom and the fixed platform on flexible washers. Copper bolts can be employed to secure the motor to the fixed platform for alignment with the curved surface of the water phantom cushion, or the motor can be directly mounted on the cushion with tape. Primarily, cross-sectional MRI imaging of a water phantom is utilized to evaluate image quality, with sagittal imaging being auxiliary observation. The devices undergoing MRI compatibility testing included the ultrasonic motor and the materials used in the robot.Results and DiscussionsExperiments were conducted in 3.0 and 1.5 T MRI environments. At Zhejiang University's 3.0 T MRI lab, magnetic components such as controllers and drivers were placed in the control room, connected to the motor located in the scanner bore parallelly via shielded lines and waveguides. During tests, the MRI scanner remained on continuously. The MRI imaging results showed that the 30 motors inside the MRI caused visible imaging artifacts, making them unsuitable for precision DBS surgery. In contrast, the 60 motors, whether parallel or perpendicular, minimally affected MRI imaging with acceptable SNR reductions. The motor speed curve in the experiment demonstrated that closed-loop control of both motors maintained consistent performance in MRI and non-magnetic environments. Tests on selected robot materials exhibited good compatibility, although metallic contact led to artifacts, indicating that metals should avoid direct contact with the imaging area. At 1.5 T in Xingaoyi Lab., all devices, including magnetic components, were placed inside the scanner room, powered by lead-acid batteries, and connected using an RS485 bus through waveguides. The MRI imaging results indicated external noise introduction by cables and artifact interference from running motors. However, powered but not running motors and devices only slightly affected the SNR. Eliminating controller exposure further reduced the SNR impact.ConclusionsExperimental results indicate alternating motor operation and MRI imaging for robotic-assisted DBS surgery. The MRI scanner remains on during surgery but does not scan or image while the robot (motor) moves. Similarly, the robot (motor) stays powered but stationary during MRI scans. The robot (motor) operates within the MRI scanner's uniform field, allowing timely adjustments to ensure precision and safety. Although full synchronization of MRI imaging and robot movement is not feasible, operating only 60 motors in a 3.0 T environment can allow complete synchronization between MRI scanning and motor operation. This approach meets real-time requirements and expected surgical outcomes, exceeding the performance of most robots that are not operable in MRI chambers. Analytical improvements are proposed for the future design of the robot's control system: 1) Adjusting the drive signals of the 60 and 30 motors to reduce MRI imaging interference due to different compatibilities and sensitive frequencies. 2) Shielding exposed controllers during 1.5 T experiments to reduce electromagnetic leakage and improve image quality. 3) Replacing external communication cables with fiber optics to control indoor devices from outside, effectively blocking external electromagnetic interference. The innovation of this study lies in the detailed experimental analysis of ultrasonic motors and robot materials under MRI conditions, proposing intermittent operation with MRI imaging and providing robust support for DBS surgery robots. Although previous studies used MRI-compatible ultrasonic motors, most did not operate within MRI chambers, limiting their compatibility for DBS surgery. This study provides specific SNR data and improvement methods based on experimental and theoretical analysis. The use of domestically produced ultrasonic motors achieved closed-loop control and compatibility in 3.0 and 1.5 T MRI environments, demonstrating their suitability in strong magnetic fields. This research contributes to the further design and manufacturing of MRI-compatible DBS robotic systems. Future work involves testing the complete robot system's MRI compatibility and developing a high-precision DBS surgery robot with real-time MRI guidance.
