Electromagnetic Actuated Single-Element Ultrasonic Imaging for Minimally Invasive Spine Surgery.

[OBJECTIVE] transkeyhole microsurgery for spinal cord tumors requires intraoperative imaging guidance to ensure safe and effective tumor resection. Although optical endoscopy has been widely adopted in clinical settings, it's limited to visualizing superficial structures. Endoscopic ultrasound (EUS) offers a promising alternative. However, EUS transducers are typically fabricated from high-frequency arrays, which provide limited imaging depth and field of view. In addition, the high cost of the transducers and complicated sterilization further restrict their use in surgery.

[METHODS] this paper introduces an economical single-element US transducer that utilizes electromagnetic actuation operating in a resonant scanning mode. An image-based method is proposed to correct the resulting nonlinear scanning. Two prototypes were developed, having outer diameters of 14 (T14) and 9 (T9) mm. The imaging performance of the transducers was evaluated by wire phantoms, tissue-mimicking phantom, ex-vivo sheep spine, and in-vivo rabbits.

[RESULTS] The T14 and T9 achieved scanning angles over 70$^\circ$ and approximately 60$^\circ$, respectively, with the former maintaining a lateral resolution of 248 $\mu$m and the latter yielding an optimal contrast-to-noise ratio of 2.43. The captured US imaging clearly visualized dural sac and unilateral nerve roots in sheep spine and enabled the accurate identification of subdural hemorrhage and key anatomy in rabbits.

[CONCLUSION] the electromagnetically actuated transducer achieves a wide scanning range despite its compact size, showing great promise for surgery by facilitating the identification of subdural anatomy and enabling customized dural opening strategies.

[SIGNIFICANCE] cost reduction enables the feasible use of the transducer as a single sterile device in surgical settings.