(Invited) Optically Innervated Surgical Sensing for Situation-Aware Surgeries
Authors: Ren Hongliang 
Published: February 2020

Aspiration instrument such as a suction tube is commonly used during neurosurgery. Through moving a finger over a port on the handheld end to adjust suction pressure, the aspirator can remove tissue debris, blood, brain tumor and retract/manipulate tissues. When using the suction tube to implement these manipulations, a small overload exerted on the brain tissue could result in iatrogenic injury to the soft, fragile and complex brain structures. Therefore, a series of delicate manipulations need to be performed to control the suction pressure and retract brain tissue during neurosurgery. Nevertheless, it is quite difficult for inexperienced surgeons to be aware of the undue forces, which might results in irreversible injury, due to the force threshold limitation of human sensing. Even for experienced experts, it is still not trivial to perform these operations using such surgical instrument without force feedback. A sensorized surgical instrument can not only quantify interaction forces to assist surgeons with safe operations, but also improves surgical skill training. Thus, developing smart aspiration instruments with the force feedback for neurosurgery is a critical challenge with significant importance for clinical scenarios.

To overcome these limitations, a low-cost FBG sensing-based sensor with a miniature elastomer fabricated by 3D-printed technology is presented and integrated at the end of the suction tube to sense the instrument-tissue interaction force/torque information, such as suction force, as well as touching and retraction force, during neurosurgery. This development possesses a simple structure and good biocompatibility, and supports disposable application due to low cost of the sensor’s components. Meanwhile, it easily achieves sterilization and antisepsis. The sensor mainly consists of a 3D-printed elastomer with an annular diaphragm and four symmetrically suspended optical fibers. Each fiber inscribed. This configuration can effectively overcome intensity fluctuation interference from the input light compared with intensity-demodulation. Two ends of every optical fiber have been mounted along the longitudinal direction of the elastomer with a suspended pretension status. Under these deployments, each FBG within the suspension fiber segment is directly compressed or stretched along its axial direction under the force and torques. Such an advantage can avoid FBG chirping failure and improve measurement precision in comparison with conventional pasted FBG-based force sensors. Consequently, the suction tube-tip force information with temperature compensation can be decoupled and achieved by a sensitivity matrix, which consists of the response of each FBG for unit-force and unit-temperature. To the best of our knowledge, the interaction force evaluation on a suction tube-tip for tissue suction and retraction, especially using FBG sensors embedded in a 3D-printed annular diaphragm as a sensing structure, has never been reported.

The interaction force between tube and tissue can be detected real-time by the designed sensor when performing the neurosurgical tasks. Meanwhile, the interaction types and orientation of the interaction force can be reflected and evaluated qualitatively by the resultant moment. An interface based on the two torque components will be developed to further assist the surgeon to achieve the quantitative orientation information of the interaction force in the future. In addition, this force sensing approach can further be extended to various kinds of tube-type medical equipment such as endoscopes and tube robots to investigate instrument-interaction forces.

Future work will involve performing clinical experiments by expert physicians for real-time monitoring of actual instrument–tissue interaction forces such as suction force and retraction force, during neurosurgery. An additional step is accurately obtaining safety thresholds of these operations as a guide to avoid iatrogenic injury during tissue manipulations and to facilitate novice surgeons to faster and better grasp neurosurgical skills. Meanwhile, several auxiliary fixtures for holding and stretching the two ends of the optical fiber will be developed to standardize the assembly procedure. It can not only further depress the assembly errors, but also guarantee a close accuracy/repeatability consistent with each newly fabricated sensor.