Features of the novel soft robotic system
Through close collaboration between clinicians and engineers, the team developed an MR-safe soft robotic system. It is a novel robotic platform that is able to use real-time intra-operative MRI guidance together with continuous control of laser beam projection for tumour ablation. The robot integrated with a laser fibre enables endoscopic intervention through a patient-specific dental anchorage in the oral cavity, and directs energy delivery to the target lesion. MRI-guided transoral laser microsurgery can be performed by the system which has the following unique features:
- It is compact (size: diameter 12mm x length 100mm) and lightweight (~200g), providing five degrees of freedom for motions. The larger actuator systems can be housed outside of the MRI suite.
- A hydraulic actuation approach is taken for its intrinsic MR compatibility while the system is fabricated with MR-safe materials.
- The laser manipulator incorporates hybrid soft and hard structures for laser steering with enhanced stiffness and lowered hysteresis.
- The system generates zero electromagnetic interference, allowing the introduction of intra-operative MRI guidance to evaluate the laser and tissue interaction process. This is essential in balancing adequate tumour resection and functional preservation. During laser ablation, MR thermal imaging can also be conducted to evaluate the heat diffusion in tissue, thus offering real-time monitoring of the ablation margin.
- A learning-based controller is used to accommodate the inherent nonlinear robot actuation and is validated with laser path following tests with a mean tracking error <200μm.
Experimental validation of intra-operative MRI-guided robotic laser ablation on ex-vivo tissue and cadaveric oropharyngeal tissue was carried out. The results showed that the robot achieved precision in an automated path following the laser spot along a trajectory defined by the surgeon.
Dr. Jason Ying Kuen CHAN, Associate Professor, Department of Otorhinolaryngology, Head and Neck Surgery at CU Medicine, stated, “The system enabled direct exposure of the ablation laser to the target lesion, without the need for positioning patients with extreme neck extension to accommodate rigid laser micromanipulators. Together with MRI guidance, clinicians could give intuitive and precise feedback of the ablation process, which is critical for function preservation of surrounding structures.”
For future work, the team is planning to further reduce the robot size. Dr. Ka Wai KWOK, Associate Professor, Department of Mechanical Engineering, Faculty of Engineering at HKU, added, “By miniaturising its size, it will be possible for the robot to access more confined sites such as the nasal cavity and sinus cavity. We will also implement some specific image sequences so that the images can be fed back to the robot in a faster way.”
Other collaborators in this project included the Department of Diagnostic Radiology at HKU, the Division of Neurosurgery at the Prince of Wales Hospital, the Department of Mechanical and Automation Engineering at CUHK and the Division of Head and Neck Surgery at the Stanford University Medical Center.