The study found that the new OTR technique is significantly faster, drastically cutting registration time, while achieving a similar level of accuracy. It also simplified the procedure and shortened the learning curve for new surgeons, highlighting OTR's major advantages.
Improving Efficiency in Robot-Assisted SEEG Surgery
Epilepsy is a severe neurological condition that often requires surgical intervention. A key technique for pinpointing seizure sources is stereo-electroencephalography (SEEG), which involves implanting electrodes deep in the brain. Increasingly, SEEG is performed with the help of stereotactic robots, which have been shown to rival or exceed manual accuracy.
While robotic systems improve targeting precision, challenges remain in the registration process (the step where the robot aligns itself with the patient’s anatomy).
Currently, the most widely used method is contact bone-fiducial registration (CBR), which requires the robotic arm to physically touch implanted bone screws to calibrate the system. Although effective, CBR is complex, time-consuming, and has a steep learning curve.
To address these limitations, the study explored a contactless alternative. The goal was to evaluate whether the new OTR method could simplify the process, speed up registration, and maintain surgical precision, all while being easier for new operators to learn.
Study Design: Comparing Contactless and Contact-Based Registration Methods
To assess the performance of OTR, researchers conducted both phantom model experiments and in vivo animal trials using 12 Bama pigs. The animals were randomly assigned to either the OTR or CBR group (six in each).
Both groups used the same core robotic system, which included a robotic arm, optical tracking components, a touchscreen interface, and an operator console. The key difference lay in how each method performed registration:
- OTR used reflective marker spheres placed on the robotic arm and skull, tracked optically in real time. A sophisticated algorithm, incorporating iterative closest point (ICP) matching, synchronized timing, and Kalman filtering, calculated the robot’s position without any physical contact.
- CBR, by contrast, required the robot to physically touch 4–6 fiducial screws placed in the skull to align with the patient’s anatomy.
All subjects underwent preoperative MRI and CT scans, which were fused to plan electrode trajectories. After registration (via either OTR or CBR), SEEG electrodes were implanted through drilled burr holes.
How it Works: Optical Tracking with No Physical Contact
The OTR system’s innovation lies in its ability to perform “touch-free” spatial calibration. Rather than requiring mechanical interaction with bone-implanted screws, the robot uses external optical markers and a real-time tracking algorithm to determine its location relative to the patient.
This approach eliminates several manual steps required by CBR, reducing procedural complexity and minimizing operator fatigue. Crucially, it also opens the door to faster, more automated workflows, particularly beneficial in high-throughput or resource-limited settings.
To assess both accuracy and usability, the researchers measured:
- Primary outcome: Euclidean distance between planned and actual electrode tip positions, based on postoperative CT scans
- Secondary outcome: Registration time and learning curve, evaluated by having novice users perform repeated trials with both methods
Results: OTR Matches Accuracy While Cutting Registration Time by 60 %
This study's results demonstrated that the contactless OTR method achieved surgical accuracy on par with the traditional CBR technique, while offering significant gains in efficiency and ease of use.
Across both phantom and animal trials, the positional accuracy of OTR was statistically equivalent to CBR. In the animal study, which involved the implantation of 72 electrodes, the mean target point error for OTR was 1.68 millimeters, compared to 1.49 millimeters for CBR. Similarly, the cortical entry point error was 0.76 millimeters with OTR and 0.70 millimeters with CBR. These differences were not statistically significant, confirming that the contactless method maintained the high precision required for SEEG procedures.
Where OTR truly distinguished itself was in operational speed. The average time required to complete registration using OTR was just under 100 seconds - specifically, 99.7 seconds - whereas CBR required over 240 seconds to complete the same step. This reduction in time represents a more than 60 % decrease in setup duration, a critical improvement for time-sensitive surgical environments.
Ease of use was another major advantage. New users were able to achieve accurate results more quickly with OTR, reaching acceptable error thresholds in fewer attempts. In particular, novice operators using OTR were able to reach a cortical entry point error below 0.5 millimeters in significantly fewer trials than with CBR. Additionally, OTR reduced the number of procedural steps from 12 to just 5, creating a more intuitive, streamlined workflow that minimized cognitive load and fatigue for the operator.
Clinical Implications: Simplified Workflow, Faster Learning, and Broader Potential
These improvements in speed and usability have several important clinical implications.
First, reducing setup time directly benefits operating room efficiency, allowing more procedures to be completed in a given time frame. Second, the simplified process reduces cognitive and physical strain on surgeons, particularly beneficial during long or complex procedures.
Although not directly measured in this study, the authors also note that the non-contact nature of OTR may help lower the risk of infection by avoiding skin and bone contact - an area worth exploring in future trials.
In terms of training, the shorter learning curve of OTR could enable faster onboarding of new users, potentially reducing the cost and duration of surgeon training programs. Additionally, the authors highlight the method’s potential for other procedures, such as deep brain stimulation (DBS), craniofacial reconstruction, brain biopsy, and orbital surgeries, due to its adaptability and precision.
The study does acknowledge a couple of limitations. For example, some phantom positions had to be excluded due to occlusion of the reflective markers, a known challenge in optical tracking systems. Moreover, while promising, results from animal models require clinical validation in humans - a step that is already underway.
A Faster, Easier Alternative to Traditional Brain Surgery Registration
In summary, this study introduces and validates a novel, contactless optical-tracking registration method for robot-assisted SEEG surgery. OTR offers comparable accuracy to the established contact-based CBR method but completes the process in less than half the time.
With its streamlined workflow, reduced number of procedural steps, shorter learning curve, and potential for lower infection risk, OTR presents a major advancement in the field of robot-assisted neurosurgery.
A multicenter clinical trial involving 50 patients is now in progress, aiming to confirm these findings in human applications and pave the way for broader clinical adoption.
Journal Reference
Hu, F., Li, X., Wu, S., Jiang, W., Shu, K., & Lei, T. (2025). Phantom and in vivo validation of a novel contactless registration method for robot-assisted SEEG surgery. Chinese Neurosurgical Journal, 11(1), 20. DOI:10.1186/s41016-025-00401-x. https://cnjournal.biomedcentral.com/articles/10.1186/s41016-025-00401-x