Simultaneous localization and calibration for electromagnetic tracking systems

Integrated Sensors for Soft Medical Robotics

Minimally invasive procedures assisted by soft robots for surgery, diagnostics, and drug delivery have unprecedented benefits over traditional solutions from both patient and surgeon perspectives. However, the translation of such technology into commercialization remains challenging. The lack of perception abilities is one of the obstructive factors paramount for a safe, accurate and efficient robot-assisted intervention. Integrating different types of miniature sensors onto robotic end-effectors is a promising trend to compensate for the perceptual deficiencies in soft robots. For example, haptic feedback with force sensors helps surgeons to control the interaction force at the tool-tissue interface, impedance sensing of tissue electrical properties can be used for tumor detection. The last decade has witnessed significant progress in the development of multimodal sensors built on the advancement in engineering, material science and scalable micromachining technologies. This review article provides a snapshot on common types of integrated sensors for soft medical robots. It covers various sensing mechanisms, examples for practical and clinical applications, standard manufacturing processes, as well as insights on emerging engineering routes for the fabrication of novel and high-performing sensing devices.

Analysis of influence of surgical instruments on accuracy of magnetic navigation system for craniofacial surgery robots

IntroductionIn craniofacial surgery, magnetic navigation systems can effectively extend the doctor's limited visual range, improve their surgical precision, shorten the operation time, and reduce the incidence of surgical complications. Owing to the ease of magnetic navigation, the accuracy of the magnetic navigation system is affected by various equipment in the operating room. Therefore, its large-scale application is lacking because the navigation accuracy requirement can be extremely high during craniofacial surgery. Therefore, the accuracy of magnetic navigation systems is crucial. Various surgical instruments have been evaluated to effectively reduce the interference of magnetic navigation systems with surgical instruments. In craniofacial surgery, magnetic navigation systems can effectively extend the doctor's limited visual range, improve their surgical precision, shorten the operation time, and reduce the incidence of surgical complications. Owing to the ease of magnetic navigation, the accuracy of the magnetic navigation system is affected by various equipment in the operating room. Therefore, its large-scale application is lacking because the navigation accuracy requirement can be extremely high during craniofacial surgery. Therefore, the accuracy of magnetic navigation systems is crucial. Various surgical instruments have been evaluated to effectively reduce the interference of magnetic navigation systems with surgical instruments. In the surgical environment, the use of surgical instruments during mandibular surgery was simulated by selecting several conventional surgical instruments to record errors in the magnetic navigation system. The fluctuation values of the magnetic navigation errors were subsequently estimated and changes in its accuracy measured. MATLAB was used to calculate and analyze the fluctuations of the magnetic navigation errors. As results, the high-frequency electrosurgical system caused the greatest interference with the magnetic navigation system during surgery while powered on, with a maximum fluctuation error value of 1.8120 mm, and the maximum fluctuation error values of the stitch scissors, teeth forceps, and a needle holder were 1.3662, 1.3781, and 0.3912 mm, respectively. The closer the instrument is to the magnetic field generator or navigation target, the greater its impact. In conclusion, stitch scissors, teeth forceps, a needle holder, and the high-frequency electrosurgical system all affect magnetic navigation system accuracy. Therefore, it is necessary to avoid magnetic navigation system use and surgical instrument disturbances during surgery or select surgical instruments that do not interfere with the system. Surgical instruments must be evaluated for electromagnetic interference before they can be used in surgery with a magnetic navigation system.

Design and Fabrication of a Fiber Bragg Grating Shape Sensor for Shape Reconstruction of a Continuum Manipulator

Continuum dexterous manipulators (CDMs) are suitable for performing tasks in a constrained environment due to their high dexterity and maneuverability. Despite the inherent advantages of CDMs in minimally invasive surgery, real-time control of CDMs' shape during nonconstant curvature bending is still challenging. This study presents a novel approach for the design and fabrication of a large deflection fiber Bragg grating (FBG) shape sensor embedded within the lumens inside the walls of a CDM with a large instrument channel. The shape sensor consisted of two fibers, each with three FBG nodes. A shape-sensing model was introduced to reconstruct the centerline of the CDM based on FBG wavelengths. Different experiments, including shape sensor tests and CDM shape reconstruction tests, were conducted to assess the overall accuracy of the shape-sensing. The FBG sensor evaluation results revealed the linear curvature-wavelength relationship with the large curvature detection of 0.045 mm and a high wavelength shift of up to 5.50 nm at a 90° bending angle in both the bending directions. The CDM's shape reconstruction experiments in a free environment demonstrated the shape-tracking accuracy of 0.216 ± 0.126 mm for positive/negative deflections. Also, the CDM shape reconstruction error for three cases of bending with obstacles was observed to be 0.436 ± 0.370 mm for the proximal case, 0.485 ± 0.418 mm for the middle case, and 0.312 ± 0.261 mm for the distal case. This study indicates the adequate performance of the FBG sensor and the effectiveness of the model for tracking the shape of the large-deflection CDM with nonconstant-curvature bending for minimally invasive orthopedic applications.

Feasibility of a Robot-Assisted Surgical Navigation System for Mandibular Distraction Osteogenesis in Hemifacial Microsomia: A Model Experiment

This study aimed to investigate the feasibility and accuracy of osteotomy and distractor placement using a robotic navigation system in a model surgical experiment of mandibular distraction osteogenesis for hemifacial microsomia. Imaging data from 5 patients with Pruzansky-Kaban type II (IIa: 4; IIb: 1) mandibular deformities were used to print 3D models for simulated mandibular distraction osteogenesis. In the experimental group, a robot-assisted surgical navigation system was used to perform the surgery under robotic guidance following registration, according to the preoperative design. Conventional surgery was performed in the control group, in which the operation was based on intraoperative estimations of the preoperative design by experienced surgeons. The accuracies of the osteotomy and distractor placement were assessed based on distance and angular error. Osteotomy accuracy was higher in the experimental group than in the control group, and the distance error ( t =9.311, P <0.001) and angular error ( t =5.385, P =0.001) were significantly reduced. The accuracy of distractor placement was also significantly higher in the experimental group, while the distance error ( t =3.048, P =0.016) and angular error ( t =3.524, P =0.024) were significantly reduced. The present results highlight the feasibility of robot-assisted distraction osteogenesis combined with electromagnetic navigation for improved surgical precision in clinical settings.

Leveraging spatial uncertainty for online error compensation in EMT

Purpose

Electromagnetic tracking (EMT) can potentially complement fluoroscopic navigation, reducing radiation exposure in a hybrid setting. Due to the susceptibility to external distortions, systematic error in EMT needs to be compensated algorithmically. Compensation algorithms for EMT in guidewire procedures are only practical in an online setting.

Methods

We collect positional data and train a symmetric artificial neural network (ANN) architecture for compensating navigation error. The results are evaluated in both online and offline scenarios and are compared to polynomial fits. We assess spatial uncertainty of the compensation proposed by the ANN. Simulations based on real data show how this uncertainty measure can be utilized to improve accuracy and limit radiation exposure in hybrid navigation.

Results

ANNs compensate unseen distortions by more than 70%, outperforming polynomial regression. Working on known distortions, ANNs outperform polynomials as well. We empirically demonstrate a linear relationship between tracking accuracy and model uncertainty. The effectiveness of hybrid tracking is shown in a simulation experiment.

Conclusion

ANNs are suitable for EMT error compensation and can generalize across unseen distortions. Model uncertainty needs to be assessed when spatial error compensation algorithms are developed, so that training data collection can be optimized. Finally, we find that error compensation in EMT reduces the need for X-ray images in hybrid navigation.

Electromagnetic navigated condylar positioning after high oblique sagittal split osteotomy of the mandible: a guided method to attain pristine temporomandibular joint conditions

OBJECTIVES

Reproduction of the exact preoperative proximal-mandible position after osteotomy in orthognathic surgery is difficult to achieve. This clinical pilot study evaluated an electromagnetic (EM) navigation system for condylar positioning after high-oblique sagittal split osteotomy (HSSO).

STUDY DESIGN

After HSSO as part of 2-jaw surgery, the position of 10 condyles was intraoperatively guided by an EM navigation system. As controls, 10 proximal segments were positioned by standard manual replacement. Accuracy was measured by pre- and postoperative cone beam computed tomography imaging.

RESULTS

Overall, EM condyle repositioning was equally accurate compared with manual repositioning (P > .05). Subdivided into 3 axes, significant differences could be identified (P < .05). Nevertheless, no significantly and clinically relevant dislocations of the proximal segment of either the EM or the manual repositioning method could be shown (P > .05).

CONCLUSIONS

This pilot study introduces a guided method for proximal segment positioning after HSSO by applying the intraoperative EM system. The data demonstrate the high accuracy of EM navigation, although manual replacement of the condyles could not be surpassed. However, EM navigation can avoid clinically hidden, severe malpositioning of the condyles.

Improved electromagnetic tracking for catheter path reconstruction with application in high-dose-rate brachytherapy

PURPOSE

Electromagnetic (EM) catheter tracking has recently been introduced in order to enable prompt and uncomplicated reconstruction of catheter paths in various clinical interventions. However, EM tracking is prone to measurement errors which can compromise the outcome of the procedure. Minimizing catheter tracking errors is therefore paramount to improve the path reconstruction accuracy.

METHODS

An extended Kalman filter (EKF) was employed to combine the nonlinear kinematic model of an EM sensor inside the catheter, with both its position and orientation measurements. The formulation of the kinematic model was based on the nonholonomic motion constraints of the EM sensor inside the catheter. Experimental verification was carried out in a clinical HDR suite. Ten catheters were inserted with mean curvatures varying from 0 to [Formula: see text] in a phantom. A miniaturized Ascension (Burlington, Vermont, USA) trakSTAR EM sensor (model 55) was threaded within each catheter at various speeds ranging from 7.4 to [Formula: see text]. The nonholonomic EKF was applied on the tracking data in order to statistically improve the EM tracking accuracy. A sample reconstruction error was defined at each point as the Euclidean distance between the estimated EM measurement and its corresponding ground truth. A path reconstruction accuracy was defined as the root mean square of the sample reconstruction errors, while the path reconstruction precision was defined as the standard deviation of these sample reconstruction errors. The impacts of sensor velocity and path curvature on the nonholonomic EKF method were determined. Finally, the nonholonomic EKF catheter path reconstructions were compared with the reconstructions provided by the manufacturer's filters under default settings, namely the AC wide notch and the DC adaptive filter.

RESULTS

With a path reconstruction accuracy of 1.9 mm, the nonholonomic EKF surpassed the performance of the manufacturer's filters (2.4 mm) by 21% and the raw EM measurements (3.5 mm) by 46%. Similarly, with a path reconstruction precision of 0.8 mm, the nonholonomic EKF surpassed the performance of the manufacturer's filters (1.0 mm) by 20% and the raw EM measurements (1.7 mm) by 53%. Path reconstruction accuracies did not follow an apparent trend when varying the path curvature and sensor velocity; instead, reconstruction accuracies were predominantly impacted by the position of the EM field transmitter ([Formula: see text]).

CONCLUSION

The advanced nonholonomic EKF is effective in reducing EM measurement errors when reconstructing catheter paths, is robust to path curvature and sensor speed, and runs in real time. Our approach is promising for a plurality of clinical procedures requiring catheter reconstructions, such as cardiovascular interventions, pulmonary applications (Bender et al. in medical image computing and computer-assisted intervention-MICCAI 99. Springer, Berlin, pp 981-989, 1999), and brachytherapy.