Magnetic navigation for thoracic aortic stent-graft deployment using ultrasound image guidance

Robot-assisted mandibular angle osteotomy using electromagnetic navigation

BACKGROUND

To explore the potential of electromagnetic (EM) navigation technology in the field of robot-assisted surgery, we set up a maxillofacial surgical robotic system (MSRS) guided by an EM navigation tool. Mandibular angle osteotomy was used to analyze the feasibility in confined surgical areas.

METHODS

Model and animal experiments were implemented to validate the system precision. Before the experiment, a customized dental splint was made and then fixed with a standard navigation part. An accurate 3D surgical plan was designed based on the preoperative CT scan. During the experiment, the splint was rigidly mounted on teeth for navigation registration, so the robot could position a specially designed template to guide the accurate osteotomy according to the preoperative plan. For the model experiment, a Coordinate Measuring Machine was used to measure the template's position and angle. For the animal experiment, surgeons completed the surgery by moving a saw along the template, while a postoperative CT scan was carried out to calculate the precision.

RESULTS

All procedures were successfully completed, with no complications in any of the experimental animals. In the model experiment, the accuracy of the navigation position and angle was 0.44±0.19 mm and 3.5°±2.1°, respectively. In the animal experiment, the lateral osteotomy line error was 0.83±0.62 mm, the interior error was 1.06±1.03 mm, and the angle between the actual cutting plane and preoperative planning plane was 5.9°±4.7°.

CONCLUSIONS

Robot-assisted surgery with EM navigation resulted feasible in the real operating environment. Moreover, this system's precision could meet clinical needs, while the proposed procedure was safe and easy on animals. Consequently, this approach has the potential to be applied to clinical craniomaxillofacial practice in the near future.

Tissue Structure Updating for In Situ Augmented Reality Navigation Using Calibrated Ultrasound and Two-Level Surface Warping

OBJECTIVE

In minimally invasive surgery (MIS), in situ augmented reality (AR) navigation systems are usually implemented using a glasses-free 3D display to represent the preoperative tissue structure, and can provide intuitive see-through guidance information. However, due to changes in intraoperative tissue, the preoperative tissue structure is not able to exactly correspond to reality, which influences the precision of in situ AR navigation. To solve this problem, we propose a method to update the tissue structure for in situ AR navigation in such way to reflect changes in intraoperative tissue.

METHODS

The proposed method to update the tissue structure is based on the calibrated ultrasound and two-level surface warping technologies. Firstly, the particle filter-based calibration is implemented to perform ultrasound calibration and obtain intraoperative position of anatomical points. Secondly, intraoperative positions of anatomical points are inputted in the two-level surface warping method to update the preoperative tissue structure. Finally, the glasses-free real 3-D display of the updated tissue structure is finished, and is superimposed onto a patient by a translucent mirror for in situ AR navigation.

RESULTS

we validated the proposed method by simulating liver tissue intervention, and achieved the tissue updating accuracy of 92.86%. Furthermore, the targeting error of AR navigation based on the proposed method was also evaluated through minimally invasive liver surgery, and the acquired mean targeting error was 1.92 mm.

CONCLUSION

The results demonstrate that the proposed AR navigation method is effective.

SIGNIFICANCE

The proposed method can facilitate MIS, as it provides accurate 3D navigation.

Pilot study on vascular intervention training based on blood flow effected guidewire simulation

A decent guidewire behavior simulation is vital to the virtual vascular intervention training. The influence of blood flow has rarely been taken into consideration in former works of guidewire simulation. This paper addresses the problem by integrating blood flow analysis and proposes a novel guidewire simulation model.The blood flow distribution inside arterial vasculature is computed by separating the vascular model into discrete cylindrical vessels and modeling the flow in each vessel with the Poiseuille Law. The blood flow computation is then integrated into a Kirchhoff rods model. The simulation could be run in real time with hardware acceleration at least 30 fps. To validate the result, an experiment environment with a 3D printed vascular phantom and an electromagnetic tracking(EMT) system was set up with clinical-used guidewire sensors applied in phantom to trace its motion as the standard for comparison. Experiment results reveal that the shown blood flow effected model presents better physical credibility with a lower and more stable root-mean-square(RMS) at 2.14mm ± 1.24mm, better than the Kirchhoff model of 4.81mm±3.80mm.

Registration and fusion quantification of augmented reality based nasal endoscopic surgery

This paper quantifies the registration and fusion display errors of augmented reality-based nasal endoscopic surgery (ARNES). We comparatively investigated the spatial calibration process for front-end endoscopy and redefined the accuracy level of a calibrated endoscope by using a calibration tool with improved structural reliability. We also studied how registration accuracy was combined with the number and distribution of the deployed fiducial points (FPs) for positioning and the measured registration time. A physically integrated ARNES prototype was customarily configured for performance evaluation in skull base tumor resection surgery with an innovative approach of dynamic endoscopic vision expansion. As advised by surgical experts in otolaryngology, we proposed a hierarchical rendering scheme to properly adapt the fused images with the required visual sensation. By constraining the rendered sight in a known depth and radius, the visual focus of the surgeon can be induced only on the anticipated critical anatomies and vessel structures to avoid misguidance. Furthermore, error analysis was conducted to examine the feasibility of hybrid optical tracking based on point cloud, which was proposed in our previous work as an in-surgery registration solution. Measured results indicated that the error of target registration for ARNES can be reduced to 0.77 ± 0.07 mm. For initial registration, our results suggest that a trade-off for a new minimal time of registration can be reached when the distribution of five FPs is considered. For in-surgery registration, our findings reveal that the intrinsic registration error is a major cause of performance loss. Rigid model and cadaver experiments confirmed that the scenic integration and display fluency of ARNES are smooth, as demonstrated by three clinical trials that surpassed practicality.

Blood flow-induced physically based guidewire simulation for vascular intervention training

PURPOSE

A realistic guidewire behavior simulation is a vital component of a virtual vascular intervention system. Such systems are a safe, low-cost means of establishing a training environment to help inexperienced surgeons develop their intervention skills. Previous attempts to simulate the complex movement of a guidewire inside blood vessels have rarely considered the influence of blood flow. In this paper, we address this problem by integrating blood flow analysis and propose a novel guidewire simulation model.

METHODS

The blood flow distribution inside the arterial vasculature was computed by separating the vascular model into discrete cylindrical vessels and modeling the flow in each vessel according to Poiseuille Law. The blood flow computation was then integrated into a robust Kirchhoff elastic model. With hardware acceleration, the guidewire simulation can be run in real time. To evaluate the simulation, an experimental environment with a 3D-printed vascular phantom and an electromagnetic tracking system was set up, with clinically used guidewire sensors applied to trace its motion as the standard for comparison.

RESULTS

The virtual guidewire motion trace was assessed by comparing it to the comparison standard. The root-mean-square (RMS) value of the newly proposed guidewire model was 2.14 mm ± 1.24 mm, lower than the value of 4.81 mm ± 3.80 mm for the previous Kirchhoff model, while maintaining a computation speed of at least 30 fps.

CONCLUSION

The experimental results revealed that the blood flow-induced model exhibits better performance and physical credibility with a lower and more stable RMS error than the previous Kirchhoff model.

Augmented Reality System for Ultrasound Guidance of Transcatheter Aortic Valve Implantation

OBJECTIVE

Transcatheter aortic valve implantation (TAVI) relies on fluoroscopy and nephrotoxic contrast medium for valve deployment. We propose an alternative guidance system using augmented reality (AR) and transesophageal echocardiography (TEE) to guide TAVI deployment. The goals of this study were to determine how consistently the aortic valve annulus is defined from TEE using different aortic valve landmarks and to compare AR guidance with fluoroscopic guidance of TAVI deployment in an aortic root model.

METHODS

Magnetic tracking sensors were integrated into the TAVI catheter and TEE probe, allowing these tools to be displayed in an AR environment. Variability in identifying aortic valve commissures and cuspal nadirs was assessed using TEE aortic root images. To compare AR guidance of TAVI deployment with fluoroscopic guidance, a TAVI stent was deployed 10 times in the aortic root model using each of the two guidance systems.

RESULTS

Commissures and nadirs were both investigated as features for defining the valve annulus in the AR guidance system. The commissures were identified more consistently than the nadirs, with intraobserver variability of 2.2 and 3.8 mm, respectively, and interobserver variability of 3.3 and 4.7 mm, respectively. The precision of TAVI deployment using fluoroscopic guidance was 3.4 mm, whereas the precision of AR guidance was 2.9 mm, and its overall accuracy was 3.4 mm. This indicates that both have similar performance.

CONCLUSIONS

Aortic valve commissures can be identified more reliably than cuspal nadirs from TEE. The AR guidance system achieved similar deployment accuracy to that of fluoroscopy while eliminating the use and consequences of nephrotoxic contrast and radiation.

A mitral annulus tracking approach for navigation of off-pump beating heart mitral valve repair

PURPOSE

To develop and validate a real-time mitral valve annulus (MVA) tracking approach based on biplane transesophageal echocardiogram (TEE) data and magnetic tracking systems (MTS) to be used in minimally invasive off-pump beating heart mitral valve repair (MVR).

METHODS

The authors' guidance system consists of three major components: TEE, magnetic tracking system, and an image guidance software platform. TEE provides real-time intraoperative images to show the cardiac motion and intracardiac surgical tools. The magnetic tracking system tracks the TEE probe and the surgical tools. The software platform integrates the TEE image planes and the virtual model of the tools and the MVA model on the screen. The authors' MVA tracking approach, which aims to update the MVA model in near real-time, comprises of three steps: image based gating, predictive reinitialization, and registration based MVA tracking. The image based gating step uses a small patch centered at each MVA point in the TEE images to identify images at optimal cardiac phases for updating the position of the MVA. The predictive reinitialization step uses the position and orientation of the TEE probe provided by the magnetic tracking system to predict the position of the MVA points in the TEE images and uses them for the initialization of the registration component. The registration based MVA tracking step aims to locate the MVA points in the images selected by the image based gating component by performing image based registration.

RESULTS

The validation of the MVA tracking approach was performed in a phantom study and a retrospective study on porcine data. In the phantom study, controlled translations were applied to the phantom and the tracked MVA was compared to its "true" position estimated based on a magnetic sensor attached to the phantom. The MVA tracking accuracy was 1.29 ± 0.58 mm when the translation distance is about 1 cm, and increased to 2.85 ± 1.19 mm when the translation distance is about 3 cm. In the study on porcine data, the authors compared the tracked MVA to a manually segmented MVA. The overall accuracy is 2.37 ± 1.67 mm for single plane images and 2.35 ± 1.55 mm for biplane images. The interoperator variation in manual segmentation was 2.32 ± 1.24 mm for single plane images and 1.73 ± 1.18 mm for biplane images. The computational efficiency of the algorithm on a desktop computer with an Intel(®) Xeon(®) CPU @3.47 GHz and an NVIDIA GeForce 690 graphic card is such that the time required for registering four MVA points was about 60 ms.

CONCLUSIONS

The authors developed a rapid MVA tracking algorithm for use in the guidance of off-pump beating heart transapical mitral valve repair. This approach uses 2D biplane TEE images and was tested on a dynamic heart phantom and interventional porcine image data. Results regarding the accuracy and efficiency of the authors' MVA tracking algorithm are promising, and fulfill the requirements for surgical navigation.

A robust and real-time vascular intervention simulation based on Kirchhoff elastic rod

A virtual reality (VR) based vascular intervention simulation system is introduced in this paper, which helps trainees develop surgical skills and experience complications in safety remote from patients. The system simulates interventional radiology procedures, in which flexible tipped guidewires are employed to advance diagnostic or therapeutic catheters into vascular anatomy of a patient. A real-time physically-based modeling approach ground on Kirchhoff elastic rod is proposed to simulate complicated behaviors of guidewires and catheters. The slender body of guidewire and catheter is modeled using more efficient special case of naturally straight, isotropic Kirchhoff rods, and the shorter flexible tip composed of straight or angled design is modeled using more complex generalized Kirchhoff rods. The motion equations for guidewire and catheter were derived with continuous elastic energy, followed by a discretization using a linear implicit scheme that guarantees stability and robustness. In addition, we used a fast-projection method to enforce the inextensibility of guidewire and catheter. An adaptive sampling algorithm was also implemented to improve the simulation efficiency without decrease of accuracy. Experimental results revealed that our system is both robust and efficient in a real-time performance.

Intra-operative 2-D ultrasound and dynamic 3-D aortic model registration for magnetic navigation of transcatheter aortic valve implantation

We propose a navigation system for transcatheter aortic valve implantation that employs a magnetic tracking system (MTS) along with a dynamic aortic model and intra-operative ultrasound (US) images. This work is motivated by the desire of our cardiology and cardiac surgical colleagues to minimize or eliminate the use of radiation in the interventional suite or operating room. The dynamic 3-D aortic model is constructed from a preoperative 4-D computed tomography dataset that is animated in synchrony with the real time electrocardiograph input of patient, and then preoperative planning is performed to determine the target position of the aortic valve prosthesis. The contours of the aortic root are extracted automatically from short axis US images in real-time for registering the 2-D intra-operative US image to the preoperative dynamic aortic model. The augmented MTS guides the interventionist during positioning and deployment of the aortic valve prosthesis to the target. The results of the aortic root segmentation algorithm demonstrate an error of 0.92±0.85 mm with a computational time of 36.13±6.26 ms. The navigation approach was validated in porcine studies, yielding fiducial localization errors, target registration errors, deployment distance, and tilting errors of 3.02±0.39 mm, 3.31±1.55 mm, 3.23±0.94 mm, and 5.85±3.06(°) , respectively.

A pilot study on magnetic navigation for transcatheter aortic valve implantation using dynamic aortic model and US image guidance

PURPOSE

In this paper, we propose a pilot study for transcatheter aortic valve implantation guided by an augmented magnetic tracking system (MTS) with a dynamic aortic model and intra-operative ultrasound (US) images.

METHODS

The dynamic 3D aortic model is constructed from the preoperative 4D computed tomography, which is animated according to the real-time electrocardiograph (ECG) input of patient. Before the procedure, the US probe calibration is performed to map the US image coordinate to the tracked device coordinate. A temporal alignment is performed to synchronize the ECG signals, the intra-operative US image and the tracking information. Thereafter, with the assistance of synchronized ECG signals, the spatial registration is performed by using a feature-based registration. Then the augmented MTS guides the surgeon to confidently position and deploy the transcatheter aortic valve prosthesis to the target.

RESULTS

The approach was validated by US probe calibration evaluation and animal study. The US calibration accuracy achieved [Formula: see text], whereas in the animal study on three porcine subjects, fiducial, target, deployment distance and tilting errors reached [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text], respectively.

CONCLUSION

Our pilot study has revealed that the proposed approach is feasible and accurate for delivery and deployment of transcatheter aortic valve prosthesis.