Projection-based visual guidance for robot-aided RF needle insertion

Purpose

The use of projector-based augmented reality (AR) in surgery may enable surgeons to directly view anatomical models and surgical data from the patient’s surface (skin). It has the advantages of a consistent viewing focus on the patient, an extended field of view and augmented interaction. This paper presents an AR guidance mechanism with a projector-camera system to provide the surgeon with direct visual feedback for supervision of robotic needle insertion in radiofrequency (RF) ablation treatment.

Methods

The registration of target organ models to specific positions on the patient body is performed using a surface-matching algorithm and point-based registration. An algorithm based on the extended Kalman filter and spatial transformation is used to intraoperatively compute the virtual needle’s depth in the patient’s body for AR display.

Results

Experiments of this AR system on a mannequin were conducted to evaluate AR visualization and accuracy of virtual RF needle insertion. The average accuracy of 1.86 mm for virtual needle insertion met the clinical requirement of 2 mm or better. The feasibility of augmented interaction with a surgical robot using the proposed open AR interface with active visual feedback was demonstrated.

Conclusions

The experimental results demonstrate that this guidance system is effective in assisting a surgeon to perform a robot-assisted radiofrequency ablation procedure. The novelty of the work lies in establishing a navigational procedure for percutaneous surgical augmented intervention integrating a projection-based AR guidance and robotic implementation for surgical needle insertion.     

Preclinical evaluation of an MRI-compatible pneumatic robot for angulated needle placement in transperineal prostate interventions

Purpose

To evaluate the targeting accuracy of a small profile MRI-compatible pneumatic robot for needle placement that can angulate a needle insertion path into a large accessible target volume.

Methods

We extended our MRI-compatible pneumatic robot for needle placement to utilize its four degrees-of-freedom (4-DOF) mechanism with two parallel triangular structures and support transperineal prostate biopsies in a closed-bore magnetic resonance imaging (MRI) scanner. The robot is designed to guide a needle toward a lesion so that a radiologist can manually insert it in the bore. The robot is integrated with navigation software that allows an operator to plan angulated needle insertion by selecting a target and an entry point. The targeting error was evaluated while the angle between the needle insertion path and the static magnetic field was between ?5.7° and 5.7° horizontally and between ?5.7° and 4.3° vertically in the MRI scanner after sterilizing and draping the device.

Results

The robot positioned the needle for angulated insertion as specified on the navigation software with overall targeting error of 0.8 ± 0.5mm along the horizontal axis and 0.8 ± 0.8mm along the vertical axis. The two-dimensional root-mean-square targeting error on the axial slices as containing the targets was 1.4mm.

Conclusions

Our preclinical evaluation demonstrated that the MRI-compatible pneumatic robot for needle placement with the capability to angulate the needle insertion path provides targeting accuracy feasible for clinical MRI-guided prostate interventions. The clinical feasibility has to be established in a clinical study.     

The impact of fMRI on multimodal navigation in surgery of cerebral lesions: four years clinical experience

Object

Neuronavigation with display of intraoperative structures, instrument locations, orientation and relationships to nearby structures can increase anatomic precision while enhancing the surgeon’s confidence and his/her perception of safety. Combination of neuronavigation with functional imaging provides multimodal guidance for surgery of cerebral lesions. We evaluated the impact of functional MRI (fMRI) on surgical decision making and outcome.

Materials and methods

A neuronavigational device (StealthStation (tm), Medtronic Inc.) was used as platform to merge fMRI data with anatomic images, and to implement intraoperative multimodal guidance. In a 52-month period, where 977 surgical procedures were performed with the aid of neuronavigation, 88 patients underwent image-guided procedures using multimodal guidance. Patient, surgical and outcome data of this series was prospectively collected.

Results

Evaluation of 88 procedures on cerebral lesions in complex regions where fMRI data were integrated using the navigation system demonstrated that the additional information was presented in a user-friendly way. Computer assisted fMRI integration was found to be especially helpful in planning the best approach, in assessing alternative approaches, and in defining the extent of the surgical exposure. Furthermore, the surgeons found it more effective to interpret fMRI information when shown in a navigation system as compared to the traditional display on a light board or monitor.

Conclusion

Multimodal navigation enhanced by fMRI was judged useful for optimization of surgery of cerebral lesions, especially in and around eloquent regions by experienced neurosurgeons.     

E-Health and telemedicine

Purpose

To compare the accuracy of a navigation system for oral implantology using either a head-mounted display (HMD) or a monitor as a device for visualization.

Methods

Drilling experiments in plastic mandibles were performed by seven investigators supported by a navigation system using an HMD. A set of drilling experiments was carried out using a traditional monitor setup as standard of reference. Prior to the experiments, CT scans of the mandibles were performed. Positions of the boreholes were determined with the planning software Mimics $^{\circledR }$ . In order to find the correct positions of the boreholes, individuals had to match two pairs of crosshairs. By an infrared tracking device, the navigation system was able to spot the artificial jaw and the angular piece of the drill allowing for the navigation. After the experiments, a second CT scan was acquired: (i) to identify the beginning and the end of the boreholes, (ii) to compare the positions of the planned implant and the boreholes and (iii) to calculate the deviations.

Results

Overall deviation of the starting point of the borehole was $1.24 \pm 0.84\,\mathrm{mm}$ for the HMD and $1.12 \pm 0.68\,\mathrm{mm}$ for the monitor, $2.68 \pm 1.65\,\mathrm{mm}$ of the end point of the borehole for the HMD and $2.46 \pm 1.34\,\mathrm{mm}$ for the monitor. The mean deviation of the axis was $4.68^{\circ }\pm 3.7^{\circ }$ for the HMD and $4.53^{\circ }\pm 4.17^{\circ }$ for the monitor.

Conclusions

As overall accuracies do not differ significantly, the two methods seem to be equal. Personal skills seem to be crucial as the results show remarkable differences among the test persons. The results of our study demonstrate that the use of an HMD has no major drawbacks compared to the monitor setting. The striking advantage is that the surgeon is no longer obliged to turn his head away from the operation site during navigation, as all data relevant for the procedure are superimposed on the image of the real world in his field of view.     

Towards markerless navigation for percutaneous needle insertions

Purpose

Percutaneous needle insertions are increasingly used for diagnosis and treatment of abdominal lesions. The challenging part of computed tomography (CT)-guided punctures is the transfer of the insertion trajectory planned in the CT image to the patient. Conventionally, this often results in several needle repositionings and control CT scans. To address this issue, several navigation systems for percutaneous needle insertions have been presented; however, none of them has thus far become widely accepted in clinical routine. Their benefit for the patient could not exceed the additional higher costs and the increased complexity in terms of bulky tracking systems and specialized markers for registration and tracking.

Methods

We present the first markerless and trackerless navigation concept for real-time patient localization and instrument guidance. It has specifically been designed to be integrated smoothly into the clinical workflow and does not require markers or an external tracking system. The main idea is the utilization of a range imaging device that allows for contactless and radiation-free acquisition of both range and color information used for patient localization and instrument guidance.

Results

A first feasibility study in phantom and porcine models yielded a median targeting accuracy of 6.9 and 19.4 mm, respectively.

Conclusions

Although system performance remains to be improved for clinical use, expected advances in camera technology as well as consideration of respiratory motion and automation of the individual steps will make this approach an interesting alternative for guiding percutaneous needle insertions.

     

Percutaneous lung biopsy: comparison between an augmented reality CT navigation system and standard CT-guided technique

Purpose

Percutaneous lung biopsies (PLBs) performed for the evaluation of pulmonary masses require image guidance to avoid critical structures. A new CT navigation system (SIRIO, “Sistema robotizzato assistito per il puntamento intraoperatorio”) for PLBs was validated.

Methods

The local Institutional Review Board approved this retrospective study. Image-guided PLBs in 197 patients were performed with a CT navigation system (SIRIO). The procedures were reviewed based on the number of CT scans, patients’ radiation exposure and procedural time recorded. Comparison was performed with a group of 72 patients undergoing standard CT-guided PLBs. Sensitivity, specificity and overall diagnostic accuracy were assessed in both groups.

Results

SIRIO-guided PLBs showed a significant reduction in procedure time, number of required CT scans and the radiation dose administered to patients ( $p<0.001$ ). In terms of diagnostic accuracy, SIRIO proved to be more accurate for small-sized lesions ( $<$ 20 mm) than standard CT-guidance.

Conclusion

SIRIO proved to be a reliable and effective tool when performing CT-guided PLBs and was especially useful for sampling small ( $<$ 20 mm) lesions.     

Robotically assisted needle driver: evaluation of safety release, force profiles, and needle spin in a swine abdominal model

Objective

The objective of this study was to evaluate two features of a new rotating needle driver in a domestic swine model: (1) a quick release safety mechanism and (2) the impact of spinning the needle on the force profile.

Materials and methods

The experiments were conducted in a multi-modality interventional suite. An initial CT scan was obtained to determine the location of the target, in the liver or lung. The robotic arm was positioned directly over the marked skin entry point. Control parameters were set to rotation speeds of 0, 90, or 180 rpm. The breakaway force magnitude was also preset to a predetermined force. The physician used the joystick to drive the needle towards the target while the system recorded needle insertion depth and forces.

Results

Sixteen insertions were completed (14 in liver and 2 in lung) and 12 released the needle upon the desired set force. The mean response time of the quick release mechanism was 202 ± 39 ms. Needle rotation resulted in reduced insertion force.

Conclusion

The robot-assisted needle insertion system was shown to be functional in a multimodality imaging clinical environment on a swine model. The system has potential future applications in precision minimally invasive procedures including biopsy and radiofrequency ablation.     

Experimental evaluation of ultrasound-guided 3D needle steering in biological tissue

Purpose

In this paper, we present a system capable of automatically steering bevel tip flexible needles under ultrasound guidance toward stationary and moving targets in gelatin phantoms and biological tissue while avoiding stationary and moving obstacles. We use three-dimensional (3D) ultrasound to track the needle tip during the procedure.

Methods

Our system uses a fast sampling-based path planner to compute and periodically update a feasible path to the target that avoids obstacles. We then use a novel control algorithm to steer the needle along the path in a manner that reduces the number of needle rotations, thus reducing tissue damage. We present experimental results for needle insertion procedures for both stationary and moving targets and obstacles for up to 90 mm of needle insertion.

Results

We obtained a mean targeting error of \(0.32\pm 0.10\) and \(0.38\,\pm \,0.19\)  mm in gelatin-based phantom and biological tissue, respectively.

Conclusions

The achieved submillimeter accuracy suggests that our approach is sufficient to target the smallest lesions ( \(\phi \)  2 mm) that can be detected using state-of-the-art ultrasound imaging systems.     

Needle deflection estimation: prostate brachytherapy phantom experiments

Purpose

The performance of a fusion-based needle deflection estimation method was experimentally evaluated using prostate brachytherapy phantoms. The accuracy of the needle deflection estimation was determined. The robustness of the approach with variations in needle insertion speed and soft tissue biomechanical properties was investigated.

Methods

A needle deflection estimation method was developed to determine the amount of needle bending during insertion into deformable tissue by combining a kinematic deflection model with measurements taken from two electromagnetic trackers placed at the tip and the base of the needle. Experimental verification of this method for use in prostate brachytherapy needle insertion procedures was performed. A total of 21 beveled tip, 18 ga, 200 mm needles were manually inserted at various speeds through a template and toward different targets distributed within 3 soft tissue mimicking polyvinyl chloride prostate phantoms of varying stiffness. The tracked positions of both the needle tip and base were recorded, and Kalman filters were applied to fuse the sensory information. The estimation results were validated using ground truth obtained from fluoroscopy images.

Results

The manual insertion speed ranged from 8 to 34 mm/s, needle deflection ranged from 5 to 8 mm at an insertion depth of 76 mm, and the elastic modulus of the soft tissue ranged from 50 to 150 kPa. The accuracy and robustness of the estimation method were verified within these ranges. When compared to purely model-based estimation, we observed a reduction in needle tip position estimation error by \(52\pm 17\)  % (mean  \(\pm \)  SD) and the cumulative deflection error by \(57\pm 19\)  %.

Conclusions

Fusion of electromagnetic sensors demonstrated significant improvement in estimating needle deflection compared to model-based methods. The method has potential clinical applicability in the guidance of needle placement medical interventions, particularly prostate brachytherapy.     

3D ultrasound registration-based visual servoing for neurosurgical navigation

Purpose

We present a fully image-based visual servoing framework for neurosurgical navigation and needle guidance. The proposed servo-control scheme allows for compensation of target anatomy movements, maintaining high navigational accuracy over time, and automatic needle guide alignment for accurate manual insertions.

Method

Our system comprises a motorized 3D ultrasound (US) transducer mounted on a robotic arm and equipped with a needle guide. It continuously registers US sweeps in real time with a pre-interventional plan based on CT or MR images and annotations. While a visual control law maintains anatomy visibility and alignment of the needle guide, a force controller is employed for acoustic coupling and tissue pressure. We validate the servoing capabilities of our method on a geometric gel phantom and real human anatomy, and the needle targeting accuracy using CT images on a lumbar spine gel phantom under neurosurgery conditions.

Results

Despite the varying resolution of the acquired 3D sweeps, we achieved direction-independent positioning errors of \(0.35\pm 0.19\) mm and \(0.61^\circ \pm 0.45^\circ \), respectively. Our method is capable of compensating movements of around 25 mm/s and works reliably on human anatomy with errors of \(1.45\pm 0.78\) mm. In all four manual insertions by an expert surgeon, a needle could be successfully inserted into the facet joint, with an estimated targeting accuracy of \(1.33\pm 0.33\) mm, superior to the gold standard.

Conclusion

The experiments demonstrated the feasibility of robotic ultrasound-based navigation and needle guidance for neurosurgical applications such as lumbar spine injections.

     

Instrument-mounted displays for reducing cognitive load during surgical navigation

Purpose

Surgical navigation systems rely on a monitor placed in the operating room to relay information. Optimal monitor placement can be challenging in crowded rooms, and it is often not possible to place the monitor directly beside the situs. The operator must split attention between the navigation system and the situs. We present an approach for needle-based interventions to provide navigational feedback directly on the instrument and close to the situs by mounting a small display onto the needle.

Methods

By mounting a small and lightweight smartwatch display directly onto the instrument, we are able to provide navigational guidance close to the situs and directly in the operator’s field of view, thereby reducing the need to switch the focus of view between the situs and the navigation system. We devise a specific variant of the established crosshair metaphor suitable for the very limited screen space. We conduct an empirical user study comparing our approach to using a monitor and a combination of both.

Results

Results from the empirical user study show significant benefits for cognitive load, user preference, and general usability for the instrument-mounted display, while achieving the same level of performance in terms of time and accuracy compared to using a monitor.

Conclusion

We successfully demonstrate the feasibility of our approach and potential benefits. With ongoing technological advancements, instrument-mounted displays might complement standard monitor setups for surgical navigation in order to lower cognitive demands and for improved usability of such systems.

     

First clinical experience in applying XperGuide in embolization of jugular paragangliomas by direct intratumoral puncture

Purpose

The purpose of this study is to introduce a novel image-guided technique utilized in the embolization of jugular paraganglioma tumors, using preoperative diagnostic scans and planning together with perioperative X-ray fluoroscopy in a combined image.

Methods

A lesion center and a skin entry point on the patient are selected and connected with a straight line, which resembles the most ideal lesion access trajectory to be followed during the needle insertion. The skin entry point and the corresponding line location are selected such that it avoids the impenetrable bones and vital anatomical structures. Two viewing incidence angles are defined to guide the cranial needle insertion: the entry view tangent to the planned trajectory, and the progression view perpendicular to the path.

Results

The proposed method was applied in two patients with jugular paragangliomas in order to navigate needles to the lesion location and subsequently embolize the tumors. The perioperative registration took less than 8 s. Using this method, it was possible to guide the needle within 5 mm of the planned path.

Conclusion

The fluoroscopic needle navigation, overlaid on the corresponding soft tissue of the underlying anatomy, combined with a planned path, has been shown to be an accurate and efficient tool for needle guidance. The patient pose varied between the preoperative data and the fluoroscopy guided intervention, but this did not hinder the procedure.     

Soft tissue navigation for laparoscopic partial nephrectomy

Purpose

Minimally invasive surgery of kidney cancer has become a standard therapy method for renal carcinomas. Due to improvements in diagnosis, carcinomas tend to be detected with a smaller size, which often allows for a tissue sparing, laparoscopic partial nephrectomy (LPN). Successful LPN requires a safe resection line inside the kidney, which spares most of healthy tissue, while assuring the complete tumor removal. This paper proposes an approach for a real-time visualization aid during LPN.

Methods

A surgical soft tissue navigation system for laparoscopic was designed, implemented and tested in vitro. The system enhances the surgeon’s perception to provide decision guidance directly before initiation of kidney resection. Preoperative planning, intraoperative imaging, and real-time image processing are incorporated in a system that can enhance an endoscope’s image by superimposing relevant medical information like tumor infiltrated tissue and risk structures. This system has a flexible design to facilitate its integration into surgical work flows. The system evaluation was divided into two parts: (1) a virtual evaluation environment, which allows for simulation of all involved system parameters; (2) in vitro surgeries were performed using a laparoscopic training unit to evaluate the overall robustness and accuracy of the navigation system with real data.

Results

The system was implemented and tested in vitro with favorable results. Real-time video recording of its operation was done to demonstrate the ability to simultaneously visualize the renal collecting system, major blood vessels, and abnormal lesion.

Conclusion

Laparoscopic partial nephrectomy can benefit from surgical computer assistance with preoperative planning, intraoperative imaging, and real time guidance integrated in a single system. The presented surgical navigation approach is suitable for testing in an intraoperative environment with human patients undergoing LPN.     

Clinical testing of an alternate method of inserting bone-implanted fiducial markers

Background

   Deep brain stimulation (DBS) surgery utilizes image guidance via bone-implanted fiducial markers to achieve the desired submillimetric accuracy and to provide means for attaching microstereotactic frames. For maximal benefit, the markers must be inserted to the correct depth since over-insertion leads to stripping and under-insertion leads to instability.

Purpose

   The purpose of the study was to test clinically a depth-release drive system, the PosiSeat \(^{\mathrm{TM}}\) , versus manual insertion (pilot hole followed by manual screwing until tactile determined correct seating) for implanting fiducial markers into the bone.

Methods

   With institutional review board approval, the PosiSeat \(^{\mathrm{TM}}\) was used to implant markers in 15 DBS patients (57 fiducials). On post-insertion CT scans, the depth of the gap between the shoulder of the fiducial markers and the closest bone surface was measured. Similar depth measurements were performed on the CT scans of 64 DBS patients (250 fiducials), who underwent manual fiducial insertion.

Results

   Median of shoulder-to-bone distance for PosiSeat \(^{\mathrm{TM}}\) and manual insertion group were 0.03 and 1.06 mm, respectively. Fifty percent of the fiducials had the shoulder-to-bone distances within 0.01–0.09 mm range for the PosiSeat group and 0.04–1.45 mm range for the manual insertion group. These differences were statistically significant.

Conclusions

   A depth-release drive system achieves more consistent placement of bone-implanted fiducial markers than manual insertion.     

MR image overlay guidance: system evaluation for preclinical use

Purpose

A clinical augmented reality guidance system was developed for MRI-guided musculoskeletal interventions Magnetic Resonance Image Overlay System (MR-IOS). The purpose of this study was to assess MRI compatibility, system accuracy, technical efficacy, and operator performance of the MR-IOS.

Methods and materials

The impact of the MR-IOS on the MR environment was assessed by measuring image quality with signal-to-noise ratio (SNR) and signal intensity uniformity with the system in various on/off states. The system accuracy was assessed with an in-room preclinical experiment by performing 62 needle insertions on a spine phantom by an expert operator measuring entry, depth, angle, and target errors. Technical efficacy and operator performance were tested in laboratory by running an experiment with 40 novice operators (20 using freehand technique versus 20 MR-IOS-guided) with each operator inserting 10 needles into a geometric phantom. Technical efficacy was measured by comparing the success rates of needle insertions between the two operator groups. Operator performance was assessed by comparing total procedure times, total needle path distance, presumed tissue damage, and speed of individual insertions between the two operator groups.

Results

The MR-IOS maximally altered SNR by 2% with no perceptible change in image quality or uniformity. Accuracy assessment showed mean entry error of 1.6 ± 0.6 mm, depth error of 0.7 ± 0.5 mm, angle error of 1.5 ± 1.1°, and target error of 1.9 ± 0.8 mm. Technical efficacy showed a statistically significant difference (p = 0.031) between success rates (freehand 35.0% vs. MR-IOS 80.95%). Operator performance showed: mean total procedure time of 40.3 ± 4.4 (s) for freehand and 37.0 ± 3.7 (s) for MR-IOS (p = 0.584), needle path distances of 152.6 ± 15.0 mm for freehand and 116.9 ± 8.7 mm for MR-IOS (p = 0.074), presumed tissue damage of 7,417.2 ± 955.6 mm² for freehand and 6062.2 ± 678.5 mm² for MR-IOS (p = 0.347), and speed of insertion 5.9 ± 0.4 mm/s for freehand and 4.3 ± 0.3 mm/s for MR-IOS (p = 0.003).

Conclusion

The MR-IOS is compatible within a clinical MR imaging environment, accurate for needle placement, technically efficacious, and improves operator performance over the unassisted insertion technique. The MR-IOS was found to be suitable for further testing in a clinical setting.     

Intra-operative fiducial-based CT/fluoroscope image registration framework for image-guided robot-assisted joint fracture surgery

Purpose

Joint fractures must be accurately reduced minimising soft tissue damages to avoid negative surgical outcomes. To this regard, we have developed the RAFS surgical system, which allows the percutaneous reduction of intra-articular fractures and provides intra-operative real-time 3D image guidance to the surgeon. Earlier experiments showed the effectiveness of the RAFS system on phantoms, but also key issues which precluded its use in a clinical application. This work proposes a redesign of the RAFS’s navigation system overcoming the earlier version’s issues, aiming to move the RAFS system into a surgical environment.

Methods

The navigation system is improved through an image registration framework allowing the intra-operative registration between pre-operative CT images and intra-operative fluoroscopic images of a fractured bone using a custom-made fiducial marker. The objective of the registration is to estimate the relative pose between a bone fragment and an orthopaedic manipulation pin inserted into it intra-operatively. The actual pose of the bone fragment can be updated in real time using an optical tracker, enabling the image guidance.

Results

Experiments on phantom and cadavers demonstrated the accuracy and reliability of the registration framework, showing a reduction accuracy (sTRE) of about \(0.88~\pm 0.2\,\hbox {mm}\) (phantom) and \(1.15\pm 0.8\,\hbox {mm}\) (cadavers). Four distal femur fractures were successfully reduced in cadaveric specimens using the improved navigation system and the RAFS system following the new clinical workflow (reduction error \(1.2\pm 0.3\,\hbox {mm}\), \(2\pm 1{^{\circ }})\).

Conclusion

Experiments showed the feasibility of the image registration framework. It was successfully integrated into the navigation system, allowing the use of the RAFS system in a realistic surgical application.

     

A method for going from 2D laparoscope to 3D acquisition of surface landmarks by a novel computer vision approach

Purpose

This paper presents a method to use the Smart Trocars—our new surgical instrument recognition system—or any accurate localization system of surgical instrument for acquiring intraoperative surface data. Complex laparoscopic surgeries need a proper guidance system which requires registering the preoperative data from a CT or MRI scan to the intraoperative patient state. The Smart Trocar can be used to localize the instruments when it comes to contact with the soft tissue surface.

Method

Two successive views through the laparoscope at different angles with the 3D localization of a fixed tool at one single location using the Smart Trocars can point out visible features during the surgery and acquire their location in 3D to provide a depth map in the region of interest. In other words, our method transforms a standard laparoscope system into a system with three-dimensional registration capability.

Result

This method was initially tested on a simulation for uncertainty assessment and then on a rigid model for verification with an accuracy within 2 mm distance. In addition, an in vivo experiment on pig model was also conducted to investigate how the method might be used during a physiologic respiratory cycle.

Conclusion

This method can be applied in a large number of surgical applications as a guidance system on its own or in conjunction with other navigation techniques. Our work encourages further testing with realistic surgical applications in the near future.

     

Warning navigation system using real-time safe region monitoring for otologic surgery

Purpose We developed a surgical navigation system that warns the surgeon with auditory and visual feedback to protect the facial nerve with real-time monitoring of the safe region during drilling. Methods Warning navigation modules were developed and integrated into a free open source software platform. To obtain high registration accuracy, we used a high-precision laser-sintered template of the patient’s bone surface to register the computed tomography (CT) images. We calculated the closest distance between the drill tip and the surface of the facial nerve during drilling. When the drill tip entered the safe regions, the navigation system provided an auditory and visual signal which differed in each safe region. To evaluate the effectiveness of the system, we performed phantom experiments for maintaining a given safe margin from the facial nerve when drilling bone models, with and without the navigation system. The error of the safe margin was measured on postoperative CT images. In real surgery, we evaluated the feasibility of the system in comparison with conventional facial nerve monitoring. Results The navigation accuracy was submillimeter for the target registration error. In the phantom study, the task with navigation ( $0.7 \pm 0.25$ mm) was more successful with smaller error, than the task without navigation ( $1.37 \pm 0.39$ mm, $P<0.05$ ). The clinical feasibility of the system was confirmed in three real surgeries. Conclusions This system could assist surgeons in preserving the facial nerve and potentially contribute to enhanced patient safety in the surgery.     

Probe versus microscope: a comparison of different methods for image-to-patient registration

Purpose

Computer-aided navigation is widely used in ENT surgery. The position of a surgical instrument is shown in the CT/MR images of the patient and can thus be a good support for the surgeon. The accuracy is highly dependent on the registration done prior to surgery. A microscope and a probe can both be used for registration and navigation, depending on the surgical intervention. A navigation system typically only reports the fiducial registration error after paired-point registration. However, the target registration error (TRE)—a measurement for the accuracy in the surgical area—is much more relevant. The aim of this work was to compare the performance of a microscope relative to a conventional probe-based approach with different registration methods.

Methods

In this study, optical tracking was used to register a plastic skull to its preoperative CT images with paired-point registration. Anatomical landmarks and skin-affixed markers were used as fiducials and targets. With both microscope and probe, four different registration methods were evaluated based on their TREs at 10 targets. For half of the experiments, a surface registration and/or external fiducials were used additionally to paired-point registration to study their influence to accuracy.

Results

Overall, probe registration leads to a smaller TRE (\(1.69 \pm 0.74\,\hbox {mm}\)) than registration with a microscope (\(2.19 \pm 0.94\,\hbox {mm}\)). Additional surface registration does not result in better accuracy of navigation for microscope and probe. The lowest mean TRE for both pointers can be achieved with paired-point registration only and radiolucent markers.

Conclusion

Our experiments showed that a probe used for registration and navigation achieves lower TREs compared using a microscope. Neither additional surface registration nor additional fiducials on an external reference element are necessary for improved accuracy of navigated ENT surgery on a plastic skull.

     

Augmented reality surgical navigation with ultrasound-assisted registration for pedicle screw placement: a pilot study

Purpose

We present a novel augmented reality (AR) surgical navigation system based on ultrasound-assisted registration for pedicle screw placement. This system provides the clinically desired targeting accuracy and reduces radiation exposure.

Methods

Ultrasound (US) is used to perform registration between preoperative computed tomography (CT) images and patient, and the registration is performed by least-squares fitting of these two three-dimensional (3D) point sets of anatomical landmarks taken from US and CT images. An integral videography overlay device is calibrated to accurately display naked-eye 3D images for surgical navigation. We use a 3.0-mm Kirschner wire (K-wire) instead of a pedicle screw in this study, and the K-wire is calibrated to obtain its orientation and tip location. Based on the above registration and calibration, naked-eye 3D images of the planning path and the spine are superimposed onto patient in situ using our AR navigation system. Simultaneously, a 3D image of the K-wire is overlaid accurately on the real one to guide the insertion procedure. The targeting accuracy is evaluated postoperatively by performing a CT scan.

Results

An agar phantom experiment was performed. Eight K-wires were inserted successfully after US-assisted registration, and the mean targeting error and angle error were 3.35 mm and \(2.74{^{\circ }}\), respectively. Furthermore, an additional sheep cadaver experiment was performed. Four K-wires were inserted successfully. The mean targeting error was 3.79 mm and the mean angle error was \(4.51{^{\circ }}\), and US-assisted registration yielded better targeting results than skin markers-based registration (targeting errors: 2.41 vs. 5.18 mm, angle errors: \(3.13{^{\circ }}\) vs. \(5.89{^{\circ }})\).

Conclusion

Experimental outcomes demonstrate that the proposed navigation system has acceptable targeting accuracy. In particular, the proposed navigation method reduces repeated radiation exposure to the patient and surgeons. Therefore, it has promising prospects for clinical use.