Accuracy of instrument tip position using fiber optic shape sensing for navigated bronchoscopy.

The purpose of this study was to evaluate the accuracy of a method for estimating the tip position of a fiber optic shape-sensing (FOSS) integrated instrument being inserted through a bronchoscope. A modified guidewire with a multicore optical fiber was inserted into the working channel of a custom-made catheter with three electromagnetic (EM) sensors. The displacement between the instruments was manually set, and a point-based method was applied to match the position of the EM sensors to corresponding points on the shape. The accuracy was evaluated in a realistic bronchial model. An additional EM sensor was used to sample the tip of the guidewire, and the absolute deviation between this position and the estimated tip position was calculated. For small displacements between the tip of the FOSS integrated tool and the catheter, the median deviation in estimated tip position was ≤5 mm. For larger displacements, deviations exceeding 10 mm were observed. The deviations increased when the shape sensor had sharp curvatures relative to more straight shapes. The method works well for clinically relevant displacements of a biopsy tool from the bronchoscope tip, and when the path to the lesion has limited curvatures. However, improvements must be made to our configuration before pursuing further clinical testing.

A novel clip-on device for electromagnetic tracking in endobronchial ultrasound bronchoscopy.

INTRODUCTION: The established method for assessment of mediastinal and hilar lymph nodes is endobronchial ultrasound bronchoscopy (EBUS) with needle aspirations. Previously, we presented an electromagnetic navigation platform for this purpose. There were several issues with the permanent electromagnetic tracking (EMT) sensor attachment on the tip of the experimental EBUS bronchoscope. The purpose was to develop a device for on-site attachment of the EMT sensor. MATERIAL AND METHODS: A clip-on EMT sensor attachment device was 3D-printed in Ultem™ and attached to an EBUS bronchoscope. A specially designed ultrasound probe calibration adapter was developed for on-site and quick probe calibration. Navigation accuracy was studied using a wire cross water phantom and clinical feasibility was tested in a healthy volunteer. RESULTS: The device attached to the EBUS bronchoscope increased its diameter from 6.9 mm to 9.5 mm. Average preclinical navigation accuracy was 3.9 mm after adapter calibration. The maneuvering of the bronchoscope examining a healthy volunteer was adequate without harming the respiratory epithelium, and the device stayed firmly attached. CONCLUSION: Development, calibration and testing of a clip-on EMT sensor attachment device for EBUS bronchoscopy was successfully demonstrated. Acceptable accuracy results were obtained, and the device is ready to be tested in patient studies.

An open electromagnetic tracking framework applied to targeted liver tumour ablation.

PURPOSE: Electromagnetic tracking is a core platform technology in the navigation and visualisation of image-guided procedures. The technology provides high tracking accuracy in non-line-of-sight environments, allowing instrument navigation in locations where optical tracking is not feasible. EMT can be beneficial in applications such as percutaneous radiofrequency ablation for the treatment of hepatic lesions where the needle tip may be obscured due to difficult liver environments (e.g subcutaneous fat or ablation artefacts). Advances in the field of EMT include novel methods of improving tracking system accuracy, precision and error compensation capabilities, though such system-level improvements cannot be readily incorporated in current therapy applications due to the 'blackbox' nature of commercial tracking solving algorithms. METHODS: This paper defines a software framework to allow novel EMT designs, and improvements become part of the global design process for image-guided interventions. An exemplary framework is implemented in the Python programming language and demonstrated with the open-source Anser EMT system. The framework is applied in the preclinical setting though targeted liver ablation therapy on an animal model. RESULTS: The developed framework was tested with the Anser EMT electromagnetic tracking platform. Liver tumour targeting was performed using the tracking framework with the CustusX navigation platform using commercially available electromagnetically tracked needles. Ablation of two tumours was performed with a commercially available ablation system. Necropsy of the tumours indicated ablations within 5 mm of the tumours. CONCLUSIONS: An open-source framework for electromagnetic tracking was presented and effectively demonstrated in the preclinical setting. We believe that this framework provides a structure for future advancement in EMT system in and customised instrument design.

Using the CustusX toolkit to create an image guided bronchoscopy application: Fraxinus.

PURPOSE: The aim of this paper is to show how a specialized planning and guidance application called Fraxinus, can be built on top of the CustusX platform (www.custusx.org), which is an open source image-guided intervention software platform. Fraxinus has been customized to meet the clinical needs in navigated bronchoscopy. METHODS: The application requirements for Fraxinus were defined in close collaboration between research scientists, software developers and clinicians (pulmonologists), and built on top of CustusX. Its superbuild system downloads specific versions of the required libraries and builds them for the application in question, including the selected plugins. New functionality is easily added through the plugin framework. The build process enables the creation of specialized applications, adding additional documentation and custom configurations. The toolkit's libraries offer building blocks for image-guided applications. An iterative development process was applied, where the clinicians would test and provide feedback during the entire process. RESULTS: Fraxinus has been developed and is released as an open source planning and guidance application built on top of CustusX. It is highly specialized for bronchoscopy. The proposed workflow is adapted to the different steps in this procedure. The user interface of CustusX has been modified to enhance information, quality assurance and user friendliness with the intention to increase the overall yield for the patient. As the workflow of the procedure is relatively constant, some actions are predicted and automatically performed by the application, according to the requirements from the clinicians. CONCLUSIONS: The CustusX platform facilitates development of new and specialized applications. The toolkit supports the process and makes important extension and injection points available for customization.

Pulmonologist evaluation on new CT visualization for guidance to lung lesions during bronchoscopy.

OBJECTIVE: Endoluminal visualization in virtual and video bronchoscopy lacks information about the surrounding structures, and the traditional 2 D axial, coronal and sagittal CT views can be difficult to interpret. To address this challenge, we previously introduced a novel visualization technique, Anchored to Centerline Curved Surface, for navigated bronchoscopy. The current study compares the ACCuSurf to the standard ACS CT views as planning and guiding tools in a phantom study. MATERIAL AND METHODS: Bronchoscope operators navigated in physical phantom guided by virtual realistic image data constructed by fusion of CT dataset of phantom and anonymized patient CT data. We marked four different target positions within the virtual image data and gave 12 pulmonologists the task to navigate, with either ACCuSurf or ACS as guidance, to the corresponding targets in the physical phantom. RESULTS: Using ACCuSurf reduced the planning time and increased the grade of successful navigation significantly compared to ACS. CONCLUSION: The phantom setup with virtual patient image data proved realistic according to the pulmonologists. ACCuSurf proved superior to ACS regarding planning time and navigation success grading. Improvements on visualisation or display techniques may consequently improve both planning and navigated bronchoscopy and thus contribute to more precise lung diagnostics.

Peripheral tumour targeting using open-source virtual bronchoscopy with electromagnetic tracking: a multi-user pre-clinical study.

Objectives: The goal was to demonstrate the utility of open-source tracking and visualisation tools in the targeting of lung cancer.Material and methods: The study demonstrates the first deployment of the Anser electromagnetic (EM) tracking system with the CustusX image-guided interventional research platform to navigate using an endobronchial catheter to injected tumour targets. Live animal investigations validated the deployment and targeting of peripheral tumour models using an innovative tumour marking routine.Results: Novel tumour model deployment was successfully achieved at all eight target sites across two live animal investigations without pneumothorax. Virtual bronchoscopy with tracking successfully guided the tracked catheter to 2-12 mm from the target tumour site. Deployment of a novel marker was achieved at all eight sites providing a reliable measure of targeting accuracy. Targeting accuracy within 10 mm was achieved in 7/8 sites and in all cases, the virtual target distance at marker deployment was within the range subsequently measured with x-ray.Conclusions: Endobronchial targeting of peripheral airway targets is feasible using existing open-source technology. Notwithstanding the shortcomings of current commercial platforms, technological improvements in EM tracking and registration accuracy fostered by open-source technology may provide the impetus for widespread clinical uptake of electromagnetic navigation in bronchoscopy.

A new visualization method for navigated bronchoscopy.

OBJECTIVE: In flexible endoscopy techniques, such as bronchoscopy, there is often a challenge visualizing the path from start to target based on preoperative data and accessing these during the procedure. An example of this is visualizing only the inside of central airways in bronchoscopy. Virtual bronchoscopy (VB) does not meet the pulmonologist's need to detect, define and sample the frequent targets outside the bronchial wall. Our aim was to develop and study a new visualization technique for navigated bronchoscopy. MATERIAL AND METHODS: We extracted the shortest possible path from the top of the trachea to the target along the airway centerline and a corresponding auxiliary route in the opposite lung. A surface structure between the centerlines was developed and displayed. The new technique was tested on non-selective CT data from eight patients using artificial lung targets. RESULTS: The new display technique anchored to centerline curved surface (ACCuSurf) made it easy to detect and interpret anatomical features, targets and neighboring anatomy outside the airways, in all eight patients. CONCLUSIONS: ACCuSurf can simplify planning and performing navigated bronchoscopy, meets the challenge of improving orientation and register the direction of the moving endoscope, thus creating an optimal visualization for navigated bronchoscopy.

Psychomotor skills assessment by motion analysis in minimally invasive surgery on an animal organ.

BACKGROUND: A high level of psychomotor skills is required to perform minimally invasive surgery (MIS) safely. To be able to measure these skills is important in the assessment of surgeons, as it enables constructive feedback during training. The aim of this study was to test the validity of an objective and automatic assessment method using motion analysis during a laparoscopic procedure on an animal organ. MATERIAL AND METHODS: Experienced surgeons in laparoscopy (experts) and medical students (novices) performed a cholecystectomy on a porcine liver box model. The motions of the surgical tools were acquired and analyzed by 11 different motion-related metrics, i.e., a total of 19 metrics as eight of them were measured separately for each hand. We identified for which of the metrics the experts outperformed the novices. RESULTS: In total, two experts and 28 novices were included. The experts achieved significantly better results for 13 of the 19 instrument motion metrics. CONCLUSIONS: Expert performance is characterized by a low time to complete the cholecystectomy, high bimanual dexterity (instrument coordination), a limited amount of movement and low measurement of motion smoothness of the dissection instrument, and relatively high usage of the grasper to optimize tissue positioning for dissection.

Lack of transfer of skills after virtual reality simulator training with haptic feedback.

BACKGROUND AND OBJECTIVE: Virtual reality (VR) simulators enrich surgical training and offer training possibilities outside of the operating room (OR). In this study, we created a criterion-based training program on a VR simulator with haptic feedback and tested it by comparing the performances of a simulator group against a control group. MATERIAL AND METHODS: Medical students with no experience in laparoscopy were randomly assigned to a simulator group or a control group. In the simulator group, the candidates trained until they reached predefined criteria on the LapSim® VR simulator (Surgical Science AB, Göteborg, Sweden) with haptic feedback (XitactTM IHP, Mentice AB, Göteborg, Sweden). All candidates performed a cholecystectomy on a porcine organ model in a box trainer (the clinical setting). The performances were video rated by two surgeons blinded to subject training status. RESULTS: In total, 30 students performed the cholecystectomy and had their videos rated (N = 16 simulator group, N = 14 control group). The control group achieved better video rating scores than the simulator group (p < .05). CONCLUSIONS: The criterion-based training program did not transfer skills to the clinical setting. Poor mechanical performance of the simulated haptic feedback is believed to have resulted in a negative training effect.

Intraoperative localized constrained registration in navigated bronchoscopy.

PURPOSE: One of the major challenges in electromagnetic navigated bronchoscopy is the navigation accuracy. An initial rigid image-to-patient registration may not be optimal for the entire lung volume, as the lung tissue anatomy is likely to have shifted since the time of computer tomography (CT) acquisition. The accuracy of the initial rigid registration will also be affected throughout the procedure by breathing, coughing, patient movement and tissue displacements due to pressure from bronchoscopy tools. A method to minimize the negative impact from these factors by updating the registration locally during the procedure is needed and suggested in this paper. METHODS: The intraoperative local registration method updates the initial registration by optimization in an area of special interest, for example, close to a biopsy position. The local registration was developed through an adaptation of a previously published registration method used for the initial registration of CT to the patient anatomy. The method was tested in an experimental breathing phantom setup, where respiratory movements were induced by a robotic arm. Deformations were also applied to the phantom to see if the local registration could compensate for these. RESULTS: The local registration was successfully applied in all 15 repetitions, five in each of the three parts of the airway phantom. The mean registration accuracy was improved from 11.8-19.4 mm to 4.0-6.7 mm, varying to some degree in the different segments of the airway model. CONCLUSIONS: A local registration method, to update and improve the initial image-to patient registration during navigated bronchoscopy, was developed. The method was successfully tested in a breathing phantom setup. Further development is needed to make the method more automatic. It must also be verified in human studies.

A multimodal image guiding system for Navigated Ultrasound Bronchoscopy (EBUS): A human feasibility study.

BACKGROUND: Endobronchial ultrasound transbronchial needle aspiration (EBUS-TBNA) is the endoscopic method of choice for confirming lung cancer metastasis to mediastinal lymph nodes. Precision is crucial for correct staging and clinical decision-making. Navigation and multimodal imaging can potentially improve EBUS-TBNA efficiency. AIMS: To demonstrate the feasibility of a multimodal image guiding system using electromagnetic navigation for ultrasound bronchoschopy in humans. METHODS: Four patients referred for lung cancer diagnosis and staging with EBUS-TBNA were enrolled in the study. Target lymph nodes were predefined from the preoperative computed tomography (CT) images. A prototype convex probe ultrasound bronchoscope with an attached sensor for position tracking was used for EBUS-TBNA. Electromagnetic tracking of the ultrasound bronchoscope and ultrasound images allowed fusion of preoperative CT and intraoperative ultrasound in the navigation software. Navigated EBUS-TBNA was used to guide target lymph node localization and sampling. Navigation system accuracy was calculated, measured by the deviation between lymph node position in ultrasound and CT in three planes. Procedure time, diagnostic yield and adverse events were recorded. RESULTS: Preoperative CT and real-time ultrasound images were successfully fused and displayed in the navigation software during the procedures. Overall navigation accuracy (11 measurements) was 10.0 ± 3.8 mm, maximum 17.6 mm, minimum 4.5 mm. An adequate sample was obtained in 6/6 (100%) of targeted lymph nodes. No adverse events were registered. CONCLUSIONS: Electromagnetic navigated EBUS-TBNA was feasible, safe and easy in this human pilot study. The clinical usefulness was clearly demonstrated. Fusion of real-time ultrasound, preoperative CT and electromagnetic navigational bronchoscopy provided a controlled guiding to level of target, intraoperative overview and procedure documentation.

A novel platform for electromagnetic navigated ultrasound bronchoscopy (EBUS).

PURPOSE: Endobronchial ultrasound transbronchial needle aspiration (EBUS-TBNA) of mediastinal lymph nodes is essential for lung cancer staging and distinction between curative and palliative treatment. Precise sampling is crucial. Navigation and multimodal imaging may improve the efficiency of EBUS-TBNA. We demonstrate a novel EBUS-TBNA navigation system in a dedicated airway phantom. METHODS: Using a convex probe EBUS bronchoscope (CP-EBUS) with an integrated sensor for electromagnetic (EM) position tracking, we performed navigated CP-EBUS in a phantom. Preoperative computed tomography (CT) and real-time ultrasound (US) images were integrated into a navigation platform for EM navigated bronchoscopy. The coordinates of targets in CT and US volumes were registered in the navigation system, and the position deviation was calculated. RESULTS: The system visualized all tumor models and displayed their fused CT and US images in correct positions in the navigation system. Navigating the EBUS bronchoscope was fast and easy. Mean error observed between US and CT positions for 11 target lesions (37 measurements) was [Formula: see text] mm, maximum error was 5.9 mm. CONCLUSION: The feasibility of our novel navigated CP-EBUS system was successfully demonstrated. An EBUS navigation system is needed to meet future requirements of precise mediastinal lymph node mapping, and provides new opportunities for procedure documentation in EBUS-TBNA.

CustusX: an open-source research platform for image-guided therapy.

PURPOSE: CustusX is an image-guided therapy (IGT) research platform dedicated to intraoperative navigation and ultrasound imaging. In this paper, we present CustusX as a robust, accurate, and extensible platform with full access to data and algorithms and show examples of application in technological and clinical IGT research. METHODS: CustusX has been developed continuously for more than 15 years based on requirements from clinical and technological researchers within the framework of a well-defined software quality process. The platform was designed as a layered architecture with plugins based on the CTK/OSGi framework, a superbuild that manages dependencies and features supporting the IGT workflow. We describe the use of the system in several different clinical settings and characterize major aspects of the system such as accuracy, frame rate, and latency. RESULTS: The validation experiments show a navigation system accuracy of [Formula: see text]1.1 mm, a frame rate of 20 fps, and latency of 285 ms for a typical setup. The current platform is extensible, user-friendly and has a streamlined architecture and quality process. CustusX has successfully been used for IGT research in neurosurgery, laparoscopic surgery, vascular surgery, and bronchoscopy. CONCLUSIONS: CustusX is now a mature research platform for intraoperative navigation and ultrasound imaging and is ready for use by the IGT research community. CustusX is open-source and freely available at http://www.custusx.org.

Airway Segmentation and Centerline Extraction from Thoracic CT - Comparison of a New Method to State of the Art Commercialized Methods.

INTRODUCTION: Our motivation is increased bronchoscopic diagnostic yield and optimized preparation, for navigated bronchoscopy. In navigated bronchoscopy, virtual 3D airway visualization is often used to guide a bronchoscopic tool to peripheral lesions, synchronized with the real time video bronchoscopy. Visualization during navigated bronchoscopy, the segmentation time and methods, differs. Time consumption and logistics are two essential aspects that need to be optimized when integrating such technologies in the interventional room. We compared three different approaches to obtain airway centerlines and surface. METHOD: CT lung dataset of 17 patients were processed in Mimics (Materialize, Leuven, Belgium), which provides a Basic module and a Pulmonology module (beta version) (MPM), OsiriX (Pixmeo, Geneva, Switzerland) and our Tube Segmentation Framework (TSF) method. Both MPM and TSF were evaluated with reference segmentation. Automatic and manual settings allowed us to segment the airways and obtain 3D models as well as the centrelines in all datasets. We compared the different procedures by user interactions such as number of clicks needed to process the data and quantitative measures concerning the quality of the segmentation and centrelines such as total length of the branches, number of branches, number of generations, and volume of the 3D model. RESULTS: The TSF method was the most automatic, while the Mimics Pulmonology Module (MPM) and the Mimics Basic Module (MBM) resulted in the highest number of branches. MPM is the software which demands the least number of clicks to process the data. We found that the freely available OsiriX was less accurate compared to the other methods regarding segmentation results. However, the TSF method provided results fastest regarding number of clicks. The MPM was able to find the highest number of branches and generations. On the other hand, the TSF is fully automatic and it provides the user with both segmentation of the airways and the centerlines. Reference segmentation comparison averages and standard deviations for MPM and TSF correspond to literature. CONCLUSION: The TSF is able to segment the airways and extract the centerlines in one single step. The number of branches found is lower for the TSF method than in Mimics. OsiriX demands the highest number of clicks to process the data, the segmentation is often sparse and extracting the centerline requires the use of another software system. Two of the software systems performed satisfactory with respect to be used in preprocessing CT images for navigated bronchoscopy, i.e. the TSF method and the MPM. According to reference segmentation both TSF and MPM are comparable with other segmentation methods. The level of automaticity and the resulting high number of branches plus the fact that both centerline and the surface of the airways were extracted, are requirements we considered particularly important. The in house method has the advantage of being an integrated part of a navigation platform for bronchoscopy, whilst the other methods can be considered preprocessing tools to a navigation system.

Versatile robotic probe calibration for position tracking in ultrasound imaging.

Within the field of ultrasound-guided procedures, there are a number of methods for ultrasound probe calibration. While these methods are usually developed for a specific probe, they are in principle easily adapted to other probes. In practice, however, the adaptation often proves tedious and this is impractical in a research setting, where new probes are tested regularly. Therefore, we developed a method which can be applied to a large variety of probes without adaptation. The method used a robot arm to move a plastic sphere submerged in water through the ultrasound image plane, providing a slow and precise movement. The sphere was then segmented from the recorded ultrasound images using a MATLAB programme and the calibration matrix was computed based on this segmentation in combination with tracking information. The method was tested on three very different probes demonstrating both great versatility and high accuracy.

Motion tracking in the liver: validation of a method based on 4D ultrasound using a nonrigid registration technique.

PURPOSE: Treatments like radiotherapy and focused ultrasound in the abdomen require accurate motion tracking, in order to optimize dosage delivery to the target and minimize damage to critical structures and healthy tissues around the target. 4D ultrasound is a promising modality for motion tracking during such treatments. In this study, the authors evaluate the accuracy of motion tracking in the liver based on deformable registration of 4D ultrasound images. METHODS: The offline analysis was performed using a nonrigid registration algorithm that was specifically designed for motion estimation from dynamic imaging data. The method registers the entire 4D image data sequence in a groupwise optimization fashion, thus avoiding a bias toward a specifically chosen reference time point. Three healthy volunteers were scanned over several breathing cycles (12 s) from three different positions and angles on the abdomen; a total of nine 4D scans for the three volunteers. Well-defined anatomic landmarks were manually annotated in all 96 time frames for assessment of the automatic algorithm. The error of the automatic motion estimation method was compared with interobserver variability. The authors also performed experiments to investigate the influence of parameters defining the deformation field flexibility and evaluated how well the method performed with a lower temporal resolution in order to establish the minimum frame rate required for accurate motion estimation. RESULTS: The registration method estimated liver motion with an error of 1 mm (75% percentile over all datasets), which was lower than the interobserver variability of 1.4 mm. The results were only slightly dependent on the degrees of freedom of the deformation model. The registration error increased to 2.8 mm with an eight times lower temporal resolution. CONCLUSIONS: The authors conclude that the methodology was able to accurately track the motion of the liver in the 4D ultrasound data. The authors believe that the method has potential in interventions on moving abdominal organs such as MR or ultrasound guided focused ultrasound therapy and radiotherapy, pending the method is enabled to run in real-time. The data and the annotations used for this study are made publicly available for those who would like to test other methods on 4D liver ultrasound data.

Liver deformation in an animal model due to pneumoperitoneum assessed by a vessel-based deformable registration.

PURPOSE: Surgical navigation based on preoperative images partly overcomes some of the drawbacks of minimally invasive interventions - reduction of free sight, lack of dexterity and tactile feedback. The usefulness of preoperative images is limited in laparoscopic liver surgery, as the liver shifts due to respiration, induction of pneumoperitoneum and surgical manipulation. In this study, we evaluated the shift and deformation in an animal liver caused by respiration and pneumopertioneum using intraoperative cone beam CT. MATERIAL AND METHODS: 3D cone beam CT scans were acquired with arterial contrast. The centerlines of the segmented vessels were extracted from the images taken at different respiration and pressure settings. A non-rigid registration method was used to measure the shift and deformation. The mean Euclidean distance between the annotated landmarks was used for evaluation. RESULTS: A shift and deformation of 44.6 mm on average was introduced due to the combined effect of respiration and pneumoperitoneum. On average 91% of the deformations caused by the respiration and pneumoperitoneum were recovered. CONCLUSION: The results can contribute to the use of intraoperative imaging to correct for anatomic shift so that preoperative data can be used with greater confidence and accuracy during guidance of laparoscopic liver procedures.

Automatic registration of CT images to patient during the initial phase of bronchoscopy: a clinical pilot study.

PURPOSE: Electromagnetic based navigated bronchoscopy using preoperative CT images has reached the clinic during the last decade. One of the challenges is the "CT to patient anatomy alignment" of the CT images acquired days or even weeks ahead of bronchoscopy. An automatic registration method, without manual registration of anatomical landmarks, was developed, implemented, and evaluated in the current study. METHODS: The registration method aligns automatically the preoperative CT images to the patient's anatomy during the initial part of the bronchoscopy. The algorithm is a modified version of an iterative closest point algorithm, which in addition to the positions also utilizes the orientation of the bronchoscope and the running direction of the CT centerline. The method was evaluated both by model-based simulated bronchoscopies and by clinical data from six real bronchoscopies. In the clinical evaluation, an electromagnetic position sensor was placed temporarily in the working channel close to the tip of a conventional bronchoscope. Position data, which were acquired while the bronchoscope was moving inside the airways, were registered to the centerline extracted from the airways in the CT image. RESULTS: A mean registration accuracy of 3.0 ± 1.4 mm was found when simulating bronchoscopies. In the clinical part of the study, the registration method was successfully applied to the data from all six patients. The positions of the bronchoscope tip aligned to the CT centerline with a mean distance range 4.7-6.5 mm. CONCLUSIONS: The authors have developed and evaluated an automatic registration algorithm for electromagnetic navigated bronchoscopy. It functioned to its purpose and did not affect the workflow for the bronchoscopic investigation of the six patients included in the study.

Perceiving haptic feedback in virtual reality simulators.

BACKGROUND: To improve patient safety, training of psychomotor laparoscopic skills is often done on virtual reality (VR) simulators outside the operating room. Haptic sensations have been found to influence psychomotor performance in laparoscopy. The emulation of haptic feedback is thus an important aspect of VR simulation. Some VR simulators try to simulate these sensations with handles equipped with haptic feedback. We conducted a survey on how laparoscopic surgeons perceive handles with and without haptic feedback. METHODS: Surgeons with different levels of experience in laparoscopy were asked to test two handles: Xitact IHP with haptic feedback and Xitact ITP without haptic feedback (Mentice AB, Gothenburg, Sweden), connected to the LapSim (Surgical Science AB, Sweden) VR simulator. They performed two tasks on the simulator before answering 12 questions regarding the two handles. The surgeons were not informed about the differences in the handles. RESULTS: A total of 85 % of the 20 surgeons who participated in the survey claimed that it is important that handles with haptic feedback feel realistic. Ninety percent of the surgeons preferred the handles without haptic feedback. The friction in the handles with haptic feedback was perceived to be as in reality (5 %) or too high (95 %). Regarding the handles without haptic feedback, the friction was perceived as in reality (45 %), too low (50 %), or too high (5 %). A total of 85 % of the surgeons thought that the handle with haptic feedback attempts to simulate the resistance offered by tissue to deformation. Ten percent thought that the handle succeeds in doing so. CONCLUSIONS: The surveyed surgeons believe that haptic feedback is an important feature on VR simulators; however, they preferred the handles without haptic feedback because they perceived the handles with haptic feedback to add additional friction, making them unrealistic and not mechanically transparent.

A study of psychomotor skills in minimally invasive surgery: what differentiates expert and nonexpert performance.

BACKGROUND: A high level of psychomotor skills is required to perform minimally invasive surgery (MIS) safely. To assure high quality of skills, it is important to be able to measure and assess these skills. For that, it is necessary to determine aspects that indicate the difference between performances at various levels of proficiency. Measurement and assessment of skills in MIS are best done in an automatic and objective way. The goal of this study was to investigate a set of nine motion-related metrics for their relevance to assess psychomotor skills in MIS during the performance of a labyrinth task. METHODS: Thirty-two surgeons and medical students were divided into three groups according to their level of experience in MIS; experts (>500 MIS procedures), intermediates (31-500 MIS), and novices (no experience in MIS). The participants performed the labyrinth task in the D-box Basic simulator (D-Box Medical, Lier, Norway). The task required bimanual maneuvering and threading a needle through a labyrinth of 10 holes. Nine motion-related metrics were used to assess the MIS skills of each participant. RESULTS: Experts (n = 7) and intermediates (n = 14) performed significantly better than the novices (n = 11) in terms of time and parameters measuring the amount of instrument movement. The experts had significantly better bimanual dexterity, which indicated that they made more simultaneous movements of the two instruments compared to the intermediates and novices. The experts also performed the task with a shorter instrument path length with the nondominant hand than the intermediates. CONCLUSIONS: The surgeon's performance in MIS can be distinguished from a novice by metrics such as time and path length. An experienced surgeon in MIS can be differentiated from a less experienced one by the higher ability to control the instrument in the nondominant hand and the higher degree of simultaneous (coordinated) movements of the two instruments.