Lars Eirik Bø

Limitations of haptic feedback devices on construct validity of the LapSim ® virtual reality simulator

BackgroundSurgeons performing laparoscopy need a high degree of psychomotor skills, which can be trained and assessed on virtual reality (VR) simulators. VR simulators simulate the surgical environment and assess psychomotor skills according to predefined parameters. This study aimed to validate a proficiency-based training setup that consisted of two tasks with predefined threshold values and handles with haptic feedback on the LapSim® VR simulator. The two tasks have been found to have construct validity in previous studies using handles without haptic feedback.MethodsThe participants were divided into three groups: novices (0–50 laparoscopic procedures), intermediates (51–300 laparoscopic procedures), and experts (more than 300 procedures). It was assumed that psychomotor skills increase with experience. All participants conducted the tasks lifting and grasping and fine dissection 20 times each. Validity of the training setup was investigated by comparing the number of times each participant passed a predefined threshold level for a set of 19 parameters.ResultsConstruct validity was established for one parameter; “misses on right side” on the lifting and grasping task, whereas the other 18 parameters did not show construct validity.ConclusionThe setup employed in this study failed to establish construct validity for more than one parameter. This indicates that the simulation of haptic feedback influences the training performance on laparoscopic simulators and is an important part of validating a training setup. A haptic device should generate haptic sensations in a realistic manner, without introducing frictional forces that are not inherent to laparoscopy.

A novel research platform for electromagnetic navigated bronchoscopy using cone beam CT imaging and an animal model

Abstract Electromagnetic guided bronchoscopy is a new field of research, essential for the development of advanced investigation of the airways and lung tissue. Consecutive problem-based solutions and refinements are urgent requisites to achieve improvements. For that purpose, our intention is to build a complete research platform for electromagnetic guided bronchoscopy. The experimental interventional electromagnetic field tracking system in conjunction with a C-arm cone beam CT unit is presented in this paper. The animal model and the navigation platform performed well and the aims were achieved; the 3D localization of foreign bodies and their navigated and tracked removal, assessment of tracking accuracy that showed a high level of precision, and assessment of image quality. The platform may prove to be a suitable platform for further research and development and a full-fledged electromagnetic guided bronchoscopy navigation system. The inclusion of the C-arm cone beam CT unit in the experimental setup adds a number of new possibilities for diagnostic procedures and accuracy measurements. Among other future challenges that need to be solved are the interaction between the C-arm and the electromagnetic navigation field, as we demonstrate in this feasibility study.

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.

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

Abstract 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.

Efficiency of ultrasound training simulators: method for assessing image realism.

Abstract Although ultrasound has become an important imaging modality within several medical professions, the benefit of ultrasound depends to some degree on the skills of the person operating the probe and interpreting the image. For some applications, the possibility to educate operators in a clinical setting is limited, and the use of training simulators is considered an alternative approach for learning basic skills. To ensure the quality of simulator-based training, it is important to produce simulated ultrasound images that resemble true images to a sufficient degree. This article describes a method that allows corresponding true and simulated ultrasound images to be generated and displayed side by side in real time, thus facilitating an interactive evaluation of ultrasound simulators in terms of image resemblance, real-time characteristics and man-machine interaction. The proposed method could be used to study the realism of ultrasound simulators and how this realism affects the quality of training, as well as being a valuable tool in the development of simulation algorithms.

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

Abstract 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.

Navigated bronchoscopy with electromagnetic tracking-cone beam computed tomography influence on tracking and registration accuracy.

Current image guidance systems for bronchoscopy are limited to the diagnosis of small tumors and placing fiducials for radiation therapy and surgery. Ideally, a navigation system should be useable for the range of bronchoscopic procedures, including therapy with concurrent radiology imaging for control. As most guidance systems rely on electromagnetic (EM) fields, it is advised to leave the C-arm mounted fluoroscopy unit outside the operating field during navigation. We have assessed the accuracy of our research navigation platform, containing an EM field generator and a C-arm fluoroscopy unit. We have simulated a regular bronchoscopy session with an initial image-to-patient registration procedure, and a subsequent bronchoscopy with the C-arm inside the EM field. The registration accuracy was significantly influenced, introducing an error that may be carried through to the bronchoscopy procedure. During the bronchoscopy session, the C-arm caused a wave drift in the tracking positions and distorted the EM field, causing a translation error up to 22 mm. Even by averaging out the drift, there was a systematic shift in the x, y, and z positions. The errors were more evident in some C-arm positions and seem to be linked more to the electrical current in the fluoroscopy unit than the metallic C-arm itself. A fluoroscopy unit may be used during a navigation procedure, but care must be taken. To enable real-time navigation, the C-arm could be removed sufficiently from the EM tracking field or correction schemes must be implemented to compensate for the distortions.

Registration of MR to Percutaneous Ultrasound of the Spine for Image-Guided Surgery

One of the main limitations of today’s navigation systems for spine surgery is that they often are not available until after the bone surface has been exposed. Also, they lack the capability of soft tissue imaging, both preoperatively and intraoperatively. The use of ultrasound has been proposed to overcome these limitations. By registering preoperative magnetic resonance (MR) images to intraoperative percutaneous ultrasound images, navigation can start even before incision. We therefore present a method for registration of MR images to ultrasound images of the spine. The method is feature-based and consists of two steps: segmentation of the bone surfaces from both the ultrasound images and the MR images, followed by rigid registration using a modified version of the Iterative Closest Point algorithm. The method was tested on data from a healthy volunteer, and the data set was successfully segmented and registered with an accuracy of \(3.67\pm 0.38\) mm.

Interactive development of a CT-based tissue model for ultrasound simulation

The objective of this study was to make an interactive method for development of a tissue model, based on anatomical information in computed tomography (CT) images, for use in an ultrasound simulator for training or surgical pre-planning. The method consisted of (1) comparison of true ultrasound B-mode images with corresponding ultrasound-like images, and (2) modification of tissue properties to decrease the difference between these images. Ultrasound-like images that reproduced many, but not all the properties of corresponding true ultrasound images were generated. The tissue model could be used for real-time simulation of ultrasound-like B-mode images on a moderately priced computer.