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European spine journal 31(4), 1013-1021 (2021). doi:10.1007/s00586-021-07035-4, Published by Springer, Berlin ; Heidelberg ; New York

Magnetic tracking systems have been widely investigated in biomedical engineering due to the transparency of the human body to static magnetic fields. We recently proposed a novel human-machine interface for prosthetic application, namely the myokinetic interface. This controls multi-articulated prostheses by tracking magnets implanted in the residual muscles of individuals with amputation. Previous studies in this area focused solely on the choice and tuning of the localization algorithm. Here, we addressed the role of the intrinsic properties of the sensors, by analysing their effects on the tracking accuracy and on the computation time of the localization algorithm, through experimentally-verified computer simulations. We observed that the tracking accuracy is primarily affected by the localization rate, which is directly related to the sampling frequency of the sensors, and less significantly affected by the sensor resolution. The computation time, instead, proved positively correlated to the number of MMs, and negatively correlated with the localization rate. Our results may contribute to the development of novel human-machine interfaces for prosthetic limbs and could be extended to a broad range of applications involving magnetic tracking.

Recently, the Sherlock 3CG™ Tip Confirmation System, including a magnetic tracking system and an intracavitary electrocardiography guidance system, has been introduced for bedside peripherally inserted central catheter (PICC) insertion. Magnetic field sources interfere with the magnetic tracking system. Electromagnetic interference of the ventricular assist device (VAD) has already been reported with various devices but not on Sherlock 3CG™. We assessed the availability of the magnetic tracking system in patients with and without a VAD during Sherlock 3CG™ insertion and evaluated the rate of optimal PICC tip position. We retrospectively reviewed 99 patients who had undergone PICC insertion using Sherlock 3CG™ on the bedside at our institutional intensive care unit from February 2018 to December 2020. Patients were divided into groups with and without a VAD. The availability of magnetic navigation and the success rate of optimal catheter tip position in each group were assessed. Among 87 cases analyzed, there were 12 and 75 cases with a VAD and without a VAD, respectively. The availability of magnetic navigation during Sherlock 3CG™ insertion was significantly lower in the group with a VAD [4/12 (33%) with VAD vs. 72/75 (96%) without VAD, P

The work deals with the problem of signal conversion in magnetic tracking devices. Magnetic tracking technology is based on computing the spatial position of an object being tracked upon measuring reference magnetic fields in low-frequency electromagnetic radiation spectrum. Magnetic tracking devices are key components of navigation sensors for virtual and augmented reality. It has been shown that the main problem one faces when developing sensory devices for magnetic tracking is the fact that signals should be measured in a wide measurement range. We have analyzed possible ways to solve the stated problem by digital and combined methods. The latter have proven to be more efficient. They consist in signal amplification due to analog compression, which is performed by logarithmic amplifiers whose negative feedback circuits contain components with non-linear volt-ampere characteristics (typically, diodes or bipo- lar transistors are used). It has been shown that the parameters of logarithmic signal compression can be controlled by modified circuits with auxiliary resistance dividers. The resistance dividers scale the logarithmic volt-ampere characteristics of emitter p-n junctions of bipolar n-p-n and p-n-p transistors. A substantial advantage of circuits with resistance dividers is that they provide the possibility to expand the range of the output voltage of logarithmic amplifiers and optimize the transition between the linear and logarithmic amplification regions. The work presents the results of simulation and experimental investigations into a logarithmic amplifier for a magnetic tracking system. Simulation was carried out using SPICE (Simulation Program with Integrated Circuit Emphasis) models. We applied an integrated approach,which provides collections of transient characteristics of logarithmic amplifiers at different sets of the parameters of resistance dividers. The simulation results have been verified using our own software- firmware magnetic tracking tools – Magnetic Tracking System Integrated Development Environment. The signal converter was built upon a programmable system-on-chip PSoC 5LP by Cypress Semiconductor.

Purpose To determine whether the use of a magnetic tracking and electrocardiography-guided catheter tip confirmation system (TCS) is safe and noninferior to fluoroscopy concerning positioning accuracy of a peripheral inserted central catheter (PICC). Methods In this prospective, randomized, single-center study, adult patients scheduled for PICC insertion were assigned 1:1 either to TCS or fluoroscopy. The primary objective was a noninferiority comparison of correct PICC tip position confirmed by X-ray obtained immediately after catheter insertion. Time needed for PICC insertion and insertion-related complications up to 14 days after the procedure were secondary outcomes to be assessed for superiority. Results A total of 210 patients (62.3 ± 14.4 years, 63.8% male) were included at a single German center between June 2016 and October 2017. Correct PICC tip position was achieved in 84 of 103 TCS (82.4%) and 103 of 104 fluoroscopy patients (99.0%). One-sided 95% lower confidence limit on the difference between proportions was −23.1%. Thus, noninferiority of TCS was not established (p > 0.99). Insertion of PICC took longer with TCS compared to fluoroscopy (8.4 ± 3.7 min vs. 5.0 ± 2.7 min, p Conclusion Noninferiority of TCS to fluoroscopy in the incidence of correct PICC tip position was not reached. Ancillary benefit of TCS over fluoroscopy including less radiation exposure and lower resource requirements may nonetheless justify the use of TCS. The study is registered with Clinical.Trials.gov (Identifier: NCT02929368).

Magnetic tracking enables instrument tracking for image-guided interventions when no line of sight is available. This paper describes the first steps towards a more cost-effective, modular, and adaptable approach that builds upon prior work in open hardware architectures for magnetic tracking in image-guided interventions. An exemplary C++ framework is implemented and demonstrated with the open-hardware Anser EMT system. System performance in speed, accuracy, and precision of the C++ implementation is analysed. Static positioning accuracy and precision are calculated within the Region of Interest (ROI) and an average position error of 1.0 (Formula presented.) 0.1 mm is demonstrated. Results show an indicative increase in the update rate using the C++ framework and substantially lower memory requirements, compared to the previously optimised Python and Matlab solvers. These preliminary results provide the basis for future development which will integrate the C++ framework in a 3D Slicer module, greatly extending the adaptability of the platform for customisation in advanced image-guided procedures.

Stroke survivors and elderly often suffer from proprioceptive impairments that may contribute to disabilities in walking. Current clinical assessments of proprioception are often subjective and not accurate, and the treatment mainly focuses on the motor impairments. Here, we developed a novel tool for proprioception assessment of the lower-limb with a magnetic tracking system. We designed a protocol for assessing proprioception in both lower-limbs using position-matching and position-recall tests. We validated the tool by examining young adults, elderly and stroke survivors. By examining the Mean Absolute Error and Bias, significant differences were found between the elderly and the young adults in the position-matching tasks. This indicates that position-matching may be effective as a screening phase in identifying proprioceptive impairments of the lower limb.

Purpose A robotic intraoperative laser guidance system with hybrid optic-magnetic tracking for skull base surgery is presented. It provides in situ augmented reality guidance for microscopic interventions at the lateral skull base with minimal mental and workload overhead on surgeons working without a monitor and dedicated pointing tools. Methods Three components were developed: a registration tool (Rhinospider), a hybrid magneto-optic-tracked robotic feedback control scheme and a modified robotic end-effector. Rhinospider optimizes registration of patient and preoperative CT data by excluding user errors in fiducial localization with magnetic tracking. The hybrid controller uses an integrated microscope HD camera for robotic control with a guidance beam shining on a dual plate setup avoiding magnetic field distortions. A robotic needle insertion platform (iSYS Medizintechnik GmbH, Austria) was modified to position a laser beam with high precision in a surgical scene compatible to microscopic surgery. Results System accuracy was evaluated quantitatively at various target positions on a phantom. The accuracy found is 1.2 mm ± 0.5 mm. Errors are primarily due to magnetic tracking. This application accuracy seems suitable for most surgical procedures in the lateral skull base. The system was evaluated quantitatively during a mastoidectomy of an anatomic head specimen and was judged useful by the surgeon. Conclusion A hybrid robotic laser guidance system with direct visual feedback is proposed for navigated drilling and intraoperative structure localization. The system provides visual cues directly on/in the patient anatomy, reducing the standard limitations of AR visualizations like depth perception. The custom- built end-effector for the iSYS robot is transparent to using surgical microscopes and compatible with magnetic tracking. The cadaver experiment showed that guidance was accurate and that the end-effector is unobtrusive. This laser guidance has potential to aid the surgeon in finding the optimal mastoidectomy trajectory in more difficult interventions.

Colonoscopy procedures are commonly performed to diagnose and prevent colorectal cancer. These procedures require highly trained practitioners to perform complex maneuvers with an endoscope. Extensive training is necessary to become proficient. To improve assessment during endoscope training the novel endoscopic control assessment system (ECAS) is proposed. This device uses a magnetic tracker to track the end of the endoscope in manikin training. In addition, camera imaging is used to track the angle of the control knobs during the training. Experiment 1 demonstrated that the magnetic tracker could sense the full range of motion of the endoscope. Experiment 2 showed that the control knob angle could be accurately tracked through 4 positions to within 0.6° accuracy. The feasibility of the ECAS system was shown and in the future, this can be employed as an effective means of assessing endoscopic training performance.

Background: functional gastrointestinal disorders (FGID) are common conditions in children and adults, often associated with abnormalities of whole gut transit. Currently, transit tests can be performed using several imaging methods, including tracking of radiopaque markers, gamma scintigraphy with the use of radioisotopes, magnetic tracking methods, tracking of movement of wireless motility capsules, and emerging magnetic resonance imaging (MRI) approaches. Objectives: to review recent literature on diagnostic imaging techniques used to investigate whole gut transit in FGIDs. Methods: a systematic review was carried out. The different techniques are described briefly, with particular emphasis on contemporary literature and new developments, particularly in the field of MRI. Conclusions: emerging MRI capsule marker methods are promising new tools to study whole gut transit in FGIDs.

The position and orientation of an object embedding with a permanent magnet can be acquired in real time via a magnetic tracking system. However, one characteristic of the magnetic tracking technique is its varied tracking accuracy along with the tracking distance. Hence, this paper tends to investigate the relationship between the tracking accuracy and the distance from the magnet to the sensor array by both simulations and experiments. Results show that the relationship is expressed as a cubic polynomial equation, and that the equation coefficients are related to the properties of the magnet and the signal-to-noise ratio of the sensor outputs. When the magnet is located at a distance from 36 to 96 mm above the sensor array, the system had the best performance, while average localization and orientation errors were 0.70 mm and 1.22°, respectively. Thus, this system achieved the best tracking accuracy compared with the state-of-the-art of magnetic tracking systems. This paper is helpful to the researchers who want to implement a magnetic tracking system or need to know clearly the valid tracking distance of a magnetic tracking system.

Background and Objectives Ultrasound-guided regional anesthesia facilitates an approach to sensitive targets such as nerve clusters without contact or inadvertent puncture. We compared accuracy of needle placement with a novel passive magnetic ultrasound needle guidance technology (NGT) versus conventional ultrasound (CU) with echogenic needles. Methods Sixteen anesthesiologists and 19 residents performed a series of 16 needle insertion tasks each, 8 using NGT (n = 280) and 8 using CU (n = 280), in high-fidelity porcine phantoms. Tasks were stratified based on aiming to contact (target-contact) or place in close proximity with (target-proximity) targets, needle gauge (no. 18/no. 22), and in-plane (IP) or out-of-plane (OOP) approach. Distance to the target, task completion by aim, number of passes, and number of tasks completed on the first pass were reported. Results Needle guidance technology significantly improved distance, task completion, number of passes, and completion on the first pass compared with CU for both IP and OOP approaches (P ⩽ 0.001). Average NGT distance to target was lower by 57.1% overall (n = 560, 1.5 ± 2.4 vs 3.5 ± 3.7 mm), 38.5% IP (n = 140, 1.6 ± 2.6 vs 2.6 ± 2.8 mm), and 68.2% OOP (n = 140, 1.4 ± 2.2 vs 4.4 ± 4.3 mm) (all P ⩽ 0.01). Subgroup analyses revealed accuracy gains were largest among target-proximity tasks performed by residents and for OOP approaches. Needle guidance technology improved first-pass completion from 214 (76.4%) per 280 to 249 (88.9%) per 280, a significant improvement of 16.4% (P = 0.001). Conclusions Passive magnetic NGT can improve accuracy of needle procedures, particularly among OOP procedures requiring close approach to sensitive targets, such as nerve blocks in anesthesiology practice.

Purpose To determine whether the use of a magnetic tracking and electrocardiography-guided catheter tip confirmation system (TCS) is safe and noninferior to fluoroscopy concerning positioning accuracy of a peripheral inserted central catheter (PICC). Methods In this prospective, randomized, single-center study, adult patients scheduled for PICC insertion were assigned 1:1 either to TCS or fluoroscopy. The primary objective was a noninferiority comparison of correct PICC tip position confirmed by X-ray obtained immediately after catheter insertion. Time needed for PICC insertion and insertion-related complications up to 14 days after the procedure were secondary outcomes to be assessed for superiority. Results A total of 210 patients (62.3 ± 14.4 years, 63.8% male) were included at a single German center between June 2016 and October 2017. Correct PICC tip position was achieved in 84 of 103 TCS (82.4%) and 103 of 104 fluoroscopy patients (99.0%). One-sided 95% lower confidence limit on the difference between proportions was −23.1%. Thus, noninferiority of TCS was not established (p > 0.99). Insertion of PICC took longer with TCS compared to fluoroscopy (8.4 ± 3.7 min vs. 5.0 ± 2.7 min, p

Electromagnetic tracking (EMT) systems play an important role in medicine, robotics, and virtual reality applications by providing accurate position and orientation referencing within a fixed volume around a magnetic field generator. Advances in sensor technology provide increasingly small, lightweight sensors capable of being integrated into hand-held devices for medical simulation, gaming, and image-guided surgery. The need for customizable tracking volumes becomes of interest as the uptake of EMT technology increases. This paper proposes a new method of creating custom tracking volumes from multiple planar field generators. A monolithic, low-cost printed circuit board design allows for tiling of multiple generators to create a larger tracking volume. Experiments were performed with two generators at different angles. Successful tracking is demonstrated with increased positional accuracy observed when transmitters are inclined with respect to one another. Horizontal tiling configurations are most accurate when a common edge is shared between adjacent field generators.

Novice urologists sometimes lose their orientation in patients with complicated pyelocaliceal shapes. Controlling a flexible ureteroscope with skill requires a great deal of time and effort and also requires a certain level of expertise. With recent engineering technological advances, there are few reports of real-time navigation system for accurate access to the upper urinary collecting system via percutaneous approach. In this section, we introduce our experimental ureteroscopic navigation system that uses a magnetic tracking device and evaluate the accuracy of ureteroscopic maneuvers in a three-dimensional (3D) pyelocaliceal system model. Our system could help surgeons with different levels to observe all renal papillaethereby by showing surgeons the real-time tip position of ureteroscope on the navigation image. In this section, we introduce our experimental model of ureteroscopic navigation system (ex vivo) using a magnetic tracking device. This concept may lead to increase the detection rate of upper urinary pathologies and the accuracy of surgical procedures. However, there are several challenges to overcome before clinical use, such as adding a built-in magnetic sensor at the tip of the flexible ureteroscope, overcoming pyelocaliceal intraoperative deformation (expansion and contraction) caused during saline irrigation and movements in kidney position with respiration.

Objective: Capsule-based methods for assessment of gastrointestinal (GI) motility have seen great improvements in recent decades. The most recent development is the electromagnetic Motilis 3D-Transit system (3D-Transit). The aim of this paper is to review and discuss the development and technical properties of magnetic tracking of GI motility.Approach: We performed a comprehensive literature review on magnetic tracking in GI research.Main results: The Motility Tracking System was the first capsule based magnetic system to be used in GI motility research. However, the potential of the system was hampered by its stationary and hospitalizing nature. This led to the development of the electromagnetic Motilis 3D-Transit system. The 3D-Transit system is a portable system that allows for assessment of both whole gut and regional transit times and contraction patterns in a fully ambulatory setting in the patients' home environment with only minor restrictions on movements. The spatiotemporal resolution of 3D-Transit allows assessment of segmental colonic transit times and permits an analysis of gastric and colonic movements with a degree of detail unrivalled by other ambulatory methods, such as the Wireless Motility Capsule. Recently, robust normative data on 3D-Transit have been published.Significance: This review provides a current perspective on the use of capsule-based magnetic tracking systems in GI research and how they represent a potentially valuable clinical resource for GI physicians and in GI research.Keywords: colonic contraction patterns; colonic transit time; gastrointestinal motility; gastrointestinal transit time; ingestible capsule; magnetic tracking.

Magnetically manipulated untethered robot, such as an active wireless capsule endoscope, has shown great potential for controlled inspection inside the gastrointestinal tract. To enable the effective manipulation of the robot, real-time pose (position and orientation) information of the robot must be obtained as an important sensory feedback. Usually, a magnetic tracking method is used to provide the pose information. Due to the magnetic disturbance, a traditional magnetic tracking method cannot work simultaneously with the magnetic manipulation system. In this paper, a simultaneously tracking and navigation method is proposed to realize a closed-loop control of the magnetically manipulated untethered robot. The main approach is to conduct a multi-object tracking of the involved magnetic objects. With the proposed method, real-time pose information can be estimated during the manipulation, and both the tracking and manipulation are carried out by a magnetic manner. Therefore, the mobile navigation of the magnetically manipulated untethered robot can be achieved by using a pre-defined map. Experimental results verified the proposed method, and a mean position error of 1.2 mm for the passive magnet has been obtained.

Background Digital rectal examination is a difficult examination to learn and teach because of limited opportunities for practice; however, the main challenge is that students and tutors cannot see the finger when it is palpating the anal canal and prostate gland inside the patients. Objective This paper presents an augmented reality system to be used with benchtop models commonly available in medical schools with the aim of addressing the problem of lack of visualization. The system enables visualization of the examining finger, as well as of the internal organs when performing digital rectal examinations. Magnetic tracking sensors are used to track the movement of the finger, and a pressure sensor is used to monitor the applied pressure. By overlaying a virtual finger on the real finger and a virtual model on the benchtop model, students can see through the examination and finger maneuvers. Methods The system was implemented in the Unity game engine (Unity Technologies) and uses a first-generation HoloLens (Microsoft Inc) as an augmented reality device. To evaluate the system, 19 participants (9 clinicians who routinely performed digital rectal examinations and 10 medical students) were asked to use the system and answer 12 questions regarding the usefulness of the system. Results The system showed the movement of an examining finger in real time with a frame rate of 60 fps on the HoloLens and accurately aligned the virtual and real models with a mean error of 3.9 mm. Users found the movement of the finger was realistic (mean 3.9, SD 1.2); moreover, they found the visualization of the finger and internal organs were useful for teaching, learning, and assessment of digital rectal examinations (finger: mean 4.1, SD 1.1; organs: mean 4.6, SD 0.8), mainly targeting a novice group. Conclusions The proposed augmented reality system was designed to improve teaching and learning of digital rectal examination skills by providing visualization of the finger and internal organs. The initial user study proved its applicability and usefulness.

In the past decade, with continual advancement in the magnetic field sensing technology, passive magnetic tracking has become an emerging trend in the field of medical intervention. By embedding a small permanent magnet in the medical instrument, the passive magnetic tracking approach makes the system possible to have untethered, compact and wearable, even modular design for better ergonomics and lower hardware requirements. In this chapter, an overview of the working principle and methods of the passive magnetic tracking technology was presented. Implementation of the technology in actual medical interventions were also demonstrated. Lastly, the challenges in the development of this technology were explored and discussed.

Objective To analyze the current clinical use of navigation at the lateral skull base among skull base surgeons in Germany. Methods A web-based questionnaire was provided to surgeons being head of the department and member of one of the following scientific societies: German Society of Head and Neck Surgery, Maxillo-Facial Surgery, Neurosurgery, and German Skull Base Society. Replies were recorded anonymously. The questionnaire included the estimated case load per year and percent of surgery performed with navigation (middle and posterior fossa), type of navigation, estimates of intraoperative inaccuracy, and reasons for not using navigation. Results Eighty nine out of 99 replies met requirements for final analysis. Overall, 37% of skull base surgeons use navigation on a regular basis (15% use no navigation). Optical tracking is more frequently used than magnetic tracking (71 vs 19). At the middle fossa, ENT surgeons split into routine users (n = 10/36) and rare users (n = 16/36), the latter stating navigation inaccuracy as a major reason for neglecting navigation. Neurosurgeons use navigation at the middle fossa significantly more often and criticize navigation inaccuracy less. At the posterior fossa, navigation is used less frequently by both ENT and neurosurgeons with similar rates of estimated inaccuracy. Conclusions A moderate use of navigation at the lateral skull base was demonstrated. Insufficient accuracy causes ENT surgeons to frequently omit navigation at the middle fossa (not neurosurgeons) and posterior fossa (also neurosurgeons). Higher intraoperative navigation accuracy is needed to enhance the use of navigation at the lateral skull base.

A new diagnostic method to measure the trajectory and orientation of a magnetized projectile traveling through opaque media in-situ has been developed. An array of magnetic field sensing coils placed around a projectile flight path produces raw voltage data that, upon analysis, yields the trajectory of the projectile. This paper discusses the theory of operation of the diagnostic, presents the analysis used to convert voltage signals to trajectory information, gives design details of the sensor array, and presents two representative experiments. In these experiments projectiles were launched from a 50-mm gun at a velocity of about 1 km/s. In both cases the projectiles perforated a 35 inch long, right circular cylinder filled with sand. Data from 24 sensing coils were recorded and analyzed to determine the trajectory and orientation of the projectiles from well before they impacted the opaque material until well after target exit. To test the validity of the method high-speed digital video cameras recorded the projectiles’ entry and exit for the same sand targets. Trajectory and orientations from the magnetic tracking technique compared well to camera observations.

This study investigated whether parameters derived from hand motions of expert and novice surgeons accurately and objectively reflect laparoscopic surgical skill levels using an artificial intelligence system consisting of a three-layer chaos neural network. Sixty-seven surgeons (23 experts and 44 novices) performed a laparoscopic skill assessment task while their hand motions were recorded using a magnetic tracking sensor. Eight parameters evaluated as measures of skill in a previous study were used as inputs to the neural network. Optimization of the neural network was achieved after seven trials with a training dataset of 38 surgeons, with a correct judgment ratio of 0.99. The neural network that prospectively worked with the remaining 29 surgeons had a correct judgment rate of 79% for distinguishing between expert and novice surgeons. In conclusion, our artificial intelligence system distinguished between expert and novice surgeons among surgeons with unknown skill levels.

Flexible manipulator enables curvilinear accessibility through small incisions or natural orifices for minimally invasive surgery and diagnosis, which makes it a good choice for minimally invasive surgery. In order to control the robot precisely and safely, the real-time position and shape information of the robot need to be measured well. In this paper, we propose a magnetic tracking based tip pose and shape detection method for wire driven flexible robots. A permanent magnet is mounted at the distal end of the robot. Its magnetic field can be sensed with a sensor array. Therefore, position and orientation of the tip can be estimated utilizing the tracking method. A shape sensing algorithm is then carried out to estimate the real-time shape based on the tip pose. With the tip pose and shape display in the reconstructed visual environment, navigation can be achieved. This method provides the advantages that no sensors are needed to mount on the robot and has no line-of-sight problem. Experimental results verified the feasibility of the proposed method. A navigation error of 1.9mm is achieved.

A novel haptic position measurement system (HPMS) utilizing a hand-held magnetic sensor is developed to measure the position and shape of soft/compliant objects. The magnetic senor, serving as a touch probe, is guided by hand to contact with the object. The haptic feedback from the contact between the sensor and object provides the guidance to the user for measurement. The HPMS is validated by measuring the diameter of a soft silicone phantom and shown capable to achieve 0.2 mm accuracy level. This result demonstrated the feasibility for HPMS as a new approach to measure the shape of soft and compliant objects.

The purpose of this study was to investigate the body sway and motion sickness individuals while exposed to the visual stimulus of a 3D movie, and examine the postural instability theory (Riccio & Stoffregen, 1991), which extended from the ecological approach. We recruited thirty participants (fifteen males and fifteen females, aged = 23.3 ± 2.3 years, height = 166.6 ± 10.3 cm and weight = 61.4 ± 11.4 kg). Participants stood and watched a 3D movie continuously for up to 40 minutes and they were instructed that they could terminate if they felt uncomfortable or for any reasons. We used the magnetic tracking system (Flock of Birds, Ascension Technologies, Inc., Burlington, VT) to collect the movement data. One receiver was attached to a bicycle helmet of the individual and the other one to the 7th cervical vertebra. The Simulator Sickness Questionnaire was used to represent the symptom severity of motion sickness and participants were divided into the sick and well groups according to their self-reported data. Results indicated that the motion sickness incidence rate was 18%. The severity of motion sickness in the sick group was higher than that of the well group, and both groups had higher symptom severity after watching the movie. Furthermore, the variability of head movement in sick group was higher than the other group in the mediolateral and vertical axis. We found that watching a 3D movie induced some people motion sickness, and the study supported the postural instability theory of motion sickness.

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 $$1.37\pm 0.43\, \text{ mm}$$ , whereas in the animal study on three porcine subjects, fiducial, target, deployment distance and tilting errors reached $$3.16\pm 0.55\,\text{ mm}$$ , $$3.80\pm 1.83\,\text{ mm}$$ , $$3.13\pm 1.12\,\text{ mm}$$ and $$5.87\pm 2.35^{\circ }$$ , respectively. Conclusion Our pilot study has revealed that the proposed approach is feasible and accurate for delivery and deployment of transcatheter aortic valve prosthesis.

This paper describes the design concepts, the making of and some applications of the first Estonian Virtual Reality Environment. Using hardware only slightly above the threshold of consumer level, we built a virtual environment (VE) aimed at scientific visualization with the lowest possible space requirements (smaller than a cube with 2 m edge length in total) and budget (approximately below 30.000 €). The system is a fully functional visualization environment that replicates most of the features and properties of a real-sized CAVE-like System, therefore allowing further prototyping and research in the field of Virtual Reality.

© 2016 SPIE. In the past ten years, numerous new surgical and interventional techniques have been developed for treating heart valve disease without the need for cardiopulmonary bypass. Heart valve repair is now being performed in a blood-filled environment, reinforcing the need for accurate and intuitive imaging techniques. Previous work has demonstrated how augmenting ultrasound with virtual representations of specific anatomical landmarks can greatly simplify interventional navigation challenges and increase patient safety. These techniques often complicate interventions by requiring additional steps taken to manually define and initialize virtual models. Furthermore, overlaying virtual elements into real-time image data can also obstruct the view of salient image information. To address these limitations, a system was developed that uses real-time volumetric ultrasound alongside magnetically tracked tools presented in an augmented virtuality environment to provide a streamlined navigation guidance platform. In phantom studies simulating a beating-heart navigation task, procedure duration and tool path metrics have achieved comparable performance to previous work in augmented virtuality techniques, and considerable improvement over standard of care ultrasound guidance.

While the average frequency of chewing and food intake have been reported before, a detailed description of the pattern of chewing and the cumulative intake of food over the course of a meal have not. In order to achieve this goal, video recording of the maxillary-mandibular region of women eating food from a plate was synchronized with video recording of the plate and computer recording of the weight-loss of the plate. Video recording of chewing correlated strongly with chewing identified by magnetic tracking of jaw displacement in a test with chewing gum at three different frequencies, thus ensuring the validity of video recording of chewing. Weight-loss data were corrected by convolution algorithms, validated against human correction, using sliding window filtering to correct errors with video events as reference points. By use of this method, women ate on average 264 g of food over 114 min, they took an average of 51 mouthfuls during the meal and displayed on average 794 chews with 15 chews per chewing sequence. The number of mouthfuls decreased and the duration of the pauses after each mouthful increased in the middle of the meal and these measures were then restored. The ratio between chewing sequences and subsequent pauses remained stable although the weight of each mouthful decreased by the end of the meal, a measure that is hypothesized to be reflected in a decelerated speed of eating. The method allows this hypothesis to be tested and its implication for clinical intervention to be examined.

Objective. This study aimed to assess the feasibility of a totally endoscopic enteral bypass using a self-orienting, dual ring, magnetic anastomosis system (MAGNAMOSIS) guided by a magnetic tracking system (3D METRIS). Materials and methods. In an anesthetized pig, 2 endoscopes were advanced, one each into the stomach and the colon. Both endoscopes were equipped with a MAGNAMOSIS ring secured with an endoscopic snare and a 3D METRIS within one working channel. The whole procedure was followed laparoscopically. The tracking system guided tips of endoscopes to a “rendez-vous” location between the colon and stomach. Results. MAGNAMOSIS magnets automatically joined in the correct configuration when guided to within 2 cm of each other. At necropsy, magnetic rings were secure without entrapment of excess bowel or mesentery. Conclusion. An endoscopic enteral bypass with magnetic anastomosis and magnetic tracking device was feasible. More accurate tracking and advanced techniques could enable endoscopic bypasses at multiple sites in the gastrointestinal tract.

The theory of spatial vortex relativistic beams in the coordinate system related to the current tubes is developed. A possibility of independent setting of the flux configuration and the axial distributions of physical parameters is specified. The problems of magnetic tracking and the deposition of the beam on the collector are considered.

Background The range of functional elbow movement has previously been studied. The data obtained have been used to provide an objective basis for the determination of disability, to determine the optimum position for elbow splinting arthrodesis and to assist in the design of elbow prostheses. The present study aimed to evaluate the functional range of elbow movement as applied to a predetermined list of activities of daily living, which might be considered relevant to modern day life. This includes the use of computers and driving, which has not been studied earlier. Methods Twenty normal volunteers were studied and the range of elbow motion required for specific activities was recorded by means of a ‘Polhemus Fastrak’ magnetic tracking measurement system. The results obtained suggests that the functional range of elbow flexion is from 1.33° to 146.57° and the rotation arc is from 56° of pronation to 104° of supination. Conclusion This data compliments the work previously carried out, and defines the functional range of movement for some of the common activities of daily living.

Objectives: The aim of this study was to reveal possible interspersion of a magnetic position tracking device into a cochlear implant system, which could lead to harmful signals on the implanted electrode. Design: Signals at the output of the speech processor's compression stage and at the implant's electrode were recorded and analyzed for unwanted distortion or corrupted pulses related to the presence of the magnetic tracking device. Results: No systematic impact of a Polhemus Liberty Latus magnetic tracking system on the output signals of an Advanced Bionics HiRes90k cochlear implant and Platinum Series speech processor was found. Conclusions: The results suggest no objections for using the Polhemus Liberty Latus magnetic position tracker with the Advanced Bionics Platinum series speech processor and HiRes90k cochlear implant in research, for example, on spatial hearing. This result is likely transferable to other cochlear implants because (i) all manufacturers adhere to equally high electromagnetic interference standards and (ii) electromagnetic signals used by the transmission links of current cochlear implants and trackers differ in frequency by roughly 2 decades, making interference unlikely.

Here, we present a new approach for the magnetic tracking of eye motion in small, fast-moving animals. We employ a thin, flat magnetic tracking transmitter instead of the conventional bulky, cubic-shape transmitting frame. The new transmitter enables convenient access to the tracked animal, causes no visual distractions, and occupies much less space. We also employ a tiny solenoidal search coil instead of the conventional scleral search coils. Such a small solenoidal search coil attached laterally to the eye does not limit the peripheral field of view and allows the animal to perform its standard behavioral tasks. The flat transmitter comprises eight transmitting coils that allow us to monitor not only the orientation of a search coil but also its location. To test the efficiency of the new approach, we have measured the location and orientation of the solenoidal search coils attached to the eyes and head of an archer fish during swimming, targeting, and shooting. The size of the coils attached to the fish eyes was 2 mm in diameter and 2 mm in length, and the size of the coil attached to the fish head was 4 mm in diameter and 4 mm in length. The transmitter size was 60 cm times 60 cm times 2 cm. At a 25 cm from the transmitter, we have obtained the tracking resolution of 3 millidegree and 8.3 mu m rms for a 200-Hz bandwidth. Such a performance is good enough to precisely monitor the fastest component in the fish eyes movements. The fish with the search coils on the eyes and head correctly hits the target up to 20 times during an experimental session, which is similar to the shooting rate of the fish without the search coils. This implies that our new design does not introduce much discomfort for the fish.

Navigation systems are useful instruments in cranial neurosurgery. For specification of position, so-called sensor-based navigation techniques use: (a) a signal emitter that generates a defined electromagnetic field in the area of the operation site; and (b) small sensors that detect the position of various operating instruments in the electromagnetic field. For a long time, owing to a lack of clinical data and long-term studies, electromagnetic systems have been regarded as error-prone and imprecise. With the development of a pulsed direct current (DC) technique, precision levels can now be reached that are comparable with those of established optical and mechanical measuring procedures. However, it must be noted that the influence on the measuring accuracy within the operating field increases with increasing susceptibility of the various metals used in the operating theatre (titanium

Tracking human body motions using inertial sensors has become a well-accepted method in ambulatory applications since the subject is not confined to a lab-bounded volume. However, a major drawback is the inability to estimate relative body positions over time because inertial sensor information only allows position tracking through strapdown integration, but does not provide any information about relative positions. In addition, strapdown integration inherently results in drift of the estimated position over time. We propose a novel method in which a permanent magnet combined with 3-D magnetometers and 3-D inertial sensors are used to estimate the global trunk orientation and relative pose of the hand with respect to the trunk. An Extended Kalman Filter is presented to fuse estimates obtained from inertial sensors with magnetic updates such that the position and orientation between the human hand and trunk as well as the global trunk orientation can be estimated robustly. This has been demonstrated in multiple experiments in which various hand tasks were performed. The most complex task in which simultaneous movements of both trunk and hand were performed resulted in an average rms position difference with an optical reference system of $19.7\pm 2.2$ mm whereas the relative trunk-hand and global trunk orientation error was $2.3\pm 0.9$ and $8.6\pm 8.7$ deg respectively.

To assess whether our ureteroscopic real-time navigation system has the possibility to reduce radiation exposure and improve performance of ureteroscopic maneuvers in surgeons of various ages and experience levels.Our novel ureteroscopic navigation system used a magnetic tracking device to detect the position of the ureteroscope and display it on a three-dimensional image. We recruited 31 urologists from five institutions to perform two tasks. Task 1 consisted of finding three internal markings on the phantom calices. Task 2 consisted of identifying all calices by ureteroscopy. In both tasks, participants performed with simulated fluoroscopy first, followed by our navigation system. Accuracy rates (AR) for identification, required time (T) for completing the task, migration length (ML), and time exposed to simulated fluoroscopy were recorded.The AR, T, and ML for both tasks were significantly better with the navigation system than without it (Task 1 with simulated fluoroscopy vs with navigation: AR 87.1 % vs 98.9%, P=0.003; T 355 s vs 191 s, P0.0001; ML 4627 mm vs 2701 mm, P0.0001. Task 2: AR 88.2% vs 96.7%, P=0.011; T 394 s vs 333 s, P=0.027; ML 5966 mm vs 5299 mm, P=0.0006). In both tasks, the participants used the simulated fluoroscopy about 20% of the total task time.Our navigation system, while still under development, could help surgeons of all levels to achieve better performances for ureteroscopic maneuvers compared with using fluoroscopic guidance. It also has the potential to reduce radiation exposure during fluoroscopy.

© 2015 SPIE. Ultrasound calibration is a necessary procedure in many image-guided interventions, relating the position of tools and anatomical structures in the ultrasound image to a common coordinate system. This is a necessary component of augmented reality environments in image-guided interventions as it allows for a 3D visualization where other surgical tools outside the imaging plane can be found. Accuracy of ultrasound calibration fundamentally affects the total accuracy of this interventional guidance system. Many ultrasound calibration procedures have been proposed based on a variety of phantom materials and geometries. These differences lead to differences in representation of the phantom on the ultrasound image which subsequently affect the ability to accurately and automatically segment the phantom. For example, taut wires are commonly used as line fiducials in ultrasound calibration. However, at large depths or oblique angles, the fiducials appear blurred and smeared in ultrasound images making it hard to localize their cross-section with the ultrasound image plane. Intuitively, larger diameter phantoms with lower echogenicity are more accurately segmented in ultrasound images in comparison to highly reflective thin phantoms. In this work, an evaluation of a variety of calibration phantoms with different geometrical and material properties for the phantomless calibration procedure was performed. The phantoms used in this study include braided wire, plastic straws, and polyvinyl alcohol cryogel tubes with different diameters. Conventional B-mode and synthetic aperture images of the phantoms at different positions were obtained. The phantoms were automatically segmented from the ultrasound images using an ellipse fitting algorithm, the centroid of which is subsequently used as a fiducial for calibration. Calibration accuracy was evaluated for these procedures based on the leave-one-out target registration error. It was shown that larger diameter phantoms with lower echogenicity are more accurately segmented in comparison to highly reflective thin phantoms. This improvement in segmentation accuracy leads to a lower fiducial localization error, which ultimately results in low target registration error. This would have a profound effect on calibration procedures and the feasibility of different calibration procedures in the context of image-guided procedures.

The wrist and thumb postures adopted during the use of three different types of computer mouse (mini mouse; standard mouse; MouseMan) to perform eight standardized tasks were evaluated. Thirty elementary students between seven to twelve years of age were studied using a magnetic tracking system. The peak value and angular range of motion of the wrist and thumb extension/flexion and radial/ulnar deviation were measured during performing 8 standard tasks. There were statistically significant larger values in the standard mice with regard to extreme wrist extension. Angular range of wrist extension observed for the standard mice were also much higher than the mini mouse and MouseMan. There were statistically significant larger values in the MouseMan with regard to extreme wrist ulnar deviation, and an average decrease in extreme thumb flexion and angular range of thumb flexion. The results from the questionnaire showed that most elementary students preferred to use the standard mouse (40%) next was the MouseMan (37%); and the last the mini mouse (23%). The recommendation of mouse types based on the hand length for elementary students was not statistically significant in our study.

The purpose of this study was to determine whether plane, end-range determination, or scapular motion affects shoulder range-of-motion measurements. In 16 healthy subjects, instrumentation with a magnetic tracking device was used to measure shoulder internal and external range of motion. The arm was supported while it was rotated either actively or passively with a measured torque. There was a significant main effect of plane for internal rotation (P < .001) but not for external rotation (P = .584). Passive humerothoracic motion was significantly greater than active humerothoracic motion for internal rotation (P < .006) and external rotation (P < .01). Active and passive humerothoracic motion was significantly greater than active and passive glenohumeral motion in 6 of the 7 active conditions and all 7 passive conditions (P < .002). Our results suggest that significant amounts of scapulothoracic motion may impact measurements of isolated glenohumeral joint motion.

We investigated whether postural instability can predict motion sickness and studied relations among instability, motion sickness, and vection. Nine men and 4 women (mean age = 19.85 years) were exposed, while standing, to an optical simulation of body sway. Head motion was recorded using a magnetic tracking system. Postural instabilities were observed prior to the onset of motion sickness. Vection was reported by most participants, including all who became ill. A discriminant analysis revealed that parameters of postural motion accurately predicted motion sickness. The results confirm that postural instability precedes motion sickness and suggest that measures of postural motion may serve as reliable predictors of motion sickness. Potential applications of this research include the development of on-line diagnostic tools that will allow for the prevention of motion sickness in operational and training settings.

© 2017 Society of Photo-Optical Instrumentation Engineers (SPIE). Ultrasound (US)-guided interventions are often enhanced via integration with an augmented reality environment, a necessary component of which is US calibration. Calibration requires the segmentation of fiducials, i.e., a phantom, in US images. Fiducial localization error (FLE) can decrease US calibration accuracy, which fundamentally affects the total accuracy of the interventional guidance system. Here, we investigate the effects of US image reconstruction techniques as well as phantom material and geometry on US calibration. It was shown that the FLE was reduced by 29% with synthetic transmit aperture imaging compared with conventional B-mode imaging in a Z-bar calibration, resulting in a 10% reduction of calibration error. In addition, an evaluation of a variety of calibration phantoms with different geometrical and material properties was performed. The phantoms included braided wire, plastic straws, and polyvinyl alcohol cryogel tubes with different diameters. It was shown that these properties have a significant effect on calibration error, which is a variable based on US beamforming techniques. These results would have important implications for calibration procedures and their feasibility in the context of image-guided procedures.

Bulk patient motion during transthoracic 3-D echocardiography (3DE) produces image plane misregistration and errors in left ventricular (LV) volume and ejection fraction (EF). To correct for patient motion, we used a magnetic locating system to track both the ultrasound transducer and the chest wall of the patient, so images could be registered in a patient-centered coordinate system ("correction"). Fourteen subjects each underwent 3DE, with deliberate patient motion, to measure LV volume and EF. Results were compared to magnetic resonance imaging (MRI). Without correction, 3DE differed significantly from MRI (EF: r = 0.78, SEE = 5.8%). Application of correction increased 3DE accuracy, despite patient motion (EF: r = 0.91, SEE = 3.7%), to a level comparable to that of 3DE in the absence of motion (EF: r = 0.93, SEE = 3.5%). Patient motion during 3DE examination can be corrected using a magnetic spatial location system.

Test-retest repeated measures and correlational design.To examine the reliability and validity of a "modified" digital inclinometer to assess scapular upward rotation during humeral elevation in the scapular planeEvidence exists that scapular motion is related to shoulder pathology; however, evaluation and treatment planning for shoulder rehabilitation often fails to include an objective assessment of scapular motion.Two-dimensional measurements by the inclinometer were taken with the arm in a static position. These data were compared to 3-dimensional measurements obtained using a magnetic tracking device with the arm fixed and during arm movement. Both methods were used to assess scapular upward rotation positions with the arm at rest and at 60 degrees , 90 degrees , and 120 degrees of humeral elevation in the scapular plane. Both scapulae were tested on a total of 39 subjects, 16 with shoulder pathology and 23 without. Reliability was assessed using repeated measurements from the inclinometer. Validity was assessed using 2 separate comparisons: inclinometer and magnetic tracking device under static arm conditions and inclinometer and magnetic tracking device during active arm elevation. Reliability and validity were assessed at all 4 arm positions.Intraclass correlation coefficients (ICC [3,1]) varied from 0.89 to 0.96. Pearson Product Moment correlation coefficients, used to assess validity of the static inclinometer, varied from r = 0.74 to 0.92 compared with the static magnetic tracking measures, and from r = 0.59 to 0.73 compared with the active magnetic tracking measures taken during arm elevation.The "modified" digital inclinometer demonstrated good to excellent intrarater reliability and good to excellent validity when measuring scapular upward rotation during static positions of humeral elevation in the scapular plane.

This study was performed to compare a novel three-dimensional echocardiography (3DE) system to clinical two-dimensional echocardiography (2DE) and magnetic resonance imaging (MRI) for determination of left ventricular mass (LVM) in humans. LVM is an independent predictor of cardiac morbidity and mortality. Echocardiography is the most widely used clinical method for assessment of LVM, as it is non-invasive, portable and relatively inexpensive. However, when measuring LVM, 2DE is limited by assumptions about ventricular shape which do not affect 3D echo. Methods: A total of 25 unselected patients underwent 3DE, 2DE and MRI. Three-dimensional echo used a magnetic scanhead tracker allowing unrestricted selection and combination of images from multiple acoustic windows. Mass by quantitative 2DE was assessed using seven different geometric formulas. Results: LVM by MRI ranged from 91 to 316 g. There was excellent agreement between 3DE and MRI (r = 0.99, SEE = 6.9 g). Quantitative 2D methods correlated well with but underestimated MRI (r = 0.84–0.92) with SEEs over threefold greater (22.5–30.8 g). Interobserver variation was 7.6% for 3DE vs. 17.7% for 2DE. Conclusions: LVM in humans can be measured accurately, relative to MRI, by transthoracic 3D echo using magnetic tracking. Compared to 2D echo, 3D echocardiography significantly improves accuracy and reproducibility.