Enhancing endoscopic measurement: validating a quantitative method for polyp size and location estimation in upper gastrointestinal endoscopy.

BACKGROUND: Accurate measurement of polyps size is crucial in predicting malignancy, planning relevant intervention strategies and surveillance schedules. Endoscopists' visual estimations can lack precision. This study builds on our prior research, with the aim to evaluate a recently developed quantitative method to measure the polyp size and location accurately during a simulated endoscopy session. METHODS: The quantitative method merges information about endoscopic positions obtained from an electromagnetic tracking sensor, with corresponding points on the images of the segmented polyp border. This yields real-scale 3D coordinates of the border of the polyp. By utilising the sensor, positions of any anatomical landmarks are attainable, enabling the estimation of a polyp's location relative to them. To verify the method's reliability and accuracy, simulated endoscopies were conducted in pig stomachs, where polyps were artificially created and assessed in a test-retest manner. The polyp measurements were subsequently compared against clipper measurements. RESULTS: The average size of the fifteen polyps evaluated was approximately 12 ± 4.3 mm, ranging from 5 to 20 mm. The test-retest reliability, measured by the Intraclass Correlation Coefficient (ICC) for polyp size estimation, demonstrated an absolute agreement of 0.991 (95% CI 0.973-0.997, p < 0.05). Bland & Altman analysis revealed a mean estimation difference of - 0.17 mm (- 2.03%) for polyp size and, a mean difference of - 0.4 mm (- 0.21%) for polyp location. Both differences were statistically non-significant (p > 0.05). When comparing the proposed method with calliper measurements, the Bland & Altman plots showed 95% of size estimation differences between - 1.4 and 1.8 mm (- 13 to 17.4%) which was not significant (p > 0.05). CONCLUSIONS: The proposed method of measurements of polyp size and location was found to be highly accurate, offering great potential for clinical implementation to improve polyp assessment. This level of performance represents a notable improvement over visual estimation technique used in clinical practice.

Distortion-Free Magnetic Tracking of Metal Instruments in Image-Guided Interventions.

Electromagnetic tracking (EMT) can benefit image-guided interventions in cases where line of sight is unavailable. However, EMT can suffer from electromagnetic distortion in the presence of metal instruments. Metal instruments are widely used in laparoscopic surgery, ENT surgery, arthroscopy and many other clinical applications. In this work, we investigate the feasibility of tracking such metal instruments by placing the inductive sensor within the instrument shaft. We propose a magnetostatic model of the field within the instrument, and verify the results experimentally for frequencies from 6 kHz to 60 kHz. The impact of the instrument's dimensions, conductivity and transmitting field frequency is quantified for ranges representative of typical metal instruments used in image-guided interventions. We then performed tracking using the open-source Anser EMT system and quantify the error caused by the presence of the rod as a function of the frequency of the eight emitting coils for the system. The work clearly demonstrates why smaller tool diameters (less than 8 mm) are less susceptible to distortion, as well as identifying optimal frequencies (1 kHz to 2 kHz) for transmitter design to minimise for distortion in larger instruments.

A Robust Tri-Electromagnet-Based 6-DoF Pose Tracking System Using an Error-State Kalman Filter.

Magnetic pose tracking is a non-contact, accurate, and occlusion-free method that has been increasingly employed to track intra-corporeal medical devices such as endoscopes in computer-assisted medical interventions. In magnetic pose-tracking systems, a nonlinear estimation algorithm is needed to recover the pose information from magnetic measurements. In existing pose estimation algorithms such as the extended Kalman filter (EKF), the 3-DoF orientation in the S3 manifold is normally parametrized as unit quaternions and simply treated as a vector in the Euclidean space, which causes a violation of the unity constraint of quaternions and reduces pose tracking accuracy. In this paper, a pose estimation algorithm based on the error-state Kalman filter (ESKF) is proposed to improve the accuracy and robustness of electromagnetic tracking systems. The proposed system consists of three electromagnetic coils for magnetic field generation and a tri-axial magnetic sensor attached to the target object for field measurement. A strategy of sequential coil excitation is developed to separate the magnetic fields from different coils and reject magnetic disturbances. Simulation and experiments are conducted to evaluate the pose tracking performance of the proposed ESKF algorithm, which is also compared with standard EKF and constrained EKF. It is shown that the ESKF can effectively maintain the quaternion unity and thus achieve a better tracking accuracy, i.e., a Euclidean position error of 2.23 mm and an average orientation angle error of 0.45°. The disturbance rejection performance of the electromagnetic tracking system is also experimentally validated.

A scintillation dosimeter with real-time positional tracking information for in vivo dosimetry error detection in HDR brachytherapy.

PURPOSE: To evaluate the performance of an electromagnetic (EM)-tracked scintillation dosimeter in detecting source positional errors of IVD in HDR brachytherapy treatment. MATERIALS AND METHODS: Two different scintillator dosimeter prototypes were coupled to 5 degrees-of-freedom (DOF) EM sensors read by an Aurora V3 system. The scintillators used were a 0.3 × 0.4 × 0.4 mm3 ZnSe:O and a BCF-60 plastic scintillator of 0.5 mm diameter and 2.0 mm in length (Saint-Gobain Crystals). The sensors were placed at the dosimeter's tip at 20.0 mm from the scintillator. The EM sampling rate was 40/s while the scintillator signal was sampled at 100 000/s using two photomultiplier tubes from Hamamatsu (series H10722) connected to a data acquisition board. A high-pass filter and a low-pass filter were used to separate the light signal into two different channels. All measurements were performed with an afterloader unit (Flexitron-Elekta AB, Sweden) in full-scattered (TG43) conditions. EM tracking was further used to provide distance/angle-dependent energy correction for the ZnSe:O inorganic scintillator. For the error detection part, lateral shifts of 0.5 to 3 mm were induced by moving the source away from its planned position. Indexer length (longitudinal) errors between 0.5 to 10 mm were also introduced. The measured dose rate difference was converted to a shift distance, with and without using the positional information from the EM sensor. RESULTS: The inorganic scintillator had both a signal-to-noise-ratio (SNR) and signal-to-background-ratio (SBR) close to 70 times higher than those of the plastic scintillator. The mean absolute difference from the dose measurement to the dose calculated with TG-43U1 was 1.5% ±0.7%. The mean absolute error for BCF-60 detector was 1.7% ± 1.2 % $\pm 1.2\%$ when compared to TG-43 calculations formalism. With the inorganic scintillator and EM tracking, a maximum area under the curve (AUC) gain of 24.0% was obtained for a 0.5-mm lateral shift when using the EMT data with the ZnSe:O. Lower AUC gains were obtained for a 3-mm lateral shifts with both scintillators. For the plastic scintillator, the highest gain from using EM tracking information occurred for a 0.5-mm lateral shift at 20 mm from the source. The maximal gain (17.4%) for longitudinal errors was found at the smallest shifts (0.5 mm). CONCLUSIONS: This work demonstrates that integrating EM tracking to in vivo scintillation dosimeters enables the detection of smaller shifts, by decreasing the dosimeter positioning uncertainty. It also serves to perform position-dependent energy correction for the inorganic scintillator,providing better SNR and SBR, allowing detection of errors at greater distances from the source.

Implementation of the Calypso system: a commissioning experience.

Background: The aim of this study was to describe the clinical implementation of the Calypso system with its potential impact on the treatment delivery. Materials and methods: The influence of the electromagnetic array was investigated on the kilovoltage cone beam computed tomography (kV-CBCT) image quality using the CATPHAN 504 CBCT images. Then, the QFix kVue Calypso couch top and the array attenuation, and their dosimetric influence on the Volumetric modulated arc therapy (VMAT) treatments of prostate was evaluated. Results: Regarding the image quality, a significant increase of noise (p < 0.01) was detected with the array in place, resulting in a significant decrease in signal noise ratio (SNR) (p < 0.01). No difference in absolute contrast was observed. Finally, there was a significant decrease in contrast noise ratio (CNR) (p < 0.01) even if the deviation was only of 2.5%. For the dosimetric evaluation, the maximum attenuation of the couch was 12.02% and 13.19% for X6 and X6 flattening filter free (FFF), respectively (configuration of rails out). Besides, the mean attenuation of the array was 1.15% and 1.67% for X6 and X6 FFF, respectively. For the VMAT treatment plans, the mean dose was reduced by 0.61% for X6 and by 0.31% for X6 FFF beams when using the electromagnetic array. Conclusions: The Calypso system does not affect significantly the kV-CBCT image quality and the VMAT plan dose distribution.

Real-Time Wireless Tumor Tracking in Navigated Liver Resections: An Ex Vivo Feasibility Study.

BACKGROUND: Surgical navigation systems generally require intraoperative steps, such as intraoperative imaging and registration, to link the system to the patient anatomy. Because this hampers surgical workflow, we developed a plug-and-play wireless navigation system that does not require any intraoperative steps. In this ex vivo study on human hepatectomy specimens, the feasibility was assessed of using this navigation system to accurately resect a planned volume with small margins to the lesion. METHODS: For ten hepatectomy specimens, a planning CT was acquired in which a virtual spherical lesion with 5 mm margin was delineated, inside the healthy parenchyma. Using two implanted trackers, the real-time position of this planned resection volume was visualized on a screen, relative to the used tracked pointer. Experienced liver surgeons were asked to accurately resect the nonpalpable planned volume, fully relying on the navigation screen. Resected and planned volumes were compared using CT. RESULTS: The surgeons resected the planned volume while cutting along its border with a mean accuracy of - 0.1 ± 2.4 mm and resected 98 ± 12% of the planned volume. Nine out of ten resections were radical and one case showed a cut of 0.8 mm into the lesion. The sessions took approximately 10 min each, and no considerable technical issues were encountered. CONCLUSIONS: This ex vivo liver study showed that it is feasible to accurately resect virtual hepatic lesions with small planned margins using our novel navigation system, which is promising for clinical applications where nonpalpable hepatic metastases have to be resected with small resection margins.

Characterization of the Workspace and Limits of Operation of Laser Treatments for Vascular Lesions of the Lower Limbs.

The increase of the aging population brings numerous challenges to health and aesthetic segments. Here, the use of laser therapy for dermatology is expected to increase since it allows for non-invasive and infection-free treatments. However, existing laser devices require doctors' manually handling and visually inspecting the skin. As such, the treatment outcome is dependent on the user's expertise, which frequently results in ineffective treatments and side effects. This study aims to determine the workspace and limits of operation of laser treatments for vascular lesions of the lower limbs. The results of this study can be used to develop a robotic-guided technology to help address the aforementioned problems. Specifically, workspace and limits of operation were studied in eight vascular laser treatments. For it, an electromagnetic tracking system was used to collect the real-time positioning of the laser during the treatments. The computed average workspace length, height, and width were 0.84 ± 0.15, 0.41 ± 0.06, and 0.78 ± 0.16 m, respectively. This corresponds to an average volume of treatment of 0.277 ± 0.093 m3. The average treatment time was 23.2 ± 10.2 min, with an average laser orientation of 40.6 ± 5.6 degrees. Additionally, the average velocities of 0.124 ± 0.103 m/s and 31.5 + 25.4 deg/s were measured. This knowledge characterizes the vascular laser treatment workspace and limits of operation, which may ease the understanding for future robotic system development.

Comparison of finger kinematics between patients with hand osteoarthritis and healthy participants with and without joint protection programs.

STUDY DESIGN: This is a cross-sectional, clinical observational study. BACKGROUND: Finger range of motion (ROM) and functional performance are critical in many daily activities. Hand osteoarthritis (H-OA) is a prevalent disease that impairs both variables. Little quantitative research has been performed on finger kinematics during activities of daily living (ADLs) across health status and method of performance (with or without joint protection programs). PURPOSE: The purpose of this research is to examine the effects of H-OA and method of performance on ROM in the thumb, index, and middle digits (flexion/extension and abduction/adduction) during ADLs. METHODS: This study was conducted using 10 healthy participants (mean age: 28 years) and nine participants with H-OA (mean age: 72 years). All participants performed baseline ROM movements followed by 9 activities of daily living. These activities involved prehension type grasps and were performed with and without the recommended joint protection procedures specific to each task. Thumb IP and MCP, index distal interphalengeal (DIP) and proximal interphalengeal (PIP), and middle DIP and PIP joints were continuously recorded using an electromagnetic tracking system for ROM analysis. RESULTS: Participants with H-OA had a statistically significant decrease in ROM when comparing values measured in the healthy cohort during active ROM (25° decrease) and ADL ROM (25° decrease) in the flex/ext direction. Similarly, following joint protection instruction, a statistically significant decrease in ROM was found during tasks in the flex/ext direction (healthy participant decrease in ROM: 17°, H-OA decrease in ROM:10°) CONCLUSIONS: This study demonstrated that people with hand arthritis move through a smaller arc of motion when performing some functional tasks as compared with the controls, and that with instruction on joint protection techniques, participants made significant changes in the amount of movement used to perform tasks, which supports a proof of principle of joint protection.

Surgical navigation for challenging recurrent or pretreated intra-abdominal and pelvic soft tissue sarcomas.

BACKGROUND: This study assessed whether electromagnetic navigation can be of added value during resection of recurrent or post-therapy intra-abdominal/pelvic soft tissue sarcomas (STS) in challenging locations. MATERIALS AND METHODS: Patients were included in a prospective navigation study. A pre-operatively 3D roadmap was made and tracked using electromagnetic reference markers. During the operation, an electromagnetic pointer was used for the localization of the tumor/critical anatomical structures. The primary endpoint was feasibility, secondary outcomes were safety and usability. RESULTS: Nine patients with a total of 12 tumors were included, 7 patients with locally recurrent sarcoma. Three patients received neoadjuvant radiotherapy and three other patients received neoadjuvant systemic treatment. The median tumor size was 4.6 cm (2.4-10.4). The majority of distances from tumor to critical anatomical structures was <0.5 cm. The tumors were localized using the navigation system without technical or safety issues. Despite the challenging nature of these resections, 89% were R0 resections, with a median blood loss of 100 ml (20-1050) and one incident of vascular damage. Based on the survey, surgeons stated navigation resulted in shorter surgery time and made the resections easier. CONCLUSION: Electromagnetic navigation facilitates resections of challenging lower intra-abdominal/pelvic STS and might be of added value.

Planar Body-Mounted Sensors for Electromagnetic Tracking.

Electromagnetic tracking is a safe, reliable, and cost-effective method to track medical instruments in image-guided surgical navigation. However, patient motion and magnetic field distortions heavily impact the accuracy of tracked position and orientation. The use of redundant magnetic sensors can help to map and mitigate for patient movements and magnetic field distortions within the tracking region. We propose a planar inductive sensor design, printed on PCB and embedded into medical patches. The main advantage is the high repeatability and the cost benefit of using mass PCB manufacturing processes. The article presents new operative formulas for electromagnetic tracking of planar coils on the centimetre scale. The full magnetic analytical model is based on the mutual inductance between coils which can be approximated as being composed by straight conductive filaments. The full model is used to perform accurate system simulations and to assess the accuracy of faster simplified magnetic models, which are necessary to achieve real-time tracking in medical applications.

A Radiolucent Electromagnetic Tracking System for Use with Intraoperative X-ray Imaging.

In recent times, the use of electromagnetic tracking for navigation in surgery has quickly become a vital tool in minimally invasive surgery. In many procedures, electromagnetic tracking is used in tandem with X-ray technology to track a variety of tools and instruments. Most commercially available EM tracking systems can cause X-ray artifacts and attenuation due to their construction and the metals that form them. In this work, we provide a novel solution to this problem by creating a new radiolucent electromagnetic navigation system that has minimal impact on -ray imaging systems. This is a continuation of our previous work where we showed the development of the Anser open-source electromagnetic tracking system. Typical electromagnetic tracking systems operate by generating low frequency magnetic fields from coils that are located near the patient. These coils are typically made from copper, steel, and other dense radiopaque materials. In this work, we explore the use of low density aluminum to create these coils and we demonstrate that the effect on X-ray images is significantly reduced as a result of these novel changes in the materials used. The resulting field generator is shown to give at least a 60% reduction in the X-ray attenuation in comparison to our earlier designs. We verify that the system accuracy of approximately 1.5 mm RMS error is maintained with this change in design.

Verification of the Deep Brain Stimulation Electrode Position Using Intraoperative Electromagnetic Localization.

BACKGROUND: Electromagnetic (EM) localization has typically been used to direct shunt catheters into the ventricle. The objective of this study was to determine if this method of EM tracking could be used in a deep brain stimulation (DBS) electrode cannula to accurately predict the eventual location of the electrode contacts. METHODS: The Medtronic AxiEMTM system was used to generate the cannula tip location directed to the planned target site. Prior to clinical testing, a series of phantom modelling observations were made. RESULTS: Phantom trials (n = 23) demonstrated that the cannula tip could be accurately located at the target site with an error of between 0.331 ± 0.144 and 0.6 ± 0.245 mm, depending on the orientation of the delivery system to the axis of the phantom head. Intraoperative EM localization of the DBS cannula was performed in 84 trajectories in 48 patients. The average difference between the planned target and the EM stylet location at the cannula tip was 1.036 ± 0.543 mm. The average error between the planned target coordinates and the actual target electrode location (by CT) was 1.431 ± 0.607 and 1.145 ± 0.636 mm for the EM stylet location in the cannula (p = 0.00312), indicating that EM localization reflected the position of the target electrode more accurately than the planned target. CONCLUSIONS: EM localization can be used to verify the position of DBS electrodes intraoperatively with a high accuracy.

Assessment of Position Repeatability Error in an Electromagnetic Tracking System for Surgical Navigation.

In this paper we present a study of the repeatability of an innovative electromagnetic tracking system (EMTS) for surgical navigation, developed to overcome the state of the art of current commercial systems, allowing for the placement of the magnetic field generator far from the operating table. Previous studies led to the development of a preliminary EMTS prototype. Several hardware improvements are described, which result in noise reduction in both signal generation and the measurement process, as shown by experimental tests. The analysis of experimental results has highlighted the presence of drift in voltage components, whose effect has been quantified and related to the variation of the sensor position. Repeatability in the sensor position measurement is evaluated by means of the propagation of the voltage repeatability error, and the results are compared with the performance of the Aurora system (which represents the state of the art for EMTS for surgical navigation), showing a repeatability error about ten times lower. Finally, the proposed improvements aim to overcome the limited operating distance between the field generator and electromagnetic (EM) sensors provided by commercial EM tracking systems for surgical applications and seem to provide a not negligible technological advantage.

Prospective study on image-guided navigation surgery for pelvic malignancies.

BACKGROUND AND OBJECTIVES: Surgery of advanced tumors and lymph nodes in the pelvis can be challenging due to the narrow pelvic space and vital surrounding structures. This study explores the application of a novel electromagnetic navigation system to guide pelvic surgery. METHODS: This was a prospective study on surgery for malignancies in the pelvis. Preoperatively obtained imaging was used to create a patient-specific three-dimensional (3D) roadmap. In the operating room, the 3D roadmap was registered to an intraoperative computed tomography scan. A tracked pointer was used during surgery for guidance. Primary endpoint was safety and feasibility, secondary endpoints were accuracy and usability. RESULTS: Twenty-eight colorectal, four liposarcomas, and one gynecological patient were included. There were no safety issues. Navigation was feasible in 31 patients. The mean target registration errors of 4.0 and 6.3 mm were achieved for straight and French position, respectively. In seven of seven patients with a locally advanced rectal tumor and in seven of eight patients with recurrences, negative margins were achieved. Thirty-three of 36 target lymph nodes were successfully removed. Surgeons using the system indicated faster localization of the tumor and improved decisiveness. CONCLUSION: This novel surgical navigation system was safe and feasible during pelvic surgery and can facilitate its users.

An electromagnetic tracking needle clip: an enabling design for low-cost image-guided therapy.

INTRODUCTION: In this study, we hypothesized a disposable low-cost needle clip with a specially designed electromagnetic (EM) tracking sensor. It could be mounted onto 16- to 22-gauge needles, allowing the tip of the needle to be tracked in CT or US image-guided procedures using the Aurora EM tracking system. MATERIAL AND METHODS: A 3 D printed EM needle clip case contains a pair of specially designed electromagnetic solenoids, positioned perpendicularly to each other in order to achieve six degrees of freedom for tracking the tip of the needle. The performance of the EM tracking needle clip was evaluated. RESULTS: A low-cost 3D-printed disposable needle clip with specially designed EM tracking sensors that can be mounted on 16- to 22-gauge needles was designed. This needle clip has a 570 mm ×600 mm ×600 mm (L × W × H) working volume, an error <0.7 mm in the axial direction and 0.8 mm in the radial direction. The targeting accuracy results are on par with the commercially available EM tracking needles. CONCLUSION: The designed EM needle clip provided successful needle tracking, with acceptable accuracy, and competitive performance compared to existing products. This proposed design may increase the clinical adoption of EM tracking needles because of its user-friendly design and low cost.

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.

Correlation between intrafractional motion and dosimetric changes for prostate IMRT: Comparison of different adaptive strategies.

PURPOSE: To retrospectively analyze and estimate the dosimetric benefit of online and offline motion mitigation strategies for prostate IMRT. METHODS: Intrafractional motion data of 21 prostate patients receiving intensity-modulated radiotherapy was acquired with an electromagnetic tracking system. Target trajectories of 734 fractions were analyzed per delivered multileaf-collimator segment in five motion metrics: three-dimensional displacement, distance from beam axis (DistToBeam), and three orthogonal components. Time-resolved dose calculations have been performed by shifting the target according to the sampled motion for the following scenarios: without adaptation, online-repositioning with a minimum threshold of 3 mm, and an offline approach using a modified field order applying horizontal before vertical beams. Change of D95 (targets) or V65 (organs at risk) relative to the static case, that is, ΔD95 or ΔV65, was extracted per fraction in percent. Correlation coefficients (CC) between the motion metrics and the dose metrics were extracted. Mean of patient-wise CC was used to evaluate the correlation of motion metric and dosimetric changes. Mean and standard deviation of the patient-wise correlation slopes (in %/mm) were extracted. RESULTS: For ΔD95 of the prostate, mean DistToBeam per fraction showed the highest correlation for all scenarios with a relative change of -0.6 ± 0.7%/mm without adaptation and -0.4 ± 0.5%/mm for the repositioning and field order strategies. For ΔV65 of the bladder and the rectum, superior-inferior and posterior-anterior motion components per fraction showed the highest correlation, respectively. The slope of bladder (rectum) was 14.6 ± 5.8 (15.1 ± 6.9) %/mm without adaptation, 14.0 ± 4.9 (14.5 ± 7.4) %/mm for repositioning with 3 mm, and 10.6 ± 2.5 (8.1 ± 4.6) %/mm for the field order approach. CONCLUSIONS: The correlation slope is a valuable concept to estimate dosimetric deviations from static plan quality directly based on the observed motion. For the prostate, both mitigation strategies showed comparable benefit. For organs at risk, the field order approach showed less sensitive response regarding motion and reduced interpatient variation.

Distorter Characterisation Using Mutual Inductance in Electromagnetic Tracking.

Electromagnetic tracking (EMT) is playing an increasingly important role in surgical navigation, medical robotics and virtual reality development as a positional and orientation reference. Though EMT is not restricted by line-of-sight requirements, measurement errors caused by magnetic distortions in the environment remain the technology's principal shortcoming. The characterisation, reduction and compensation of these errors is a broadly researched topic, with many developed techniques relying on auxiliary tracking hardware including redundant sensor arrays, optical and inertial tracking systems. This paper describes a novel method of detecting static magnetic distortions using only the magnetic field transmitting array. An existing transmitter design is modified to enable simultaneous transmission and reception of the generated magnetic field. A mutual inductance model is developed for this transmitter design in which deviations from control measurements indicate the location, magnitude and material of the field distorter to an approximate degree. While not directly compensating for errors, this work enables users of EMT systems to optimise placement of the magnetic transmitter by characterising a distorter's effect within the tracking volume without the use of additional hardware. The discrimination capabilities of this method may also allow researchers to apply material-specific compensation techniques to minimise position error in the clinical setting.

Choledochoscopic Examination of a 3-Dimensional Printing Model Using Augmented Reality Techniques: A Preliminary Proof of Concept Study.

BACKGROUND: We applied augmented reality (AR) techniques to flexible choledochoscopy examinations. METHODS: Enhanced computed tomography data of a patient with intrahepatic and extrahepatic biliary duct dilatation were collected to generate a hollow, 3-dimensional (3D) model of the biliary tree by 3D printing. The 3D printed model was placed in an opaque box. An electromagnetic (EM) sensor was internally installed in the choledochoscope instrument channel for tracking its movements through the passages of the 3D printed model, and an AR navigation platform was built using image overlay display. The porta hepatis was used as the reference marker with rigid image registration. The trajectories of the choledochoscope and the EM sensor were observed and recorded using the operator interface of the choledochoscope. RESULTS: Training choledochoscopy was performed on the 3D printed model. The choledochoscope was guided into the left and right hepatic ducts, the right anterior hepatic duct, the bile ducts of segment 8, the hepatic duct in subsegment 8, the right posterior hepatic duct, and the left and the right bile ducts of the caudate lobe. Although stability in tracking was less than ideal, the virtual choledochoscope images and EM sensor tracking were effective for navigation. CONCLUSIONS: AR techniques can be used to assist navigation in choledochoscopy examinations in bile duct models. Further research is needed to determine its benefits in clinical settings.

[Design of Electromagnetic Tracking System Using Rotating Magnetic Field Based on DSP].

This paper realized an electromagnetic tracking system based on electrically-controlled rotating magnetic field. A tracking system using the digital signal processor (DSP) as the control processing device was developed, including a controllable constant current source module, a magnetic field source module, a three-axis magnetic sensor and ADC interface circuit. The experimental results verified that each time the system could be stable positioning, average error of position was 0.282 cm, the average error of orientation was 0.696o, the positioning time was 1.572 s. Through calibration and further improvement of the hardware circuit, the performance of the system is expected to further improve.