Evaluation of a new electromagnetic tracking system using a standardized assessment protocol

Center of Biomedical Engineering and Physics, Medical University of Vienna, Austria. Ludwig-Boltzmann Institute of Nuclear Medicine, Vienna, Austria.
Physics in Medicine and Biology (Impact Factor: 2.76). 06/2006; 51(10):N205-10. DOI: 10.1088/0031-9155/51/10/N01
Source: PubMed


This note uses a published protocol to evaluate a newly released 6 degrees of freedom electromagnetic tracking system (Aurora, Northern Digital Inc.). A practice for performance monitoring over time is also proposed. The protocol uses a machined base plate to measure relative error in position and orientation as well as the influence of metallic objects in the operating volume. Positional jitter (E(RMS)) was found to be 0.17 mm +/- 0.19 mm. A relative positional error of 0.25 mm +/- 0.22 mm at 50 mm offsets and 0.97 mm +/- 1.01 mm at 300 mm offsets was found. The mean of the relative rotation error was found to be 0.20 degrees +/- 0.14 degrees with respect to the axial and 0.91 degrees +/- 0.68 degrees for the longitudinal rotation. The most significant distortion caused by metallic objects is caused by 400-series stainless steel. A 9.4 mm maximum error occurred when the rod was closest to the emitter, 10 mm away. The improvement compared to older generations of the Aurora with respect to accuracy is substantial.

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    • "Localization System (Calypso Medical Technologies, Inc.), perform well in relatively clean environments [19]. But when metallic objects exist in the working volume, tracking errors may achieve several millimeters or even centimeters in position and several degrees in orientation [20]–[23]. Therefore, correction of tracking errors caused by the magnetic field distortions is critical for medical applications. One way to reduce error is to experimentally establish the dependencies between the actual target parameters and the reported values of the tracking system. "
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    ABSTRACT: We propose a novel self-correcting tracking technique that can minimize the dynamic distortion during magnetic tracking. In our method, the magnetic field distortion is estimated through field expansion and then minimized in an iterative tracking procedure. Sparse sensor arrays are designed to measure the spatial gradient tensors of the magnetic field for our method. Numerical results demonstrate that the tracking error caused by field distortion could be reduced from several tens of millimeters to below 2 millimeters.
    Full-text · Article · Aug 2014 · IEEE Transactions on Magnetics
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    • "Many studies assessing EM tracking systems for CAI can be found in the literature, e.g., [3], [6], [7], [15], [19], [25], [36], [39], [45], [51], [59], [60], [61], [66], [74], [82], [83], [86], [89], [102], [120], [122], [152], [154], [159], [165], [169], [170], [172], [196], [202], [206], [207]. However, in many cases, the results of these studies are not comparable because different measurement protocols and evaluation methods were used. "
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    ABSTRACT: Object tracking is a key enabling technology in the context of computer-assisted medical interventions. Allowing the continuous localization of medical instruments and patient anatomy, it is a prerequisite for providing instrument guidance to subsurface anatomical structures. The only widely used technique that enables real-time tracking of small objects without lineof- sight restrictions is electromagnetic (EM) tracking. While EM tracking has been the subject of many research efforts, clinical applications have been slow to emerge. The aim of this review paper is therefore to provide insight into the future potential and limitations of EM tracking for medical use. We describe the basic working principles of EM tracking systems, list the main sources of error, and summarize the published studies on tracking accuracy, precision and robustness along with the corresponding validation protocols proposed. State-of-the-art approaches to error compensation are also reviewed in depth. Finally, an overview of the clinical applications addressed with EM tracking is given. Throughout the paper, we report not only on scientific progress, but also provide a review on commercial systems. Given the continuous debate on the applicability of EM tracking in medicine, this paper provides a timely overview of the state-of-the-art in the field.
    Full-text · Article · May 2014 · IEEE Transactions on Medical Imaging
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    • "This implies that preoperative data-based catheter navigation can include substantial positioning errors because of CA deformation. Additionally, in discussions on the accuracy of EM tracking systems [15,16], CA deformation was considered to be more important than the registration or calibration procedure as a factor affecting errors in catheter navigation. In this study, the range of CA deformation was assessed at 5 important CA bifurcations for catheterization. "
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    ABSTRACT: Background To improve the accuracy of catheter navigation, it is important to develop a method to predict shifts of carotid artery (CA) bifurcations caused by intraoperative deformation. An important factor affecting the accuracy of electromagnetic maxillofacial catheter navigation systems is CA deformations. We aimed to assess CA deformation in different head and neck positions. Methods Using two sets of computed tomography angiography (CTA) images of six patients, displacements of the skull (maxillofacial segments), C1–C4 cervical vertebrae, mandible (mandibular segment), and CA along with its branches were analyzed. Segmented rigid bones around CA were considered the main causes of CA deformation. After superimposition of maxillofacial segments, C1–C4 and mandible segments were superimposed separately for displacement measurements. Five bifurcation points (vA–vE) were assessed after extracting the CA centerline. A new standardized coordinate system, regardless of patient-specific scanning positions, was employed. It was created using the principal axes of inertia of the maxillofacial bone segments of patients. Position and orientation parameters were transferred to this coordinate system. CA deformation in different head and neck positions was assessed. Results Absolute shifts in the center of gravity in the bone models for different segments were C1, 1.02 ± 0.9; C2, 2.18 ± 1.81; C3, 4.25 ± 3.85; C4, 5.90 ± 5.14; and mandible, 1.75 ± 2.76 mm. Shifts of CA bifurcations were vA, 5.52 ± 4.12; vB, 4.02 ± 3.27; vC, 4.39 ± 2.42; vD, 4.48 ± 1.88; and vE, 2.47 ± 1.32. Displacements, position changes, and orientation changes of C1–C4 segments as well as the displacements of all CA bifurcation points were similar in individual patients. Conclusions CA deformation was objectively proven as an important factor contributing to errors in maxillofacial navigation. Our study results suggest that small movements of the bones around CA can result in small CA deformations. Although patients’ faces were not fixed properly during CT scanning, C1–C4 and vA–vE displacements were similar in individual patients. We proposed a novel method for accumulation of the displacement data, and this study indicated the importance of surrounding bone displacements in predicting CA bifurcation.
    Full-text · Article · Sep 2012 · BioMedical Engineering OnLine
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