This paper proposes an assessment protocol that incorporates both hardware and analysis methods for evaluation of
electromagnetic tracker accuracy in different clinical environments. The susceptibility of electromagnetic tracker
measurement accuracy is both highly dependent on nearby ferromagnetic interference sources and non-isotropic. These
inherent limitations combined with the various hardware components and assessment techniques used within different
studies makes the direct comparison of measurement accuracy between studies difficult. This paper presents a multicenter
study to evaluate electromagnetic devices in different clinical environments using a common hardware phantom
and assessment techniques so that results are directly comparable. Measurement accuracy has been shown to be in the
range of 0.79-6.67mm within a 180mm3 sub-volume of the Aurora measurement space in five different clinical
environments.
Radiofrequency ablation is becoming an increasingly attractive option for minimally invasive treatment of liver tumors.
In this procedure, the tumor and its margin are ablated using radiofrequency ablation probes that cover a region from
2cm to 7cm in diameter. For a large or irregularly shaped tumor, multiple ablations with overlapping probe placements
are required. In this paper, we propose a treatment planning system to optimize these placements. A general optimization
framework based on inverse planning methods is designed to generate the treatment plan. An objective function is
defined to describe the coverage of the ablation volumes. Powell's method and simulated annealing algorithms are used
to find the solution. Pre-computed mask volumes and an initial placement based on a Euclidean Distance Transform are
used to speed up the computation, which can generally take a few seconds to several minutes. To ensure accurate
placement of the ablation probe, we also propose a system architecture for integrating the treatment planning system
with our previously developed image-guided surgery system, which uses an electromagnetic tracking device. We
present some preliminary results from synthetic data to validate our treatment planning algorithm and system concept.
The Image-Guided Surgery Toolkit (IGSTK) is an open source C++ software library that provides the basic components
needed to develop image-guided surgery applications. The focus of the toolkit is on robustness using a state machine
architecture. This paper presents an overview of the project based on a recent book which can be downloaded from
igstk.org. The paper includes an introduction to open source projects, a discussion of our software development process
and the best practices that were developed, and an overview of requirements. The paper also presents the architecture
framework and main components. This presentation is followed by a discussion of the state machine model that was
incorporated and the associated rationale. The paper concludes with an example application.
Electromagnetic trackers have found inroads into medical applications as a tool for navigation in recent years. Their susceptibility to interference from both electromagnetic and ferromagnetic sources have prompted several accuracy assessment studies in past years. To the best of our knowledge, this is the first accuracy study conducted to characterize measurement accuracy of an NDI AURORA electromagnetic tracker within a CyberKnife radiosurgery suite. CyberKnife is a frameless, stereotactic radiosurgery device used to ablate tumors within the brain, spine and in recent years, the chest and abdomen. This paper uses a data collection protocol to collect uniformly distributed data points within a subset of the AURORA measurement volume in a CyberKnife suite. The key aim of the study is to determine the extent to which large metal components of the CyberKnife stereotactic radiosurgery device and robot mount contribute to overall system performance for the AURORA electromagnetic device. A secondary goal of the work is to determine the variation in accuracy and device behavior with the presence of ionizing radiation when the LINAC is turned on.
An effective treatment method for organs that move with respiration (such as the lungs, pancreas, and liver) is a major goal of radiation medicine. In order to treat such tumors, we need (1) real-time knowledge of the current location of the tumor, and (2) the ability to adapt the radiation delivery system to follow this constantly changing location. In this study, we used electromagnetic tracking in a swine model to address the first challenge, and to determine if movement of a marker attached to the skin could accurately predict movement of an internal marker embedded in an organ. Under approved animal research protocols, an electromagnetically tracked needle was inserted into a swine liver and an electromagnetically tracked guidewire was taped to the abdominal skin of the animal. The Aurora (Northern Digital Inc., Waterloo, Canada) electromagnetic tracking system was then used to monitor the position of both of these sensors every 40 msec. Position readouts from the sensors were then tested to see if any of the movements showed correlation. The strongest correlations were observed between external anterior-posterior motion and internal inferior-superior motion, with many other axes exhibiting only weak correlation. We also used these data to build a predictive model of internal motion by taking segments from the data and using them to derive a general functional relationship between the internal needle and the external guidewire. For the axis with the strongest correlation, this model enabled us to predict internal organ motion to within 1 mm.
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