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 line-of-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.

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Electromagnetic tracking in medicine--a review of technology, validation, and applications.

Highly accurate spatial measurement systems are among the enabling technologies that
have made image-guided surgery possible in modern operating theaters. Assessing the
accuracies of such systems is subject to much ambiguity, though. The underlying
mathematical models that convert raw sensor data into position and orientation
measurements of sufficient accuracy complicate matters by providing measurements
having non-uniform error distributions throughout their measurement volumes.
Users are typically unaware of these issues, as they are usually presented with only
a few specifications based on some "representative" statistics that were themselves
derived using various data reduction methods. As a result, much of the important
underlying information is lost. Further, manufacturers of spatial measurement
systems often choose protocols and statistical measures that emphasize the strengths
of their systems and diminish their limitations. Such protocols often do not reflect
the end users' intended applications very well. Users and integrators thus need to
understand many aspects of spatial metrology in choosing spatial measurement systems
that are appropriate for their intended applications. We examine the issues by
discussing some of the protocols and their statistical measures typically used by
manufacturers. The statistical measures for a given protocol can be affected by many
factors, including the volume size, region of interest, and the amount and type of
data collected. We also discuss how different system configurations can affect the
accuracy. Single-marker and rigid body calibration results are presented, along with
a discussion of some of the various factors that affect their accuracy. Although the
findings presented here were obtained using the NDI Polaris optical tracking systems,
many are applicable to spatial measurement systems in general.

Accuracy assessment and interpretation for optical tracking systems

Contemporary imaging modalities can now provide the surgeon with high quality three- and four-dimensional images depicting not only normal anatomy and pathology, but also vascularity and function. A key component of image-guided surgery (IGS) is the ability to register multi-modal pre-operative images to each other and to the patient. The other important component of IGS is the ability to track instruments in real time during the procedure and to display them as part of a realistic model of the operative volume. Stereoscopic, virtual- and augmented-reality techniques have been implemented to enhance the visualization and guidance process. For the most part, IGS relies on the assumption that the pre-operatively acquired images used to guide the surgery accurately represent the morphology of the tissue during the procedure. This assumption may not necessarily be valid, and so intra-operative real-time imaging using interventional MRI, ultrasound, video and electrophysiological recordings are often employed to ameliorate this situation. Although IGS is now in extensive routine clinical use in neurosurgery and is gaining ground in other surgical disciplines, there remain many drawbacks that must be overcome before it can be employed in more general minimally-invasive procedures. This review overviews the roots of IGS in neurosurgery, provides examples of its use outside the brain, discusses the infrastructure required for successful implementation of IGS approaches and outlines the challenges that must be overcome for IGS to advance further.

https://iopscience.iop.org/article/10.1088/0031-9155/51/14/R01/pdf

Image-guidance for surgical procedures

An apparatus and method for diagnosis or treatment of a vessel or organ. The apparatus includes a deformable body such as a catheter having a tissue ablation end effector and an irrigation channel in fluid communication therewith. At least two sensors are disposed within a distal extremity of the deformable body, the sensors being responsive to a wave in a specified range of frequency to detect deformations resulting from a contact force applied to the distal extremity. A microprocessor can be operatively coupled with the sensors to receive outputs therefrom, the microprocessor being configured to resolve a multi-dimensional force vector corresponding to the contact force. In one embodiment, the sensors are fiber Bragg grating sensors, and the wave is injected into the fiber Bragg grating strain sensors from a laser diode.

Medical apparatus system having optical fiber load sensing capability

Navigation with electromagnetic tracking for interventional radiology procedures: a feasibility study.

Electromagnetic tracking systems have found increasing use in medical applications during the last few years. As with most non-trivial spatial measurement systems, the complex determination of positions and orientations from their underlying raw sensor measurements results in complicated, non-uniform error distributions over the specified measurement volume. This makes it difficult to unambiguously determine accuracy and performance assessments that allow users to judge the suitability of these systems for their particular needs. Various assessment protocols generally emphasize different measurement aspects that typically arise in clinical use. This can easily lead to inconclusive or even contradictory conclusions. We examine some of the major issues involved and discuss three useful calibration protocols. The measurement accuracy of a system can be described in terms of its 'trueness' and its 'precision'. Often, the two are strongly coupled and cannot be easily determined independently. We present a method that allows the two to be disentangled, so that the resultant trueness properly represents the systematic, non-reducible part of the measurement error, and the resultant precision (or repeatability) represents only the statistical, reducible part. Although the discussion is given largely within the context of electromagnetic tracking systems, many of the results are applicable to measurement systems in general.

Accuracy assessment protocols for elektromagnetic tracking systems.

A flexible instrument includes a flexible member having a proximal portion, an intermediate portion, and a distal portion At least one optical sensor positioned proximate the proximal portion of the flexible member provides a proximal end position signal indicative of the position of the proximal portion of the flexible member At least one flexible member sensor positioned proximate one of the other portions of the flexible member provides a second position signal indicative of the position of the other portion of the flexible member

Stephen Eldon Leis

Papers

Accuracy assessment protocols for elektromagnetic tracking systems.

A flexible instrument with optical sensors