Electromagnetic (EM) tracking systems

Electromagnetics in Surgical Navigation: Accurate Object Tracking

This article was recently published by Medical Product Outsourcing and written by Garrett Plank. He explores how Electromagnetic (EM) tracking systems enable real-time motion tracking when clinicians have no line of sight during a patient’s procedure. Find the original article here:

Electromagnetic (EM) tracking systems enable real-time motion tracking when clinicians have no line of sight during a patient’s procedure. However, while these systems have long played a role in treatment and diagnosis, many came into existence before the wide adoption of robotic and minimally invasive surgical techniques. This leads to the problem that off-the-shelf systems have—limitations that prevent them from meeting modern surgical navigation needs. For example, many can handle only fixed and limited navigation volumes and a limited number of sensors. Instrument tracking may not be possible throughout the entire procedure space, requiring additional X-ray radiation and exposing patients and medical staff to its harmful effects.

At the same time, EM tracking is an ideal option for advanced object tracking and is very effective in locating medical instruments inside the body when there is no clear line of sight. This adds crucial value in enabling minimally invasive and robotic techniques to be applied to more types of procedures in more disciplines. To tap into this potential, next-generation EM systems are solving the technology’s inherent challenges from the ground up.

The Shortcomings of Early EM Tracking

Older EM tracking systems rely on bulky electromagnetic field generators, often incompatible with imaging equipment commonly used during procedures such as computed tomography (CT), fluoroscopy, or cone-beam CT (CBCT). The presence of metal in the surgical space—along with additional equipment such as fluoroscopes, robots, and other metal objects and systems in the room—may introduce interference and cause tracking errors in such an EM system. Without detection or correction of these distortions, tracking accuracy and precision is inadequate. Manufacturers’ attempts to implement these off-the-shelf EM systems have been met with challenges. They typically cannot meet all the demands of minimally invasive procedures and function with low position sample rates. Customization can be complex and exacerbated by the demands of manufacturing, maintenance, sensor integration, and support.

Customization, Distortion Detection, and Mitigation

Illustrated by the EM tracking system developed by Radwave and integrating sensors from TT Electronics, this optimized system consists of three primary components: the control unit, antenna, and sensors offering both five and six degrees of freedom (5DOF/6DOF). Each component can be customized based on the specific requirements of a particular medical device and its procedure domain.

In a modern EM tracking platform, the antenna generates a magnetic field that creates the sensing volume. Its primary design is as a flat panel that can be placed underneath the patient and appears radiolucent (transparent to X-rays) during fluoroscopy. The Radwave platform approach makes it suitable to support a broad range of surgical procedures and tools; sensors that enter this sensing volume, such as various surgical tools, can be tracked within sub-millimeter accuracy.

For example, the standard sensing volume created by its field generator antenna is 40cm × 50cm × 45cm. While this is a large volume (supporting navigation from thigh to heart), it can be further expanded to track sensors at a greater distance from the antenna. The physical antenna and its resulting sensing volume can also be reduced, if desired, for specific procedures.

Minimizing Radiation to Patients and Healthcare Providers

The system offers high location confidence in up to 24 sensors, with simultaneously high sampling rates of information across all sensors. In a novel advancement of EM tracking capabilities, the antenna is used to recognize if distortion is present, including its relative strength and the direction of its origin. In many surgical procedures, a number of reference sensors may be placed on the patient’s body to sense distortion from the surrounding hospital equipment. The optimized EM tracking platform mitigates this challenge by identifying distortion and executing a range of mitigations to provide accurate location information from the full array of sensors in the sensing volume.

Legacy antenna designs often struggle with image artifacts, for example when a C-arm collects lateral or oblique image angles during a procedure. With the next-gen EM tracking system’s distortion detection and mitigation capabilities, fluoroscopy image quality remains consistently high regardless of the Carm’s angle. As a result, there is no need to shift or move the antenna outside of the fluoroscopy field of view, further simplifying the procedure’s workflow.

Accelerating Time-to-Market

It is worthwhile to note while accuracy is vital, it’s not the only benefit of implementing a next-gen EM tracking system. The platform approach also provides a design and manufacturing advantage in highly competitive medical device design markets. While design and development time can vary, depending on the required level of customization the smart platform approach significantly accelerates time-to-market for device developers. This provides a sharp contrast to legacy or in-house EM systems that can face years of development to accommodate even moderate changes in the evolution of devices, sensors, or medical use cases.

Today’s optimized EM tracking system can detect and mitigate distortion and simultaneously track a wide array of sensor sizes and types, all while maintaining high sampling rates. As a result, developers can access seamless integration into a growing range of devices used for various minimally invasive surgical and robotic procedures. The market for surgical navigation is booming, and solving the challenges of EM tracking is likely to fuel even greater growth in these diverse clinical applications.

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