Electromagnetic Tracking Advances with Distortion Detection & Mitigation

Advancements in electromagnetic (EM) tracking systems enable a greater application of minimally invasive procedures.  This adds value to interventional or robotic-navigated procedures, which are less invasive and proven to have fewer complications, shorter hospital stays, faster recovery, and lower overall costs.  EM tracking systems increase access, precision, and navigation during procedures – augmenting a clinician’s training and skill by tapping into the capabilities of tiny sensor assemblies integrated with finished medical devices and navigation equipment.  It is an advantage that is applicable in a great range of clinical applications, improving patient outcomes in cardiology and electrophysiology, vascular, interventional radiology and oncology, neurology, ENT, orthopedics, pulmonology, and other procedural areas.

Yet, inaccuracies may be introduced when metal is present in an EM system’s “sensing volume,” causing its sensors to become untrackable or be tracked imprecisely.  Think of a surgical suite or treatment setting with C-Arms or conductive material in patient beds.  This need to maintain accuracy and precision in the presence of metal has historically been the primary EM challenge for designers and OEMs of medical devices.  Today, a number of factors are working together to break new ground in EM tracking.  Novel advancements feature detection and mitigation of distortion caused by equipment in a surgical setting.  Coupled with advanced electromagnetic sensors, these capabilities improve accuracy and precision to enable a flexible platform approach for a broad number of devices and procedures.  Solving inherent distortion challenges enables broad viability for EM systems, empowering physicians with smart, minimally invasive options for highly precise navigation of more areas of the human body.

Managing distortion for clinical advantage

Electromagnetic tracking offers the advantages of surgical navigation beyond line of sight; however, have been impeded by the limitations of distortion as well as frequency interference caused by other equipment used in the procedure.  Surgical suites that remain static and unmoving during a procedure can be mapped beforehand, allowing correction to an EM system’s sensor readings.  However, other metal tools cannot be mapped in advance, such as a fluoroscopic C-Arm, metal robot components, and various fixation and surgical tools that may require movement around, in, and out of the procedure space.

Legacy EM systems also often rely on wide EM frequency bands, creating interference with other medical equipment that may be in close proximity, such as electrocardiograms, other biopotential signals, and fluoroscopic images produced by the C-Arm.  To access EM tracking precision, clinicians would be forced to minimize active equipment – selectively trading off real-time clinical insight to gain surgical navigation beyond the physician’s line of sight.  As a result, detecting EM interference with all sensor types and mitigating any resulting distortion in real-time has been the development focus for modern EM systems.

High precision and reduced patient radiation

Today’s optimized EM tracking platform offers high confidence in up to 24 sensors.  Each of these in turn delivers precise location information previously unavailable in a comparably high sampling rate.  Further, due to its unique pairing with sensors offering both five and six degrees of freedom (5DOF and 6DOF), high sampling rates are maintained when all 24 sensors are tracked.

The EM platform’s antenna is designed as a flat panel, placed underneath the patient, and used to generate a magnetic field.  It is radiolucent (transparent to X-rays) during fluoroscopy, and its pioneering design generates a magnetic field to create a sensing volume; sensors placed within that volume can be tracked to sub-millimeter accuracy within the selected surgical tool.  The sensing volume created is large, enabling navigation from a patient’s thigh to the heart.  While legacy antenna designs introduced image artifacts – for example, when a C-Arm entered the sensing field to gather lateral or oblique image angles to support the procedure – today’s optimized antenna reduces radiation to the patient and does not impede the quality of images generated through fluoroscopy.  Fluoroscopy images remain consistently high quality regardless of the C-Arm’s angle, and the amount of fluoroscopy can be reduced, further simplifying the procedure’s workflow.

Distortion mitigation as a novel advancement

During a procedure, the antenna can recognize the presence of distortion, along with its source direction information.  In many surgical settings today, a spectrum of reference sensors may be placed externally on a patient.  While front and side sensors may deliver high confidence, those at the patient’s back may sense distortion and deliver lower confidence to the clinician.  The optimized platform globally identifies the distortion; the system executes various mitigations, enabling all information from the full array of sensors within the sensing volume.

The EM platform is capable of tracking sensors of many different types, shapes, and sizes, including both 5DOF and 6DOF sensors.  Sensors are pre-calibrated for compatibility with the EM tracking platform, including sensors designed for devices used in cardiology and electrophysiology, vascular, interventional radiology and oncology, neurology, ENT, orthopedics, pulmonology, and a range of other procedural areas.  A device’s location is pinpointed throughout the sensing volume, as its integrated sensor enters the EM field and is tracked with an EM tracking system.

EM tracking technology can further advance minimally invasive and robotic surgeries by providing highly accurate location tracking for instruments and tools.  For developers of minimally invasive devices, systems, and surgical tools, time to market is accelerated with standard or customized sensors pre-calibrated to perform with the EM platform.  Sensor precision is enhanced, validated to perform with the tracking platform’s distortion detection and mitigation capabilities.  The platform itself is easily integrated into medical navigation equipment via a simple, encrypted API fueled by an open-source software developer kit.  The platform is also highly customizable, offering a variable sensing volume that can be sized according to the needs of a specific surgical procedure.

Solving EM tracking’s inherent distortion challenges brings surgical navigation beyond the line of sight to more use cases.  It is a groundbreaking advancement that increases the potential for minimally invasive options in many more clinical applications.

REFERENCE:  MD+DI; 11 JAN 2023; Garrett Plank