US-12616390-B2 - Electromagnetic tracking and position measurement system having interference reduction from nearby instrumentation by filtering time-division multiplexed signal via step function

US12616390B2US 12616390 B2US12616390 B2US 12616390B2US-12616390-B2

Abstract

An electromagnetic tracking (EMT) system is configured for determining a frequency for generating at least a portion of a magnetic field signal using a transmitter coil of a plurality of transmitter coils. The EMT system configures a time-division multiplexed (TDM) control signal configured to cause the transmitter coil to transmit bursts of the magnetic field signal at the frequency. The EMT system configures a filter for filtering the TDM control signal, the filter configured to shape each burst to reduce or eliminate a harmonic artifact of the bursts. The EMT system causes the transmitter coil to generate the shaped bursts of the magnetic field signal. The EMT system receives, from a sensor, a sensor signal that corresponds to the magnetic field signal, the sensor including the output response indicative of the location of the sensor relative to the transmitter.

Inventors

Westley S. Ashe
William Petrow

Assignees

NORTHERN DIGITAL INC.

Dates

Publication Date: 20260505
Application Date: 20241126

Claims (16)

1 . A system for tracking and position measurement comprising: a transmitter configured to generate a magnetic field signal; a receiver configured to generate a signal representing an output response indicative of a location of the receiver relative to the transmitter based on the magnetic field signal generated by the transmitter; and a computing device in communication with the transmitter and the receiver, the computing device configured to: configure a control signal for controlling transmissions of the magnetic field signal from the transmitter, the control signal causing the transmitter to periodically transmit bursts of the magnetic field signal; configure a filter for filtering the control signal to prepare each burst for transmitting at the transmitter, each prepared burst reducing or preventing a harmonic artifact of the respective burst at the receiver; cause the transmitter to periodically generate the prepared bursts of the magnetic field signal, the generation based on the control signal; and receive, from the receiver, the signal representing the output response indicative of the location of the receiver relative to the transmitter, wherein the filter comprises a windowing filter that prepares a burst by reducing a rate of change of an excitation signal applied to the magnetic field signal, and wherein the filter is configured based on a determined threshold or based on a determined signal strength of a harmonic artifact for the magnetic field signal transmitted by the transmitter.
2 . The system of claim 1 , wherein the receiver comprises a core for a receiver coil of the receiver, the core having a relative magnetic permeability value greater than 1.
3 . The system of claim 2 , wherein the core comprises one of a ferrite material or a permalloy material.
4 . The system of claim 1 , wherein a coil of the transmitter is configured to generate a magnetic field signal at a frequency value that is different from other magnetic field signals at other frequencies, the other magnetic signals being generated by other coils of the transmitter.
5 . The system of claim 4 , wherein each burst is prepared by applying a filter signal that prevents interference of the magnetic field signal of a coil with adjacent measurement modalities of other coils.
6 . The system of claim 1 , wherein the filter is configured to reduce the harmonic artifact received at another electronic device in an environment to below a threshold level specified for the electronic device.
7 . The system of claim 1 , wherein the receiver is part of a sensor is selected from a group comprising: a hall-effect sensor, a magnetoresistive sensor, a magneto-optical sensor, and a fluxgate magnetometer.
8 . The system of claim 1 , wherein the computing device is further configured to: determine a parameter value representing a magnetic property of a receiver core of the receiver; and configure the filter for filtering the control signal based on the parameter value for the receiver core of the receiver.
9 . The system of claim 1 , wherein configuring the filter for filtering the control signal comprises adjusting a size of a signal envelope based on the determined threshold or the signal strength of the particular harmonic artifact for the magnetic field signal transmitted by the transmitter.
10 . A method for tracking and position measurement comprising: configuring, by a computing device, a control signal for controlling transmissions of a magnetic field signal from a transmitter of a magnetic tracking system, the control signal configured to cause the transmitter to periodically transmit bursts of the magnetic field signal; configuring, by the computing device, a filter for filtering the control signal to prepare each burst for transmitting at the transmitter, each prepared burst reducing or preventing a harmonic artifact of the respective burst at a receiver; causing, by the computing device, the transmitter to periodically generate the prepared bursts of the magnetic field signal, the generation based on the control signal; and receiving, at the computing device via a receiver of the magnetic tracking system, a signal representing an output response indicative of a location of the receiver relative to the transmitter; and wherein the filter comprises a windowing filter that prepares a burst by reducing a rate of change of an excitation signal applied to the magnetic field signal, and wherein the filter is configured based on a determined threshold or based on a determined signal strength of a harmonic artifact for the magnetic field signal transmitted by the transmitter.
11 . The method of claim 10 , further comprising: obtaining, by the computing device, threshold data from one or more other devices after a first transmission of the magnetic tracking system; and in response to obtaining the threshold data, configuring, by the computing device, the filter to prepare each burst for a second transmission.
12 . The method of claim 10 , wherein a receiver coil of the receiver comprises a core that has a relative magnetic permeability value greater than 1.
13 . The method of claim 12 , wherein the core comprises one of a ferrite material or a permalloy material.
14 . The method of claim 10 , wherein the receiver is part of a sensor selected from a group comprising: a hall-effect sensor, a magnetoresistive sensor, a magneto-optical sensor, and a fluxgate magnetometer.
15 . The method of claim 10 , wherein the computing device is further configured to: determine a parameter value representing a magnetic property of a receiver core of a receiver coil; and configure the filter for filtering the control signal based on the parameter value for the receiver core of the receiver coil.
16 . The method of claim 10 , wherein configuring the filter for filtering the control signal comprises adjusting a size of a signal envelope based on the determined threshold or the signal strength of the particular harmonic artifact for the magnetic field signal transmitted by the transmitter.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation application of and claims the benefit of priority to U.S. application Ser. No. 17/686,112, filed on Mar. 3, 2022, which claims priority to U.S. Patent Application Ser. No. 63/156,695, filed on Mar. 4, 2021, the entire contents of which are hereby incorporated by reference. TECHNICAL FIELD This disclosure relates to electromagnetic tracking systems. More specifically, this disclosure relates to reducing interference with nearby instrumentation in a tracking environment. BACKGROUND Electromagnetic Tracking (EMT) systems are used to aid in locating instruments and anatomy in medical procedures. These systems utilize a magnetic transmitter in proximity to a magnetic sensor. The sensor can be spatially located relative to the transmitter. SUMMARY An Electromagnetic Tracking (EMT) system can be used to track the position and/or orientation of a sensor (e.g., the pose) relative to a transmitter. The EMT system is configured to transmit tracking signals including time division multiplexed (TDM) alternating current (AC) signals. This includes transmitting sinusoid pulses or bursts from each of a plurality of transmitting coils by cycling each transmitter ON and OFF. The EMT system includes a receiver configured to receive the sinusoid pulses or bursts. A coil in the receiver produces a signal in response to receiving the transmitted signal. The signal produced by the receiver is associated with one of the transmitters. Based on receiver signals representing each of the transmitted signals, the EMT system can determine an approximate pose of a tracked object at the location of the receiver. For transmission of the TDM-AC signal, the EMT system multiplies a shaping signal with the sine burst signal. The shaping signal is used to alternate each transmitter between the ON state and the OFF state. The EMT system forms the shaping signal to create a signal envelope for the sine burst. Rather than a square-wave shaping signal, the EMT system is configured to produce a shaping signal that ramps up from OFF to fully ON and ramps down from fully ON to OFF. The EMT can form the shaping signal by applying one or more filters to the shaping signal. The shaping signal enables the transmitter to transmit a sine burst having a maximum signal amplitude for a period of time while also reducing transmitted harmonic signals resulting from cycling between OFF and ON states at a particular frequency. The exact shape of the shaping signal is tuned to reduce the harmonic signal amplitude while also preserving the sine burst amplitude such that the sine burst is strong enough to generate a signal at the receiver. The EMT system includes sensor coils having magnetic core designs. These cores can be smaller relative to air-cores that are linear while still producing a relatively strong signal suitable for tracking purposes such as for use in medical catheters. The relative smaller size of the receiver having a coil with a magnetic core enables the receiver to be smaller than the receiver would be using coils with air cores, which produce a linear response but generally require a relatively stronger transmitted signal. The EMT system uses TDM-AC transmitted signals that are shaped as previously described to enable use of smaller, non-linear receiver coils in the receiver. This combination of features provides one or more of the following advantages. The EMT system does not cause intermodulation distortion (IMD) in the coils of the receiver. This is because, rather than transmitting EM signals at multiple frequencies using a division multiplexed (FDM)-based transmission, the EMT system transmits EM signals using TDM-AC-based transmissions. IMD can cause tracking errors in the EMT system. The use of TDM-AC signals allows the use of magnetic cores (which provide a stronger response than air cores) in receive coils. The use of shaped TDM-AC signals by the EMT system reduces or eliminates harmonic signals (e.g., transmitted signals that are at different frequencies than the sinusoid burst frequency—also called a center frequency or selected frequency). As previously described, the harmonic frequencies are an artifact of cycling the transmitters between OFF and ON states to perform TDM-AC transmission. The shaping signal causes the transmitters to “ramp up” and “ramp down” transmission of the respective TDM-AC signals. The shaping signal reduces the strength of transmitted harmonic frequencies while preserving signal strength for the selected center frequency. The reduction in the strength of transmitted harmonic signals reduces interference that may occur with the operation of nearby electronic instrumentation, such as electrocardiographs (EKGs) that are normally sensitive to signals below 1 KHz, or for other biomedical instrumentation (e.g. medical impedance location devices), which are generally susceptible to noise above 10 KHz. Additionally, the shaped signal prevents in