EP0964261A2
Expired / Lapsed
EP
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Error compensation for device tracking systems employing electromagnetic fields
Assignee: General Electric Co
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Filing: 1999-05-24
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Granted: —
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Expires: 2019-05-24
Abstract
Abstract The present invention is capable of more accurately tracking an invasive device (120) in a subject's body (101) in the presence of eddy current inducing structures. Current patterns applied (150) to the tracking system's transmit coils (131,133,135) are modified (140) to compensate for the effect of the eddy currents. The current supplied to the coils is a linear combination of the current needed to create the desired electromagnetic field in the region of interest; and one or more error terms. These terms are determined experimentally during system calibration and are mathematically modeled as a series of exponential functions having a given amplitude and time constant. The error terms in the current applied to the transmit coils cancel the magnetic fields created by eddy currents within the tracking region and result in an actual electromagnetic field which is close to the desired ideal electromagnetic field. The fidelity of the electromagnetic field is further increased by reducing eddy currents within the eddy current inducing structures. This is done by constructing shield coils which are placed between the transmit coil and the eddy current inducing structures. These shield coils create canceling magnetic fields within the eddy current inducing structures without substantially altering the electromagnetic fields in the region over which the invasive device is tracked.
Inventors
- 👤 Charles Lucian Dumoulin
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-09 22:38
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/28; G01R33/285; G01R33/44; G01R33/48; G01R33/54; G01R33/56; G01R33/565; G01R33/56518
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
153 words
A system for determining a position of a device (120) within a
selected tracking volume, in the presence of at least one eddy
current inducing structure comprising: a) at least one transmit coil (131,133,135) at a known location
capable of creating a magnetic field within the selected tracking
volume; b) at least one receive coil (121,123, 125) incorporated into the
device (120) being tracked; c) system electronics (150) operating to supply current of a selected
amplitude, frequency and duration to the transmit coil(s)
(131,133,135), and capable of receiving signals detected by the
receive coil(s) (121,123,125), incorporated into the device (120);
and d) a current correction means (140) capable of modifying the current
supplied to the transmit coil(s) (131,133,135) by the electronics
subsystem so that the resulting magnetic field within the selected
tracking volume is substantially free of deviations from an ideal
magnetic field caused by eddy currents in the eddy current
inducing structure(s).
Claim 2
Dependent Claim
42 words
The system for determining a position of a device (120) within a
selected tracking volume of claim 1 wherein the current modification
means (140) modifies the current applied by combining an ideal
current I i with an compensation current I c .
Claim 3
Dependent Claim
44 words
The system for determining a position of a device (120) within a
selected tracking volume of claim 2 wherein the current correction
means (140) defines the compensation current I c mathematically by
at least one exponential function having a selected amplitude and
time constant.
Claim 4
Dependent Claim
54 words
The system for determining a position of a device (120) within a
selected tracking volume of claim 3 wherein current correction
means (140) operates to determine the amplitude and time
constant of the compensation current iteratively by providing a
plurality of different current waveforms measuring results and
choosing the waveform with the best result.
Claim 5
Dependent Claim
32 words
The system for determining a position of a device (120) within a
selected tracking volume of claim 1 wherein the eddy current
inducing structure is part of a Magnetic Resonance Imaging system
Claim 6
Independent Claim
134 words
A system for determining a position of a device (120) within a
selected tracking volume, in the presence of at least one eddy
current inducing structure comprising: a) at least one transmit coil (131,133,135) at a known location
capable of creating a magnetic field within the selected tracking
volume; b) at least one receive coil (121,123,125) incorporated into the
device (120) being tracked; c) system electronics (150) operating to supply current of a selected
amplitude, frequency and duration to the transmit coil(s),
(131,133,135) and capable of receiving signals detected by the
receive coil(s) (121,123,125), incorporated into the device (120);
and d) at least one shield coil (1020) placed near at least one
corresponding transmit coil (131, 133, 135) to null the magnetic
fields created by the transmit coil(s) in the eddy current inducing
structure(s).
Claim 7
Dependent Claim
32 words
The system for determining a position of a device (120) within a
selected tracking volume of claim 6 wherein the eddy current
inducing structure is part of a Magnetic Resonance Imaging
system.
Claim 8
Dependent Claim
33 words
The system for determining a position of a device (120) within a
selected tracking volume of claim 6 wherein the shield coil (1020)
is placed in series with the corresponding transmit coil
(131,133,135).
Claim 9
Dependent Claim
32 words
The system for determining a position of a device (120) within a
selected tracking volume of claim 6 wherein the shield coil (1020) is
driven independently of the corresponding transmit coil
(131,133,135).
Claim 10
Dependent Claim
27 words
The system for determining a position of a device (120) within a
selected tracking volume of claim 6 wherein the shield coil (1020)
has a planar geometry.
Claim 11
Dependent Claim
37 words
The system for determining a position of a device (120) within a
selected tracking volume of claim 6 wherein the shield coil (1020)
has a complex geometry matched to the geometry of the eddy
current inducing structure(s).
Claim 12
Independent Claim
184 words
A system for determining a position of a device (120) within a
selected tracking volume, in the presence of at least one eddy
current inducing structure comprising: a) at least one transmit coil (131,133,135) capable of creating a
magnetic field within the selected tracking volume; b) at least one receive coil (121,123,125) incorporated into the
device (120) being tracked; c) a system electronics subsystem (150) capable of supplying
current of a selected amplitude, frequency and duration to the
transmit coil(s) (131,133,135) and capable of receiving signals
detected by the receive coil(s) (121,123,125) incorporated into the
device (120) ; d) a current modification means (140) capable of modifying the
current supplied to the transmit coil(s) (131,133,135) by the
electronics subsystem (150) so that the resulting magnetic field
within the selected tracking volume is substantially free of
deviations from an ideal magnetic field caused by eddy currents
within the eddy current inducing structure; and e) at least one shield coil (1020) placed near at least one
corresponding transmit coil (131,133,135) to null the magnetic
fields created by the transmit coil(s) in the eddy current inducing
structure.
Claim 13
Independent Claim
125 words
A system for determining a position of a device (120) within a
selected tracking volume, in the presence of at least one eddy
current inducing structure comprising: a) at least one transmit coil (131, 133,135) capable of creating a
magnetic field within the selected tracking volume; b) at least one receive coil (121,123,125) incorporated into the
device (120) being tracked; and c) a system electronics subsystem (150) capable of supplying
current of a selected amplitude, frequency and duration to the
transmit coil(s) (131,133,135) and capable of receiving signals
detected by the receive coil(s) (121,123,125) incorporated into
the device (120), and capable of modifying the received signals
so that deviations from an ideal magnetic field caused by eddy
currents within the eddy current structure are removed.
References Cited (Backward Citations)
No citation records indexed.
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