Note: Descriptions are shown in the official language in which they were submitted.
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INCONSISTENT FIELD-BASED PATCH LOCATION COORDINATE CORRECTION
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application 62/214,273, filed September 4, 2015 and U.S.
Patent Application 15/228,627, filed August 4, 2016, which are
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to medical imaging,
and specifically to a method for correcting measurements
indicating an inconsistent field-based location coordinates of a
skin patch affixed to a patient.
BACKGROUND OF THE INVENTION
[0003] A wide range of medical procedures involve placing objects,
such as sensors, tubes, catheters, dispensing devices, and
implants, within the body. Real-time imaging methods are often
used to assist doctors in visualizing the object and its
surroundings during these procedures. In most situations,
however, real-time three-dimensional imaging is not possible or
desirable. Instead, systems for obtaining real-time spatial
coordinates of the internal object are often utilized.
[0004] U.S. Patent Application 2007/0016007, to Govari et al.,
whose disclosure is incorporated herein by reference, describes
a hybrid magnetic-based and impedance-based position sensing
system. The system includes a probe adapted to be introduced
into a body cavity of a subject.
[0005] U.S. Pat. No. 6,574,498, to Gilboa, whose disclosure is
incorporated herein by reference, describes a system for
determining the position of a work piece within a cavity of an
opaque body. The system claims to use a transducer that
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interacts with a primary field, and several transducers that
interact with a secondary field.
[0006] U.S. Pat. No. 5,899,860, to Pfeiffer, et al., whose
disclosure is incorporated herein by reference, describes a
system for determining the position of a catheter inside the
body of a patient. A correction function is determined from the
difference between calibration positions derived from received
location signals and known, true calibration positions,
whereupon catheter positions, derived from received position
signals, are corrected in subsequent measurement stages
according to the correction function.
[0007]
Documents incorporated by reference in the present patent
application are to be considered an integral part of the
application except that to the extent any terms are defined in
these incorporated documents in a manner that conflicts with the
definitions made explicitly or implicitly in the present
specification, only the definitions in the present specification
should be considered.
[0008]
The description above is presented as a general overview of
related art in this field and should not be construed as an
admission that any of the information it contains constitutes
prior art against the present patent application.
SUMMARY OF THE INVENTION
[0009]
There is provided, in accordance with an embodiment of the
present invention a method for sensing, using an array of
patches fixed to a surface of a body of a subject, the patches
including respective electrodes in contact with the surface, and
at least one
of the patches including a patch sensor
configured to output a signal in response to a magnetic field
applied to the body, the method including at a first time,
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processing the signal so as to compute first field-based
location coordinates of the at least one of the patches, and
computing first impedance-based location coordinates of the at
least one of the patches by measuring an impedance to an
electrical current applied to the body, at a second time,
subsequent to the first time, processing the signal so as to
compute second field-based location coordinates of the at least
one of the patches, and computing second impedance-based
location coordinates of the at least one of the patches by
measuring the an impedance to the electrical current, computing
a first relation between the first field-based location
coordinates and the first impedance-based location coordinates,
and a second relation between the second field-based location
coordinates and the second impedance-based location coordinates,
when there is a difference between the second relation and the
first relation, computing a field-based location coordinate
correction responsively to the difference, and applying the
field-based location coordinate correction in tracking a
position of a magnetic tracking sensor inside the body, based on
signals received from the magnetic tracking sensor in response
to the applied magnetic field.
[0010]
In embodiments of the present invention, the first relation
for a given patch may include a first distance and a first
orientation from the first impedance-based location coordinates
of the given patch to the first field-based location coordinates
of the given patch, and wherein the second relation for the
given patch includes a second distance and a second orientation
from the second impedance-based location coordinates of the
given patch to the second field-based location coordinates of
the given patch.
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[0011]
In some embodiments, the field-based location coordinate
correction for the second field-based location coordinates of
the given patch includes the first distance and the first
orientation. In additional embodiments, the method may include
at a third time, subsequent to the second time, processing the
signal so as to compute third field-based location coordinates
of the at least one of the patches, computing third impedance-
based location coordinates of the at least one of the patches by
measuring the an impedance to the electrical current, and
applying the field-based location coordinate correction to the
third field-based location coordinates.
[0012]
In further embodiments, the magnetic field is applied to
the body by positioning the body over multiple coils configured
to generate the magnetic field.
In supplemental embodiments,
the object includes a medical probe having a probe electrode,
and wherein the electrical current is applied to the body by
conveying the electrical current to the probe electrode.
In
additional embodiments, the signal includes a first signal, and
wherein measuring the impedance includes receiving, from the at
least one patches, a second signal in response to the impedance
of the electrical current conveyed by the probe electrode.
[0013]
There is also provided, in accordance with an embodiment of
the present invention an apparatus for method for sensing,
including an array of patches fixed to a surface of a body of a
subject, the patches including respective electrodes in contact
with the surface, and at least one of the patches including a
patch sensor configured to output a signal in response to a
magnetic field applied to the body, and a control console
configured at a first time, to process the signal so as to
compute first field-based location coordinates of the at least
one of the patches, and to compute first impedance-based
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location coordinates of the at least one of the patches by
measuring an impedance to an electrical current applied to the
body, at a second time, subsequent to the first time, to process
the signal so as to compute second field-based location
coordinates of the at least one of the patches, and to compute
second impedance-based location coordinates of the at least one
of the patches by measuring the an impedance to the electrical
current, to compute a first relation between the first field-
based location coordinates and the first impedance-based
location coordinates, and a second relation between the second
field-based location coordinates and the second impedance-based
location coordinates, when there is a difference between the
second relation and the first relation, to compute a field-based
location coordinate correction responsively to the difference,
and to apply the field-based location coordinate correction in
tracking a position of a magnetic tracking sensor inside the
body, based on signals received from the magnetic tracking
sensor in response to the applied magnetic field.
[0014]
There is further provided, in accordance with an embodiment
of the present invention, a computer software product for
sensing, using an array of patches fixed to a surface of a body
of a subject, the patches including respective electrodes in
contact with the surface, and at least one of the
patches
including a patch sensor configured to output a signal in
response to a magnetic field applied to the body, the product
including a non-transitory computer-readable medium, in which
program instructions are stored, which instructions, when read
by a computer, cause the computer to process, at a first time,
the signal so as to compute first field-based location
coordinates of the at least one of the patches, and to compute
first impedance-based location coordinates of the at least one
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of the patches by measuring an impedance to an electrical
current applied to the body, to process at a second time,
subsequent to the first time, the signal so as to compute second
field-based location coordinates of the at least one of the
patches, and to compute second impedance-based location
coordinates of the at least one of the patches by measuring the
an impedance to the electrical current, to compute a first
relation between the first field-based location coordinates and
the first impedance-based location coordinates, and a second
relation between the second field-based location coordinates and
the second impedance-based location coordinates, when there is a
difference between the second relation and the first relation,
to compute a field-based location coordinate correction
responsively to the difference, and to apply the field-based
location coordinate correction in tracking a position of a
magnetic tracking sensor inside the body, based on signals
received from the magnetic tracking sensor in response to the
applied magnetic field.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The disclosure is herein described, by way of example only,
with reference to the accompanying drawings, wherein:
[0016] Figure 1 is a schematic pictorial illustration of a medical
system configured to correct an inconsistent location of one or
more adhesive skin patches while performing a procedure on a
heart, in accordance with an embodiment of the present
invention;
[0017] Figure 2 is a schematic pictorial of a catheter in the
heart, in accordance with an embodiment of the present
invention;
[0018] Figure 3 is a flow diagram that illustrates a method of
correcting an inconsistent physical location of a given adhesive
skin patch by using location measurements from additional skin
patches, in accordance with an embodiment of the present
invention;
[0019] Figures 4A-4E are schematic diagrams illustrating rigid
bodies that are constructed from locations of the adhesive skin
patches in order to correct the inconsistent physical location
of the given skin patch, in accordance with an embodiment of the
present invention;
[0020] Figure 5 is a flow diagram that illustrates a method of
correcting an inconsistent apparent location of multiple
adhesive skin patches caused by magnetic interference, in
accordance with an embodiment of the present invention; and
[0021] Figures 6A-6C are schematic diagrams illustrating first,
second and corrected second location coordinates for the
multiple adhesive skin patches, in accordance with an embodiment
of the present invention.
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DETAILED DESCRIPTION OF EMBODIMENTS
OVERVIEW
[0022] Various diagnostic and therapeutic procedures involve
mapping of the electrical potential on the inner surface of a
cardiac chamber. Electrical mapping can be performed, for
example, by inserting a medical probe (e.g., a catheter), whose
distal end is fitted with a position sensor and a mapping
electrode, into the cardiac chamber. The cardiac chamber is
mapped by positioning the probe at multiple points on the inner
chamber surface. At each point, the electrical potential is
measured using the electrode, and the distal end position is
measured using the position sensor. The measurements are
typically presented as a map of the electrical potential
distribution over the cardiac chamber surface.
[0023]
While positioning the medical probe within the cardiac
chamber, impedance-based and/or magnetic-based position sensing
systems can be used to determine a location of the probe within
the cardiac chamber.
Location sensing systems, such as those
described in U.S. Patent 8,456,182, whose disclosure is
incorporated herein by reference, can determine a location of
the probe by using locations of a set of three adhesive skin
patches (also referred to herein as patches) that are affixed to
a back of a patient.
Location measurements received from the
patches can be used to define a rigid body in a body coordinate
system, and to determine a location of the probe within the
rigid body. The body coordinate system can be updated as the
adhesive skin patches move due to normal patient activities such
as breathing.
[0024] Typically, the adhesive skin patches move and have
respective locations that are consistent with one another so
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that the rigid body referred to above does not deform, but there
may be instances when movement of one or more of the patches
results in each of the one or more patches having a location
that is not consistent with locations of the remaining patches.
Embodiments of the present invention provide methods and systems
for detecting and correcting an inconsistent location of one or
more of the adhesive skin patches.
[0025] In a disclosed embodiment, the inconsistent location
comprises a physical location of one of the adhesive skin
patches. For example, if the patient is lying on a table, the
one adhesive skin patch may "stick" to the table as the patient
moves. In an alternative embodiment, the inconsistent location
comprises apparent locations of a plurality of the patches. For
example, the positioning system may be based on magnetic
sensors, and magnetic interference may cause an "apparent"
movement (i.e., not a physical movement) of the plurality of the
patches to their respective apparent inconsistent locations.
SYSTEM DESCRIPTION
[0026]
Figures 1 is a schematic pictorial illustration of a
medical system 20, and Figure 2 is a schematic illustration of a
probe used in the system, in accordance with an embodiment of
the present invention. System 20 may be based, for example, on
the CARTO system, produced by Biosense Webster Inc. (Diamond
Bar, California). System 20 comprises a medical probe 22, such
as a catheter, and a control console 24.
In embodiments
described hereinbelow, it is assumed that probe 22 is used for
diagnostic or therapeutic treatment, such as performing ablation
of heart tissue in a heart 26. Alternatively, probe 22 may be
used, mutatis mutandis, for other therapeutic and/or diagnostic
purposes in the heart or in other body organs.
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=
[0027]
An operator 28 inserts probe 22 through the vascular system
of a patient 30 so that distal end 32 (Figure 2) of probe 22
enters a chamber of heart 26.
In the configuration shown in
Figure 1, operator 28 uses a fluoroscopy unit 34 to visualize
distal end 32 inside heart 26. Fluoroscopy unit 34 comprises an
X-ray source 36, positioned above patient 30, which transmits X-
rays through the patient. A flat panel detector 38, positioned
below patient 30, comprises a scintillator layer 40 which
converts the X-rays which pass through patient 30 into light,
and a sensor layer 42 which converts the light into electrical
signals. Sensor layer 42 typically comprises a two dimensional
array of photodiodes, where each photodiode generates an
electrical signal in proportion to the light detected by the
photodiode.
[0028]
Control console 24 comprises a processor 44 that converts
the electrical signals from fluoroscopy unit 34 into an image
46, which the processor presents as information regarding the
procedure on a display 48.
Display 48 is assumed, by way of
example, to comprise a cathode ray tube (CRT) display or a flat
panel display such as a liquid crystal display (LCD), light
emitting diode (LED) display or a plasma display. However other
display devices can also be employed to implement embodiments of
the present invention.
In some embodiments, display 48 may
comprise a touchscreen configured to accept inputs from operator
28, in addition to presenting image 46.
[0029]
System 20 can use magnetic position sensing to determine
position coordinates of distal end 32 inside heart 26.
In
configurations where system 20 uses magnetic based position
sensing, console 24 comprises a driver circuit 50 which drives
field generators 52 to generate magnetic fields within the body
of patient 30. Typically, field generators 52 comprise coils,
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which are placed below the patient at known positions external
to patient 30.
These coils generate magnetic fields in a
predefined working volume that contains heart 26.
A magnetic
field sensor 54 (also referred to herein as position sensor 54)
within distal end 32 of probe 22 generates electrical signals in
response to the magnetic fields from the coils, thereby enabling
processor 44 to determine the position of distal end 32 within
the cardiac chamber. Magnetic position tracking techniques are
described, for example, in U.S. Patents 5,391,199, 6,690,963,
5,443,489, 6,788,967, 5,558,091, 6,172,499 and 6,177,792, whose
disclosures are incorporated herein by reference.
[0030]
Additionally, system 20 can use impedance-based position
sensing to determine position coordinates of distal end 32
inside heart 26.
In configurations where system 20 uses
impedance-based position sensing, position sensor 54 is
configured as a probe electrode, typically formed on an
insulating exterior surface 76 of the distal end, and console 24
is connected by a cable 56 to body surface electrodes, which
comprise three primary adhesive skin patches 58 and one or more
ancillary adhesive skin patches 60.
In some embodiments,
primary adhesive skin patches 58 are affixed to a back 62 of
patient 30, and the one or more ancillary adhesive skin patches
are affixed to a front 64 of the patient.
In operation,
processor 44 can determine position coordinates of probe 22
inside heart 26 based on the impedance measured between the
probe electrode and patches 58 and 60. Impedance-based position
tracking techniques are described, for example, in U.S. Patents
5,983,126, 6,456,864 and 5,944,022, whose disclosures are
incorporated herein by reference.
[0031]
In some embodiments, each patch 58 and 60 may also comprise
magnetic field sensors (e.g., coils) that can measure the
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magnetic fields produced by field generators 52, and convey the
magnetic field measurements to console 24.
Based on the
measurements received from patches 58 and 60, processor 44 can
determine current positions for each of the primary and the
ancillary adhesive skin patches. Both magnetic-based and
impedance-based systems described hereinabove generate signals
which vary according to the position of distal end 32.
[0032]
Processor 44 receives and processes the signals generated
by position sensor 54 in order to determine position coordinates
of distal end 32, typically including both location and
orientation coordinates.
The method of position sensing
described hereinabove is implemented in the above-mentioned
CARTOTm system and is described in detail in the patents and
patent applications cited above.
[0033] Processor 44 typically comprises a general-purpose
computer, with suitable front end and interface circuits for
receiving signals from probe 22 and controlling the other
components of console 24.
Processor 44 may be programmed in
software to carry out the functions that are described herein.
The software may be downloaded to console 24 in electronic form,
over a network, for example, or it may be provided on non-
transitory tangible media, such as optical, magnetic or
electronic memory media.
Alternatively, some or all of the
functions of processor 44 may be carried out by dedicated or
programmable digital hardware components.
[0034]
Based on the signals received from probe 22 and other
components of system 20, processor 44 drives display 48 to
update image 46 to present a current position of distal end 32
in the patient's body, as well as status information and
guidance regarding the procedure that is in progress. Processor
44 stores data representing image 46 in a memory 66.
In some
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embodiments, operator 28 can manipulate image 46 using one or
more input devices 68.
In embodiments, where display 48
comprises a touchscreen display, operator 28 can manipulate
image 46 via the touchscreen display.
[0035]
In the configuration shown in Figure 2, probe 22 also
comprises a force sensor 70 contained within distal end 32 and
an ablation electrode 72 mounted on a distal tip 74 of probe 22.
Force sensor 70 measures a force applied by distal tip 74 on the
endocardial tissue of heart 26 by generating a signal to the
console that is indicative of the force exerted by the distal
tip on the endocardial tissue.
In one embodiment, the force
sensor may comprise a magnetic field transmitter and receiver
connected by a spring in distal tip 74, and may generate an
indication of the force based on measuring the deflection of the
spring. Further details of this sort of probe and force sensor
are described in U.S. Patent Application Publications
2009/0093806 and 2009/0138007, whose disclosures
are
incorporated herein by reference. Alternatively, distal end 32
may comprise another type of force sensor.
[0036]
Electrode 72 typically comprises one or more thin metal
layers formed over exterior surface 76 of distal end 32.
Console 24 also comprises a radio frequency (RF) ablation module
78. Processor 44 uses ablation module 78 to monitor and control
ablation parameters such as the level of ablation power applied
via electrode 72.
Ablation module 78 may also monitor and
control the duration of the ablation that is provided.
SINGLE PATCH LOCATION CORRECTION
[0037]
Figure 3 is a flow diagram that illustrates a method of
correcting an inconsistent physical location of a single primary
adhesive skin patch 58 by using location measurements from
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ancillary patches 60, and Figures 4A-4E, referred to
collectively as Figure 4, are schematic diagrams illustrating
rigid bodies 100-108 that are constructed from locations 110-134
of the primary and the ancillary skin patches, in accordance
with an embodiment of the present invention.
In the example
shown in Figure 4, locations 110-132 comprise three-dimensional
coordinates in a coordinate system 136 comprising an X-axis 138,
a Y-axis 140, and a Z-axis 142.
[0038]
In embodiments described hereinbelow, locations 110-132 are
indicative of spatial relationships that correspond to rigid
bodies 100-106.
Thus, in the example shown in Figure 4,
locations 110, 112, 114 are indicative of first spatial
relationships which define rigid body 100, locations 122, 124,
126 are indicative of second spatial relationships which define
rigid body 102, locations 110, 112, 114, 116, 118, 120 are
indicative of third spatial relationships which define rigid
body 104, and locations 122, 126, 128, 130 and 132 are
indicative of fourth spatial relationships which define rigid
body 106. In embodiments described herein, rigid body 100 may
also be referred to as a first rigid body, rigid body 102 may
also be referred to as a second rigid body, rigid body 104 may
also be referred to as a third rigid body, and rigid body 106
may also be referred to as a fourth rigid body.
[0039]
In an initial step 80, operator 28 affixes primary adhesive
skin patches 58 to back 62 of patient 30, and affixes ancillary
skin patches 60 to front 64 of the patient. In a first receive
step 81, processor 44 receives, at a first time, first position-
dependent signals from patches 58 and 60. In the flow diagram
shown in Figure 3, primary patches 58 may be referred to as back
patches, and ancillary patches 60 may be referred to as front
patches.
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[0040] In a first compute step 82, processor 44 computes
respective first location coordinates 110, 112, 114 for patches
58, and respective first location coordinates 116, 118, 120 for
patches 60.
In a first identification step 83, processor 44
identifies the first spatial relationships between patches 58,
using, as shown in Figure 4A, the respective first location
coordinates of locations 110, 112 and 114 of the primary
adhesive skin patches, i.e., as rigid body 100.
[0041]
In a second receive step 84, processor 44 receives, at a
second time subsequent to the first time, second position-
dependent signals from patches 58 and 60. In a second compute
step 85, processor 44 computes respective second location
coordinates 122, 124, 126 for patches 58 and respective second
location coordinates 128, 130, 132 for patches 60. In a second
identification step 86, processor 44 identifies the second
spatial relationships between patches 58, using, as shown in
Figure 4B, the respective second location coordinates of
locations 122, 124 and 126 of primary adhesive skin patches 58,
i.e., as rigid body 102.
[0042]
In a detection step 87, processor 44 detects a discrepancy
between the first and the second spatial relationships. The
discrepancy is caused by a change of location of only one
primary patch 58 relative to the other primary patches.
The
detected discrepancy indicates that the second location of the
only one primary patch is inconsistent with the second locations
of the remaining primary patches 58.
[0043]
In the present example, the inconsistent location is a
result of a physical movement of the only one primary patch 58
from location 112 (Figure 4A) to location 124 (Figure 4B) not
being consistent with movements of the remaining primary patches
58 from locations 110 and 114 to locations 122 and 126 (i.e.,
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both locations 112 and 124 comprise physical locations of the
only one primary patch). For example, processor 44 may detect
the discrepancy between the first and the second spatial
relationships by detecting that rigid body 100 and rigid body
102 are no longer congruent, and that the non-congruency is
effectively caused by the movement of only one of the patch
locations defining the bodies. In other words, by detecting the
incongruence between rigid bodies 100 and 102, processor 44
detects a discrepancy between the first and the second spatial
relationships caused by a given patch 58 that has first location
112 and the other patches 58 that have respective first
locations 110 and 114.
[0044]
In a third identification step 88, processor 44 identifies
the third spatial relationships between patches 58 and 60,
using, as shown in Figure 4C, the respective first location
coordinates indicated by locations 110, 112, 114, 116, 118, and
120 of the primary and the ancillary skin patches, i.e., as
rigid body 104.
[0045]
During a medical procedure, processor 44 receives signals
from all of the primary and the ancillary adhesive skin patches.
Typically, as shown in Figures 4A and 4B, the processor defines
rigid bodies 100 and 102 based on respective locations of
primary patches 58.
In embodiments of the present invention,
upon detecting an inconsistent movement/location of a given
patch 58, processor 44 can calculate a correction for location
124 of the given patch by using locations of ancillary patches
60 and the remaining primary patches to create rigid bodies 104
(Figure 4C), 106 (Figure 4D) and 108 (Figure 4E), as explained
hereinbelow.
[0046]
In a fourth identification step 89, processor 44 identifies
the fourth spatial relationships between patches 60 and the
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other patches 58 (i.e., the fourth spatial relationships do not
include the given patch 58 that moved inconsistently), using, as
shown in Figure 4D, the respective second location coordinates
of locations 122, 126, 128, 130 and 132 of the primary and the
ancillary adhesive skin patches, i.e., as rigid body 106.
[0047]
In a calculation step 90, processor 44 calculates, based on
the spatial relationships, a location correction for the only
one primary patch.
In some embodiments, the spatial
relationships comprise the third and the fourth spatial
relationships. Finally, in an application step 91, processor 44
applies the location correction to the second location of the
only one primary patch, thereby determining a corrected second
location for the only one primary patch, and the method ends.
In some embodiments, processor 44 applies the location
correction while using the second location coordinates of
patches 58 in order to track an object such as probe 22 in the
patient's body.
[0048]
To calculate the location correction using the third and
the fourth spatial relationships (i.e., rigid bodies 104 and
106), processor 44 can determine corrected second location 134
for the only one primary patch by determining, based on rigid
body 104, an expected second location (i.e., the corrected
second location) for the only one primary patch in rigid body
106 (as indicated by an arrow 144), thereby defining rigid body
108. Location 134 comprises a three-dimensional coordinates in
coordinate system 136.
[0049]
Once processor 44 has calculated the location correction
for the only one primary patch, processor 44 can apply the
location correction to subsequent signals indicating subsequent
locations of the only one primary patch.
Therefore, upon
processor 44 receiving, at a third time subsequent to the second
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time, third position-dependent signals from the only one primary
patch, the processor can compute, based on the third position-
dependent signals, third location coordinates for the only one
primary patch, and apply the location correction to the third
location of the only one primary patch, thereby determining a
corrected third location for the only one primary patch.
[0050] While embodiments described herein use three ancillary
patches 60 to correct an inconsistent movement of only one
primary patch 58, configurations comprising any number of
ancillary patches 60 whose respective location measurements can
be used to define rigid bodies 104, 106 and 108 are considered
to be within the spirit and scope of the present invention.
Therefore, in embodiments of the present invention, at least
four adhesive patches (i.e., three primary patches 58 and at
least one ancillary patch 60) may be affixed to patient 30.
MULTIPLE PATCH LOCATION CORRECTION
[0051] Figure 5 is a flow diagram that illustrates a method of
correcting inconsistent apparent locations of a plurality of
primary adhesive skin patch 58, and Figures 6A-6C, referred to
collectively as Figure 6, are schematic diagrams illustrating
first patch location coordinates 170-174, second patch location
coordinates 176-180 and corrected second patch location
coordinates 182-186, in accordance with an embodiment of the
present invention.
[0052] In the example shown in Figure 6, locations 170-186
comprise three-dimensional coordinates in a coordinate system
188 comprising an X-axis 190, a Y-axis 192, and a Z-axis 194.
In embodiments described herein, locations 170-174 are
indicative of first spatial relationships represented by a rigid
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body 196, and locations 176-180 are indicative of second spatial
relationships indicated by a rigid body 198.
[0053]
In an initial step 150, operator 28 affixes primary
adhesive skin patches 58 to back 62 of patient 30, and in a
first receive step 152, processor 44 receives, at a first time,
first position-dependent signals from patches 58.
The first
position-dependent signals are generated using the magnetic
position sensing referred to above.
In embodiments of the
present invention, the first position-dependent signals may also
indicate a first magnetic interference level for each primary
patch 58.
In the example shown in Figure 1, the magnetic
interference level(s) typically provide a measure of a proximity
of X-ray source 36 to field generators 52. In the flow diagram
shown in Figure 5, primary patches 58 may also be referred to as
back patches.
[0054] In a first compute step 154, processor 44 computes
respective first location coordinates and computes a first
magnetic interference index (i.e., a value) based on the first
magnetic interference levels.
In a first identification step
156, processor 44 identifies the first spatial relationships
between primary patches 58, using, as shown in Figure 6A, the
respective first location coordinates of locations 170, 172 and
174 of the primary adhesive patches, i.e., as rigid body 196.
[0055]
In a second receive step 158, processor 44 receives, at a
second time subsequent to the first time, second position-
dependent signals from primary patches 58.
In embodiments of
the present invention, the second position-dependent signals may
also indicate a second magnetic interference level for each
primary patch 58.
[0056]
In a second compute step 160, processor 44 computes
respective second location coordinates and respective second
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magnetic interference levels for each primary patch 58, and
computes a second magnetic interference index based on the
second magnetic interference levels. In a second identification
step 162, the processor identifies the second spatial
relationships between primary patches 58, using, as shown in
Figure 6B, the respective second location coordinates of
locations 176, 178 and 180 of the primary adhesive skin patches,
i.e., as rigid body 198.
[0057] In a detection step 164, processor 44 detects a discrepancy
between the first and the second magnetic indices and a
discrepancy between the first and the second spatial
relationships of a plurality of primary patches 58 relative to
the other primary patches. The detected discrepancy indicates
that the second locations of a plurality of primary patches 58
are inconsistent with the second locations of the remaining
primary patches 58.
[0058] In the present example, location 176 comprises a physical
first location of a first given primary patch 58, location 178
comprises a physical first location of a second given primary
patch 58, location 182 comprises an apparent second location of
the first given primary patch, and location 186 comprises an
apparent second location of the second given primary patch. In
embodiments of the present invention, the inconsistent (i.e.,
apparent) locations are a result of a difference between the
first and the second magnetic field measurements, the difference
causing an apparent movement of the first and the second given
primary patches from locations 170, 172 and 174 (Figure 6A) to
locations 176, 178 and 180 (Figure 63).
In some embodiments,
processor 44 can detect the discrepancy between the first and
the second spatial relationships by detecting a difference
between rigid body 196 and rigid body 198.
CA 02938570 2016-08-12
[0059]
In a calculation step 166, processor 44 calculates, based
on the first location coordinates, location corrections for the
plurality of primary patches. In some embodiments, the location
correction for a given patch 58 comprises a distance and
orientation from the second location of the given patch to the
first location of the given patch (or vice versa). Finally, in
an application step 168, processor 44 applies the location
corrections to the second locations of the plurality of the
primary patches, thereby determining corrected second locations
for the plurality of the primary patches, and the method ends.
[0060]
In the example shown in Figure 6, based on the distances
and the orientations are indicated by arrows 206, 208 and 210,
processor 44 determines corrected second locations 200, 202 and
204 for the plurality of the primary patches.
Locations 200,
202 and 204 comprise three-dimensional coordinates in coordinate
system 188.
In embodiments where the detected movement of
patches 58 is caused by magnetic interference (i.e., the
detected movement is apparent), then the corrected location
coordinates are in accordance with the first location
coordinates.
Therefore, in the example shown in Figure 6,
location 200 is in accordance with location 170, location 202 is
in accordance with location 202, and location 174 is in
accordance with location 204.
[0061]
Once processor 44 has calculated the location correction
for patches 58, processor 44 can apply the location correction
to subsequent signals indicating subsequent locations of the
back patches.
Therefore, upon processor 44 receiving, at a
third time subsequent to the second time, third position-
dependent signals from patches 58, the processor can compute,
based on the third position-dependent signals, third location
coordinates for the back patches, and apply the location
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=
correction to the third locations of the back patches, thereby
determining a corrected third location for patches 58.
[0062]
In embodiments of the present invention, processor 44 can
track an object (e.g., probe 22) in the patient's body relative
to the respective location coordinates of patches 58 while
applying the respective location corrections to the respective
location coordinates of the patches.
Additionally, while
embodiments described herein use three primary patches 58 whose
respective location measurements can be used to define rigid
bodies 100-108 and 196-198, configurations comprising more than
three patches 58 are considered to be within the spirit and
scope of the present invention.
[0063]
It will be understood that the description above provides
two embodiments for locating and correcting inconsistent second
locations of one or more patches 58. In a first embodiment, as
described supra in the description referencing Figures 3 and 4,
processor 44 detects an inconsistent second location for only
one patch 58, but does not detect a discrepancy in the magnetic
interference index between the first and the second times. In a
second embodiment, as described supra in the description
referencing Figures 5 and 6,
processor 44 detects respective
inconsistent second locations for a plurality of patches 58
while detecting a discrepancy in the in the magnetic
interference index between the first and the second times.
[0064]
It will be appreciated that the embodiments described above
are cited by way of example, and that the present invention is
not limited to what has been particularly shown and described
hereinabove.
Rather, the scope of the present invention
includes both combinations and subcombinations of the various
features described hereinabove, as well as variations and
modifications thereof which would occur to persons skilled in
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the art upon reading the foregoing description and which are not
disclosed in the prior art.
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