Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEM AND METHOD FOR IDENTIFYING A LOCATION AND/OR AN
ORIENTATION OF AN ELECTROMAGNETIC SENSOR BASED ON A MAP
BACKGROUND
Technical Field
[0001] The present disclosure generally relates to electromagnetic
navigation, and
more particularly to systems and methods for generating a map for
electromagnetic
navigation and identifying a location and/or an orientation of a sensor based
on the map.
Discussion of Related Art
100021 Electromagnetic navigation (EMN) has helped expand medical
imaging,
diagnosis, prognosis, and treatment capabilities by enabling a location and/or
an
orientation of a medical device and/or of a target of interest to be
accurately determined
within a patient's body. Generally, an antenna generates an electromagnetic
(EM) field in
an EM volume, a sensor incorporated onto a medical device senses an EM signal
or
strength based on the field, and the EMN system identities a sensor location
based on the
sensed EM strength. The EM strength at each location in the EM volume is
previously
measured or mapped to enable the sensor location to be identified in the EM
volume by
comparing the sensed EM strength and the previously measured EM strength.
[0003] In some cases, it may be desirable for the sensor to be a small-
sized sensor,
such as a single-coil sensor, because, for instance, a small sized sensor may
be navigable
to additional locations (e.g., narrower portions of a luminal network) within
the patient, to
which a larger-sized sensor may not be navigable. Additionally, in contrast to
large-size
sensors which sometimes must be removed from the patient during a procedure to
make
room in a working channel for other tools, the small-sized sensor may remain
within the
patient throughout the procedure without interfering with the other tools,
thereby
facilitating EMN functionality throughout the procedure.
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100041 To enable a small-sized sensor such as a single-coil sensor to be
accurately
located within an EM volume, it may be necessary to generate multiple (for
instance, 6 or
more) geometrically diverse EM fields within the EM volume. However, because
each of
the EM fields would require generation of a measured mapping of the
corresponding EM
strength at each location in the EM volume, increasing the number of EM fields
would
increase the number of mappings, which can be time consuming and laborious.
Additionally, to improve the accuracy with which the sensor location can be
determined,
precise measurements at many (for example, thousands) of gridpoints within the
EM
volume may be needed, which could make the generating of the mapping even more
time
consuming. Also, because of the potential variability during the manufacturing
processes
and tolerances of electrical equipment, the mapping process may need to be
completed for
each new antenna that is produced and for each electromagnetic navigation
system
installation.
100051 Given the foregoing, a need exists for improved systems and
methods for
generating a map for electromagnetic navigation and identifying a location
and/or an
orientation of a sensor based on the map.
SUMMARY
100061 The present disclosure is related to systems and methods for
generating a
map of EM field strength, for example, a high density (HD) map, for
electromagnetic
navigation and identifying a sensor location and/or orientation based on the
map. In one
example, the HD map has a greater (e.g., finer) gtidpoint resolution (that is,
more
g,ridpoints) in the EM volume than that of a low density (LD) grid in the EM
volume
according to which EM field strength measurements are taken and stored in a LD
map.
The HD map, in some aspects, is generated based on the previously generated LD
map of
measured EM field strength and also based on EM field strength calculations
based, for
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instance on geometric configurations of antennas in an antenna assembly. In
this manner,
the location and/or the orientation of the sensor navigated within the
patient's body can be
accurately identified without the need to take EM field strength measurements
at each of
the many gridpoints of the HD map within the EM volume. This can enable the
use of a
small-sized sensor in EMN procedures while minimizing any increased burden of
map
generation.
100071 In accordance with one aspect of the present disclosure, a method
is
provided for generating a high density (HD) map for identifying a location
and/or an
orientation of an electromagnetic (EM) sensor within an EM volume in which an
EM
field is generated by way of an antenna assembly. The method includes
receiving a
measured EM field strength at each gridpoint of a first set of gridpoints of
the EM volume
from a measurement device. An EM field strength at each gridpoint of a second
set of
gridpoints of the EM volume is calculated based on a geometric configuration
of an
antenna of the antenna assembly. The HD map is generated based on the measured
EM
field strength at each gridpoint of the first set of gridpoints and the
calculated EM field
strength at each gridpoint of the second set of gridpoints.
100081 In another aspect of the present disclosure, the antenna assembly
generates
at least six EM waveforms as components of the EM field.
100091 In a further aspect of the present disclosure, the EM field
strength is
calculated along a three axes coordinate system for each of the at least six
EM waveforms.
MOM In yet another aspect of the present disclosure, the EM field
strength is
measured by way of a sensor having three coils corresponding to the three
axes,
respectively.
100111 In still another aspect of the present disclosure, the second set
of gridpoints
includes each gridpoint of the first set of gridpoints.
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[00121 In another aspect of the present disclosure, the generating the HD
map
includes calculating an error between the measured EM field strength and the
calculated
EM field strength, at each gridpoint of the first set of gridpoints. An error
for each
gridpoint of the second set of gridpoints is interpolated based on the
calculated error at
each gridpoint of the first set of gridpoints. The interpolated error and the
calculated EM
field strength at each gridpoint of the second set of gridpoints are added to
generate the
HD map
100131 In a further aspect of the present disclosure, the error is
calculated based
on a difference between the measured EM field strength and the calculated EM
field
strength at each gridpoint of the first set of gridpoints.
100141 In yet another aspect of the present disclosure, the error is
based on at least
one of an Li or L2 norm of differences between the measured EM field strength
and the
calculated EM field strength along the three axes.
[0015] In still another aspect of the present disclosure, the method
further includes
calculating a pseudo-inverse of the calculated EM field strength at each
gridpoint of the
second set of gridpoints.
[00161 In another aspect of the present disclosure, the HD map further
includes
the pseudo-inverse of the calculated EM field strength at each gridpoint of
the second
plurality of gridpoints.
100171 In accordance with another aspect of the present disclosure an
apparatus is
provided for generating an HD map for identifying a location and/or an
orientation of an
EM sensor within an EM volume in which an EM field is generated by way of an
antenna
assembly. The apparatus includes a processor and a memory storing processor-
executable
instructions that, when executed by the processor, cause the processor to
receive, from a
measurement device, a measured EM field strength at each gridpoint of a first
set of
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gridpoints of the EM volume. An EM field strength at each gridpoint of a
second set of
gridpoints of the EM volume is calculated based on a geometric configuration
of at least
one antenna of the antenna assembly. The HD map is generated based on the
measured
EM field strength at each gridpoint of the first set of gridpoints and the
calculated EM
field strength at each gridpoint of the second set of gridpoints.
100181 In another aspect of the present disclosure, the antenna assembly
generates
at least six EM waveforms as components of the EM field.
100191 In still another aspect of the present disclosure, the EM field
strength is
calculated along a three axes coordinate system for each of the at least six
EM waveforms.
100201 In a further aspect of the present disclosure, the EM field
strength is
measured with a sensor having three coils corresponding to the three axes,
respectively.
100211 In yet another aspect of the present disclosure, the second set of
gridpoints
includes each gridpoint of the first set of gridpoints.
100221 In another aspect of the present disclosure, the generating of the
HD map
includes calculating an error between the measured EM field strength and the
calculated
EM field strength, at each gridpoint of the first set of gridpoints. An error
for each
gridpoint of the second plurality of gridpoints is interpolated based on the
calculated error
at each gridpoint of the first plurality of gridpoint. The interpolated error
and the
calculated EM field strength at each gridpoint of the second plurality of
gridpoints are
added to generate the HD map.
100231 In yet another aspect of the present disclosure, the error is
calculated based
on a difference between the measured EM field strength and the calculated EM
field
strength at each gridpoint of the first set of gridpoints.
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[0024] In a further aspect of the present disclosure, the error is based
on an Li
and/or L2 norm of differences between the measured EM field strength and the
calculated
EM field strength along the three axes.
[0025] In still another aspect of the present disclosure, the memory
further stores
instructions that, when executed by the processor, cause the processor to
calculate a
pseudo-inverse of the calculated EM field strength at each gridpoint of the
second set of
gridpoints.
100261 In another aspect of the present disclosure, the HD map further
includes
the pseudo-inverse of the calculated EM field strength at each gridpoint of
the second set
of gridpoints.
[0027] In accordance with another aspect of the present disclosure, a
method is
provided for identifying a location and/or an orientation of an EM sensor
navigated
within an EM volume. The method includes retrieving, from a memory, a
calculated EM
field strength at each gridpoint of a second set of gridpoints of the EM
volume. An EM
field is generated by way of an antenna assembly. A measured EM field strength
is
received from the EM sensor. A first gridpoint among a first set of gridpoints
of the EM
volume is identified based on the measured EM field strength and a HD map. The
location and/or the orientation of the EM sensor are identified based on the
HD map,
using the first gridpoint as an initial condition. The second set of
gridpoints includes the
first plurality of gridpoints.
[0028] In another aspect of the present disclosure, the antenna assembly
includes
at least six antennas, each of the antennas including multiple loops.
[0029] In yet another aspect of the present disclosure, the multiple
loops have a
geometric configuration.
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100301 In a
further aspect of the present disclosure, the HD map includes a
calculated EM field strength for each gridpoint of the second set of
gridpoints in the EM
volume.
100311 In
still another aspect of the present disclosure, the calculated EM field
strength is based on the respective geometric configurations of the at least
six antennas.
100321 In
another aspect of the present disclosure, the HD map further includes a
pseudo-inverse of the calculated EM field strength at each gridpoint of the
second
plurality of gridpoints.
100331 In yet
another aspect of the present disclosure, the identifying the first
gridpoint includes identifying an orientation vector ii00,4 , where (a,b,c) is
a gridpoint in
the first set of gridpoints, satisfying the following condition: fi(a,,,)004 =
V. where
is a pseudo-inverse of lT3(0,), which is a calculated EM field strength at
gridpoint
(a,b,c) in the HD map. A difference between r300,,w 1100,0 and V is
calculating. A
gridpoint (A,B,C), from among the first set of gridpoints, where a difference
between
= ii and V is the smallest, is selected, as the first gridpoint.
100341 In a
further aspect of the present disclosure, the identifying the location
and/or the orientation includes identifying an orientation vector iiol,em ,
where (d,e,f) is a
gridpoint in the second set of gridpoints and is located nearby (e.g. within a
predetermined distance) from the first gridpoint (A,B,C), satisfying the
following
condition: ii0A0 =-11l-Ei(dA0-1= V. where (dm -1 is a pseudo-inverse of 13(de-
, which is a
calculated EM field strength at gridpoint (d,e,f) in the HD map. A difference
between
liom = nom and V is calculated. A second gridpoint (D,E,F) from among the
second set
of gridpoints, where a difference between a(D,F,F) = li(D,F,F) and V is the
smallest, is selected.
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[0035] In still another aspect of the present disclosure, ii(D,E,1) is
related to the
orientation of the EM sensor.
[0036] In another aspect of the present disclosure, the second gridpoint
(D,E,F) is
the location of the EM sensor.
100371 In accordance with another aspect of the present disclosure, a
system is
provided for identifying a location and/or an orientation of an EM sensor
navigated
within an EM volume. The system includes an antenna assembly, the EM sensor, a
processor, and a memory. The antenna assembly is configured to radiate an EM
field
within the EM volume. The EM sensor is configured to measure an EM field
strength
based on the radiated EM field. The memory stores a calculated EM field
strength at each
gridpoint of a second set of gridpoints of the EM volume. The memory also
stores
processor-executable instructions that, when executed by the processor, cause
the
processor to retrieve, from the memory, the calculated EM field strength at
each gridpoint
of the second set of gridpoints. A first gridpoint among a first set of
gridpoints of the EM
volume is identified based on the measured EM field strength and the HD map.
The
location and/or the orientation of the EM sensor are identified based on the
HD map,
using the first gridpoint as an initial condition. The second set of
gridpoints includes the
first set of gridpoints.
[0038] In a further aspect of the present disclosure, the antenna
assembly includes
at least six antennas, each of the antennas including a plurality of loops.
[0039] In still another aspect of the present disclosure, the plurality
of loops has a
geometric configuration.
100401 In another aspect of the present disclosure, the HD map includes a
calculated EM field strength at each gridpoint of the second set of gridpoints
in the EM
volume.
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100411 In yet
another aspect of the present disclosure, the calculated EM field
strength is based on the respective geometric configurations of the at least
six antennas.
100421 In
another aspect of the present disclosure, the HD map further includes a
pseudo-inverse of the calculated EM field strength at each gridpoint of the
second set of
gridpoints.
100431 In
another aspect of the present disclosure, the identifying the first
gridpoint includes identifying an orientation vector ii.00,x) , where (a,b,c)
is a gridpoint in
the first set of gridpoints, satisfying the following condition: ii046,0 floo4-
-1= V, where
a pseudo-inverse of ft which
is a calculated EM field strength at gridpoint
(a,b,c) in the HD map. A difference between ,
= ii (a, b,c) and V is calculated. A
gridpoint (A,B,C) from among the first plurality of gridpoints, where a
difference
between 13(,,B,c) =ii and V is the smallest, is selected as the first
gridpoint.
100441 In yet
another aspect of the present disclosure, the identifying the location
and/or the orientation includes identifying an orientation vector flow , where
(d,e,f) is a
gridpoint in the second set of gridpoints and is located nearby (e.g., within
a
predetermined distance from) the first gridpoint (A,B,C), satisfying the
following
condition: now) rzii@A0-1= V. where 13 0A0-lis a pseudo-inverse of 13.0,0 ,
which is a
calculated EM field strength at gridpoint (d,e,f) in the HD map. A difference
between
1101,,0 = ii(dAn and V is calculated. A second gridpoint (D,E,F) from among
the second
plurality of gridpoints, where a difference between 1µF) = liAE,F) and V is
the smallest is
selected.
100451 In
another aspect of the present disclosure, ii(DAF) is related to the
orientation of the EM sensor.
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100461 In a further aspect of the present disclosure, the second
gridpoint (D,E,F)
is the location of the EM sensor.
10471 Any of the aspects and embodiments of the present disclosure may
be
combined without departing from the scope of the present disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0048] Objects and features of the presently disclosed systems and
methods will
become apparent to those of ordinary skill in the art when descriptions of
various
embodiments are read with reference to the accompanying drawings, of which:
[0049] FIG. 1 shows an example electromagnetic navigation (EMN) system,
in
accordance with the present disclosure;
100501 FIG. 2 is a block diagram of a portion of the EMN system of FIG.
1, in
accordance with the present disclosure;
100511 FIG. 3 is a graphical illustration of example low density
measurements and
related curves, in accordance with the present disclosure;
[0052] FIG. 4 is a flowchart illustrating an example method for
generating a high
density map, in accordance with the present disclosure;
[0053] FIG. 5 is a flowchart illustrating an example method for
identifying a
location and/or an orientation of a sensor, in accordance with the present
disclosure;
[0054] FIG. 6 is a graphical illustration of an example error function,
having
multiple local minima, of a discrepancy between a measurement value and a
calculated
value, in accordance with the present disclosure; and
[0055] FIG. 7 is a block diagram of a computing device for use in various
embodiments of the present disclosure.
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DETAILED DESC RI P11 ON
100561 The present disclosure is related to systems and methods for
generating a
high density (HD) map and identifying a location and/or an orientation of a
sensor, which
may include at least one coil, based on the IID map. In some aspects, the
respective
geometric configurations the antennas enable automated and highly repeatable
processes
for reproducing such antennas and/or for mathematically calculating the
expected or
theoretical EM strength at every I ID gridpoint within an EM volume (for
instance, where
the antennas have geometric configurations based on linear portions of printed
circuit
board (PCB) traces, which facilitate use of the superposition principle in
computing the
total contribution of the fields generated by way of each antenna to the total
combined
EM field within the volume). These mathematical calculations may be combined
with
actual measurements made in a coarse coordinate system, which includes fewer
gridpoints than the number of gridpoints used for the mathematically
calculated EM
strength. In this way, the time and/or cost related to making the measurements
can be
lowered and a HD map can be generated and used in a repeatable, efficient, and
cost-
effective manner.
100571 Further, the present disclosure is related to systems and methods
for
identifying a location and/or an orientation of an EM sensor by using the HD
map. In
general, the EM sensor senses EM strengths, and an EMN system compares the
sensed
EM strengths with the expected EM strengths of the HD map and identifies the
location
and the orientation of the EM sensor.
100581 In an aspect of the present disclosure, a fine coordinate system
(e.g., a HD
coordinate system or set of gridpoints) is used to describe a coordinate
system of the EM
volume, which includes more gridpoints than those in a coarse coordinate
system (e.g., a
LD coordinate system or set of gridpoints) of the EM volume. In some aspects,
every
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gridpoint of the coarse coordinate system may be included in the fine
coordinate system.
In general, the coarse coordinate system is utilized for actual EM field
strength
measurements and the fine coordinate system is utilized for mathematical
calculations of
EM field strength.
100591 FIG. 1 illustrates an example electromagnetic navigation (EMN)
system
100, which is configured to identify a location and/or an orientation of a
medical device,
or sensor thereof, navigating (e.g., to a target) within the patient's body by
using an
antenna assembly, which includes a plurality of antennas and generates EM
fields. The
EMN system 100 is further configured to augment CT, MRI, or fluoroscopic
images in
navigation through patient's body toward a target of interest, such as a
deceased portion
in a hull inal network of a patient's lung.
f00601 The EMN system 100 includes a catheter guide assembly 110, a
bronchoscope 115, a computing device 120, a monitoring device 130, an EM board
140, a
tracking device 160, and reference sensors 170. The bronchoscope 115 is
operatively
coupled to the computing device 120 and the monitoring device 130 via a wired
connection (as shown in FIG. 1) or wireless connection (not shown).
100611 The bronchoscope 115 is inserted into the mouth of a patient 150
and
captures images of the lumina' network of the lung. In the EMN system 100,
inserted into
the bronchoscope 115 is a catheter guide assembly 110 for achieving access to
the
periphery of the luminal network of the lung of the patient 150. The catheter
guide
assembly 110 may include an extended working channel (EWC) 111 with an EM
sensor
112 at the distal portion of the EWC 111. A locatable guide catheter (LG) may
be inserted
into the EWC 111 with another EM sensor at the distal portion of the LG. The
EM sensor
112 at the distal portion of the EWC 111 or the LG is used to identify a
location and/or an
orientation of the EWC 111 or the LG while navigating through the luminal
network of
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the lung. Due to the size restriction in the EWC 111 or the LG, in some
embodiments, the
EM sensor 112 may include only one single coil for detecting EM strength of an
EM field
over the patient 150. However, the number of coils in the EM sensor is not
limited to one
but may be two or more.
100621 The computing device 120, such as, a laptop, desktop, tablet, or
other
similar computing device, includes a display 122, one or more processors 124,
memory
126, an AC current driver 127 for providing AC current signals to the antenna
assembly
145, a network card 128, and an input device 129. The particular configuration
of the
computing device 120 illustrated in FIG. 1 is provided as an example, but
other
configurations of the components shown in FIG. 1 as being included in the
computing
device 120 are also contemplated. In particular, in some embodiments, one or
more of the
components (122, 124, 126, 127, 128, and/or 129) shown in FIG. 1 as being
included in
the computing device 120 may instead be separate from the computing device 120
and
may be coupled to the computing device 120 and/or to any other component(s) of
the
system 100 by way of one or more respective wired or wireless path(s) to
facilitate the
transmission of power and/or data signals throughout the system 100. For
example,
although not shown in FIG. 1, the AC current driver 127 may, in some example
aspects,
be separate from the computing device 120 and may be coupled to the antenna
assembly
145 and/or coupled to one or more components of the computing device 120, such
as the
processor 124 and the memory 126, by way of one or more corresponding paths.
100631 In some aspects, the EMN system 100 may also include multiple
computing devices, wherein the multiple computing devices are employed for
planning,
treatment, visualization, or helping clinicians in a manner suitable for
medical operations.
The display 122 may be touch-sensitive and/or voice-activated, enabling the
display 122
to serve as both input and output devices. The display 122 may display two
dimensional
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(2D) images or three dimensional (3D) model of a lung to locate and identify a
portion of
the lung that displays symptoms of lung diseases.
100641 The one or more processors 124 execute computer-executable
instructions.
The processors 124 may perform image-processing functions so that the 3D model
of the
lung can be displayed on the display 122 or location algorithm to identify a
location and
an orientation of the EM sensor 112. In embodiments, the computing device 120
may
further include a separate graphic accelerator (not shown) that performs only
the image-
processing functions so that the one or more processors 124 may be available
for other
programs. The memory 126 stores data and programs. For example, data may be
mapping
data for the EMN or any other related data such as a HD map, image data,
patients'
medical records, prescriptions and/or history of the patient's diseases.
[0065] The HD map may include a plurality of gridpoints in a fme
coordinate
system of the EM volume in which a medical device (e.g., the EWC 111, LG,
treatment
probe, or other surgical devices) is to be navigated, and expected EM
strengths at each of
the plurality of gridpoints. When the EM sensor 112 senses EM strength at a
point, the
one or more processors 124 may compare the sensed EM strength with the
expected EM
strengths in the HD map and identify the location of the EM sensor 112 within
the EM
volume. Further, an orientation of the medical device may be also calculated
based on the
sensed EM strength and the expected EM strengths in the HD map.
[0066] As shown in FIG. 1, the EM board 140 is configured to provide a
flat
surface for the patient 150 to lie upon and includes an antenna assembly 145.
When the
patient 150 lies upon on the EM board 140, the antenna assembly 145 generates
an EM
field sufficient to surround a portion of the patient 150 or the EM volume.
The antenna
assembly 145 includes a plurality of antennas, each of which may include a
plurality of
loops. In one aspect, each antenna is configured to generate an EM waveform
having a
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corresponding frequency. The number of antennas may be at least six. In an
aspect, the
number of antennas may be nine so that nine different EM waveforms can be
generated.
100671 In another aspect, a time multiplexing method is employed in
generating
the EM waveforms. For example, the antennas of the antenna assembly 145 may
generate
EM waveforms with the same frequency at different times during a period. In
another
aspect, frequency multiplexing method may be employed, where each antenna
generates
EM waveform having a frequency different from each other. In still another
aspect,
combination of the time multiplexing and frequency multiplexing methods may be
employed. The antennas are grouped into more than one group. Antennas in the
same
group generate EM waveforms having the same frequency but at different times.
Antennas in different groups may generate EM waveforms having different
frequencies
from each other. Corresponding de-multiplexing method is to be used to
separate EM
waveforms.
100681 In an aspect, each antenna may have a geometric configuration (for
instance, where the antennas each have geometric configurations based on
linear portions
of printed circuit board (PCB) traces or wires, which facilitate use of the
superposition
principle in computing the total contribution of the fields generated by way
of each
antenna to the total combined EM field within the volume) so that each portion
of the
plurality of loops can be expressed as mathematical relationship or equations,
as
described in further detail below. The magnetic field can thus be computed for
each trace
on the antenna and the contributions from all traces can be summed. Based on
this
geometric configuration, expected EM strength at each gridpoint in the HD map
can be
theoretically or mathematically calculated. Additional aspects of such example
antennas
and methods of manufacturing the antennas are disclosed in U.S. Patent
Application No.
15/337,056 , entitled "Electromagnetic Navigation Antenna Assembly and
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Electromagnetic Navigation System Including the Same," filed on October 28,
2016 and
having attorney docket number 356580.USU1 (1988-252 A), the entire contents of
which
are hereby incorporated by reference herein.
100691 FIG. 2 shows a block diagram of a portion of the example
electromagnetic
navigation system 100 of FIG. 1, according to the present disclosure. In
general, the
computing device 120 of the EMN system 100 controls the antenna assembly 145
embedded in the EM board 140 to generate an EM field, receives sensed results
from the
EM sensor 112, and determines a location and an orientation of the EM sensor
112 in the
EM volume.
[0070] The computing device 120 includes a clock 205, which generates a
clock
signal used for generating the EM field and sampling the sensed results. Since
the same
clock signal is used for generating the EM field and sampling the sensed EM
field,
synchronization between the magnetic field generation circuitry (e.g., a
waveform
generator 210) and the waveform acquisition circuitry (e.g., a digitizer 215)
may be
achieved. In other words, when the clock 205 provides a clock signal to the
waveform
generator 210 and the digitizer 215, the EM waveforms generated by the antenna
assembly 145 are digitally sampled by digitizer 215 substantially at the same
time. The
digitizer 215 may include an analog-to-digital converter (ADC, which is not
shown) to
digitally sample the sensed results and an amplifier (which is not shown) to
amplify the
magnitude of the sensed result so that the magnitude of the sensed results is
within the
operable range of the ADC. In an aspect, the digitizer 215 may include a pre-
amplifier
and post-amplifier so that the magnitude of the sensed result is amplified to
be within the
operable range of the ADC by the pre-amplifier and digital samples are also
amplified to
the magnitude of the sensed result by the post-amplifier.
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10711 The demodulator 220 demodulates the digital samples to remove
unwanted
signals (e.g., noises) and to restore the EM waveforms, which have been
generated by the
antenna assembly 145. The demodulator 220 may use time de-multiplexing method,
frequency de-multiplexing method, or combination of both to separate and
identify the
EM waveforms depending on the method used by the antennas of the antenna
assembly
145 to generate the EM waveforms, and to determine EM strength affected by
each of the
antenna of the antenna assembly 145.
100721 For example, when the antenna assembly 145 includes six antennas,
the
demodulator 220 is capable of identifying six EM strengths, which is sensed by
the EM
sensor 112, for the six antennas, respectively. In a ease when the number of
antennas is
nine, the outputs of the demodulator 220 may be expressed in a form of a nine
by one
matrix. Based on the modulation method (e.g., time multiplexing, frequency
multiplexing,
or a combination thereof) utilized by the antennas, the demodulator 220
demodulates the
sensed result.
100731 For example, when the antennas of the antenna assembly 145 utilize
frequency multiplexing, the demodulator 220 may use a set of fmely tuned
digital filters.
Orthogonal frequency division multiplexing may also be utilized, in which the
EM field
and sampling frequencies are chosen in such a way that only the desired
frequency from a
specific antenna is allowed to pass while other frequencies are precisely
stopped. In an
aspect, the demodulator 220 may use a multiple tap orthogonal frequency
matched filter,
in which the digital filter for a specific frequency is tuned to the desired
demodulation
window.
100741 The memory 126 may store data and programs related to
identification of a
location and an orientation. The data includes a high density (11D) map 225,
which
includes a plurality of gridpoints according to the fme coordinate system for
the EM
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volume and expected EM strengths at the gridpoints. The HD map 225 may be
based on
three-axis coordinate system, where each gridpoint has three coordinates
corresponding to
the three axes, respectively. In this case, the expected EM strength at each
gridpoint may
include one EM strength value along each axis for each EM waveform. For
example, if
there are nine antennas generating nine different EM waveforms, each of which
having a
separate frequency, and three axes are x, y, and z axes, the expected EM
strength may
include nine EM strength values along the x axis, nine EM strength values
along the y
axis, and nine EM strength values along the z axis, at each gridpoint. Such
expected EM
strength at each gridpoint may be expressed in a nine by three matrix form.
[0075] The HD map 225 may be made with computations 230, which includes
theoretically calculated EM strengths at each axis at each gridpoint in the
fine coordinate
system, and measurement 235, which includes measurements at each axis at each
gridpoint in the coarse coordinate system. The fine coordinate system includes
all the
gridpoints in the coarse coordinate system and the gridpoints of the fine
coordinate
system are more finely distributed than those of the coarse coordinate system.
By using
the geometric configuration of the antennas of the antenna assembly 145,
measurement
may not have to be made with the fine coordinate system. Rather, the
measurement may
be made in the coarse coordinate system and theoretical computations may be
made in the
fine coordinate system. By combining the measurements 235 in the coarse
coordinate
system with the theoretical computations 230 in the fine coordinate system,
the HD map
225 may be generated. Generation of the HD map 225 based on the measurement
235 and
calculations 230 will be described in further detail with respect to FIG. 4
below.
[0076] After passage of time or due to foreign objects near the EMN
system 100,
measurements by the EM sensor 112 or other hardware may need to be calibrated.
Such
calibration data may be also stored in the memory 126 in a form of sensor
calibration 240
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and hardware calibration 245.
100771 When the computing device 120 receives measurement data from the
EM
sensor 112 via the demodulator 220, the computing device 120 uses the location
algorithm 250, which is also stored in the memory 126, with the HD map 225 to
identify
the location and the orientation of the EM sensor 112 in the fme coordinate
system.
Identification of the location and/or the orientation will be described in
further detail with
respect to FIG. 5 below.
[0078] The location algorithm 250 may utilize any error minimization
algorithm
in identifying the location and the orientation of the EM sensor 112. For
example,
Levenberg-Marquardt algorithm may be employed to minimize errors between the
expected EM strengths of the HD density map and the sensed results. Other
error
minimization methods or algorithms, which a person having ordinary skill in
the art can
readily appreciate, may also be utilized without departing from the scope of
this
disclosure.
100791 The memory 126 further includes applications 255, which can be
utilized
by the computing device 120 of the EMN system 100 and which uses information
regarding the location and the orientation of the EM sensor 112. Such
application 255
may be a displaying application, which displays a graphical representation of
a medical
device, on which the EM sensor 112 is mounted or installed, at the location of
the EM
sensor 112 and along the orientation of the EM sensor 112 in the EM volume, an
application for treatment, which determines whether a medical device is near a
target of
interest, or any other applications, which use the location and the
orientation of the EM
sensor 112.
[0080] FIG. 3 is a graphical illustration of multiple curves 320, 325,
330, and 340,
as well as discrete EM field strength measurements 315a-315i taken in the
coarse
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coordinate system. The horizontal axis may represent any axis among x, y, and
z axes for
the EM volume and the vertical axis represents a magnitude of EM field
strengths.
Gridpoints of the coarse coordinate system are shown separated by 50
millimeters and
measured EM strengths at the gridpoints of the coarse coordinate system are
shown as
black dots 31 5a-3 I 5i.
[00811 In some aspects, measurements may be taken at a specific hospital
rooms
and beds, where the EMN system 100 will be used, by way of a measurement jig,
which
includes three coils sensing an EM field strength in each of three different
directions (e.g.,
x, y, and z axes). Examples of such a measurement jig are disclosed by
Provisional U.S.
Patent Application No. 62/237,084, entitled "Systems And Methods For Automated
Mapping And Accuracy-Testing," filed on October 5, 2015, the entire contents
of which
are hereby incorporated herein by reference.
[00821 Based on the measurement values at LD gridpoints 315a-315i,
interpolation may be used to generate first and second interpolated curves,
320 and 325.
In one example, the first interpolated curve 320 is generated by a linear
interpolation
method and the second interpolated curve 325 is generated by B-spline
interpolation.
Calculated EM strengths at gridpoints in the HD map are also interpolated to
generate a
third interpolated curve 330.
[0083] As shown in box 335, the first, second, and third interpolated
curves 320,
325, 330 are substantially different from each other between two gridpoints
315h and
315i. The first interpolated curve 320 is lower than the third interpolated
curve 330, and
the second interpolated curve 325 is much higher than the second and third
interpolated
curves 325 and 330. Due to these big differences, an error may be apparent if
only one of
the three interpolated curves is used.
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100841 In order to minimize such differences, a fourth interpolated curve
340 is
used. The fourth curve 340 is generated by calculating discrepancies between
theoretical
calculations and measurements at the LD gridpoints, such as 315a--315i, and
interpolating
the discrepancies for the HD gridpoints. By adding the fourth interpolated
curve 340 to
the third interpolated curve 330 at the HD gridpoints, expected EM strength at
each
gridpoints in the HD map is obtained and higher accuracy may be obtained.
Detailed
descriptions regarding how to generate the RD map is described with respect to
FIG. 4
below.
100851 FIG. 4 is a flowchart illustrating an example method 400 for
generating an
HD map based on theoretical calculations in the fine coordinate system and
measurements in the coarse coordinate system. Measurements may be performed
for the
EM field generated by the antennas of the antenna assembly 145 of FIG. 1, each
of which
having a corresponding geometric configuration. At 410, EM field measurements
at all
gridpoints in the coarse coordinate system are received from a measurement
jig. The
measurements may include three different measurements along three axes in the
coarse
coordinate system for each EM waveform. Thus, when there are nine antennas,
the
measurements at one gridpoint may include three values for the three different
axes and
nine of three values for the nine different waveforms, respectively. In an
aspect, these
measurements may be in a form of nine by three matrix.
100861 At 420, based on the geometric configuration of each antenna of
the
antenna assembly 145, EM field strength is theoretically or mathematically
calculated. As
described above, each antenna includes a plurality of loops, which have
geometric
configurations. In other words, each loop of the antenna can be expressed in a
form of
mathematical equations or is made of simply linear portions. Thus, EM strength
at any
gridpoints in the fine coordinate system may be calculated by using Biot-
Savart-Laplace
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law as follows:
B(r) ¨ idie x (1),
4ir lr
where B(r) is the EM strength at the gridpoint r influenced by the linear
portion C, tio is a
magnetic constant of the vacuum permeability, 471x10---7 Vs/(Am), fc is a
symbol of
line integral on the linear portion C, I is the magnitude of the current
passing through the
linear portion C, dl is a vector whose magnitude is the length of the
differential element
of the linear portion C in the direction of current, r' is a displacement
vector from the
differential element dl of the linear portion C to the gridpoint r, and x is a
vector symbol
representing a cross product between two vectors. Since the linear portion C
is a simple
line and each loop of the antenna includes multiple linear portions, total EM
strength at
the gridpoint r can be a sum of the EM strengths influenced by all the linear
portions of
the antenna. Further, the EM strength at the gridpoint r by the plural
antennas is
calculated in the same way. In other words, the total EM strength at gridpoint
r may
include three calculated values for the three different axes (e.g., x, y, and
z axes) for one
antenna, and nine of three calculated values for the nine antennas, in a case
when there
are nine antennas. In an aspect, the calculated EM strength may be expressed
in a nine by
three matrix form.
[00871 At 430, a discrepancy is calculated between the measured EM field
and the
calculated EM field at each gridpoint in the coarse coordinate system. In an
aspect, the
discrepancy may be made smaller by calibrating parameters of the three coil
sensor of the
measurement jig, calibrating the antennas, or calibrating parameters (e.g.,
frequencies or
phases for the waveform generator 210) of the computing device of the EMN
system.
100881 At 440, the calculated discrepancies at gridpoints in the coarse
coordinate
system are interpolated for gridpoints in the ftne coordinate system. Any
method of
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interpolation including linear interpolation, b-spline interpolation, etc. may
be used.
100891 At 450, the interpolated discrepancies are added to the
theoretical
calculations of the EM field to from expected EM field strength at each
gridpoint in the
fine coordinate system. The expected EM field strength at each gridpoint may
be in a
form of a nine by three matrix in a case when there are nine separate EM
waveforms. The
HD map may further include a pseudo-inverse of the expected EM field strength
at each
gridpoint in the HD map. This pseudo-inverse may be used in identifying a
location and
an orientation of the EM sensor, which is described in further detail with
respect to FIG. 5
below.
100901 FIG. 5 is a flowchart illustrating an example method 500 for
identifying a
location and/or an orientation of an EM sensor, for example, mounted on a
medical
device, which is navigated within a patient's body, in accordance with the
present
disclosure. The method 500 may be used while a medical device navigates inside
the
patient's body. At 510, the HD map, which includes expected EM field strength
at each
gridpoint of the HD map, is retrieved from a memory. As described above, the
expected
EM field strengths are based on the theoretical computations in the fine
coordinate system
and measurements in the coarse coordinate system.
100911 The EM sensor mounted on the medical device periodically transmits
sensed EM field strength to an EMN computing device, which digitally samples
the
sensed EM field strength. The EMN computing device measures the EM field
strength
based on the digital samples in step 520.
100921 At 530, it is determined whether an initial location is set as an
initial
condition. If it is determined that the initial location is not set, the EMN
computing device
compares all gridpoints in the coarse coordinate system with the measured EM
field
strength, simply pickups, to fmd an approximate gridpoint in the coarse
coordinate system
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near the location of the EM sensor, as an initial location, at 540.
100931 In an embodiment, a following error function may be used at 540:
N 2 \ 2
E = E klEta (a, b, c) = n(a,b,c)¨ I + b(H -g2J (2),
a=1
where E is the error value, a is a counter, N is the number of antennas,
(a,b,c) is a
gridpoint in the coarse coordinate system, I3.(a, b,c) is a vector, one by
three matrix,
including an expected EM field strength at (a,b,c) influenced by the a-th
antenna, "." is a
symbol of dot product between two vectors, (a,b,c) is an orientation of the EM
sensor,
and Vc, is a vector, one by one matrix, including a pickup influenced by the a-
th antenna,
b is a parameter to control a gain weight, and g is a gain of the EM sensor.
In an aspect,
the parameter b is used when the gain of the EM sensor is known and fixed. The
value for
the parameter b may be chosen so as not to dominate the error function E. In
another
aspect, when the gain of the EM sensor is not known, the parameter b may be
set to zero
or the gain squared, g2, is assumed to be equal to the squared norm of the
orientation
vector 11.
100941 In some examples, for convenience, the parameter b is assumed to
be zero.
In this case, the error function E becomes:
1. (B. (a, b, c) = ¨n(a, b, c) ¨ vj (3)-
a.1
This error function is useful in identifying a location in the coarse or fine
coordinate
system. hi an aspect, the error function is not limited to the above equation
(2) or (3) and
can be any error function that a person of ordinary skill in the art would
readily appreciate
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without departing from the scope of this disclosure. For example, the error
function E
may be:
T3(a, b, c) ¨ V or b, c) ¨ V ,
1 2
where 111 or112 represents an LI or L2 norm of the vector inside of the
symbol,
respectively.
100951 Referring briefly to FIG. 6, a curve of an error function along
one axis is
shown to illustrate how selection of an initial location may impact the
determination of a
location that provides the global minimum of the error. The horizontal axis
represents a
location along one axis (e.g., x, y, or z axis) and the vertical axis
represents a magnitude
of the error function. If the initial location is set to be near X0 or X1, the
location giving a
local minimum will be between Xo and X1. If the initial location is set to be
X5 or X6, the
location giving a local minimum will be between X5 and X6. In contrast, if the
initial
location is set to be one of X2, X3, or X4, the location giving a local
minimum will be
between X3 and X4, which gives the accurate global minimum. Thus, referring
back to
FIG. 5, in a case when there is no set initial location, the method 500
evaluates the error
function at every gridpoint in the coarse coordinate system to find a first
gridpoint, which
provides the global minimum, in step 540.
100961 The error function E includes a term, the orientation vector n,
which, at
540, may also be identified as follows:
n(a, b, c) = ii(a,b,c)-1 = V (4),
where ii(a,b, 01 is a pseudo-inverse of iii(a,b,c) , and V includes pickups.
In one
example, if the total number of antennas in the antenna assembly is nine,
B(a,b,c) is a
nine by three matrix, li(a, b, c)' is a three by nine matrix, and V is a nine
by one matrix.
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Thus, B(a, b, c)1 V results in a three by one matrix, which is a column vector
representing an orientation matrix, n(a,b, c) at gridpoint (a,b,c) in the
coarse coordinate
system.
[0097] Based on equation (3), the error function is evaluated. Errors of
all
gridpoints in the coarse coordinate system are compared with each other, and
the
gridpoint that provides the smallest error is selected as a first gridpoint
and is set as the
initial location at 540. After the initial location is set at 540, 550
follows. Also, at 530,
when it is determined that the initial location is set, the step 550 is
performed.
[0098] At 550, a predetermined number of gridpoints around the initial
location
are selected to calculate the error function in the same way as in equation
(2) or (3). For
example, if the predetermined number of gridpoints is three, three gridpoints
from the
initial location in both directions along x, y, and z axes form a cube, 7 by 7
by 7
gridpoints. Thus, 343 gridpoints are selected to calculate the error function,
and one
among the selected gridpoints, which provides the smallest error, is selected
as a second
gridpoint, i.e., the location of the EM sensor. The corresponding orientation
vector is also
set as the orientation of the EM sensor in step 550. The second gridpoint is
set as the
initial location in step 560.
[0099] According to one aspect, in step 540, the error may be compared
with a
predetermined threshold. If the error is less than the predetermined
threshold, that
gridpoint is selected as the second gridpoint or the location of the EM sensor
and
corresponding orientation vector is selected as the orientation of the EM
sensor.
[001001 In step 570, it is determined whether the target has been reached.
When it
is determined that the target has not been reached, steps 520-570 are repeated
until the
target is reached. Otherwise, the method 500 ends.
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[00101] Turning now to FIG. 7, there is shown a block diagram of a
computing
device 700, which can be used as the computing device 120 of the EMN system
100, the
tracking device 160, or a computer performing the method 400 of FIG. 4 or the
method
500 of FIG. 5. The computing device 700 may include a memory 702, a processor
704, a
display 706, network interface 708, an input device 710, and/or output module
712.
[00102] The memory 702 includes any non-transitory computer-readable
storage
media for storing data and/or software that is executable by the processor 704
and which
controls the operation of the computing device 700. In an embodiment, the
memory 702
may include one or more solid-state storage devices such as flash memory
chips.
Alternatively or in addition to the one or more solid-state storage devices,
the memory
702 may include one or more mass storage devices connected to the processor
704
through a mass storage controller (not shown) and a communications bus (not
shown).
Although the description of computer-readable media contained herein refers to
a solid-
state storage, it should be appreciated by those skilled in the art that
computer-readable
storage media can be any available media that can be accessed by the processor
704. That
is, computer readable storage media include non-transitory, volatile and non-
volatile,
removable and non-removable media implemented in any method or technology for
storage of information such as computer-readable instructions, data
structures, program
modules or other data. For example, computer-readable storage media include
RAM,
ROM, EPROM, EEPROM, flash memory or other solid state memory technology, CD-
ROM, DVD, Blu-Ray or other optical storage, magnetic cassettes, magnetic tape,
magnetic disk storage or other magnetic storage devices, or any other medium
which can
be used to store the desired information and which can be accessed by the
computing
device 700.
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(001031 The memory 702 may store application 716 and data 714. The
application
716 may, when executed by the processor 704, cause the display 706 to present
user
interface 718 on its screen.
f 001041 The processor 704 may be a general purpose processor, a
specialized
graphic processing unit (GPU) configured to perform specific graphics
processing tasks
while freeing up the general purpose processor to perform other tasks, and/or
any number
or combination of such processors.
1001051 The display 706 may be touch-sensitive and/or voice-activated,
enabling
the display 706 to serve as both an input and output device. Alternatively, a
keyboard (not
shown), mouse (not shown), or other data input devices may be employed.
1001061 The network interface 708 may be configured to connect to a
network such
as a local area network (LAN) consisting of a wired network and/or a wireless
network, a
wide area network (WAN), a wireless mobile network, a Bluetooth network,
and/or the
intemet. For example, the computing device 700 may receive measurement data
and
variables, and perform the method 400 of FIG. 4 to generate a H13 map. The
computing
device 700 may receive updates to its software, for example, application 716,
via network
interface 708. The computing device 700 may also display notifications on the
display
706 that a software update is available.
1001071 In another aspect, the computing device 700 may receive computed
tomographic (CT) image data of a patient from a server, for example, a
hospital server,
intemet server, or other similar servers, for use during surgical ablation
planning. Patient
CT image data may also be provided to the computing device 700 via a removable
memory.
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1001081 Input device 710 may be any device by means of which a user may
interact
with the computing device 700, such as, for example, a mouse, keyboard, foot
pedal,
touch screen, and/or voice interface.
1001091 Output module 712 may include any connectivity port or bus, such
as, for
example, parallel ports, serial ports, universal serial busses (USB), or any
other similar
connectivity port known to those skilled in the art.
1001101 The application 716 may be one or more software programs stored in
the
memory 702 and executed by the processor 704 of the computing device 700.
During
generation of the HD map, one or more software programs in the application 716
may be
loaded from the memory 702 and executed by the processor 704 to generate the
HD map.
In an embodiment, during a navigation phase, one or more programs in the
application
716 may be loaded, identify the location and the orientation of an EM sensor
mounted on
a medical device, and display the medical device at the location along the
orientation on a
screen overlaid with other imaging data, such as CT data or a three
dimensional model of
a patient. In another embodiment, during a treatment phase, one or more
programs in the
application 716 may guide a clinician through a series of steps to identify a
target, size the
target, size a treatment zone, and/or determine an access route to the target
for later use
during the procedure phase. In some other embodiments, one or more programs in
the
application 716 may be loaded on computing devices in an operating room or
other
facility where surgical procedures are performed, and is used as a plan or map
to guide a
clinician performing a surgical procedure by using the information regarding
the location
and the orientation.
1001111 The application 716 may be installed directly on the computing
device 700,
or may be installed on another computer, for example a central server, and
opened on the
computing device 700 via the network interface 708. The application 716 may
run
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natively on the computing device 700, as a web-based application, or any other
format
known to those skilled in the art. In some embodiments, the application 716
will be a
single software program having all of the features and functionality described
in the
present disclosure. In other embodiments, the application 716 may be two or
more
distinct software programs providing various parts of these features and
functionality. For
example, the application 716 may include one software program for generating a
HD map,
another one for identifying a location and an orientation, and a third program
for
navigation and treatment program. In such instances, the various software
programs
forming part of the application 716 may be enabled to communicate with each
other
and/or import and export various data including settings and parameters.
1001121 The application 716 may communicate with a user interface 718
which
generates a user interface for presenting visual interactive features to a
user, for example,
on the display 706 and for receiving input, for example, via a user input
device. For
example, user interface 718 may generate a graphical user interface (GUI) and
output the
GUI to the display 706 for viewing by a user.
1001131 In a case that the computing device 700 may be used as the EMN
system
100, the control workstation 102, or the tracking device 160, the computing
device 700
may be linked to the display 130, thus enabling the computing device 700 to
control the
output on the display 130 along with the output on the display 706. The
computing device
700 may control the display 130 to display output which is the same as or
similar to the
output displayed on the display 706. For example, the output on the display
706 may be
mirrored on the display 130. Alternatively, the computing device 700 may
control the
display 130 to display different output from that displayed on the display
706. For
example, the display 130 may be controlled to display guidance images and
information
during the surgical procedure, while the display 706 is controlled to display
other output,
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such as configuration or status information of an electrosurgical generator
101 as shown
in FIG. 1.
1001141 The application 716 may include one software program thr use
during the
planning phase, and a second software program for use during the treatment
phase. In
such instances, the various software programs forming part of application 716
may be
enabled to communicate with each other and/or import and export various
settings and
parameters relating to the navigation and treatment and/or the patient to
share information.
For example, a treatment plan and any of its components generated by one
software
program during the planning phase may be stored and exported to be used by a
second
software program during the procedure phase.
1001151 Although embodiments have been described in detail with reference
to the
accompanying drawings for the purpose of illustration and description, it is
to be
understood that the inventive processes and apparatus are not to be construed
as limited.
It will be apparent to those of ordinary skill in the art that various
modifications to the
foregoing embodiments may be made without departing from the scope of the
disclosure.
For example, various steps of the methods described herein may be implemented
concurrently and/or in an order different from the example order(s) described
herein.
31
