Note: Descriptions are shown in the official language in which they were submitted.
LOW PROFILE DUAL PAD MAGNETIC FIELD LOCATION SYSTEM WITH
SELF TRACKING
CROSS REFERENCE TO RELATED APPLICATION
[0001] The present application is a non-provisional of Provisional
Application
No. 62/591,238 filed November 28, 2017 which is incorporated herein by
reference
as if fully set forth.
SUMMARY
[0002] A magnetic field location system and method are provided for use in
tracking a distal end of a catheter or the like in a surgical or exploratory
procedure
within a living body disposed on a support structure, such as a patient bed,
table or
gurney. Dual low-profile elongated field generation pads are provided that are
configured for selective placement along respective sides of the living body
disposed
on the support structure. Each field generation pad includes a plurality of
magnetic
coils operable to generate magnetic fields.
[0003] A securing structure is provided to releasably secure the dual
field
generation pads to the support structure when selectively placed on the
support
structure. The dual field generation pads and associated securing structure
are
preferably configured such that the dual field generation pads are able to be
selectively placed on and secured to the support structure in less than 60
seconds
and are also able to be removed from the support structure in less than 60
seconds.
Preferably, each of the first and second elongated field generation pads are
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configured with a low-profile height not exceeding 20 mm and a weight not
exceeding 3 Kg.
[0004] A processor is coupled to the magnetic coils of the dual field
generation
pads. The processor is configured to execute a process for correlation of
magnetic
fields generated by the field generation pads such that a reference magnetic
field is
defined that extends within a desired portion of the living body disposed on
the
support structure. This enables precise location and tracking of a distal end
of a
catheter via a magnetic sensor of the catheter within the reference magnetic
field.
[0005] The dual field generation pads are preferably relatively symmetric
and
define relatively symmetric magnetic coil arrays when placed by the sides of
the
living body. In one embodiment, the magnetic fields generated by the dual
field
generation pads are generated by two magnetic coils disposed in each field
generation pad at a defined distance from each other. In such an embodiment,
each
magnetic coil can be configured as a tri-axial coil unit, such as tri-coil
bobbins that
have a combined weight of approximately 200 grams. In another embodiment, the
magnetic fields generated by the dual field generation pads are generated by
six
linearly aligned and equally spaced magnetic coils disposed in each field
generation
pad, where each magnetic coil is configured as a single coil unit.
[0006] To secure each field generation pad to the support structure, two
securing mechanisms can be attached to each field generation pad at predefined
locations spaced apart from each other. In such case, each securing mechanism
can
have an arm having an end attached to the respective field generation pad and
a
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support structure engaging portion. The support structure engaging portion of
the
arm can be configured such that the support structure engaging portion engages
a
side of the support structure when the respective field generation pad is
selectively
placed on the support structure, thereby defining the relative placement of
the
respective field generation pad on the support structure.
[0007] The pad attaching end of the arm of each such securing mechanism
may have an adjustable coupling to enable the positioning of the respective
support
structure engaging portion at an extended or a retracted position relative to
the
respective field generation pad. As such, the dual field generation pads are
placed
furthest from each other and closest to the sides of the support structure
when all of
the support structure engaging portions are in the retracted position and are
placed
closest to each other and furthest from the sides of the support structure
when all of
the support structure engaging portions are in the extended position.
[0008] In one embodiment, each securing mechanism has a clamp configured
to be operated to a clamping position from an open position. The clamps are
preferably operated when the respective support structure engaging portions
are
engaged with respective sides of the support structure so that field
generation pads
are secured in their selectively placed positions on the support structure. In
another embodiment, each securing mechanism may have a coupling component
configured for connection beneath the support structure. In such case, the
securing
structure can include a first joining member configured to attachment to the
coupling components of the first securing mechanisms and a second joining
member
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configured for attachment to the coupling components of the second securing
mechanism to secure the selective placement of the field generation pads on
the
support structure when the joining member are attached.
[0009] These and other objects, features and advantages of the present
invention will be apparent from the following detailed description of
illustrative
embodiments thereof, which is to be read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The present invention is illustrated by way of example, and not by
way
of limitation, in the figures of the accompanying drawings.
[0011] Figure 1 is example schematic, pictorial illustration of a magnetic
location system for use in tracking a distal end of a catheter of the like
within a
living subject during a medical procedure.
[0012] Figure 2A is a perspective view of an embodiment the magnetic
location system comprising dual low-profile elongated field generation pads
secured
to a patient table.
[0013] Figure 2B is a top view of the dual low-profile elongated field
generation pads shown in Fig. 2A.
[0014] Figure 2C is a bottom view of the embodiment of the magnetic
location
system shown in Fig. 2A.
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[0015] Figure 3 is a perspective view of the of magnetic location system
shown
in Fig. 2A with an installable arm rest.
[0016] Figure 4A is a top view of another embodiment of one of the dual
low-
profile elongated field generation pads shown in Fig. 2A illustrating an array
of rod-
connected field generating coil units in phantom.
[0017] Figure 4B is a cross section of the low-profile elongated field
generation
pad along line 4B of Fig. 4A.
[0018] Figure 5A is a perspective view of the securing mechanism for the
dual
low-profile elongated field generation pads of Fig. 2A in an "open" position.
[0019] Figure 5B is a side view of the securing mechanism for the dual low-
profile elongated field generation pads of Fig. 2A in the "open" position.
[0020] Figure 6A is a perspective view of the securing mechanism for the
dual
low-profile elongated field generation pads of Fig. 2A in a "clamping"
position.
[0021] Figure 6B is a side view of the securing mechanism for the dual low-
profile elongated field generation pads of Fig. 2A in the "clamping" position.
[0022] Figure 7 is a bottom view of a portion of one of the dual low-
profile
elongated field generation pads of Fig. 2A.
[0023] Figure 8A is an end view of another embodiment of a securing
mechanism for the dual low-profile elongated field generation pads of Fig. 2A.
[0024] Figure 8B is a bottom perspective view of the securing mechanism
for
the dual low-profile elongated field generation pads of Fig. 8A.
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[0025] Figure 9 is a bottom view of another alternative of a securing
mechanism for the dual low-profile elongated field generation pads of Fig. 2A.
DETAILED DESCRIPTION
[0026] Various methods and systems are known in the art for tracking the
coordinates of objects involved in medical procedures. For example, magnetic
navigation systems may be used for navigating tools, such as medical
implements,
catheters, wireless devices, etc. One such magnetic navigation system can be
found
in the CARTO system, produced by Biosense Webster, Inc. (Diamond Bar,
California).
[0027] In magnetic navigation systems, magnetic fields are, for example,
generated by a location pad that includes a plurality of magnetic field
generators.
In a magnetic navigation system, magnetic position sensing may be used to
determine position coordinates of the distal end of a tool inside a patient's
organ.
For this purpose, a driver circuit in a console or a location pad drives the
plurality of
field generators to generate magnetic fields that extend within the body of a
patient.
[0028] Typically, the field generators comprise a plurality of coils,
which are,
for example in the CARTOTm system, incorporated into a unitary location pad
that
is placed below the patient's torso at known position external to the patient,
such as
below the patient table. The unitary pad system was a significant improvement
over the direct application of individual magnetic field generation coils to a
patient's
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torso such as disclosed in U.S. Pat. No. 6,618,612, where coil placement was
more
cumbersome, could interfere with a performance of a desired medical procedure,
and could require disinfectant cleaning for re-use.
[0029] The coils generate magnetic fields in a predefined working volume
that
contains the patient's organ to be explored. One or more magnetic field
sensors
located on a medical tool detect the magnetic fields and generate electrical
signals
in response to these magnetic fields. A signal processor processes these
signals in
order to determine the position coordinates of the medical tool, typically
including
both location and orientation coordinates. Each coil transmits at a different
frequency so that the processor can separate the magnetic fields from each
source.
This method of position sensing is implemented in the above-mentioned CARTOTm
system and is described in detail in U.S. Pat. Nos. 5,391,199, 6,690,963,
6,484,118,
6,239,724, 6,618,612 and 6,332,089, in PCT Patent Publication WO 96/05768, and
in
U.S. Patent Application Publications 2002/0065455 Al, 2003/0120150 Al and
2004/0068178 Al, whose disclosures are all incorporated herein by reference.
[0030] The CARTO system has conventionally employed a unitary location
pad for generating the magnetic field used for magnetic location sensing. The
unitary pad contains multiple magnetic coils that create a magnetic field and
is
generally placed beneath the patient. The unitary pad generates an ultralow
magnetic reference field from which the location of the tool (having a
magnetic field
sensor) can be determined. This provides the physician with visibility and
orientation of the patient's internal anatomy. The construction of suitable
magnetic
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coils, i. e. reference field transducers, is disclosed, for example, in U.S.
Pat. No.
6,618,612.
[0031] The inventive location system described herein features magnetic
field
generator coil units 201 disposed in dual low-profile elongated field
generation pads
202 that are easier to install on the top of a patient table, such as a bed or
gurney
28, on either side of the patient's torso, than currently existing unitary pad
or
individual field generator systems. The system also includes a self-tracking
algorithm to define the magnetic reference field used by a catheter sensor
when
implementing location sensing and to make installation easier. An example,
self-
tracking algorithm for the pads is discussed below.
[0032] A clamping mechanism, such as clamps 203 of Figs. 4A-7, can be used
to secure the field generation pads 202 in place for use. As an alternative, a
flexible
band, such as elastic member 801 of Fig. 8A-B, can be used for securing the
field
generation sensor pads 202 on a patient's bed. In lieu of the elastic members
801, a
rack and pinion mechanism 901, such as illustrated in Fig. 9, may be employed.
[0033] In particular, a first embodiment employs dual low-profile elongated
field generation pads 202 rather than the triangular location pad currently
used in
the CARTOTm system or individual coil units. The dual low-profile elongated
field
generation pads 202 are preferably situated on an axis, such as the
longitudinal
axis, of the patient table 28 on either side of a patient and secured in place
by a
securing structure attach them to the patient table 28. The securing structure
is
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designed to prevent the dual low-profile elongated field generation pads 202
from
moving during the medical or exploratory procedure.
[0034] Clamping mechanisms 203 are provided as the securing structure for
the embodiment illustrated in Figs 2A-7. The clamping mechanisms 203 allow a
physician and/or location pad installer to add the dual low-profile elongated
field
generation pads 202 before the procedure starts and/or during the procedure.
Thus,
the patient barely needs to move to add the dual low-profile elongated field
generation pads 202 whereas the known unitary location pad and individual coil
configurations require considerable effort to allow the location pad or
individual coil
units to be appropriately positioned. Situating the dual low-profile elongated
field
generation pads 202 on the table 28 permits the field generating coils 201 to
be close
to the patient to generate magnetic field gradients for assuring location
accuracy
and to be distanced from items such as fluoroscopy system collimators which
are
undesired metal sources that interfere with the magnetic location system.
[0035] Figure 1 is a schematic, pictorial illustration of a magnetic
position
tracking system 100 used in cardiac catheterization applications, in
accordance with
an embodiment of the present invention. System 100 comprises dual low-profile
elongated field generation pads 202, which comprises one or more field
generators,
such as field generating coils. Embodiments of the dual low-profile elongated
field
generation pads 202 are described in more detail with respect to Figures 2-9.
[0036] A patient 24 lies on a catheterization or patient table 28. A
physician
32 inserts a catheter 36 into a chamber of a heart 38 (shown as balloon
insert) of the
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patient 24. System 100 determines and displays the position and orientation
coordinates a distal end 40 of catheter 36 inside the heart 38.
[0037] In the exemplary configuration of Figure 1, the dual low-profile
elongated field generation pads 202 comprise embedded field generating coil
units
201, 401 see Figures 2A, 4A and 4B. The dual low-profile elongated field
generation
pads 202 are placed on top of the table 28 along or under the patient's torso
24, such
that the coils 201 become located in fixed positions external to the patient
24 and
are operable to generate magnetic fields in a defined working volume around
the
heart. A field definition algorithm is implemented once the pads are
positioned
which defines the magnetic field for sensor use.
[0038] A position sensor 42 fitted in the distal end 40 of the catheter 36
senses
the magnetic fields in its vicinity. The position sensor 42 produces and
transmits, in
response to the sensed fields, position signals to a console 44. The console
44
comprises a tracking processor 48 that calculates the location and orientation
of
catheter 36 with respect to the coils 201, based on the position signals sent
by
position sensor 42. Typically, the console 44 also drives the coils 201
through a
connector cable 49 to generate the appropriate magnetic fields and to
implement the
field definition algorithm. The location and orientation coordinates of
catheter 36
are displayed to the physician using a display 50.
[0039] Although Figure 1 shows an example system 100 for cardiac
catheterization or other procedures, the dual low-profile elongated field
generation
pads 202 can be used in other position tracking applications, such as for
tracking
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orthopedic implants and other medical tools.
[0040] The
dual low-profile elongated field generation pads 202 may also be
compatible with fluoroscopy systems used by the magnetic tracking system.
Accordingly, in one embodiment, the dual low-profile elongated field
generation
pads 202 may be radiolucent when centered in a horizontal plane below a Fluoro
iso-center for a Fluoro C-arm orientation of LA060 - RA060 (@CRA/CAU 0). Also,
the dual low-profile elongated field generation pads 202 may be designed to
minimize interference with the Fluoro C-arm movement (considering LAO-RAO
rotation). The dual low-profile elongated field generation pads 202 may be
robust
and flexible to withstand mechanical shocks, such as a drop of up to one meter
onto
a hard surface (e.g., floor), without damage.
[0041] The
functional interface of the dual low-profile elongated field
generation pads 202 with the tracking processor 48 of the system 100 may be
implemented through a wireless connection. In that case, the location pad will
be
connected only to a power supply through a power cable in lieu of the
connector
cable 49. The wireless connection can be based on standard wireless protocols
(such
as WLAN IEEE802.11) + implementation for synchronization.
[0042]
Figure 2A illustrates example dual low-profile elongated field
generation pads 202 positioned along the longitudinal axis of the patient
table 28.
In this example, the dual low-profile elongated field generation pads 202 have
four
tri-coils magnetic field generation units 201, two for each pad 202. For each
pad,
the field generation units 201 are disposed at opposite ends the pad 202 at a
fixed
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distance such that the pad's two field generation coil units 201 are
preferably
spaced no greater than 500 mm from the center of each other. The distance is
selected to assure sufficient magnetic field generation using relatively low
profile
field generation coil units 201. To maintain the fixed spacing of the coil
units
within each pad, a connecting rod 204 can be provided having ends secured to
each
field generation coil unit 201 within the pad 202.
[0043] In
the Figure 2A example, the field generation coil units 201 are
preferably tri-coil bobbins that weigh about 200 grams together so that each
pad
weighs only 1-2 Kg and is 540 mm in length, 140 mm in width and 8.5 mm in
height. As such, the dual low-profile elongated field generation pads 202 are
easy to
install, have a low profile and low weight compared to existing systems. To
permit
relatively easy handling and placement of the pads 202, they generally do not
exceed 3 Kg in weight and do not have a height exceeding 20 mm.
[0044] The
dual low-profile elongated field generation pads 202 are installed
to produce a magnetic field that defines a desired magnetic field zone in the
system
100. In above embodiment, the distance between the dual low-profile elongated
field generation pads 202 when installed preferably does not exceed 50 cm to
maintain sufficient magnetic field gradients within the working volume.
[0045] In
connection with installing the pads 202, the tracking processor 48
can be programmed to detect if the pads 202 are positioned within a
predetermined
maximum distance, such as 50 cm, of each other. The processor can generate a
signal that is relayed to the console to display an indication on the display
50 as to
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whether the pads 202 are positioned close enough to each other to properly
generate
the magnetic sensing field.
[0046] Preferably the pads are symmetric to each other with each having a
same number of field generation coil units in each spatial direction,
typically
multiples of three, are used. The dual low-profile elongated field generation
pads
202 may support Improved "Single Axis Sensor" (SAS) accuracy. In contrast to
the
Figure 2A embodiment, where tri-axial coils 201 are disposed at each end of
each of
the pads 202, Figs. 4A and 4B illustrates in another embodiment, wherein an
array
of six single axis coils 401 are equally distributed along the length of each
of the
dual low-profile elongated field generation pads 202. Connecting rod members
404
are provided to maintain an equal fixed spacing between the single axis field
generation coils 401 within each pad 202.
[0047] The dual low-profile elongated field generation pads 202 include a
securing mechanism, such as clamps 203, to secure the pads 202 to the patient
table
28 to prevent unintentional movement of the pads 202 such as a result of
lateral
force lower than about 100 Newtons. In one embodiment, the dual low-profile
elongated field generation pads 202 have an ergonomic design that is in line
with
the design elements of the entire system to emphasize the fact that dual low-
profile
elongated field generation pads 202 are parts of one system 100.
[0048] The securing structure, such as clamp mechanisms 203, is
preferably
designed to permit installation of the dual low-profile elongated field
generation
pads 202 within one minute and uninstallation in even less time. In busy
surgical
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practices, patient surgical operations, mappings and/or other procedures are
often
performed on a relatively tight time schedule. The present invention greatly
facilitates the efficient conduct of such successive procedures by permitting
the very
rapid uninstallation of the field generation pads from the table of a patient
who had
undergone a procedure and installation of the pads on the table of another
patient
scheduled for a next procedure.
[0049] The locatioie pad 20 may comprise a holding structure that avoids
interference with a patient table arm rest 205 on the patient table 28. As
shown in
Figure 3, in one embodiment, the field generation pad 202 may be integrated
with
the arm rest 205 as a single device.
[0050] Figures 2A-7 illustrate a simple clamp type mechanism 203 for
securing the low-profile elongated field generation pads 202 to the patient
table 28.
In this example, each pad is provided with two clamp mechanisms 203. As best
seen in Figures 5A-6B, the securing clamp mechanisms 203 each include a pad
attaching arm 206 connected to a respective field generation pad 202. The arms
206
each have a table engaging portion 208 which is configured to abut against a
side of
the patient table 28 when the pad 202 is installed so that the engagement of
the
table engaging portions 208 define the location of the pads 202 relative to
the table
28, as best seen in Figures 2A and 2B.
[0051] Figures 5A and 5B illustrate views of one of the clamping
mechanisms
203 in an open state that enables the field generation pad 202 to be
positioned on
the table 28 so that the table engaging portion 208 of each clamp mechanism
203
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abuts a respective side of the table 28. Figures 6A and 6B illustrate views of
the
clamping mechanism 203 in a clamping state with the field generation pad 202
appropriately positioned on the table 28.
[0052] The example clamping mechanisms 203 are of a lever type design,
each
having a handle portion 501 that can be easily gripped to toggle between the
open
and clamping positions by an individual installing the field generation pad
202.
The lever handle 501 of the clamping mechanism 203 pivots about a pivot shaft
502
to displace a clamping end portion 503 between clamping and open positions. As
shown in Figures 6A and 6B, the handle 501 has been pushed downward which
pivots the clamping end portion 503 upwards against the bottom of the patient
table. In this clamping position, enough force is exerted on the patient table
so that
the attached field generation pad 202 is not easily moveable.
[0053] Figure 7 shows a bottom view of a portion of one of the field
generation
pads 202 illustrating the optional adjustability of the attachment of the arm
206 of
the clamping mechanism 203 to the pad 202. The arm 206 is equipped with an
adjustable coupling 207 which allows adjustment of the distance the table
engaging
portion 208 from the field generation pad 202. The adjustable coupling 207 can
be
configured, for example, as a slot/tab mechanism, a slide type mechanism, or
projecting pins that are engageable in a variety of locations with respect to
a series
of defined holes.
[0054] The adjustable coupling 207 enables the table engaging portion 208
of
the arm 206 of the securing mechanism 203 to be positioned at an extended
position
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or a retracted position relative to the pad 202 and may be configured to
permit the
attachment of the arm 206 to the table engaging portion 208 at one or more
positions therebetween. When installed on the table 28, the dual field
generation
pads 202 will be furthest from the respective sides of the table 28 and
closest to
each other when the table engaging portions 208 of the securing mechanisms 203
are in the extended position. When the table engaging portions 208 of the
securing
mechanisms 203 are in the retracted position, the dual field generation pads
202
will be closest to the respective sides of the table 28 and furthest from each
other
when installed. The adjustability of the coupling of the securing mechanisms
203 to
the pads 202 enables use of the pads with both wide and narrow tables.
[0055]
Figures 8A and 8B illustrate an alternative embodiment of a table
securing mechanism 803 for the field generation pads 202. The securing
mechanisms 803 each include a pad attaching arm 806 along with a table
engaging
portion 808 similar to the arm 206 and table engaging portion 208 of the
clamping
mechanism 203 described above. In addition, each securing mechanism 803
includes a boss 804 mounted on a portion of the arm 806 that extends to the
underside of the table 28. The boss 804 is configured to receive an end of an
elastic
member or the like 801. The elastic member 801 serves to secure the field
generation pads 202 in position on the patient table 28. The arm 806 may
include
an adjustable coupling, such as arm coupling 207 of clamping mechanism 203, to
accommodate different table widths when the securing mechanisms 803 are used.
Elastic member 801 may be made of rubber or other elastic material of
appropriate
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length to exert a sufficient securing tension to prevent inadvertent movement
of the
pads 202 when installed on the patient table 28.
[0056] As
shown in the example illustrated in Fig. 8B, when the dual field
generation pads 202 are installed, each pad 202 is secured to the table by two
securing mechanisms 803 which each oppose a respective securing mechanism 803
of the other pad 202. Two elastic members 801 are used, each one securing a
respective opposing pair of securing mechanisms 803.
[0057] In
lieu of the elastic member 801, a rack and pinion mechanism 901,
such as shown in Fig. 9, or other connecting device may be used to connect the
securing mechanisms 803 of opposing dual field generation pads 202. In an
embodiment when the joining member is not elastic, it may also have visible
distance markings (i.e. mm or cm) or known lengths in order to assure that the
dual
pads 202 are within a desired maximum distance from each other.
[0058] As
referenced above, a self-tracking process is performed to determine
where the dual field generation pads 202 are co-located. This self-tracking
enables
the use of the two pads 202 whose physical proximity may change during the
course
of a medical procedure and/or during the set-up for a medical procedure. This
tracking uses the position of the components relative to one another. Each
component has at least one transmitter and sensor to communicate with the
other
components. Each pad 202 includes sensors that read the magnetic field induced
by
the transmitting coils of the other pad. Such sensors may be incorporated into
the
field generation units 201, for example, see U.S. Pat. No. 6,618,612. These
readings
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enable one to learn the relative position of the two pads.
[0059] The self-tracking algorithm provides the locations and orientations
of
the transmitting coils in a defined coordinate system. The transmitting coils
must
have been previously calibrated, that is their magnetic moments (up to any
desired
order of spherical harmonics) must be known. There are many ways to define the
coordinate system. For concreteness, a coordinate system whose origin is the
centroid of the location of all the transmitting coils can be chosen. The x-y
plane is
defined by a plane containing the centers of any two coils of one of the pads
202 and
the center of a coil on the other pad 202. In an example of working to order 1
(dipole) in a spherical harmonics expansion, the concept can be readily
extended to
any order, a rotation matrix can be defined as
Rot[ , 19 4]
cos (B)cos(0) cos(0)sin(0)
[ ¨1. sin(6)
= cos()sin(0)sin(0) ¨ 1. cos(tp)sin(0)
cos(0)cos(0) + sin(0)sin(0)sin(0) cos(9)sin(b)
cos(0)cos(0)sin(0) + sin(49)sin(0)
cos(0)sin(6)sin(0) ¨ 1. cos(0)sin(0) cos(0)cos(*)
[0060] and a dipole polynomial matrix as
- ¨2X2 + y2 + z2 3xy 3xz -
(x2 + y2 + z2)5/2 (x2 + y2 + z2)5/2 (x2 + y2
+ z2)5/2
3xy x2 _ 2y2 + z2 3yz
bDipol[x, y, z] ¨
(x2 +y2 + z2)5/2 (x2 +y2 +z2)5/2 (x2 +y2
+z2)5/2
3xz 3 yz x2 + y2 _ 2Z2
(x2 + y2 + z2)5/2 (x2 + y2 + z2)5/2 (x2 + y2
+ z2)5/2 _
[0061] Let (xi, yi, zi) be the location of transmitter i and (xj, yi, zi)
be the
location of transmitter j. Assuming, without loss of generality, that at the
center of
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each coil there is a magnetic sensor, the field measured by the sensor at the
center
of transmitter i transmitted by coil j can be expressed as:
me as/ --
Rotkp, 9,
-r Tensor i Rot{(1), 9 1/J] transmitter j bD ipol[Ro t[cp , 9, Mir
Jcramsmitter j(Xj ¨ Xi, Yj
yi, zi ¨ zo]
where In7 is the magnetic dipole vector for transmitter j.
[0062] This equation has twelve unknowns, six location variables and six
orientation variables. A set of N transmitting coils will have a total of nine
N
unknowns (three location variables and six orientation variables, three for
the
transmitter and three for the sensor). Each sensor measuring the field from
all the
transmitters (excluding the one it is associated with) measures 3(N-1) values,
for a
total of 3 N (N-1) equations.
[0063] For any system with four or more coils the number of equations is
greater than the number of unknowns. The system can also be solved using an
optimization algorithm, with the cost function being the sum (sum of the
squares) of
the difference between the measurements and the right side of Equation 1. The
condition that the origin of the coordinate system is the centroid of the
coils centers
is included as a constraint. If distances between coils are well known and
fixed, they
can be included as extra constraints.
[0064] It will be appreciated by persons skilled in the art that the
present
teachings are not limited to what has been particularly shown and described
hereinabove. Rather, the scope of the present invention includes both
combinations
and sub-combinations of the various features described hereinabove, as well as
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variations and modifications thereof that are not in the prior art, which
would occur
to persons skilled in the art upon reading the foregoing description.
LIST OF ELEMENTS
24 patient
28 support structure
36 catheter
38 heart
40 distal end of catheter
42 position sensor
44 console
48 tracking processor
49 connector cable
50 display
100 magnetic field location system
201 field generating coil unit
202 low-profile elongated field generation pad
203 clamping/securing mechanism
204 connecting rod
205 arm rest
206 securing mechanism arm
207 adjustable coupling
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CA 3024920 2018-11-22
208 table engaging arm portion
401 single axis coil
404 connecting rod members
501 clamp handle
502 pivot shaft
503 clamping end portion
801 elastic member
803 securing mechanism
804 boss
806 securing mechanism arm
808 table engaging arm portion
901 rack and pinion mechanism
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CA 3024920 2018-11-22
