U.S. patent application number 16/259742 was filed with the patent office on 2019-05-23 for probe for determining magnetic marker locations.
The applicant listed for this patent is Health Beacons, Inc.. Invention is credited to Kevin J. Derichs, Robert J. Petcavich, Murray A. Reicher.
Application Number | 20190150779 16/259742 |
Document ID | / |
Family ID | 55347211 |
Filed Date | 2019-05-23 |
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United States Patent
Application |
20190150779 |
Kind Code |
A1 |
Derichs; Kevin J. ; et
al. |
May 23, 2019 |
PROBE FOR DETERMINING MAGNETIC MARKER LOCATIONS
Abstract
A probe including a first sensor having a first magnetometer and
a first accelerometer and a second sensor having a second
magnetometer and a second accelerometer is configured for
determining the distance and direction to a marker. The marker may
be magnetic and may be surgically inserted into a patient's body to
mark a specific location. The probe may be used to locate the
marker, thus identifying the location. The probe may include a
microprocessor that receives an output from the first sensor and an
output from the second sensor and determines the distance and
direction to the marker.
Inventors: |
Derichs; Kevin J.; (Buda,
TX) ; Petcavich; Robert J.; (The Woodlands, TX)
; Reicher; Murray A.; (Rancho Santa Fe, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Health Beacons, Inc. |
Concord |
MA |
US |
|
|
Family ID: |
55347211 |
Appl. No.: |
16/259742 |
Filed: |
January 28, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14832528 |
Aug 21, 2015 |
10188310 |
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16259742 |
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62041132 |
Aug 24, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 2034/2051 20160201;
G01R 33/02 20130101; A61B 5/05 20130101; A61B 2090/3908 20160201;
A61B 2034/2048 20160201; A61B 2090/3954 20160201 |
International
Class: |
A61B 5/05 20060101
A61B005/05; G01R 33/02 20060101 G01R033/02 |
Claims
1. A method for determining a distance and direction between a
probe and a magnetic marker implanted in a patient, the method
comprising: providing the probe, wherein the probe comprises a
first sensor including a first magnetometer and a first
accelerometer, and a second sensor including a second magnetometer
and a second accelerometer, wherein the probe is configured to
determine a position, in three-dimensional space, of the magnetic
marker; balancing the probe while away from the magnetic marker;
moving the balanced probe so that the magnetic marker is within
range of the first magnetometer; determining the distance and
direction between the probe and the magnetic marker by comparing an
output of the first sensor with an output of the second sensor;
aligning the probe with the magnetic marker based on the determined
distance and direction between the probe and the magnetic marker;
and inserting a portion of the aligned probe into an incision in
the patient and directing the probe toward the magnetic marker.
2. The method of claim 1, further comprising continuously
indicating the alignment of the probe with the magnetic marker
through visual or audio feedback.
3. A probe for detecting a magnetic marker, the probe comprising: a
first sensor including a first magnetometer and a first
accelerometer located in a handheld housing; a second sensor
including a second magnetometer and a second accelerometer, the
second sensor located in the housing and separated from the first
sensor; and a processor located in the housing and electrically
connected to the first sensor and the second sensor, the processor
configured to receive an output from the first sensor and an output
from the second sensor and determine a distance and direction
between one of the first sensor and the second sensor and a
magnetic marker.
4. The probe of claim 3, wherein each of the first and the second
magnetometers are configured to detect the field strength of the
magnetic field of a magnetic maker within a range measured from
each of the first and second magnetometers, and wherein the first
and second sensors are separated by a distance greater than the
range.
5. The probe of claim 4, wherein the distance separating the first
and second sensors is at least twice the range of the first and
second magnetometers, such that the field strength of the magnetic
field of a magnetic marker can only be substantially detected by
either the first magnetometer or the second magnetometer.
6. The probe of claim 4, wherein the processor is configured to
determine the distance between one of the first sensor and the
second sensor and a magnetic marker by calculating a difference
between the output of the first sensor and the output of the second
sensor.
7. The probe of claim 6, wherein the difference represents the
field strength of the magnetic marker.
8. The probe of claim 7, further comprising a memory configured to
store a lookup table containing data relating the magnetic field
strength of a magnetic marker to a distance from the magnetic
marker.
9. The probe of claim 3, wherein the handheld housing is configured
as a wand comprising: a base, wherein the first sensor is located
in the base; an extension member extending from the base, the
extension member defining the distance; and a tip, wherein the
second sensor is located in the tip, and wherein the processor
determines the distance and direction between the tip and a
magnetic marker.
10. The probe of claim 1, wherein the first and second sensors are
located with a sensing portion which is configured to be removable
from the housing.
11. The probe of claim 10, wherein the sensing portion is
disposable.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 14/832,528, filed Aug. 21, 2015, which claims the priority
benefit under 35 U.S.C. .sctn. 119(e) of U.S. Provisional
Application No. 62/041132, filed on Aug. 24, 2014, and titled
"MAGNETIC MARKER, SCANNING DEVICE, AND METHODS OF PERFORMING
SURGERY USING THE SAME," which is hereby incorporated by reference
in its entirety.
BACKGROUND
[0002] Marking potentially cancerous tissue for subsequent surgical
removal, such as marking a lesion in breast tissue for later
removal in a lumpectomy procedure, remains a big challenge for the
health care system. It is desirable to place tissue markers at
locations of interest in patients, sometimes deep within a
patient's tissue, that are both small and easily detectable by some
type of external scanning device. In addition, any markers that are
placed in the body should have a minimal or no MRI image footprint
that may obscure anatomical features (e.g., tumors) that may be
located in the imaged area. Another important consideration is the
complexity of inserting such markers, which vary in size and
detection range, so as to minimize pain and discomfort during the
procedure.
SUMMARY
[0003] The systems, methods, and devices described herein each have
several aspects, no single one of which is solely responsible for
its desirable attributes. Without limiting the scope of this
disclosure, several non-limiting features will now be discussed
briefly.
[0004] In one aspect, a probe for detecting a magnetic marker
includes a first sensor, including a first magnetometer and a first
accelerometer located in a handheld housing, a second sensor,
including a second magnetometer and a second accelerometer, the
second sensor located in the housing and separated from the first
sensor, and a processor located in the housing and electrically
connected to the first sensor and the second sensor, the processor
configured to receive an output from the first sensor and an output
from the second sensor and determine a distance and direction
between one of the first sensor and the second sensor and a
magnetic marker.
[0005] In some embodiments, the first and the second magnetometers
are configured to detect the field strength of the magnetic field
of a magnetic maker within a range measured from each of the first
and second magnetometers. The first and second sensors may be
separated by a distance greater than the range. In some
embodiments, the distance separating the first and second sensors
is at least twice the range of the first and second magnetometers,
such that the field strength of the magnetic field of a magnetic
marker can only be substantially detected by either the first
magnetometer or the second magnetometer.
[0006] In some embodiments, the processor is configured to
determine the distance between one of the first sensor and the
second sensor and a magnetic marker by calculating a difference
between the output of the first sensor and the output of the second
sensor. The difference may represent the field strength of the
magnetic marker.
[0007] In some embodiments, the probe also includes a memory
configured to store a lookup table containing data relating the
magnetic field strength of a magnetic marker to a distance from the
magnetic marker.
[0008] In some embodiments, the housing of the probe is configured
as a wand and includes a base, wherein the first sensor is located
in the base, an extension member extending from the base, the
extension member defining the distance between the first and second
sensors, and a tip, wherein the second sensor is located in the
tip, and wherein the processor determines the distance and
direction between the tip and the magnetic marker.
[0009] In another aspect, a method for determining the distance and
direction between a probe and a magnetic marker includes providing
a probe which includes a first sensor, having a first magnetometer
and a first accelerometer, and a second sensor, having a second
magnetometer a second accelerometer, the probe configured to
determine the position in three-dimensional space of a magnetic
marker, balancing the probe while away from the magnetic marker,
moving the balanced probe so that the magnetic marker is within a
range of the magnetic marker, and determining the distance and
direction between the probe and the magnetic marker by comparing an
output of the first sensor with an output of the second sensor.
[0010] In some embodiments, balancing the probe includes
compensating for a gain and an offset in the output of the first
magnetometer and the output of the second magnetometer, wherein the
gain and the offset are caused by hard and soft iron effects. In
some embodiments, the output of each of the first and second
magnetometers comprises X, Y, and Z, values, and balancing the
probe further includes rotating the probe through 360 degrees
around each of three orthogonal axes. In some embodiments,
balancing also includes, for each of the first and second
magnetometers, recording the minimum and maximum X, Y, and Z values
output during the rotation, calculating a length between the
minimum and maximum values for each of X, Y, and Z, calculating a
gain factor by dividing the length for each of X, Y, and Z by the
average length of the X, Y, and Z for both magnetometers, and
calculating an offset value for each of X, Y, and Z by, for each of
X, Y, and Z, adding half the length of X, Y, and Z, to the minimum
value for X, Y, and Z. In some embodiments, the method includes
adjusting raw output data into balanced output data by subtracting
the offset value and then multiplying the result by the gain factor
for each of X, Y, and Z.
[0011] In some embodiments of the method, the output of the first
sensor comprises first magnetometer output data and first
accelerometer output data, and the output of the second sensor
comprises second magnetometer output data and second accelerometer
output data, and wherein determining the distance and direction
between the probe and the magnetic marker further includes
calculating a difference between the first magnetometer output data
and the second magnetometer output data to determine distance
between the probe and the magnetic marker, and determining the
orientation of the probe using one of the first accelerometer data
or the second accelerometer data.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The features of this disclosure will become more fully
apparent from the following description and appended claims, taken
in conjunction with the following figures.
[0013] FIG. 1 illustrates an example system for detecting the
position of a marker within a patient's body using a handheld
probe, according to one embodiment.
[0014] FIG. 2A is a diagram illustrating the handheld probe and
example components and the placement thereof, according to one
embodiment.
[0015] FIGS. 2B through 2D illustrate additional example
embodiments of a handheld probe.
[0016] FIGS. 3A and 3B show the three axes for each of the
magnetometer and accelerometer, respectively, in a sensor pair.
[0017] FIG. 4 is a diagram illustrating conceptually the output
data from the magnetometer in each of the base sensor pair and the
tip sensor pair before the probe is balanced.
[0018] FIG. 5 is a flowchart illustrating an example method for
balancing the magnetometers of the tip sensor pair and the base
sensor pair of the probe.
[0019] FIG. 6A is a table containing sample magnetometer output
data obtained during the probe balancing process and FIG. 6B is a
table which presents calculations of the gain and offset values
used during the balancing process using the sample data of FIG.
6A.
[0020] FIG. 6C shows a probe configured to display set of bars that
provide visual feedback to the user during the balancing process,
according to one embodiment.
[0021] FIG. 7 is a diagram illustrating conceptually the output
data from the magnetometer in each of the base sensor pair and the
tip sensor pair after the probe is balanced.
[0022] FIG. 8 is a table containing sample balanced data. The data
in the table represents the raw data of FIG. 6A in balanced
form.
[0023] FIG. 9 is an example method for using the probe to determine
the three-dimensional location of a marker within a patient's
body.
[0024] FIG. 10 is a diagram illustrating conceptually determination
of the magnetic field strength of a marker with the probe by
subtracting the base sensor pair's magnetometer output data from
the tip sensor pair's magnetometer output data.
[0025] FIG. 11 provides tables showing sample data in both raw and
balanced form that is representative of a marker positioned within
range of the tip sensor pair. It further illustrates calculation of
the magnitude of the magnetic field strength of a marker using that
data.
[0026] FIG. 12A provides an example of a lookup table which relates
the magnetic field strength of a marker to a distance to that
marker.
[0027] FIG. 12B through 12D provide a table of another set of
sample data and the calculation of gain and offset values used to
balance a probe, according to one embodiment, as well as two
example measurements that are calculated with the probe at
different distances from a marker.
[0028] FIG. 13A is a diagram illustrating the use of accelerometer
data to determine the orientation of the probe.
[0029] FIG. 13B illustrates three example instances of a graphical
representation of the distance and direction from the tip sensor
pair of the probe to the marker, according to one embodiment.
[0030] FIG. 14 is a flowchart illustrating operation of the probe
150 including both balancing and measurement, according to one
embodiment.
[0031] FIGS. 15A through 15C provide examples of a graphical user
interface that may be used on an external device in communication
with the probe.
DETAILED DESCRIPTION
Example System Overview
[0032] FIG. 1 illustrates an example system 100 for determining the
position of a marker 110 within a patient's body 101 using a
handheld probe 150, according to one embodiment. In this example a
marker 110 is embedded in tissue of a patient 101 and a probe 150
is used to identify the marker 110 without insertion into tissue,
such as by moving across the skin of the patient 101 in areas near
where the marker 110 is believed to be located. In this example, an
external device 170, such as a computer, mobile phone, or tablet,
is illustrated in communication with the probe 150. In some
embodiments, the probe 150 operates independent of any external
device 170 and/or doesn't require any external device 170. As used
herein, "the system" or "the system 100" includes one or more of
various components that may be used to place and/or locate markers
within mammalian tissue. For example, in one embodiment, the system
100 includes the handheld probe 150 and one or more markers 110,
and in other embodiments the system 100 also includes the external
device 170.
[0033] As will be described more fully herein, the marker 110 may
be surgically inserted into a patient's body 101 to mark the
location of tissue, for example, potentially cancerous breast
tissue (or any other tissue), for removal. In some embodiments, the
marker 110 is inserted into the body via a natural opening or a
surgical opening. The probe 150 may then be used to determine the
location of the marker 110 within the patient's body 101. In the
embodiment of FIG. 1, the probe 150 includes a tip sensor pair 151
configured to communicate with one or more microprocessors to sense
and determine the distance and direction to the marker 110 within a
range 153 of the sensing tip 164 of the probe 150. The distance and
direction to the marker 110 may be shown to a user on a display
155, indicated audibly using a speaker 156, and/or relayed to the
external device 170 and shown on a display 171 thereof.
[0034] In this embodiment, the marker 110 comprises a magnet, such
as a magnet with a bio-compatible coating/layer surrounding the
magnet or simply a magnet. In some embodiments, the marker 110 is a
micro magnet that has a strong magnetic field relative to its size.
For example, the magnet may be a neodymium rare earth magnet, or
may comprise other magnetic materials such as ferrite, samarium
cobalt, yttrium cobalt, and combinations thereof. Various other
types of magnets can be used in conjunction with the probe 150. In
some embodiments, the probe 150 must be balanced with reference to
the specific characteristics of the particular magnet. In some
embodiments, the marker 110 has a magnetic field strength in the
range of between about 1,000 to about 20,000 Gauss. A magnetic
field strength of approximately 5,000 Gauss may be preferred in
some applications. These field strength ranges are provided for
example only--other field strengths may be used. The example
magnetic field strength calculations herein are presented in units
of Gauss, although units of Tesla may also be used in some
embodiments. The conversion factor is 1 Tesla equals 10,000
Gauss.
[0035] The marker 110 can comprise various geometric shapes, such
as spheres, rods, rings, discs, cylinders, and blocks, among
others. In one embodiment, the marker 110 is configured as a micro
rod having a diameter from about 0.2 mm to about 2.0 mm, with about
0.75 mm to about 1.5 mm being preferred in some applications. A
marker 110 configured as a micro rod may have a length of about 1
mm to about 3 mm, with about 2 mm being preferred in some
applications. These size ranges are provided as examples; other
size ranges and shapes of the marker 110 may also be used with the
system 100. In some embodiments, the marker 110 is configured to be
as small as possible, for ease of insertion into the patient's body
101 and precision of marking, while still having a magnetic field
strength sufficiently strong to be detected by the probe 150
external to the patient's body 101.
[0036] In FIG. 1, the marker 110 is illustrated as a micro rod
magnet (not shown to scale with reference to other objects in FIG.
1). The magnet has north and south poles on opposing ends of the
micro rod. The shape of the magnetic field of such a marker 110 is
illustrated with magnetic field lines 111 in the figure. In
general, the magnetic field lines 111 form loops extending between
the north and south poles of the magnet. Markers 110 with other
magnetic field shapes may be used with probe 150 according to the
principles described herein.
[0037] In some embodiments, the marker 110 is gold coated. A gold
coating may increase the biocompatibility of the marker 110. In
some embodiments, the coating may be omitted.
[0038] In some embodiments, the marker 110 includes an
anti-migration device. The anti-migration device may be configured
to ensure that the marker 110 remains in the position in which it
is placed. For example, the anti-migration device could include a
hook or anchor, such as is described in U.S. Pat. No. 8,939,153,
issued on Jan. 27, 2015, and entitled "Transponder Strings," which
is hereby incorporated by reference in its entirety and for all
purposes. In some embodiments, a collagen plug or sleeve may
encapsulate, or partially encapsulate, the marker 110. The collagen
plug or sleeve may resist migration of the marker 110 after the
marker 110 is implanted into the patient's body.
[0039] In use, one or more markers 110 may be loaded into a syringe
that can penetrate mammalian tissue to a depth of about 0.5 mm to
about 300 millimeters depending on the type of tissue and the depth
of the tissue to be marked. The system 100 may have particularly
beneficial application in marking breast tumors, which can range in
depth from between about 0.1 mm to about 75 mm or more, although,
the system 100 is not limited to this application. Using the
syringe, the markers 110 may be inserted into or near the tumorous
tissue to be marked using ultrasound, CAT scanning or MRI real time
imaging. This allows the markers 110 to be accurately placed, as
the medical professional inserting the markers 110 is able to see
the location of the tumor and marker 110 in real time. However,
placement of the markers 110 often occurs hours, days, or weeks
prior to the subsequent surgical procedure wherein the markers 110
are located and the surrounding tissue is examined (and possibly
biopsied in the case of a tumor). During surgical removal of the
tumorous tissue it is generally not possible to use ultrasound, CAT
scanning or MRI imaging in the operating room. Thus, use of the
probe 150 is desirable as it is allows the location of the tumorous
tissue to be accurately determined by detecting the location of the
marker 110.
[0040] In some embodiments, the marker 110 can be injected along
with a conventional non-magnetic marker. In some cases where the
marker 110 is injected along with a conventional non-magnetic
marker, the marker 110 can be connected to a suture, such as 2-0
proline with the suture extending to the skin surface and then
covered with a sterile dressing. If the biopsy is found to be
negative, the doctor could remove the suture and marker 110,
leaving behind the conventional marker. This would allow use of the
marker 110 for all or most biopsies, knowing that the magnet could
be removed if a surgical excision is not required based on a
negative biopsy result. Similarly, in some embodiments, the marker
110 could be implanted connected to a suture as described above,
but the suture could extend to another marker 110 or RFID that is
left subcutaneously. If the biopsy is negative, the two magnets
could be easily removed together, because embodiments of the
present system could be used to locate the subcutaneous marker
110.
[0041] In some embodiments, multiple magnetic markers and/or other
tags may be included in a string of markers, such as connected via
a suture, with one of the markers near the lesion of interest and
one near the skin surface so it may be more easily located,
possibly with one or more markers in between. For example, magnetic
markers may be included in the various configurations of markers
disclosed in U.S. Pat. No. 8,939,153, issued on Jan. 27, 2015, and
entitled "Transponder Strings," which is hereby incorporated by
reference in its entirety and for all purposes. For example, any of
the transponders mentioned in that patent may be replaced with a
magnetic marker and located using the probe 150 discussed
herein.
[0042] In some embodiments, the marker 110 is attached to an RFID
or light based chip (such as a Pharmaseq) so that the marker 110 is
essentially labeled with a serial number. This may be useful for
differentiating between multiple markers 110.
[0043] The probe 150 will be described in greater detail below.
However, in general, the probe 150 may include at least some of the
following features: a battery, a microprocessor, wireless
communications capability, and at least two
magnetometers/accelerometers, a reference
magnetometer/accelerometer and a sensing
magnetometer/accelerometer. As used herein, a pair of
magnetometer/accelerometer sensors, whether both sensors are on a
single chip or multiple chips (e.g., an EEPROM, FPGA, ASIC, or
other chip), may be referred to as a "sensor pair," such as a "base
sensor pair" and a "tip sensor pair." In a preferred embodiment,
the probe 150 is configured to determine the location in
three-dimensional space of the marker 110 with a resolution of
about 0.1 mm, although a more or less precise resolution is
possible and may be suitable depending on the particular
application. The probe 150 may further be configured to detect
markers 110 within a range of up to 12 inches or more.
[0044] In one embodiment, the tip sensor pair 151 is positioned in
the sensing tip 164 of the probe 150 and the base sensor pair is
positioned outside of the range 153 of the tip sensing pair 151. In
one embodiment, the distance to the marker 110 may be determined by
taking the difference of the magnetic field measured by the tip
sensor pair and the magnetic field measured by the base sensor
pair. This difference represents the magnetic field strength of the
marker 110 and is proportional to a distance of the probe 150 the
marker 110. The accelerometer data from either the tip sensor pair
or base sensor pair may then be used to determine the orientation
of the probe 150 itself and the direction to the marker 110. This
process, only briefly summarized here, will be presented in greater
detail below.
[0045] In some embodiments, analysis and determination of the
distance and direction to the magnetic marker 110 may be executed
by the probe 150 itself, for example, in a microprocessor. In some
embodiments, the data obtained from the probe 150 (e.g., the
sensing and base sensor pairs) may be relayed to an external device
170 and analyzed there. The distance and direction to the marker
110 may be displayed on the probe 150 itself and/or a display 171
of the external device 170. The external device 170 may be a
computer, tablet, smartphone, or similar device. The external
device may include a display 171 and one or more inputs 173, such
as a keyboard, mouse, touchscreen, or the like. In some
embodiments, the probe 150 can be used as an input device for the
external device. For example, by selecting an appropriate input
button 154 on the probe 150, the probe may operate as a 3D mouse
for manipulating content on the display 171 of the external device.
The external device 170 may further include one or more processors,
memories, or storage devices. In the system 100, the probe 150 and
the external device 170 may be connected via a link 181 so as to
communicate with each other. The link 181 may be wired or wireless,
for example through a Bluetooth or Wi-Fi connection, and may
further be direct, with no intermediate device, or indirect, with
communication routed through one or more additional devices. In
some embodiments of the system 100, the external device 170 may be
omitted.
[0046] The system 100 may allow for marking of tumors previously
inaccessible to surgeons, such as brain tumors because of the small
size of the injection needle that may be used to insert the small
micro-magnets and the long range 153 in which the probe 150 can
locate marker 110. For example, the range 153 of the probe may be 6
inches or more (for example, the radius of the range 153 is 6
inches or more), such as up to 12 inches or more in some
embodiments. This may not be possible with RFID markers due to the
size and strength limitations thereof. Other applications of the
system 100 include, but are not limited to, locating endotracheal
tubes, catheters, magnetic contrast agents, magnetic tumor antibody
agents, surgical sponges, and instruments, such as by attaching
magnetic markers to these objects.
Example Probe Components and Functions
[0047] FIG. 2A is a diagram illustrating the handheld probe 150 and
example components and the placement thereof, according to one
embodiment. The embodiment of FIG. 2A is merely one example of a
configuration of the handheld probe 150; the components may be
arranged differently in other embodiments without departing from
the scope of this disclosure.
[0048] In the example of FIG. 2A, the probe 150 includes a housing
160 with the internal components of the probe 150 positioned
therein. The housing 160 may be formed of plastic, non-magnetic
metal, or other suitable material. In some embodiments, the housing
160 is formed of an easily cleanable material for sterile use in an
operating room or other medical environment. In some embodiments,
the housing 160 may be removable and/or disposable. In the example,
the housing 160 is configured in size and shape to include a base
161, a protruding portion 162, and an extension portion 163 as
shown. A majority of the internal components of the probe 150 may
be located within the base 161 and/or the protruding portion 162.
In some embodiments, the base 161 is configured as a handle, which
may allow a user to hold the probe 150 in a wand-like manner. In
some embodiments, the protruding portion 162 may be configured as a
grip, which can allow a user to hold the probe 150 in the same
orientation as one would hold a pencil. For example, the protruding
portion 162 may be configured with a generally spherical shape that
fits into a user's palm to provide stability to the probe 150
during use. In some embodiments, the protruding portion 162 is not
configured as a grip. This may allow the base sensor pair 152 to
remain out in the open when positioned within the protruding
portion 162. The housing 160 may also include an extension portion
163 that extends generally away from the base 161 and protruding
portion 162 toward the sensing tip 164 of the probe 150. In some
embodiments, the user may hold the extension portion 163 during
use. In some embodiments, the probe may not include a protruding
portion 162. In some embodiments, the housing 160 of the probe 150
may comprise a constant cross-sectional shape along its length. For
example, in some embodiments, the housing 160 of the probe 150 is
configured as cylindrical wand with a constant circular
cross-section along its length.
[0049] In some embodiments, the housing 160 may have an overall
length of approximately 220 mm, an overall width of approximately
25 mm, and an overall height of approximately 15 mm, although these
dimensions are provided as examples only, and the size of the
housing is not intended to be limited thereto.
[0050] In this example, the internal components of the probe 150
include a tip sensor pair 151, a base sensor pair 152, one or more
input buttons 154, a display 155, a buzzer or speaker 156, a
microprocessor 157, an RF (wireless) module 158, and a battery 159.
In other embodiments, a probe may include any portion of these
components and/or additional components.
[0051] As used herein, the terms "accelerometer-magnetometer" or
"sensor pair" may refer to a dual three-axis accelerometer and
three-axis magnetometer paired together on a single chip or on
separate chips adjacent one another. For example, each
accelerometer-magnetometer or sensor pair may be a LSM303D
available from STMicroelectronics of Geneva, Switzerland. The
product sheet for this accelerometer-magnetometer is available at
http://www.st.com/st-web-ui/static/active/en/resource/technical/document/-
datasheet/DM00057547.pdf, and is hereby incorporated by reference
in its entirety. A combination magnetometer-accelerometer pair,
packaged in a single chip may be preferred in some embodiments of
the probe 150 as it will tend to reduce the distance and placement
error between the individual magnetometer and accelerometer
sensors. However, this is not required in all embodiments of the
probe 150 and discrete accelerometers and magnetometers may be
used. As noted above, a sensor pair includes a magnetometer sensor
and an accelerometer sensor. A magnetometer sensor measures
magnetic field strength and typically provides a three component
data output representing the three-orthogonal components of the
magnetic field (itself a vector, with direction and magnitude). An
accelerometer sensor measures not only the acceleration of the
sensor, but also the sensor's orientation to earth's gravity. The
accelerometer typically similarly provides a three component data
output representing the acceleration of the sensor. FIGS. 3A and 3B
and the accompanying description provide additional information
about the axes and function of the accelerometer-magnetometers.
[0052] In the example of FIG. 2A, the tip sensor pair 151 is
positioned at the sensing tip 164 or end of the extension portion
163 and separated from the base sensor pair 152 by a distance D,
and the base sensor pair 152 is positioned within the base 161. In
some embodiments, the base sensor pair 152 may be positioned in the
base 161, the protruding portion 162, and/or the extension portion
163. In some embodiments, the base sensor pair 152 is positioned
within the protruding portion 162 so as to not be covered by a
user's hand when the probe 150 is held. In the illustrated
embodiment, each of the sensor pairs 151 and 152 have a range 153
within which they can sense the magnetic field of a marker 110. The
range 153 is generally spherical and centered on the sensor pair.
The size of the spherical range is represented by a radius R.
Notably, in FIG. 2A only the range 153 of the tip sensor pair 151
is shown, although the base sensor pair 152 has a similar range
centered on itself. The range 153 is a factor of the sensitivity of
the sensor pair as well as the strength of the magnetic field of
the marker 110. For example, a marker 110 with a stronger magnetic
field (e.g., a larger magnet) can be sensed at a greater radius R
from the tip sensor pair 151.
[0053] In one embodiment, the distance D between the tip sensor
pair 151 and the base sensor pair 152 may be configured to be at
least twice the radius R. This configuration reduces the likelihood
of a marker 110 being sensed by both the tip sensor pair 151 and
the base sensor pair 152. However, this need not be the case in all
embodiments. In another embodiment, the distance D is at least as
large as the radius R. In some embodiments, the distance D may be
approximately 500 mm to approximately 50 mm or less. In some
embodiments the radius R may be approximately 250 mm to 1 mm. These
ranges are provided only by way of example, and are not intended to
be limiting of this disclosure. In some embodiments, as the radius
R of the range 153 is decreased, the resolution or precision of the
probe 150 increases because the incremental scale of the
magnetometer in a sensor pair is divided over a shorter distance.
For example, the LSM303D chip referenced above outputs raw
magnetometer data on a 16-bit binary scale. When the radius R of
range 153 is divided into the chips binary scale, a shorter radius
R produces a higher resolution because each bit represents a
smaller incremental distance.
[0054] In one embodiment, the tip sensor pair 151 and the base
sensor pair 152 are aligned with each other so that the three-axes
(as shown in FIGS. 3A and 3B) of each are also aligned. That is,
the x-axis of the tip sensor pair 151 and the x-axis of the base
sensor pair 152 are configured to be parallel; the y-axis of the
tip sensor pair 151 and the y-axis of the base sensor pair 152 are
configured to be parallel; and the z-axis of the tip sensor pair
151 and the z-axis of the base sensor pair 152 are configured to be
parallel. This configuration may produce increased accuracy in the
results and simplify the computations involved in determining the
location of the marker 110. Further, in one embodiment, the tip
sensor pair 151 and the base sensor pair 152 are aligned along a
central longitudinal axis of the probe 150.
[0055] The tip sensor pair 151 and the base sensor pair 152 are
each electrically connected to the microprocessor 157, such that
the microprocessor 157 receives the data output from each. The
microprocessor 157 may be a ATmega16U4/ATmega32U4 available from
Atmel. The data sheet for this microprocessor is available at
http://www.atmel.com/Images/Atmel-7766-8-bit-AVR-ATmega16U4-32U4_Datashee-
t.pdf and incorporated herein by reference. Other microprocessors
may be used. In general, the microprocessor 157 analyzes the output
data from the tip sensor pair 151 and the base sensor pair 152 to
determine the distance and direction to the marker 110.
Accordingly, the microprocessor 157 may be configured with
instructions for making this determination. The process by which
the microprocessor 157 determines the distance and direction to the
magnetic marker 110 will be described in greater detail below. In
some embodiments, the probe 150 may include more than one
microprocessor 157.
[0056] In the example of FIG. 2A, a display 155 is electrically
connected to the microprocessor 157. The display 155 extends
through a window in the housing 160 such that it is viewable by the
user. The display 155 may provide information to the user regarding
the distance and direction to the marker 110 as determined by the
microprocessor. In some embodiments, the display 155 provides
information regarding the position of the marker 110 to the user in
text, for example: "Distance: 10.5 mm." In some embodiments, the
display 155 provides a graphical representation of the information.
For example, the display may include an arrow that points towards
the marker 110. The arrow may update in real time as the user moves
the probe 150 relative to the marker. The display 155 may provide a
combination of textual and graphical information to the user. The
display 155 may also provide additional information to the user.
For example, as will be described below, a balancing process may be
performed with the probe 150 before use, and the display 155 may
provide the user information regarding the balancing. Further, the
display 155 may allow a user to access various menus and settings
for using the probe 150, for example, volume settings, battery
information, and/or magnetic field strength range adjustment
settings that may be used increase sensitivity as the measured
distance decreases, among others. Input buttons 154 may be included
for navigating the menus, and may include, for example, a "select"
button and a "next" button. However, the probe 150 may be modified
to include other input and selection methods. For example, the
probe 150 may include a touchscreen, or input can be entered
through the external device 170. In some embodiments, the display
155 and/or the input buttons 154 may be omitted.
[0057] In the example of FIG. 2A, an RF (wireless) module 158 is
included in the probe 150 and connected to the microprocessor 157.
In some embodiments, the RF module 158 is a Bluetooth module or a
Wi-Fi module. The RF module 158 may allow a wireless connection to
the external device 170 or another wireless enabled device. In some
embodiments, the RF module 158 may be omitted, and the probe 150
may not connect to any other device. In some embodiments, the probe
150 connects to another device via a wired connection. For example,
the probe 150 may include a USB port that may be used to connect
the probe 150 to the external device 170 via a USB cable.
[0058] In the illustrated embodiment, the probe 150 includes a
buzzer or speaker 156 connected to the microprocessor 157. The
buzzer or speaker 156 provides another mechanism by which the probe
150 can communicate information regarding the location of the
marker 110 to the user. For example, the microprocessor 157 may be
configured with instructions that cause the speaker 156 to emit a
tone indicative of the position of the marker 110 relative to the
probe 150. In one embodiment, the frequency (pitch) of the tone may
indicate the distance to the marker 110 and a warble (or small
undulation in the frequency) in the tone may indicate the
orientation of the probe 150 relative to the marker 110. For
example, a user may move the probe 150 relative to the patient's
body 101 while listening to the tone emitted by the speaker 156. As
the frequency of the tone increases, for example, the user will
understand the probe is being moved closer to the marker 110. The
user may also adjust the orientation of the probe 150 so as to
remove the warble from the tone. When the user finds a probe
orientation that removes the warble from the tone, this indicates
that the probe 150 is pointed at the marker 110. Other audible
methods for communicating the location of the marker 110 are
possible. Moreover, the buzzer or speaker 156 may be configured to
vibrate to provide a haptic feedback to the user regarding the
position of the marker 110. In some embodiments, the buzzer or
speaker 156 may be omitted.
[0059] In the example, a battery 159 is included to power the
components of the probe 150. In some embodiments the battery may be
rechargeable, and the probe 150 may include a recharging port. In
some embodiments, the battery 159 may be omitted, and the probe 150
may include a wired connection to a power source. For example, the
probe 150 may be powered via USB connection to the external device
170.
[0060] In some embodiments, the internal components of the probe
150 may be assembled onto a single printed circuit board (PCB) that
is configured to fit within the housing 160. However, in other
embodiments the components may be separate or assembled onto more
than one PCBs.
[0061] While many embodiments of the probe 150 are described herein
as including two sensor pairs (each including a magnetometer and
accelerometer), in some embodiments the probe 150 includes only a
single accelerometer along with two magnetometers (spaced in the
same manners as discussed herein with reference to spacing of the
sensing and tip sensor pairs). For example, in one embodiment the
probe 150 may include base sensor pair 152 (having a magnetometer
and accelerometer as discussed herein) and only a magnetometer
(without an associated accelerometer) near the sensing tip 164 of
the probe 150; or alternatively may include tip sensor pair 151
(having a magnetometer and accelerometer as discussed herein) and
only a magnetometer (without an associated accelerometer) in the
base 161 of the probe 150. In another embodiment, the probe 150 may
include magnetometers at each of the sensing tip 164 and base 161
of the probe (e.g., spaced in a similar manner as discussed herein
with reference to spacing of base and tip sensor pairs) and a
single accelerometer (e.g., on a separate chip) placed at any
location within the probe 150. In some embodiments, the probe 150
may not include an accelerometer and instead include a base and tip
magnetometer and provide the functionality and features associated
with the magnetometers. Any probe embodiments disclosed herein may
be adjusted to include any of these different combinations of
accelerometer and/or magnetometer sensors. Such adjustments to the
use of magnetometer sensor pairs are applicable to the removable
and/or disposable sensing tips also, such as those discussed with
reference to FIGS. 2C and 2D. For example, in one embodiment a
removable sensing tip may include two magnetometers (spaced within
the sensing tip) and an accelerometer may be included in the probe
base 161 (to which the sensing tip is removably attachable) so that
the sensing tip size may be further reduced since an accelerometer
is not included in the sensing tip.
[0062] FIGS. 2B through 2D illustrate additional embodiments of a
handheld probe. FIG. 2B shows an embodiment of the probe 150 with
the housing 160 closed, encapsulating the internal components. The
input buttons 154, the display 155, and an on/off switch 165 extend
through the housing for access by the user. The housing 160
includes the base 161, the protruding portion 162, and the
extension portion 163. The sensing tip 164 is configured as a nub
and accommodates the tip sensor pair 151. The base sensor pair 152
is positioned within the protruding portion 162. In the example of
FIG. 2B, the probe 150 includes a laser pointer 1641 positioned at
the sensing tip 164. The laser pointer 1641 is aligned with the
longitudinal axis of the probe 150 so as to point in substantially
the same direction as the probe 150 itself. The light beam 1641a
emitted by the laser pointer 1641 provides a visual illustration of
the location 1641b at which the probe 150 is pointed.
[0063] FIG. 2C shows an example of a probe 150c, wherein the
extension portion 163c (or sensing member 163c) comprises a
narrower member that may be insertable into tissue, such as into an
incision in tissue. In one embodiment, the sensing member 163c is
sized and comprised of materials the same as or similar to a
surgical needle. In these embodiments, the sensing member 163c may
be made from a non-magnetic material. For example, the sensing
member 163 may be made from a polyether ether ketone (PEEK)
material, among others. The Sensor Processing Board illustrated in
FIGS. 2C and 2D may include the same or similar microprocessor 157
as discussed herein and may execute similar software or firmware.
Additionally, although not illustrated, the probes of FIGS. 2C and
2D (as well as other probes discussed herein) may include some or
all of the other components of the probe 150 of FIG. 2A as well as
any other components and/or functionalities discussed herein.
[0064] Depending on the implementation (e.g., the sensing member
size) and ongoing development of sensors of smaller sizes, the
sensor pairs may be of varying sizes. For example, in one
embodiment each sensor pair is 3 mm.times.3 mm.times.1 mm (plus a
circuit board thickness) in size. In other embodiments, the sensor
pairs may be larger or smaller. For example, each sensor pair may
be sized to fit within a sensing member having a diameter that is
approximately 1 mm or less. The tip sensor pair 151c is positioned
at the distal end of the sensing member 163c that may be inserted
into tissue. The base sensor pair 152c can be positioned in the
base 161c or in the proximal end of the sensing member 163c
opposite the tip sensor pair 151c. In some embodiments, the probe
150c, with the sensing member 163c configured as a needle, is used
to probe within the patient's body 101, for example, by inserting
the sensing member 163c at least partially into the patient's
tissue while gripping the probe base 161c. In the example of FIG.
2C, the probe 150 is configured as a narrower device, wherein the
probe tip is a blunt or sharp needle. In one embodiment, the tip of
the needle is a fixed distance and location relative to the tip
sensor pair, such that the device can calculate and report to the
user the proximity of the tip of the needle to the implanted
magnet. The benefit is that it is easier to very specifically
locate a small lesion with a needle compared to a 1 cm thick blunt
probe.
[0065] FIG. 2D shows an example of a probe 150d with a removable
sensing member 163d. In some embodiments, the removable sensing
member 163d may be disposable. The tip sensor pair 151d and the
base sensor pair 152d are located in the sensing member 163d and
spaced apart as described above. The disposable sensing member 163d
may include a wired or wireless connection 159d to the probe base
161d. In some embodiments, the disposable tip 163d includes a plug
that is receivable into a socket on the probe base 161d.
Advantageously, the embodiment of the probe 150d with a removable
and/or disposable sensing member 163d may allow the probe 150d to
work with variously configured removable sensing members 163d. For
example, the probe base 161d can be coupled to removable sensing
members of different sizes and sensitivities, such as sensing
members having larger or smaller diameters and different spacings
between reference and sensor pairs configured to better detect
magnetic markers of varying sizes and/or properties.
[0066] In another embodiment, the sensing member 163d may
communicate directly to the external device 170, such as a smart
phone or tablet. In this embodiment, the external device 170 may
include the logic (e.g., hardware, firmware, and/or software) for
performing the various functions discussed herein with reference to
the microprocessor 157, such as receiving raw data from the two
sensor pairs of the sensing member 163d and performing the
necessary calculations and processing of the data to balance the
sensor pairs and provide measurement information based on the
received sensor data. In this embodiment, the removable and/or
disposable sensing member 163d may communication wirelessly with
the external device 170 (e.g., via a WiFi, RF, or Bluetooth signal)
and/or may be wired to the external device 170 (e.g., via a port on
the proximal end of the sensing member 163d). Thus, in one
embodiment, the user can download an application on a mobile device
that communicates wirelessly with the sensing member 163d. In one
embodiment, various kits of components, such as a kit including
multiple sensing members 163d (perhaps of different sizes and/or
sensitivities, or each of a same size sensitivity) could be
manufactured/shipped to users so that multiple sensing members 163d
are readily available for use. Another kit may include a single
base and multiple sensing members.
[0067] The components of the various embodiments of the probe 150
discussed herein may be arranged in any other configurations
between multiple devices.
Example Balancing of Sensor Pairs
[0068] FIGS. 3A and 3B show the three axes for each of the
magnetometer and accelerometer, respectively, in a sensor pair.
While FIGS. 3A and 3B show the magnetometer and accelerometer
separately, in some embodiments of the probe 150 (which includes
any of the probes 150, 150a, 150b, 150c, 150d, or other unnumbered
probe mentioned herein), the magnetometer and accelerometer are
integrated together into an accelerometer-magnetometer pair, for
example, as in the tip sensor pair 151 or base sensor pair 152, as
discussed above. In those embodiments, the magnetometer and
accelerometer substantially occupy the same physical location, and
the three axes of each may share a common, or nearly common,
origin.
[0069] FIG. 4 is a diagram illustrating conceptually the output
data from the magnetometers in each of the base sensor pair 152 and
the tip sensor pair 151 before the probe 150 is balanced. As used
herein, the output data may be described as "raw" because, at this
stage, it is only a sensor binary number and has not yet been
converted into units of Gauss or balanced, as will be described
below. In other words, FIG. 4 is representative of the raw output
data of the magnetometers of each of the base sensor pair 152 and
the tip sensor pair 151 before balancing. This is represented by
the two ellipsoids 251 and 252, which correspond to the output data
of the magnetometers of the tip sensor pair 151 and the base sensor
pair 152, respectively. In an unbalanced state, the size, shape,
orientation, and position of the two ellipsoids 251, 252 are likely
different. The balancing process, however, determines mathematical
transformations that may be applied to the output data of one or
both of the magnetometers such that it can be represented by two
spheres 351, 352 of equal size (as shown in FIG. 7). An example
balancing process is described in detail for a single sensor pair
in the following application notes provided by Freescale
Semiconductor: "Implementing a Tilt-Compensated eCompass using
Accelerometers and Magnetometer Sensors," Doc. No. AN4248,
available at
http://cache.freescale.com/files/sensors/doc/app_note/AN4248.pdf;
"Layout Recommendations for PCBs Using a Magnetometer Sensor," Doc.
No. AN4247, available at
http://cache.freescale.com/files/sensors/doc/app_note/AN4247.pdf;
and "Calibrating an eCompass in the Presence of Hard and Soft-Iron
Interference," Doc. No. AN4246, available at
http://cache.freescale.com/files/sensors/doc/app_note/AN4246.pdf,
all of which are incorporated herein by reference in their
entirety.
[0070] The ellipsoids 251, 252 in FIG. 4 are representative of the
output data of the magnetometers of each of the tip sensor pair 151
and the base sensor pair 152 as the magnetometers are rotated in
all directions in a substantially constant magnetic field. The
output of a magnetometer comprises three values (for example, x, y,
and z values) representing the orthogonal component parts of the
magnetic field vector measured by the magnetometer. For a
calibrated magnetometer rotating in a constant magnetic field, the
x, y, and z output values should fall on the surface of a uniform
sphere centered on 0, 0, 0, regardless of the magnetometers
orientation (see FIG. 7 and corresponding description). The radius
of the sphere 351, 352 will be representative of the strength of
the measured magnetic field. However, for an uncalibrated
magnetometer, as is shown in FIG. 4, the x, y, and z output values
for each magnetometer will trace an ellipsoid 251, 252 as the
magnetometer is rotated in a constant magnetic field. The ellipsoid
will not likely be centered at 0, 0, 0. Moreover, when
magnetometers of the tip sensor pair 151 and the base sensor pair
152 are not balanced, the size and shape of the two ellipsoids 251,
252 will likely be different and, thus, comparison of measurements
between the two magnetometers may be inaccurate due to these
differences. By using a bases sensor pair 152 and a tip sensor pair
151 and taking the difference of the magnetometer output of each,
the probe 150 is able to differentiate the magnetic field of the
marker 110 from the general magnetic field in the environment of
the probe.
[0071] Differences in the output value set for each of the
magnetometers may be largely or entirely caused by "hard iron" and
"soft iron" interference. "Hard iron" interference is caused by
magnetic fields generated by permanently magnetized ferromagnetic
components of the probe 150 itself, for example, a permanent
magnetic field generated by the buzzer or speaker 156, other
components of the probe 150, or other magnetic fields in the area
where the probe 150 is used. Because the magnetometers and the
other components of the probe 150 are in fixed positions with
respect to each other, the hard iron interference manifest itself
as an additive magnetic field vector when measured in the
magnetometer reference frame. That is, the hard iron interference
induces a constant offset in the x, y, and z output data from each
magnetometer, regardless of the orientation of the magnetometer.
This offset results in the shifting of the ellipsoids 251, 252
discussed above. In some embodiments, the components of the probe
150 which may tend to produce hard iron interference are positioned
within the probe housing 160 away from the tip sensor pair 151 and
the base sensor pair 152, thus minimizing the hard iron
interference.
[0072] "Soft iron" interference is caused by the induction of
temporary magnetic fields into normally unmagnetized ferromagnetic
components of the probe 150, such as the battery 159, by the
Earth's geomagnetic field. Soft iron interference therefore depends
on the orientation of the probe 150 relative to the Earth's
geomagnetic field. Soft iron interference, therefore may add to or
subtract from the x, y, and z output of a magnetometer depending on
the magnetometer's orientation. This manifests itself in the
irregular shape of the ellipsoid 251, 252, as compared with a
sphere. In some embodiments, the components of the probe 150 which
may tend to produce soft iron interference are positioned within
the probe housing 160 away from the tip sensor pair 151 and the
base sensor pair 152, thus minimizing the hard iron
interference.
[0073] FIG. 5 is a flowchart illustrating an example method 500 for
balancing the magnetometers of the tip sensor pair 151 and the base
sensor pair 152 of the probe 150. FIG. 6A is a table containing
sample magnetometer output data that will be used for purposes of
providing an example of the method 500 and, similarly, FIG. 6B is a
table which presents calculations of a gain and offset that may be
used to balance the sensing magnetometer and reference magnetometer
that provided the sample data of FIG. 6A. The method of FIG. 5 may
be performed by the probe 150 alone and/or in communication with
the device 170. Depending on the embodiment, the method of FIG. 5
may include fewer or additional blocks and the blocks may be
performed in an order that is different than illustrated.
[0074] The method 500 begins with an unbalanced set of
magnetometers in a probe 150. In this embodiment, the probe 150 is
balanced away from (out of range of) any markers 110. At block 505,
the probe 150 is rotated through 360 degrees around each of three
orthogonal axes and the minimum and maximum x, y, and z output
values are recorded. For example, the probe 150 is rotated 360
degrees in each of the pitch, roll, and yaw directions. As the
probe 150 rotates, the magnetometer of each of the tip sensor pair
151 and the base sensor pair 152 outputs a substantially real time
stream of x, y, and z values. For each of the tip sensor pair 151
and base sensor pair 152, the maximum and minimum values for each
of the x, y, and z values are stored. In some embodiments, the
maximum and minimum values are stored in a memory associated with
the microprocessor 157, such as a solid state storage device.
[0075] For example, in some embodiments, the microprocessor 157
stores the first x output value it receives from the magnetometer
of the tip sensor pair 151. The microprocessor 157 then checks each
successive x output value against the stored value and replaces the
stored value if the successive x value is higher. After one
complete rotation of the probe 150, the maximum x value will be
stored. This process can be similarly repeated for determining the
minimum x value (by checking each successive x value against the
stored value and replacing the stored value if the successive value
is lower).
[0076] In some embodiments, the probe 150 may be rotated through
greater than or less than 360 degrees around the three orthogonal
axes. In some embodiments, the three axes are not necessarily
orthogonal. However, rotating for at least a full 360 degrees
around each of the three orthogonal axes will likely increase the
accuracy of balancing.
[0077] FIG. 6C shows a probe 150 configured to display set of bars
199 that provide visual feedback to the user during the balancing
process, according to one embodiment. The bars aid the user in
successfully balancing the probe 150. For example, the set of bars
199 includes the three individual bars as shown, one bar
corresponding to each of the three orthogonal axes around which the
probe 150 is rotated during balancing. In the example, as the user
rotates the probe 150, each of the three bars 199 is indicative of
the real-time calibration of one of the three axes of the probe
150. For example, the bars may indicate a range across an axis, and
the result displayed may reflect the constantly changing gain for
each axis. In this embodiment, the constantly changing gain may be
determined as the maximum value for that axis minus the minimum
value for that axis all divided by the average of all the axes.
Thus, the bars show the constantly changing gain adjusted values of
the magnetometer during balancing because as the probe 150 is
rotated the maximum and minimum values for each axis change over
the balancing time as higher and lower values are recorded and
stored. This, in turn, results in the individual lengths along each
axis (e.g., the distance between the maximum and minimum values)
also changing over the balancing time and also the average length
of all six axes (e.g., the sum of the six individual lengths
divided by six) changing over the balancing time. For example, in
an implementation where the final gain values after balancing for
all axes are 1.00, the bars may display a range of 0.70 to 1.30
with the middle acceptable range box of 1.00.+-.0.02. When the bars
display within the middle acceptable range box, the user will know
that the probe 150 is balanced. By displaying the data as the three
bars the probe 150 does not need to auto-scale the graph range from
a minimum to a maximum value for each axis. Accordingly, the probe
150, via the bars 199 on the display 155, is configured to provide
feedback to the user during balancing which may aid a user in
understanding how to rotate the probe 150. Other methods for
providing feedback, for example other visual or audible means,
regarding the progress of balancing may be used. For example, in
one embodiment an audible alert is provided when the probe 150 has
been rotated sufficiently around each axes such that balancing is
complete.
[0078] Sample minimum and maximum x, y, and z values for each of
the tip sensor pair 151 and the base sensor pair 152 are shown in
the table of FIG. 6A. The values in the table of FIG. 6A are
considered "raw" values because they are unbalanced data received
directly from the magnetometers of tip sensor pair 151 and the base
sensor pair 152. Conceptually, the maximum and minimum x, y, and z
values represent the end points of the three semi-principal axes of
the ellipsoids 251, 252 of FIG. 4. In other words, the maximum and
minimum values for x, y, and z define the end points of the three
orthogonal axes that mathematically define the shape of the
ellipsoids 251, 252.
[0079] Next, at block 510, the individual length between the
maximum and minimum x, y, and z values is determined. This length
is representative of the length of the three semi-principal axes of
the ellipsoids 251, 252. As shown in FIG. 5, the length is
calculated by taking the difference of the maximum and minimum
values, or, as shown in FIG. 6B, taking the sum of the absolute
values of the maximum and minimum values. The resulting length for
each of the x, y, and z directions for the tip sensor pair 151 and
the base sensor pair 152 are shown in the "Individual Length"
column of FIG. 6B.
[0080] At block 515, a gain factor for each of the x, y, and z
directions of each sensor pair 151, 152 is calculated by dividing
the individual length of each of the x, y and z directions by the
average length of the x, y, and z directions. The average length of
the x, y, and z directions is calculated by dividing the sum of the
individual x, y, and z lengths of both magnetometers by six. The
resulting gain factors calculated from the sample data of FIG. 6A
are shown in FIG. 6B (in the "Gain" column). Conceptually, the gain
factors are scalar quantities that will be used to transform the
ellipsoids 251, 252 of FIG. 4 into the spheres 351, 352 of FIG.
7.
[0081] At block 520, an offset value is calculated for each of the
x, y, and z directions of each sensor pair 151, 152 by adding the
average of the maximum and minimum values to the minimum values.
Calculated offset values using the sample data of FIG. 6A are shown
in FIG. 6B (in the "Offset" column). Conceptually, the offset
values represent the shift of the center of the ellipsoids 251, 252
away from center (0, 0, 0) along each of the x, y, and z
directions. The offset values are used to translate the ellipsoid
251, 252 back to a common center.
[0082] At block 525, the raw output data from the magnetometers of
the tip sensor pair 151 and base sensor pair 152 is balanced by
subtracting each of the corresponding offset values from the
corresponding raw output data and then multiplying by the
corresponding gain value.
[0083] FIG. 7 is a diagram illustrating conceptually the output
data from the magnetometer in each of the base sensor pair 152 and
the tip sensor pair 151 after the probe 150 is balanced. As shown
in the figure, the range of possible outputs from each can now be
represented as equal sized spheres 351, 352. Moreover, each sphere
351, 352 has a common center, such as 0, 0, 0. With the probe 150
correctly balanced, as the probe 150 rotates in a constant magnetic
field, the output data from each magnetometer (in x, y, z form)
will fall on the surface of the spheres 351, 352. The radius of the
spheres 351, 352, which does not depend on direction, is constant
and corresponds to the strength of the constant magnetic field
acting on the sensor pairs 151, 152. Accordingly, assuming no
changes to the constant magnetic field around the probe 150, it is
balanced to correctly measure a magnetic field, regardless of the
orientation of the probe 150. In some embodiments, the probe 150
may further be configured with a zero adjust function, as discussed
below, to account for small variations in the magnetic field around
the probe. For example, these variations may be caused by changes
in the Earth's geomagnetic field over time. The zero adjust
function compensates for subtle soft and hard iron interferences
present based on the orientation of the probe that may exist even
after balancing. Conceptually, these interferences may be viewed as
minor bumps or variations on the spheres 351, 352. The zero adjust
function corrects for these bumps.
[0084] FIG. 8 is a table containing sample balanced data. The data
in the table represents the raw data of FIG. 6A in balanced form.
In the first two columns, the minimum and maximum values have been
adjusted by subtracting the appropriate offset values. In the last
two columns, which contain fully balanced data, the gain factor has
been applied. At this point, for each of the base and tip
magnetometers, all of the maximum values are equal, all of the
minimum values are equal, and the minimum and maximum values are
equal in absolute value but have the opposite sign.
Example Magnetic Marker Measurements Using Balanced Sensor
Pairs
[0085] FIG. 9 is a flowchart illustrating an example method 900 for
using the probe 150 to determine the three-dimensional location of
a marker 110 within a patient's body 101. The method 900 will be
discussed in connection with FIGS. 10-13, which include example
data for purposes of illustration. Depending on the embodiment, the
method of FIG. 9 may include fewer or additional blocks and the
blocks may be performed in an order that is different than
illustrated.
[0086] The method 900 begins with a balanced probe 150 and at least
one marker 110 implanted into the tissue of a patient. At block
905, the probe 150, and specifically the tip sensor pair 151, is
brought within range of the marker 110 (for example, as illustrated
in FIG. 1). This may be done by holding the probe 150 by hand and
moving the tip sensor pair 151 over the surface of the patient's
body 101 where the marker 110 is believe to be implanted. In some
embodiments, the probe 150 contacts the patient's skin. In some
embodiments, the probe 150 does not contact the patient's skin. In
one embodiment, each of the tip sensor pair 151 and base sensor
pair 152 outputs substantially real time accelerometer and
magnetometer data to the microprocessor 157.
[0087] At block 910, the base sensor pair's 152 magnetometer data
is subtracted from the tip sensor pair's 151 magnetometer data.
This difference is representative of the magnetic field strength of
the marker 110. Block 910 is shown conceptually in FIG. 10.
[0088] In the example of FIG. 10, the probe 150 has been balanced
so that the magnetometer output data of the tip sensor pair 151 and
the base sensor pair 152 can be represented as equal sized,
concentric spheres 351a, 352. However, because the marker 110 is
within the range 153 of the tip sensor pair 151, the magnetic field
of the marker 110 is also reflected in the tip sensor pair's
magnetometer data output. This component due to the magnetic field
of the marker 110 is represented by the shape 351b in FIG. 10.
Notably, because the marker 110 is not within range of the base
sensor pair 152, its magnetometer data output is not affected by
the marker 110. Upon subtraction of the base sensor pair's 152
magnetometer data from the tip sensor pair's 151 magnetometer data,
the result is substantially wholly due to the magnetic field of the
marker 110. The result is represented conceptually in FIG. 10 by
shape 450. Subtracting the base sensor pair 152 data from the tip
sensor pair 151 data removes any components that act equally on
both base and tip magnetometers, for example, the component due to
the Earth's geomagnetic field.
[0089] The magnetic field of the marker 110, measured at the tip
sensor pair 151 is a vector quantity with length and direction.
After taking the difference described above, the probe 150 will
have resulting x, y, and z values representing the component parts
of that vector. The magnitude of the magnetic field strength
b.sub.x, then, can be calculated using the Pythagorean Theorem, for
example, to calculate a major axis length of the ellipsoid.
[0090] FIG. 11 provides tables showing sample data in both raw and
balanced form that is representative of raw and balanced data from
a probe 150 that is positioned within a measurement range of a
magnetic marker. It further illustrates calculation of the
magnitude of the magnetic field strength b.sub.x of a marker 110
using that data. The top table presents columns for raw, offset
adjusted, and fully balanced (offset and gain adjusted) data for
each of the tip sensor pair 151 and base sensor pair 152, for an
example marker 110 positioned 17.1 mm from the tip sensor pair 151.
As shown, there is a difference in the balanced data between the
tip sensor pair 151 and base sensor pair 152. This difference is
caused by the magnetic field of the marker 110 acting on the tip
sensor pair 151. The differential is calculated with results
displayed in the first column, labeled "Differential," of the
bottom table (e.g., for the x-axis, by subtracting the "After Gain
Corrected" x data for the base sensor pair from the "After Gain
Corrected x data from the tip sensor pair).
[0091] In some embodiments, the calculated differential represents
raw magnetometer output data that needs to be converted into a
magnetic field strength value with units of Gauss. For example, the
magnetometer raw output data of an LSM303D chip is firmware
selectable, and the magnetometer selected allows for different
full-scale output sensitivity. The LSM303D allows for selection of
.+-.2/.+-.4/.+-.8/.+-.12 gauss, dynamically selectable magnetic
full-scale output over a signed-16 bit number, from -32768 to
+32767. The example data presented in FIG. 11 was generated by an
LSM303D chip with the .+-.12 gauss magnetic scale selected.
Accordingly, to convert the raw output data to Gauss, the raw
output is divided by 32768 and multiplied by 12. Or, in more
general terms, the raw output is converted into a magnetic field
strength value represented in Gauss by dividing the raw output by
the magnetometers scale and multiplying by the Gaussian value
represented by each incremental unit of the scale. This is
represented in the table of FIG. 11 by the column labeled
"Differential/32768*12."
[0092] The magnitude b.sub.x of the marker's 110 magnetic field
measured at the tip sensor pair 151 may be determined using the
Pythagorean Theorem, as shown in the third column of the bottom
table of FIG. 11.
[0093] In some embodiments, the determined magnitude b.sub.x of the
magnetic field of the marker 110 may be adjusted as shown in the
column titled "Zero Adjust." The zero adjust is used to compensate
for any changes in the magnetic field around the probe, not caused
by the marker 110, since the time when the probe 150 was balanced.
For example, the Earth's geomagnetic field changes slowly over
time. While the balancing process described above calibrates the
base sensor pair 152 and the tip sensor pair 151 to account for the
Earth's geomagnetic field at the time the probe 150 is balanced,
the zero adjust may further compensate for changes in the Earth's
geomagnetic field since balancing. The zero adjust may also
compensate for other magnetic field changes not caused by the
Earth's magnetic field. This zero adjust value modifies the output
of the probe 150 due to minor changes in the environment and
orientation of the probe. It is not a fixed value, but a user
selectable minor offset correction. In the example of FIG. 11, the
magnitude of 0.385 Gauss was zero adjusted by a value of -0.076
Gauss for an adjusted Gauss value of 0.309 Gauss. Determination of
the zero adjust value is described more fully below in reference to
FIG. 14.
[0094] Returning to the method 900 of FIG. 9, the distance to the
marker 110, as measured from the tip sensor pair 151, can either be
retrieved from a lookup table (block 915) or calculated directly
(block 920). Both blocks 915 and 920 use the magnitude b.sub.x of
the magnetic field of the marker 110 determined at block 910.
[0095] At block 915, the distance to the marker 110 is retrieved
from a lookup table (an example of which is shown in FIG. 12A)
which contains entries relating the magnitude b.sub.x of the
magnetic field of the marker 110 to distance. In some embodiments,
the lookup table is stored in a memory associated with the
microprocessor 157.
[0096] The lookup table can be created either experimentally or
mathematically. For example, field strength to distance calibration
may be performed by placing the micro magnet to be used under the
sensing probe tip to record the value of the closest distance or
strongest field strength measurement, this will be the first point,
then moving the micro magnet to any known measured distance (e.g.
20 mm, 25.4 mm, 50.8 mm) and recording the value as the second
point. Since the magnetic field strength falls off roughly
exponentially over the distance, multiple calibration points will
add to the accuracy.
[0097] Another method for calibrating the second point (with a
built in reference) is to move the micro magnet along the side of
the probe between the sensing probe tip sensor and the reference
sensor. Since these two sensors are always at a fix distance in
relationship to each other, a lowest field strength differential
value displayed will be at the midpoint between these two sensors
(where their magnitudes cancel each out), this low point value is
at the distance which will always be 1/2 the distance between the
two sensors.
[0098] Another method for calibrating the distance to field
strength is to use an automated process, including use of the
equation below to setup a look-up table for distance verses field
strength. For a cylindrical marker 110 with a radius of R and
Length L, the magnitude of the magnetic field B.sub.x at the
centerline of the marker 110 a distance X from the marker 110 can
be calculated with following formula (where B.sub.r is the residual
induction of the material):
Bx = Bx 2 ( ( L + X ) R 2 + ( L + X ) 2 - X R 2 + X 2 ) ( Eq . 1 )
##EQU00001##
[0099] Using Equation 1, a lookup table can be populated for a
marker 110 with a known size (R and L) and a known residual
induction (B.sub.r). In general the residual induction B.sub.r is a
known value which can be obtained from the manufacturer of the
magnet. For example, the table can be populated by calculating
B.sub.x at incremental distances X. The example lookup table in
FIG. 12A has calculated B.sub.x for distances X with a step size of
0.1 mm (e.g., the first column illustrates distances from 0.0 mm to
17.7 mm). Accordingly, by comparing the determined B.sub.x found in
block 910 with the corresponding B.sub.x values in the last column
of the lookup table of FIG. 12A, the distance X to the marker 110
can be determined within a resolution of 0.1 mm. Depending on the
embodiment, the next B.sub.x value that is closest, next highest,
or next lowest compared to the calculated B.sub.x from the probe
150 for use in finding a corresponding distance. In other
embodiments, distances may be interpolated or scaled based on
multiple B.sub.x values included in the lookup table (e.g., the
next highest and next lowest values) and their relationships to a
measured B.sub.x value.
[0100] Alternatively, at block 920 the distance to the marker 110
can be calculated directly by solving Equation 1 for X, given the
B.sub.x value determined at block 910. This, however, may be
computationally difficult for the microprocessor 157.
[0101] Equation 1 is specific to rod shaped magnets; however,
similar equations are known in the art for magnets of other shapes,
for example, spherical, cuboid, or other three dimensionally shaped
magnets. Markers 110 with different shapes may be used by
substituting an appropriate and corresponding equation for Equation
1.
[0102] FIG. 12B through 12D provides another table of sample data
and the calculation of gain and offset values used to balance a
probe, according to one embodiment, as well as two example
measurements that are calculated with the probe at different
distances from a marker.
Example Orientation Determination
[0103] A magnetometer sensor will measure the earth's magnetic
field to determine North, East, South & West (NESW) orientation
when held in the same orientation plane as when it was calibrated.
But if the magnetometer sensor moves through pitch, roll or yaw,
then heading information calculated for NESW will not be correct.
To cancel the effects of the pitch, roll and yaw, an accelerometer
is used.
[0104] As noted above, an accelerometer (measures acceleration of
the sensor) but it also measures the sensors orientation to earth's
gravity which at 9.8 m/s.sup.2 is used to determine UP and DOWN
orientation. Thus, one or both of the accelerometers in the base
and/or tip sensor pairs may be used at block 925 to determine
orientation data of the probe 150.
[0105] FIG. 13A is a diagram illustrating the use of accelerometer
data to determine the orientation of the probe. As previously
described, an accelerometer is used to determine the orientation of
an object relative to the direction of gravity. Because both the
tip sensor pair 151 and the base sensor pair 152 are rigidly
attached with reference to one another in the probe 150, the data
from the accelerometer of either can be used to calculate the
orientation of the probe 150. In the example of FIG. 13A, the
orientation of the probe 150 is described in terms of yaw, pitch,
and roll. Yaw represents rotation in a horizontal plane relative to
North, pitch represents the up or down tilt of the probe 150, and
roll represents the rotation of the probe 150 around its
longitudinal axis. The three circles in FIG. 13A represent that the
probe 150 is pointed north (in the yaw direction), horizontally
level (in the pitch direction), and rotated counter-clockwise
slightly (in the roll direction).
[0106] If the probe 150 is not accelerating, both the tip sensor
pair 151 and the base sensor pair 152 will output x, y, and z
accelerometer data representative of a vector pointing in the
direction of gravity. Thus, the accelerometer output provides a
determination of an orientation of the probe 150 relative to the
direction of gravity. By calculating the yaw, pitch, and roll of
the probe 150 (with reference to gravity for a non-accelerating
probe 150), the probe 150 can determine the specific orientation of
the probe 150 with reference to gravity, which can then be used in
to adjust the magnetometer data output to display a direction
component output by the probe 150. In one embodiment, the yaw,
pitch, and roll of the probe 150 are determined mathematically
using the formulas shown in FIG. 13A by taking the arctangent of
appropriate rations of the x, y, and z components of the
accelerometer data.
[0107] At block 930 of FIG. 9, the resulting distance to the marker
110 and probe orientation are displayed. As discussed previously,
this may be accomplished in a plurality of ways, including
graphically, on a display 155 of the probe 150 or a display 171 of
the external device, or audibly, using the speaker 156, among
others. In one embodiment, this is done is by first limiting the
data to be able to convert a 3D space for display on a 2D screen.
For example, when the probe 150 is zero adjusted, the yaw, pitch
and roll (See display at 1505 of FIG. 15C) are stored and
orientation of the probe 150 is represented at the middle of the 2D
display 155 of the probe 150. As the probe 150 is moved from that
orientation and the field strength vector is created, the yaw,
pitch and roll of the probe 150 are mapped where the peak value is
in relation to when it was last zeroed or home in the middle of the
display.
[0108] FIG. 13B illustrates three example instances of a graphical
representation for displaying the distance and direction from the
tip sensor pair 151 of the probe 150 to the marker 110, according
to one embodiment. In the examples of FIG. 13B, the dot 1301
represents the location of the marker 110 in relationship to the
probe 150 which is represented by the arrow 1305. As the user moves
the probe 150, the dot 1301 will move around the display, with the
center representing that the marker 110 is straight ahead. The
arrow 1305 will change width, length and direction to show the
orientation of the probe in the hand. For example, in the first
(top) instance the dot 1301 indicates that the marker 110 is to the
left of the probe 150 by 10.0 mm and the probe 150 is pointed away
from the marker 110. In the first (top) instance, if the dot 1301
stays fixed on the screen and the arrow 1305 appears to swing to
the left and touches the dot 1301, so that both are touching at the
dot's 1301 left location and display indicates 0.0 mm, the marker
110 is straight in line with the probe 150 but off center from when
the probe was zeroed. In the second (middle) instance the dot 1301
is shown to the right of the probe 150, indicated the marker 110 is
located to the right of the probe 150 by 2.4 mm, and the probe 150
is pointed generally toward the marker 110. In the third (bottom)
instance the dot 1301 is shown in the center of the display,
indicating that the marker 110 is straight ahead of the probe 150
at a distance of 0.0 mm. To get to the third instance (bottom) from
the first (top) instance, not only was the tip of the probe 150
swung over to the left to meet the marker 110 at 0.0 mm, but the
back end of the probe 150 would need to have moved to the left to
move the arrow and dot to the center of the display, to match to
original direction that the probe 150 was facing when zero
adjusted. Thus, these graphics illustrate spatial alignment of the
probe 150 independent of its location. These are merely example
depictions of a graphical representation of the distance and
direction to the marker 110, and other graphical, audible, tactile,
and/or other representations of the distance and/or direction are
contemplated.
Overview of Balancing and Measuring Processes
[0109] FIG. 14 is a flowchart 1400 illustrating operation of the
probe 150 including both balancing and measurement, according to
one embodiment. As with the processes above, in some embodiments
the process may be performed by the probe 150 alone, or it may be
performed by the probe 150 in communication with an external device
170. Depending on the embodiment, the method of FIG. 14 may include
fewer or additional blocks and the blocks may be performed in an
order that is different than illustrated,
[0110] In the example of FIG. 14, the probe 150 is initially
balanced at block 1405, at which point it is ready to make
measurements at block 1410. Block 1412 represents storage of the
zero adjust value or values, which are used to account for subtle
soft and hard iron interferences present based on the orientation
of the probe 150 and changes in the surrounding magnetic field
since balancing. In some embodiments, the zero adjust value or
values are stored immediately prior to moving the probe 150 into
the field of the marker 110. For example, when the zero adjust
function is selected, which could be prior to every measurement by
the probe, differential x, y, and z values are calculated by
subtracting the raw x, y, and z magnetometer output values from the
tip sensor pair from raw x, y, and z magnetometer output values
from the base sensor pair (e.g., see FIG. 15B). In some
embodiments, the zero adjust function will also store the yaw,
pitch, and roll values for the probe 150 (e.g., calculated with the
formulas of FIG. 13A) to record a location and/or orientation for
these differential values. In some embodiments, from that point
until the probe 150 is zero adjusted again, these values are used
to adjust the offset of the values. During probe balancing, the
zero adjust values are all zero.
[0111] In one example, when no marker 110 is within the range 153
of the probe 150, and if, for example, the range 153 is 50 mm, the
display should indicate that the distance to the marker 110 is
greater than 50.0 mm, XX distance, or otherwise indicate that no
marker 110 is within range. However, continuing this example, if
the probe 150 has not been zero adjusted, the probe 150 may display
fluctuating values indicating that a marker is approximately 40-50
mm from the probe 150, even though no marker 110 is within range.
This may be because the probe 150 is detecting small changes in the
magnetic field that are different than those present at the time or
location of balancing. After selecting the zero adjust function,
the probe 150 will correctly indicate that no marker 110 is within
range.
[0112] In some embodiments, the probe 150 includes a manual zero
adjust function where the operator can select when to perform the
zero adjust function. In some embodiments, the probe 150 may be
configured with an automatic zero adjust function, wherein the
microprocessor is configured with instructions that execute the
zero adjust function based on continuing population of all the
points on the balanced spheres 351, 352.
[0113] In some embodiments, the zero adjust values can be stored
during the balancing of the probe 150, but this would require
rotating the probe 150 one hundred and eighty times changing the
side movement in one degree increments of orientation on each
rotation for a total of 64800 degrees of rotation to cover every
possible point on the spheres 351, 352.
[0114] At block 1415, real time raw data is received from the
accelerometer and magnetometer of each of the tip sensor pair 151
and the base sensor pair 152. At block 1420, the raw data is
balanced using the calculated gain and offsets determined at block
1405. At block 1425 the magnetometer readings from the base sensor
pair 152 are subtracted from the magnetometer readings from the tip
sensor pair 151, and at block 1430 this difference is converted to
the actual distance of the marker 110 from the probe 150. At block
1435, the accelerometer data is calculated to determine the
orientation and movement of the probe 150.
[0115] In some embodiments, the movement of the probe 150 in the
magnetic field is used to determine the direction to the marker 110
from the probe. For example, the probe 150 may provide feedback
regarding direction in a manner similar to a metal detector. The
probe 150 may measure and display the distance to the marker and/or
may produce an output tone indicative of the field strength as the
probe 150 is moved toward and away from the marker 110. As in metal
detecting, the user may move the probe 150 direction feedback in
order to mentally determine the direction to the marker 110. As
presented above, in reference to FIG. 13B, in some embodiments,
this same concept can be implemented graphically. The graphics
displayed may not indicate an absolute heading but a graphical
representation of the direction in which the magnetic field
strength of the marker 110 will be the strongest.
[0116] In some embodiments, to get an absolute measured location
without any movement of the probe 150 may use at least two
magnetometer sensors located at the tip of the probe 150 which then
would triangulate the location of the marker 110. For example, with
two magnetometers positioned at the tip of the probe 150 and
separated by a distance, each magnetometer can be used to calculate
respective (and slightly different in most positions) distances to
the marker 110 according to the methods described herein. Then,
because the distance between the two magnetometers at the tip of
the probe 150 is known, the location of the marker 110 can be
triangulated.
[0117] At block 1440, the resulting location of the marker 110 is
communicated to the user. For example, the location data may be
provided on the probe itself, or may be sent to an external device
170, such as a smart phone or tablet with a compatible operating
system such as Android, Apple OS, or Microsoft Windows. The
wireless device can display the location and distance of the probe
sensing tip to the micro magnets enabling the surgeon to determine
the best path to tumor and tissue marker removal to minimize
discomfort and scarring to the patient. As noted above, the probe
150 and/or the wireless device can also have an audio cue as to the
distance to the tissue marker and as the probe gets closer the
audio pitch can change accordingly so that the surgeon can have
both visual and audio feedback as to where to operate on the
patient.
Example User Interfaces
[0118] FIGS. 15A through 15C provide examples of a graphical user
interface (GUI) 1500 that may be used on an external device 170 in
communication with the probe 150, or partially or fully on a
display of the probe 150. FIG. 15A is an example of a GUI display
before balancing and FIG. 15B is an example of a GUI display after
balancing. As shown in the example of FIGS. 15A and 15B, the GUI
may allow the user to run, zero, calibrate (e.g., including
balancing), start, or quit, as well as options for reconnecting,
accessing gauges, and/or viewing raw data. This interface is
provided for example only and is not intended to be limiting.
[0119] FIG. 15C shows examples of a GUI on an external device 170
and on a display 155 of the probe 150 (although, the display 155 is
shown removed from the probe in FIG. 15C). In the example, the
display 155 textually relates the measured distance to the marker
110 and graphically indicates the direction to the marker using an
arrow 1551. The GUI on the external device 170 textually indicates
the distance to the marker in a first portion 1510 and graphically
indicates the orientation of the probe 150 in a second portion
1505. The orientation of the probe is shown by providing graphical
representation of the yaw, pitch and roll of the probe 150 as
described in reference to FIGS. 13A and 13B.
[0120] Also shown in FIG. 15C is an example of a graphical
indicator 1599 that shows real-time raw data from the magnetometer
sensors. In this example, the graphical indicator 1599 includes
three sets of colored (shaded) bars. From left to right, the sets
of colored bars represent the base sensor pair X, Y, Z value, the
tip sensor pair X, Y, Z value and the differential between the two.
If the probe 150 is not in a magnetic field of a marker 110, the
first two sets of bars (those for the base sensor pair and the tip
sensor pair) should appear to be the same height, resulting in the
third set of bars having a height of zero (or, possibly not even
shown). If the probe 150 is not in a magnetic marker field and the
third set of bars (representing the differential between the base
sensor pair and the tip sensor pair) are drawn and/or any have a
bar height, then the probe 150 should be zero adjusted. After
pressing "Zero" button on the display screen or using the selection
button on the probe 150 the data will be zero adjusted as described
above. If the probe 150 is in a magnetic marker field, the third
set of bars will show a differential relative to the corrected
differential field strength of the marker, as in shown FIG. 15C.
During balancing only the three bars representing the differential
represent a relative gain value similar to the bars on the display
in FIG. 6C.
Example Uses of Magnetic Markers
[0121] In addition to marking potential breast cancer lesions as
discussed throughout this disclosure, the system discussed herein
may be utilized in a wide number of applications. For example, the
system could be used to mark lung nodules, lymph nodes, parathyroid
nodules, thyroid nodules, or GI lesions. For example, a
gastroenterologist might mark one or more biopsied colonic polyps
that are biopsied during a colonoscopy. A pulmonologist might mark
one or more lung or bronchial lesions found during a bronchoscopy.
A radiologist might mark one or more axillary lymph nodes in a
patient with breast cancer. This would facilitate removal of
cancerous lesions by a surgeon later.
[0122] Even when a lesion is not marked pre-operatively, a surgeon
that removes abnormal tissue might mark one or more parts of the
surgical specimen in order to direct the pathologist's attention to
the proper location. For example, when a mastectomy is performed, a
pathologist cannot microscopically examine the entire breast. If a
surgeon or radiologist marks the suspicious areas of the specimen
based on visual, palpable, or imaging-based guidance, this can
facilitate more accurate pathological examination.
[0123] Other uses may include locating surgical instruments and
sponges used in the operating room and locating magnetic antibody
and targeted molecular probes that can attach to cancer cells.
[0124] In some embodiments, the probe 150 can be attached to an
endoscopic or laparoscopic instrument. In some embodiments, the
probe 150 itself may be as simple as a magnet on the tip of a wire
or other probe, in which case the system can be used to show the
proximity between the magnet at the probe tip relative to an
implanted magnet. In that case, the detector could remain external
to the patient but would indicate by audio tone or display the
relative proximity or location of the probe tip magnet to an
implanted magnet. The display could show the relative location of
the two or more magnets as the probe is moved (like following the
path of a plane vs. a fixed object on a radar screen).
[0125] The system also has application outside of the medical
field, such as locating pipes that are submerged in the ground,
such as irrigation pipes; locating construction materials within
walls, such as wall stud locations; and locating various drilling
and mining equipment pipes where location relative to the Earth's
magnetic field is important. Similar to the medical embodiments
discussed above, magnetic markers may be placed in such locations
of interest and then located using a probe with both a base sensor
pair and a tip sensor pair.
Example Computer Architecture
[0126] As noted above, the probe 150 and/or the external device 170
may include various computing components, which may perform some or
all of the functions discussed herein. While the probe 150
typically includes fewer components than the external device 170 to
maintain a smaller size, it may include any of the components
and/or functionalities discussed below with reference to the device
170.
[0127] The device 170 may include, for example, a single computing
device, a computer server, or a combination of one or more
computing devices and/or computer servers. Depending on the
embodiment, the components illustrated in the device 170 may be
distributed amongst multiple devices, such as via a local area or
other network connection. In other embodiments the device 170 may
include fewer and/or additional components than are discussed
below.
[0128] The various devices disclosed herein, including the probe
150 and the external device 170, may be in communication via a
network, which may include any combination of communication
networks, such as one or more of the Internet, LANs, WANs, MANs,
etc., for example.
[0129] The device 170 includes one or more central processing units
("CPU"), which may each include one or more conventional or
proprietary microprocessor(s). The device 170 may further include
one or more memories/storage, such as random access memory ("RAM"),
for temporary storage of information, read only memory ("ROM") for
permanent storage of information, and/or a mass storage device,
such as a hard drive, diskette, or optical media storage device.
The memory/storage may store software code, or instructions, for
execution by the processor in order to cause the computing device
to perform certain operations, such as described herein.
[0130] The methods described herein may be executed on the
computing devices in response to execution of software instructions
or other executable code read from a tangible computer readable
medium. A computer readable medium is a data storage device that
can store data that is readable by a computer system. Examples of
computer readable mediums include read-only memory, random-access
memory, other volatile or non-volatile memory devices, CD-ROMs,
magnetic tape, flash drives, and optical data storage devices.
[0131] The various illustrative logical blocks, modules, and
algorithm steps described in connection with the embodiments
disclosed herein, especially those disclosed with reference to the
microprocessor 157 and the probe 150 can be implemented as
electronic hardware, such as a digital signal processor (DSP), an
application specific integrated circuit (ASIC), a field
programmable gate array (FPGA) or other programmable logic device,
discrete gate or transistor logic, discrete hardware components, or
any combination thereof designed to perform the functions described
herein. Such processes may be embodied directly in hardware, in a
software module executed by a processor, or in a combination of the
two. A software module can reside in RAM memory, flash memory, ROM
memory, EPROM memory, EEPROM memory, registers, hard disk, a
removable disk, a CD-ROM, or any other form of computer-readable
storage medium known in the art. An exemplary storage medium can be
coupled to the processor such that the processor can read
information from, and write information to, the storage medium. In
the alternative, the storage medium can be integral to the
processor.
[0132] The exemplary device 170 may include one or more input
devices and interfaces, such as a keyboard, trackball, mouse,
drawing tablet, joystick, game controller, touchscreen (e.g.,
capacitive or resistive touchscreen), touchpad, accelerometer,
and/or printer, for example. The computing device 170 may also
include one or more displays (also referred to herein as a display
screen), which may also be one of the I/O devices in the case of a
touchscreen, for example. Display devices may include LCD, OLED, or
other thin screen display surfaces, a monitor, television,
projector, or any other device that visually depicts user
interfaces and data to viewers. The device 170 may also include one
or more multimedia devices, such as camera, speakers, video cards,
graphics accelerators, and microphones, for example.
[0133] The device 170 may also include one or more modules. In
general, the word "module," as used herein, refers to logic
embodied in hardware or firmware, or to a collection of software
instructions, possibly having entry and exit points, written in any
programming language, such as, for example, Java, Python, Perl,
Lua, C, C++, C#, etc. A software module may be compiled and linked
into an executable program, installed in a dynamic link library, or
may be written in an interpreted programming language such as, for
example, BASIC, Perl, or Python. It will be appreciated that
software modules may be callable from other modules or from
themselves, and/or may be invoked in response to detected events or
interrupts. Software modules configured for execution on computing
devices may be provided on a computer readable medium, such as a
compact disc, digital video disc, flash drive, or any other
tangible medium. Such software code may be stored, partially or
fully, on a memory device of the executing computing device, such
as the device 170, for execution by the computing device. It will
be further appreciated that hardware modules may be comprised of
connected logic units, such as gates and flip-flops, and/or may be
comprised of programmable units, such as programmable gate arrays
or processors.
Variations to the Disclosed Embodiments
[0134] Conditional language, such as, among others, "can," "could,"
"might," or "may," unless specifically stated otherwise, or
otherwise understood within the context as used, is generally
intended to convey that certain embodiments include, while other
embodiments do not include, certain features, elements and/or
steps. Thus, such conditional language is not generally intended to
imply that features, elements and/or steps are in any way required
for one or more embodiments or that one or more embodiments
necessarily include logic for deciding, with or without user input
or prompting, whether these features, elements and/or steps are
included or are to be performed in any particular embodiment.
[0135] It should be emphasized that many variations and
modifications may be made to the above-described embodiments, the
elements of which are to be understood as being among other
acceptable examples. All such modifications and variations are
intended to be included herein within the scope of this disclosure.
The foregoing description details certain embodiments of the
invention. It will be appreciated, however, that no matter how
detailed the foregoing appears in text, the invention can be
practiced in many ways. As is also stated above, it should be noted
that the use of particular terminology when describing certain
features or aspects of the invention should not be taken to imply
that the terminology is being re-defined herein to be restricted to
including any specific characteristics of the features or aspects
of the invention with which that terminology is associated. The
scope of the invention should therefore be construed in accordance
with the appended claims and any equivalents thereof.
* * * * *
References