U.S. patent application number 13/587328 was filed with the patent office on 2013-10-31 for magnetic field detector for implantable medical devices.
This patent application is currently assigned to Medtronic, Inc.. The applicant listed for this patent is Michael W. Newman. Invention is credited to Michael W. Newman.
Application Number | 20130289663 13/587328 |
Document ID | / |
Family ID | 49477950 |
Filed Date | 2013-10-31 |
United States Patent
Application |
20130289663 |
Kind Code |
A1 |
Newman; Michael W. |
October 31, 2013 |
MAGNETIC FIELD DETECTOR FOR IMPLANTABLE MEDICAL DEVICES
Abstract
A torque sensor is described that detects the presence of an
external magnetic field based on a torque imposed on a conductive
coil of the sensor. The torque sensor includes a conductive coil
forming a loop having one or more turns and a plurality of sensing
elements adjacent to portions of the conductive coil. The sensing
elements are configured to generate an output that changes as a
function of a force imposed on the first sensing element by the
respective portions of the conductive coil.
Inventors: |
Newman; Michael W.; (Dublin,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Newman; Michael W. |
Dublin |
CA |
US |
|
|
Assignee: |
Medtronic, Inc.
|
Family ID: |
49477950 |
Appl. No.: |
13/587328 |
Filed: |
August 16, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61639159 |
Apr 27, 2012 |
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Current U.S.
Class: |
607/62 ;
324/301 |
Current CPC
Class: |
A61N 1/3718
20130101 |
Class at
Publication: |
607/62 ;
324/301 |
International
Class: |
G01R 33/24 20060101
G01R033/24; A61N 1/36 20060101 A61N001/36 |
Claims
1. A sensor comprising: a conductive coil forming a loop having one
or more turns; a first sensing element adjacent to a first portion
of the conductive coil and configured to generate an output that
changes as a function of a force imposed on the first sensing
element by the first portion of the conductive coil; a second
sensing element adjacent to the first portion of the conductive
coil and configured to generate an output that changes as a
function of a force imposed on the second sensing element by the
first portion of the conductive coil, wherein the first portion of
the conductive coil is located between the first sensing element
and the second sensing element; a third sensing element adjacent to
a second portion of the conductive coil and configured to generate
an output that changes as a function of a force imposed on the
third sensing element by the second portion of the conductive coil,
wherein the second portion of the conductive coil is located on the
opposite side of the loop as the first portion of the conductive
coil; and a fourth sensing element adjacent to the second portion
of the conductive coil and configured to generate an output that
changes as a function of a force imposed on the fourth sensing
element by the second portion of the conductive coil, wherein the
second portion of the conductive coil is located between the third
sensing element and the fourth sensing element.
2. The sensor of claim 1, wherein the conductive coil comprises a
first conductive coil, the sensor further comprising: a second
conductive coil forming a second loop having one or more turns, the
second conductive coil orthogonal to the first conductive coil; a
fifth sensing element adjacent to a first portion of the second
conductive coil and configured to generate an output that changes
as a function of a force imposed on the fifth sensing element by
the first portion of the second conductive coil; a sixth sensing
element adjacent to the first portion of the second conductive coil
and configured to generate an output that changes as a function of
a force imposed on the sixth sensing element by the first portion
of the second conductive coil, wherein the first portion of the
second conductive coil is located between the fifth sensing element
and the sixth sensing element; a seventh sensing element adjacent
to a second portion of the second conductive coil and configured to
generate an output that changes as a function of a force imposed on
the seventh sensing element by the second portion of the second
conductive coil, wherein the second portion of the second
conductive coil is located on the opposite side of the second loop
than the first portion of the second conductive coil; and an eighth
sensing element adjacent to the second portion of the second
conductive coil and configured to generate an output that changes
as a function of a force imposed on the eighth sensing element by
the second portion of the second conductive coil, wherein the
second portion of the second conductive coil is located between the
seventh sensing element and the eighth sensing element.
3. The sensor of claim 2, further comprising a housing enclosing
the first and second conductive coils and the first, second, third,
fourth, fifth, six, seventh and eighth sensing elements.
4. The sensor of claim 2, further comprising: a first housing
enclosing the first conductive coil and the first, second, third,
and fourth sensing elements; and a second housing enclosing the
second conductive coil and the fifth, six, seventh and eighth
sensing elements.
5. The sensor of claim 1, wherein the sensing elements comprise
piezoelectric sensing elements.
6. The sensor of claim 1, wherein the first and second portions of
the conductive coil reside along a first axis of the loop, the
sensor further comprising: a ninth sensing element adjacent to a
third portion of the conductive coil and configured to generate an
output that changes as a function of a force imposed on the ninth
sensing element by the third portion of the conductive coil; a
tenth sensing element adjacent to the third portion of the
conductive coil and configured to generate an output that changes
as a function of a force imposed on the tenth sensing element by
the third portion of the conductive coil, wherein the third portion
of the conductive coil is located between the tenth sensing element
and the eleventh sensing element; an eleventh sensing element
adjacent to a fourth portion of the conductive coil and configured
to generate an output that changes as a function of a force imposed
on the eleventh sensing element by the fourth portion of the
conductive coil, wherein the fourth portion of the conductive coil
is located on the opposite side of the loop as the third portion of
the conductive coil; and a twelfth sensing element adjacent to the
fourth portion of the conductive coil and configured to generate an
output that changes as a function of a force imposed on the twelfth
sensing element by the fourth portion of the conductive coil,
wherein the fourth portion of the conductive coil is located
between the eleventh sensing element and the twelfth sensing
element, wherein the third and fourth portions of the conductive
coil reside along a second axis of the loop.
7. (canceled)
8. An implantable medical device comprising: a torque sensor that
includes: a conductive coil forming a loop having one or more
turns; a first sensing element adjacent to a first portion of the
conductive coil and configured to generate an output that changes
as a function of a force imposed on the first sensing element by
the first portion of the conductive coil; a second sensing element
adjacent to the first portion of the conductive coil and configured
to generate an output that changes as a function of a force imposed
on the second sensing element by the first portion of the
conductive coil, wherein the first portion of the conductive coil
is located between the first sensing element and the second sensing
element; a third sensing element adjacent to a second portion of
the conductive coil and configured to generate an output that
changes as a function of a force imposed on the third sensing
element by the second portion of the conductive coil, wherein the
second portion of the conductive coil is located on the opposite
side of the loop as the first portion of the conductive coil; and a
fourth sensing element adjacent to the second portion of the
conductive coil and configured to generate an output that changes
as a function of a force imposed on the fourth sensing element by
the second portion of the conductive coil, wherein the second
portion of the conductive coil is located between the third sensing
element and the fourth sensing element; and a control module
configured to analyze the output of the torque sensor to detect the
presence of an external magnetic field and control operation of the
implantable medical device based on the analysis.
9. The implantable medical device of claim 8, wherein the control
module is further configured to transition operation of the
implantable medical device to a magnetic resonance imaging (MRI)
operating mode in response to detecting the presence of the
external magnetic field.
10. The implantable medical device of claim 8, wherein the control
module is further configured to supply a current to the conductive
coil of the torque sensor to generate an internal magnetic field
that interacts with the external magnetic field to produce the
torque imposed on the conductive coil.
11. The implantable medical device of claim 10, wherein the control
module periodically supplies the current to the conductive coil in
accordance with a predefined duty cycle.
12. The implantable medical device of claim 10, further comprising
a magnetic field strength sensor separate from the torque sensor,
the magnetic field strength sensor configured to output a signal
that varies as a function of the strength of the external magnetic
field, wherein the control module supplies the current to the
conductive coil of the torque sensor in response to detecting that
the strength of the external magnetic field exceeds a strength
threshold.
13. The implantable medical device of claim 12, wherein the control
module is configured to determine if a torque imposed on the
conductive coil exceeds a threshold torque value, detect presence
of a static magnetic resonance imaging (MRI) field when the torque
exceeds the threshold torque value, and transition operation of the
implantable medical device to an MRI operating mode in response to
detecting the presence of the external magnetic field.
14. The implantable medical device of claim 13, wherein the control
module is configured to detect presence of a telemetry head magnet
when the torque imposed on the conductive coil does not exceed the
threshold torque value and transition operation of the implantable
medical device to a telemetry head operating mode in response to
detecting the presence of the external magnetic field.
15. The implantable medical device of claim 13, wherein the control
module is configured to determine that the torque imposed on the
conductive coil exceeds a threshold torque value when a first force
on the first sensing element and a second force on the third
sensing element are detected at substantially the same time and
that each of the first force and the second force exceeds a
threshold force value.
16. The implantable medical device of claim 8, wherein the
conductive coil of the torque sensor comprises a first conductive
coil, the torque sensor further comprising: a second conductive
coil forming a second loop having one or more turns, the second
conductive coil orthogonal to the first conductive coil; a fifth
sensing element adjacent to a first portion of the second
conductive coil and configured to generate an output that changes
as a function of a force imposed on the fifth sensing element by
the first portion of the second conductive coil; a sixth sensing
element adjacent to the first portion of the second conductive coil
and configured to generate an output that changes as a function of
a force imposed on the sixth sensing element by the first portion
of the second conductive coil, wherein the first portion of the
second conductive coil is located between the fifth sensing element
and the sixth sensing element; a seventh sensing element adjacent
to a second portion of the second conductive coil and configured to
generate an output that changes as a function of a force imposed on
the seventh sensing element by the second portion of the second
conductive coil, wherein the second portion of the second
conductive coil is located on the opposite side of the second loop
than the first portion of the second conductive coil; and an eighth
sensing element adjacent to the second portion of the second
conductive coil and configured to generate an output that changes
as a function of a force imposed on the eighth sensing element by
the second portion of the second conductive coil, wherein the
second portion of the second conductive coil is located between the
seventh sensing element and the eighth sensing element.
17. The implantable medical device of claim 16, wherein the torque
sensor further comprises a housing enclosing the first and second
conductive coils and the first, second, third, fourth, fifth, six,
seventh and eighth sensing elements.
18. The implantable medical device of claim 16, wherein the torque
sensor further comprises: a first housing enclosing the first
conductive coil and the first, second, third, and fourth sensing
elements; and a second housing enclosing the second conductive coil
and the fifth, six, seventh and eighth sensing elements.
19. The implantable medical device of claim 8, wherein the first
and second portions of the conductive coil of the torque sensor
reside along a first axis of the loop, the torque sensor further
comprising: a ninth sensing element adjacent to a third portion of
the conductive coil and configured to generate an output that
changes as a function of a force imposed on the ninth sensing
element by the third portion of the conductive coil; a tenth
sensing element adjacent to the third portion of the conductive
coil and configured to generate an output that changes as a
function of a force imposed on the tenth sensing element by the
third portion of the conductive coil, wherein the third portion of
the conductive coil is located between the tenth sensing element
and the eleventh sensing element; an eleventh sensing element
adjacent to a fourth portion of the conductive coil and configured
to generate an output that changes as a function of a force imposed
on the eleventh sensing element by the fourth portion of the
conductive coil, wherein the fourth portion of the conductive coil
is located on the opposite side of the loop as the third portion of
the conductive coil; and a twelfth sensing element adjacent to the
fourth portion of the conductive coil and configured to generate an
output that changes as a function of a force imposed on the twelfth
sensing element by the fourth portion of the conductive coil,
wherein the fourth portion of the conductive coil is located
between the eleventh sensing element and the twelfth sensing
element, wherein the third and fourth portions of the conductive
coil reside along a second axis of the loop.
20. The implantable medical device of claim 8, further comprising a
therapy module configured to deliver electrical stimulation therapy
to a patient, wherein the control module adjusts operation of the
therapy module based on the detection.
21. An implantable medical system comprising: at least one
implantable medical lead that includes one or more electrodes; and
an implantable medical device coupled to the at least one
implantable medical lead and configured to transmit a therapy via
the one or more electrodes of the at least one implantable medical
lead, the implantable medical device including: a torque sensor
that includes: a conductive coil forming a loop having one or more
turns; a first sensing element adjacent to a first portion of the
conductive coil and configured to generate an output that changes
as a function of a force imposed on the first sensing element by
the first portion of the conductive coil; a second sensing element
adjacent to the first portion of the conductive coil and configured
to generate an output that changes as a function of a force imposed
on the second sensing element by the first portion of the
conductive coil, wherein the first portion of the conductive coil
is located between the first sensing element and the second sensing
element; a third sensing element adjacent to a second portion of
the conductive coil and configured to generate an output that
changes as a function of a force imposed on the third sensing
element by the second portion of the conductive coil, wherein the
second portion of the conductive coil is located on the opposite
side of the loop as the first portion of the conductive coil; and a
fourth sensing element adjacent to the second portion of the
conductive coil and configured to generate an output that changes
as a function of a force imposed on the fourth sensing element by
the second portion of the conductive coil, wherein the second
portion of the conductive coil is located between the third sensing
element and the fourth sensing element; a control module configured
to analyze the output of the torque sensor to detect the presence
of an external magnetic field; and a therapy module configured to
deliver electrical stimulation therapy to a patient, wherein the
control module adjusts operation of the therapy module based on the
detection.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/639,159, filed on Apr. 27, 2012, the content of
which is incorporated herein by reference in its entirety.
TECHNICAL FIELD
[0002] The disclosure relates to sensors and techniques for
detecting magnetic fields, such as magnetic fields generated by
magnetic resonance imaging (MRI) devices.
BACKGROUND
[0003] Magnetic resonance imaging (MRI) is a medical imaging
technique used to visualize detailed internal structures of a
patient. A patient is placed at least partially within an MRI
device during an MRI scan. The MRI device may generate a variety of
magnetic and electromagnetic fields, including a static magnetic
field (hereinafter "static MRI field"), gradient magnetic fields,
and radio frequency (RF) fields. The static MRI field may be
generated by a primary magnet within the MRI device and may be
present prior to initiation of the MRI scan. The gradient magnetic
fields may be generated by electromagnets and may be present during
the MRI scan. The RF magnetic fields may be generated by
transmitting/receiving coils and may be present during the MRI
scan. If the patient undergoing the MRI scan has an implantable
medical device (IMD), the various fields produced by the MRI device
may have undesirable effects on the IMD.
SUMMARY
[0004] To reduce the effects that the various fields produced
during an MRI scan have on the IMD, some IMDs may be programmed to
an MRI-compatible mode of operation (also referred to herein as an
MRI operating mode or MRI mode) during the MRI scan. Typically, a
clinician programs the IMD using a programming device at some point
in time prior to a scheduled MRI scan. After the patient receives
the MRI scan, the clinician may reprogram the IMD back to normal
settings. The reprogramming process undertaken prior to, and after,
scanning a patient with an IMD may be inconvenient to both the
patient and the clinician. In some scenarios, a patient having an
IMD may require an emergency MRI scan. Such scenarios may not
provide an adequate window of time around the MRI scan to allow for
reprogramming of the IMD.
[0005] An IMD according to the present disclosure may automatically
detect the presence of an MRI device (e.g., by detection of the
static MRI field) prior to initiation of an MRI scan. For example,
the IMD may detect the MRI device based on one or both of a
strength of the magnetic field and/or a torque caused the magnetic
field on a torque sensor. Furthermore, the IMD may differentiate
the static MRI field from other magnetic fields, such as magnetic
fields generated by handheld magnetic devices, including telemetry
head magnets, thus improving the specificity with which the IMD
identifies the source of a detected magnetic field based at least
in part on the torque imposed by the magnetic field.
[0006] In response to detection of the static MRI field, the IMD
may transition from a normal operating mode to an MRI operating
mode prior to initiation of the MRI scan. While operating in the
MRI mode, the IMD may be configured such that it is less
susceptible to being adversely affected by the gradient and RF
fields emitted by the MRI device. The capability of the IMD to
automatically detect the MRI device and transition to the MRI mode
may eliminate the need for manual reprogramming of the IMD prior to
the MRI scan, or provide a failsafe reprogramming mode in the event
manual reprogramming is not undertaken.
[0007] In one example, this disclosure is directed to a sensor that
includes a conductive coil forming a loop having one or more turns,
a first sensing element adjacent to a first portion of the
conductive coil and configured to generate an output that changes
as a function of a force imposed on the first sensing element by
the first portion of the conductive coil, and a second sensing
element adjacent to the first portion of the conductive coil and
configured to generate an output that changes as a function of a
force imposed on the second sensing element by the first portion of
the conductive coil. The first portion of the conductive coil is
located between the first sensing element and the second sensing
element. The sensor also includes a third sensing element adjacent
to a second portion of the conductive coil and configured to
generate an output that changes as a function of a force imposed on
the third sensing element by the second portion of the conductive
coil and a fourth sensing element adjacent to the second portion of
the conductive coil and configured to generate an output that
changes as a function of a force imposed on the fourth sensing
element by the second portion of the conductive coil. The second
portion of the conductive coil is located on the opposite side of
the loop as the first portion of the conductive coil. Also, the
second portion of the conductive coil is located between the third
sensing element and the fourth sensing element.
[0008] In another example, this disclosure is directed to an
implantable medical device comprising a torque sensor and a control
module configured to analyze the output of the torque sensor to
detect the presence of an external magnetic field and control
operation of the implantable medical device based on the analysis.
The torque sensor includes a conductive coil forming a loop having
one or more turns, a first sensing element adjacent to a first
portion of the conductive coil and configured to generate an output
that changes as a function of a force imposed on the first sensing
element by the first portion of the conductive coil, and a second
sensing element adjacent to the first portion of the conductive
coil and configured to generate an output that changes as a
function of a force imposed on the second sensing element by the
first portion of the conductive coil. The first portion of the
conductive coil is located between the first sensing element and
the second sensing element. The sensor also includes a third
sensing element adjacent to a second portion of the conductive coil
and configured to generate an output that changes as a function of
a force imposed on the third sensing element by the second portion
of the conductive coil and a fourth sensing element adjacent to the
second portion of the conductive coil and configured to generate an
output that changes as a function of a force imposed on the fourth
sensing element by the second portion of the conductive coil. The
second portion of the conductive coil is located on the opposite
side of the loop as the first portion of the conductive coil. Also,
the second portion of the conductive coil is located between the
third sensing element and the fourth sensing element.
[0009] This summary is intended to provide an overview of the
subject matter described in this disclosure. It is not intended to
provide an exclusive or exhaustive explanation of the techniques as
described in detail within the accompanying drawings and
description below. Further details of one or more examples are set
forth in the accompanying drawings and the description below. Other
features, objects, and advantages will be apparent from the
description and drawings, and from the statements provided
below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a conceptual diagram illustrating a magnetic
resonance imaging (MRI) environment that includes an MRI
device.
[0011] FIG. 2 is a conceptual diagram of an example implantable
medical system.
[0012] FIG. 3 shows a schematic view of illustrating components of
an IMD.
[0013] FIGS. 4A and 4B illustrate an example magnetic field torque
sensor.
[0014] FIGS. 5A and 5B illustrate another example magnetic field
torque sensor.
[0015] FIG. 6 is a block diagram that illustrates an example
control module of an IMD in further detail.
[0016] FIG. 7 is a flow diagram illustrating an example method of
operation of an IMD including a torque sensor in accordance with
this disclosure.
[0017] FIG. 8 is a flow diagram illustrating an example method of
operation of an IMD in accordance with this disclosure.
[0018] FIG. 9 is a flow diagram illustrating another example method
of operation of an IMD in accordance with this disclosure.
DETAILED DESCRIPTION
[0019] FIG. 1 is a conceptual diagram illustrating a magnetic
resonance imaging (MRI) environment 10 that includes an MRI device
16. MRI device 16 may include a patient table on which patient 12
is placed prior to and during an MRI scan. The patient table is
adjusted to position at least a portion of patient 12 within a bore
of MRI device 16 (the "MRI bore"). While positioned within the MRI
bore, the portion of patient 12 being scanned is subjected to a
number of magnetic and RF fields to produce images of body
structures for diagnosing injuries, diseases, and/or disorders.
[0020] MRI device 16 includes a scanning portion that houses a
primary magnet of MRI device 16 that generates a static MRI field.
The static MRI field is a large non time-varying magnetic field
that is typically always present around MRI device 16 whether or
not an MRI procedure is in progress. MRI device 16 also includes a
plurality of gradient magnetic field coils that generate gradient
magnetic fields. Gradient magnetic fields are pulsed magnetic
fields that are typically only present while the MRI procedure is
in progress. MRI device further includes one or more RF coils that
generate RF fields. RF fields are pulsed high frequency fields that
are also typically only present while the MRI procedure is in
progress. Although the structure of MRI devices may vary, it is
contemplated that the techniques used herein to detect the static
MRI field, which is generally applicable to a variety of other MRI
device configurations, such as open-sided MRI devices or other
configurations.
[0021] The magnitude, frequency or other characteristic of the
static MRI field, gradient magnetic fields and RF fields may vary
based on the type of MRI device 16 producing the field or the type
of MRI procedure being performed. A 1.5 T MRI device, for example,
will produce a static magnetic field of approximately 1.5 Tesla and
have a corresponding RF frequency of approximately 64 megahertz
(MHz) while a 3.0 T MRI device will produce a static magnetic field
of approximately 3.0 Tesla and have a corresponding RF frequency of
approximately 128 MHz. However, other MRI devices may generate
different fields that may be detected in accordance with the
techniques of this disclosure.
[0022] Patient 12 is implanted with an implantable medical system
14. In one example, implantable medical system 14 may include an
IMD connected to one or more leads. The IMD may be an implantable
cardiac device that senses electrical activity of a heart of
patient 12 and/or provides electrical stimulation therapy to the
heart of patient 12. For example, the IMD may be an implantable
pacemaker, implantable cardioverter defibrillator (ICD), cardiac
resynchronization therapy defibrillator (CRT-D), cardioverter
device, or combinations thereof. The IMD may alternatively be a
non-cardiac implantable device, such as an implantable
neurostimulator or other device that provides electrical
stimulation therapy or other therapy such as drug delivery.
[0023] Some or all of the various types of fields produced by MRI
device 16 may have undesirable effects on implantable medical
system 14. In one example, the gradient magnetic fields and/or the
RF fields generated during the MRI procedure may induce energy on
the conductors of the leads (e.g., in the form of a current). The
induced energy on the leads may be conducted to the IMD and
inappropriately detected as physiological signals, a phenomenon
often referred to as oversensing. The detection of the induced
energy on the leads as physiological signals may result in the IMD
delivering therapy when it is not desired (e.g., triggering a
pacing pulse) or withholding therapy when it is desired (e.g.,
inhibiting a pacing pulse).
[0024] Upon detecting the presence of MRI device 16, the IMD is
configured to operate in an MRI operating mode or MRI mode.
Operation of the IMD in the "MRI mode" may refer to an operating
state of the IMD that it is less susceptible to being adversely
affected by the gradient magnetic fields and RF fields emitted by
MRI device 16 than the "normal mode" of operation. As such,
operation of the IMD in the MRI mode may reduce, and possibly
eliminate, the undesirable effects that may be caused by the
gradient magnetic fields and RF fields of MRI device 16. When
operating in the MRI mode, the IMD is configured to operate with
different functionality compared to the "normal mode" of operation.
In one example, the IMD may operate in either a non-pacing mode
(e.g., sensing only mode) or in an asynchronous pacing mode while
operating in the MRI mode. The IMD may also turn off high voltage
therapy (e.g., defibrillation therapy) while operating in the MRI
mode. The IMD may also turn off telemetry functionality, e.g.,
wakeup or other telemetry activity, during operation in the MRI
mode. In some examples, the MRI mode may use other sensors (e.g., a
pressure or acceleration sensor), different sense circuitry, or
different sense algorithms to more accurately detect cardiac
activity of the patient. Other adjustments may be made as described
herein. In this manner, patient 12 having implanted medical system
14 may receive an MRI procedure with a reduced likelihood of
interference with operation of the IMD.
[0025] The IMD may transition to the MRI mode automatically in
response to detecting MRI device 16. In accordance with the
techniques of this disclosure, the IMD may include a magnetic field
torque sensor configured to detect the presence of the static MRI
field generated by the primary magnet of MRI device 16. Details of
example magnetic field torque sensors will be described herein. In
some instances, the IMD may detect the presence of the static MRI
field based the magnitude of the magnetic field as well as the
torque.
[0026] After the MRI procedure is complete, the IMD may transition
back to the normal mode of operation, e.g., turn high voltage
therapy back on and/or have pacing that is triggered and/or
inhibited as a function of sensed signals. The IMD may
automatically revert to the normal mode of operation in response to
no longer detecting the presence of MRI device 16, after expiration
of a timer, or in response to some other predefined criteria, or a
combination thereof. Alternatively, the IMD may be manually
programmed into the normal mode of operation via a command received
from an external device, such as programming device, via wireless
telemetry.
[0027] FIG. 2 is a conceptual diagram of an example implantable
medical system 20, which may correspond with implantable medical
system 14 of FIG. 1, in further detail. Implantable medical system
20 is also illustrated in conjunction with a programmer 22 and
telemetry head 24. Implantable medical system 20 includes an IMD 26
connected to leads 28 and 30.
[0028] IMD 26 may provide electrical stimulation to heart 32 via
leads 28 and 30. For example, IMD 26 may be an implantable
pacemaker, implantable cardioverter defibrillator (ICD), cardiac
resynchronization therapy defibrillator (CRT-D), cardioverter
device, or combinations thereof. IMD 26 includes a housing 34 and a
connector block 36. Housing 34 and connector block 36 may form a
hermetic seal that protects components of IMD 26. In some examples,
housing 34 may comprise a metal or other biocompatible enclosure
having separate halves. Connecter block 36 may include electrical
feedthroughs, through which electrical connections are made between
conductors within leads 28 and 30 and electronic components
included within housing 34. As will be described in further detail
herein, housing 34 may house one or more processors, memories,
transmitters, receivers, sensors, sensing circuitry, therapy
circuitry and other appropriate components. Housing 34 is
configured to be implanted in a patient, such as patient 12.
[0029] Leads 28 and 30 each include one or more electrodes. In the
example illustrated in FIG. 2, leads 28 and 30 each include a
respective tip electrodes 38 and 40 and ring electrodes 42 and 44
located near a distal end of their respective leads 28 and 30. When
implanted, tip electrodes 38 and 40 and/or ring electrodes 42 and
44 are placed relative to or in a selected tissue, muscle, nerve or
other location within the patient 12. In the example illustrated in
FIG. 2, tip electrodes 38 and 40 are extendable helically shaped
electrodes to facilitate fixation of the distal end of leads 28 and
30 to the target location within patient 12. In this manner, tip
electrodes 38 and 40 are formed to define a fixation mechanism. In
other embodiments, one or both of tip electrodes 38 and 40 may be
formed to define fixation mechanisms of other structures. In other
instances, leads 28 and 30 may include a fixation mechanism
separate from tip electrode 38 and 40. Fixation mechanisms can be
any appropriate type, including a grapple mechanism, a helical or
screw mechanism, a drug-coated connection mechanism in which the
drug(s) serves to reduce infection and/or swelling of the tissue,
or other attachment mechanism.
[0030] One or more conductors (not shown in FIG. 2) extend within
leads 28 and 30 from connector block 36 along the length of the
lead to engage respective tip electrodes 38 and 40 and ring
electrode 42 and 44. In this manner, each of electrodes 38, 40, 42
and 44 is electrically coupled to a respective conductor within its
associated lead body. For example, a first electrical conductor can
extend along the length of the body of lead 28 from connector block
36 and electrically couple to tip electrode 38 and a second
electrical conductor can extend along the length of the body of
lead 28 from connector block 36 and electrically couple to ring
electrode 42. The respective conductors may electrically couple to
circuitry, such as a therapy module or a sensing module, of IMD 26
via connections in connector block 36. The electrical conductors
transmit therapy from a therapy module within IMD 26 to one or more
of electrodes 38, 40, 42, and 44 and transmit sensed electrical
signals from one or more of electrodes 38, 40, 42, and 44 to the
sensing module within IMD 26.
[0031] IMD 26 may communicate with programmer 22 using any of a
variety of wireless communication techniques known in the art.
Examples of communication techniques may include, for example, low
frequency inductive telemetry or RF telemetry, although other
techniques are also contemplated. Programmer 22 may be a handheld
computing device, desktop computing device, a networked computing
device, or other computing device configured to communicate with
IMD 26. Programmer 22 may include a non-transitory
computer-readable storage medium having instructions that, when
executed, cause a processor of programmer 22 to provide the
functions attributed to programmer 22 in the present
disclosure.
[0032] Programmer 22 retrieves data from IMD 26. Data retrieved
from IMD 26 using programmer 22 may include cardiac EGMs stored by
IMD 26 that indicate electrical activity of heart 32. Data may also
include marker channel data that indicates the occurrence and
timing of sensing, diagnosis, and therapy events associated with
IMD 26. Additionally, data may include information regarding the
performance or integrity of IMD 26 or other components of
implantable medical system 20, such as leads 28 and 30, or a power
source of IMD 26. Programmer 22 may also transfer data to IMD 26.
Data transferred to IMD 26 using programmer 22 may include, for
example, values for operational parameters, electrode selections
used to deliver electrical stimulation, waveform selections used
for electrical stimulation, configuration parameters for detection
algorithms, or the other data. Although not illustrated in FIG. 2,
IMD 26 may communicate with other devices not implanted within
patient 12, such as a patient monitor.
[0033] Programmer 22 may, in one example, communicate with IMD 26
via a telemetry head 24. Telemetry head 24 may include a telemetry
head magnet 46. Telemetry head magnet 46 generates a magnetic field
("telemetry head field"). IMD 26 may detect the presence of
telemetry head magnet 46 (e.g., by detecting the telemetry head
field) and may operate in a telemetry head mode in response to
detection of telemetry head magnet 46. Operation of IMD 26 in the
"telemetry head mode" may describe a typical operating state of IMD
26 in response to detection of telemetry head magnet 46, and may be
different from the MRI mode and the normal mode. For example, after
IMD 26 detects telemetry head magnet 46, IMD 26 may enter the
telemetry head mode and may communicate with programmer 122 or
other external device by wireless telemetry via telemetry head 24
or RF telemetry or other telemetry technique, to transfer data to
programmer 22 and/or receive data from programmer 22. IMD 26 may
also disable tachycardia detection when operating in the telemetry
head mode, but may still keep sensing functionality enabled.
[0034] In some examples, telemetry head magnet 46 may include a
permanent magnet. The permanent magnet may have an area that is
approximately equal to the area of IMD 26 so that when telemetry
head 24 is placed over top of IMD 26, the permanent magnet may
substantially cover IMD 26. In some examples, telemetry head magnet
46 may include handheld magnetic devices other than a permanent
magnet, such as an electromagnet that generates the telemetry head
field.
[0035] As described above with respect to FIG. 1, IMD 26 also
operates in the MRI mode in response to detecting the static
magnetic field associated with MRI device 16. As such, IMD 26 may
operate in different operating modes in response to detecting
magnetic fields from different sources, e.g., operate in the MRI
mode in response to detecting the static MRI field and operate in
the telemetry head mode in response to detecting the telemetry head
field. To this end, IMD 26 may be configured to differentiate
between magnetic fields from the different sources based on
characteristics associated with the magnetic fields.
[0036] Typically, the strength (or magnitude) of the static
magnetic field associated with MRI device 16 is much larger than
the strength (or magnitude) of the telemetry head magnet 46 or
other magnetic fields patient 12 encounters. MRI device 16 may have
a static magnetic field that has a magnitude that is larger than
approximately 0.5 Tesla. The strength of telemetry head magnet 46,
on the other hand, is typically in the millitesla (mT) range. For
example, telemetry head magnet 46 may have a magnitude in the range
of approximately 10 mT to 100 mT. In accordance with the techniques
of this disclosure, IMD 26 may include a magnetic field torque
sensor to distinguish the telemetry head field (or other magnetic
fields typically encountered by patient 12) from the static MRI
field based on output from the magnetic field torque sensor.
[0037] Additionally, other devices that generate magnetic fields
similar to telemetry head magnet 46 may come in proximity to IMD
26. Such devices may include, but are not limited to, permanent
magnets and electromagnets other than the patient magnet. Telemetry
head magnet 46 may, therefore, generally represent any magnetic
device (e.g., handheld magnetic device) or other magnetic field
source that generates a magnetic field similar to that of telemetry
head magnet 46. In general, most "environmental" magnetic field
sources, such as welders, electric motors, and theft detection
gates, to name a few, will exhibit a magnetic field similar to that
of telemetry head magnet 46, while few magnetic field sources may
exhibit a magnetic field in scale as large as the permanent magnet
of MRI device 16.
[0038] Although IMD 26 is illustrated as an implantable cardiac
stimulation device (e.g., a pacemaker, ICD, CRT-D, or the like), in
other examples, an implantable device that detects the static MRI
field and operates in the MRI mode according to the present
disclosure may include an implantable drug pump or an implantable
neurostimulator that provides at least one of deep brain
stimulation, vagus nerve stimulation, gastric stimulation, pelvic
floor stimulation, spinal cord stimulation, or other stimulation.
In other examples, an implantable device that detects the static
MRI field and operates in the MRI mode may include any other active
implantable medical device that includes electronics that the
fields produced by MRI device 16 may interfere with. In other
examples, a device that detects the static MRI field and operates
in the MRI mode may include an external device.
[0039] FIG. 3 shows a schematic view of illustrating components of
IMD 26 within housing 34. Housing 34 defines a cavity 50 in which
components of IMD 26 are housed. IMD 26 includes a power source 52
housed within cavity 50. Power source 52 may include a battery,
e.g., a rechargeable or non-rechargeable battery. IMD 26 may also
include a printed circuit board (PCB) 54 that includes electronic
components of IMD 26, which in the example of FIG. 3 include, but
are not limited to, a control module 56, magnetic field torque
sensor(s) 58, and magnetic field strength sensor 60.
[0040] PCB 54 may not be limited to typical PCB structures, but may
instead represent any structure within IMD 26 that is used to
mechanically support and electrically connect control module 56,
magnetic field torque sensor(s) 58, magnetic field strength sensor
60, power source 52, and other electronic components within housing
34. In some examples, PCB 54 may include one or more layers of
conductive traces and conductive vias that provide electrical
connection between control module 56, magnetic field torque
sensor(s) 58, and magnetic field strength sensor 60 as well as and
electrical connection between power source 52 and control module
56, magnetic field torque sensor(s) 58, and magnetic field strength
sensor 60 such that power source 52 may provide those components.
Conductors within leads 28 and 30 may be connected to control
module 56 on PCB 54 through connecting wires 62. For example,
connecting wires 62 may be connected to conductors within leads 28
and 30 at one end (e.g., via one or more feed throughs), and
connected to PCB connection points 64 on PCB 54 at the other
end.
[0041] Although the electronic components of IMD 26 are illustrated
as included on a single PCB, it is contemplated that the electronic
components described herein may be included elsewhere within IMD
26, e.g., on other supporting structures within IMD 26, such as
additional PCBs (not shown). In other examples, electronic
components within IMD 26 may be mounted to the inside of housing 34
within cavity 50 or mounted to the outside of housing 34 and
connected to components on the inside of housing 34 through a feed
through (not shown) in housing 34. In still other examples,
electronic components may be mounted on or within connector block
36 or connected to one or more of leads 28 and 30.
[0042] Control module 56, and modules included within control
module 56, represents functionality that may be included in IMD 26
of the present disclosure. Modules of the present disclosure may
include any discrete and/or integrated electronic circuit
components that implement analog and/or digital circuits capable of
producing the functions attributed to the modules herein. For
example, the modules may include analog circuits, e.g.,
amplification circuits, filtering circuits, and/or other signal
conditioning circuits. The modules may also include digital
circuits, e.g., combinational or sequential logic circuits, memory
devices, etc. The memory may be any non-transitory
computer-readable storage medium, including any volatile,
non-volatile, magnetic, or electrical media, such as a random
access memory (RAM), read-only memory (ROM), non-volatile RAM
(NVRAM), electrically-erasable programmable ROM (EEPROM), Flash
memory, or any other memory device. Furthermore, the memory may
include instructions that, when executed by one or more processing
circuits, cause the modules to perform various functions attributed
to the modules herein.
[0043] The functions attributed to the modules herein may be
embodied as one or more processors, hardware, firmware, software,
or any combination thereof. Depiction of different features as
modules is intended to highlight different functional aspects and
does not necessarily imply that such modules must be realized by
separate hardware or software components. Rather, functionality
associated with one or more modules may be performed by separate
hardware or software components, or integrated within common or
separate hardware or software components.
[0044] Field strength sensor 60 generates signals that vary as a
function of the strength of the magnetic field. Field strength
sensor 60 may, for example, generate and output a voltage signal
that varies as a function of the strength of the magnetic field. In
another example, field strength sensor 60 may only output a signal
when a magnetic field exceeds a threshold field strength, as is the
case for a Reed switch or other magnetic switch that closes in
response to being exposed to a magnetic field that exceeds a
minimum amplitude or strength. Field strength sensor 60 may, for
example, be one or more types of magnetic field sensors that may
include, but are not limited to, Hall-effect sensors, giant
magnetoresistance (GMR) based sensors, anisotropic
magnetoresistance (AMR) based sensors, tunneling magnetoresistance
(TMR) based sensors, or any other type of magnetic field sensor
suitable for measuring a magnitude of a magnetic field to which it
is exposed.
[0045] Magnetic field torque sensor(s) 58 generates signals that
vary as a function of a torque exerted on sensor(s) 58 by an
external magnetic field. FIGS. 4A and 4B illustrate one example
magnetic field torque sensor 58. Magnetic field torque sensor 58
includes a coil 66 constructed of a conductive material having one
or more turns and force sensors 68A-D (collectively referred to
herein as "force sensors 68") within a housing 69. Coil 66 may be
constructed of wire, metal, conductive trace, or other conductor or
conductive material. In the example of FIGS. 4A and 4B, coil 66 is
formed into a square configuration having a single turn forming a
plane 70. However, coil 66 may be formed into other configurations,
e.g., rectangle, oval, circle or other shape. Additionally, coil 66
may be formed to have more than one turn of the conductive
material. For example, coil 66 may be formed to have a plurality of
turns formed in a single plane, e.g., in a spiral shape. In other
examples, coil 66 may be formed to have a plurality of turns formed
in a multiple planes, e.g., coil 66 being wound such that each turn
is located on top of the previous turn. Other configurations are
also contemplated.
[0046] A current is supplied to coil 66 by one of the components of
IMD 26. The flow of electric current through coil 66 produces a
magnetic field. The magnetic field produced by the current supplied
to coil 66 will be referred to herein as the "internal magnetic
field." As such, coil 66 of magnetic field torque sensor 58
functions as a small electromagnet. When patient 10 and IMD 26 are
subjected to a magnetic field generated by an external source
(referred to herein as the "external magnetic field"), such as the
primary magnet of MRI device 16, the external magnetic field and
the internal magnetic field interact such that a magnetic moment of
coil 66 attempts to align with the external magnetic field. The
interaction of the internal magnetic field and the external
magnetic field imposes a torque on coil 66. The torque (T) exerted
on a current loop, e.g., defined by coil 66, is given by:
T=.mu..times.B, (1)
where .mu. is the magnetic moment of coil 66, and B is the external
magnetic field. The torque (T), magnetic moment (.mu.), and the
external magnetic field (B) are all vector quantities. The
magnitude of the magnetic moment (.mu.) is equal to:
.mu.=NIA (2)
where I is the current through coil 66, A is the area of the loop
formed by coil 66, and N is equal to the number of turns of coil
66. The direction of the magnetic moment of coil 66 is determined
by the vector cross product. In the example illustrated in FIG. 4A,
the vector direction of the magnetic moment of coil 66 is along the
positive z-axis. The external magnetic field (B) may be defined
as:
B=B.sub.1{circumflex over (x)}+B.sub.2y+B.sub.3{circumflex over
(z)} (3)
where B.sub.1 is the magnitude of the vector component of the
external magnetic field in the x-direction ({circumflex over (x)}),
B.sub.2 is the vector component of the external magnetic field in
the y-direction (y), and B.sub.3 is the vector component of the
external magnetic field in the z-direction ({circumflex over
(z)}).
[0047] The torque exerted on coil 66 produces forces on some of
force sensors 68. Force sensors 68 are configured to measure the
force in the direction of rotation and output a signal
representative of the force. In the example illustrated in FIGS. 4A
and 4B, the interaction of the internal and external magnetic
fields creates a torque (represented as arrow "T" in FIGS. 4A and
4B) having an axis of rotation around the y-axis, which is
orthogonal to the direction of the dipole moment of coil 66. The
forces (represented as arrows "F1" and "F2" in FIGS. 4A and 4B)
created by the torque act on opposing sides of coil 66 and in
opposing directions.
[0048] Force sensors 68 are arranged adjacent to portions of coil
66 to measure the force imposed by the torque on the respective
portions of coil 66. Force sensor 68A is arranged adjacent to a
first portion of coil 66 extending along the y-axis and force
sensor 68B is arranged adjacent to an opposite side of the first
portion of coil 66. In other words, force sensor 68A and force
sensor 68B may be viewed as sandwiching the first portion of coil
66, i.e., the first portion of coil 66 is located between force
sensors 68A and 68B. Force sensor 68C and 68D are similarly
arranged adjacent to opposite sides of a second portion of coil 66
extending along the y-axis, such that the second portion of coil 66
is located (or sandwiched) between force sensors 68C and 68D. The
first portion of coil 66 and the second portion of coil 66 are
located on opposite sides of the loop. In the example torque sensor
illustrated in FIGS. 4A and 4B, force sensors 68A and 68C are
located in a first plane 72 that is substantially parallel to plane
70 defined by coil 66 and force sensors 68B and 68D are located in
a second plane 74 that is substantially parallel to plane 70
defined by coil 66.
[0049] As indicated above, force sensors 68 are configured to
measure a force exerted on sensors 68 at their respective locations
along coil 66 by the torque on coil 66 caused by the interaction of
the internal and external magnetic fields. Force sensors 68
generate signals representative of the force measured at their
respective locations. In one example, force sensors 68 may output a
voltage that varies as a function of the force exerted on the
respective sensors 68. As coil 66 is subjected to the external
magnetic field, the torque on coil 66 creates forces on some or all
of force sensors 68, thereby changing the output (e.g., voltage)
generated by sensors 68. In one example, force sensors 68 may be
mechanically coupled to coil 66 such that the torque results in an
increased pressure on some or all of force sensors 68 in the
direction of rotation. In other examples, force sensors 68 may not
be mechanically coupled to coil 66, but instead arranged so that
sensors 68 are immediately adjacent to the respective portions of
coil 66 and any physical displacement of coil 66 due to the torque
exerted by the interaction of the internal and external magnetic
fields initiates contact with force sensors 68.
[0050] Force sensor 68 measure the force exerted along the axis
corresponding to the direction of the magnetic moment of the coil
66. In the example of FIGS. 4A and 4B, force sensors 68 measure the
force exerted along the Z-axis, in either the positive and negative
direction. The torque on coil 66 generates a force F1 in the
positive Z-direction on force sensor 68A and a force F2 in the
negative Z-direction on force sensor 68D. Force sensors 68B and 68C
measure little, if any, force since the torque on coil 66 is away
from sensors 68B and 68C. When the magnetic field torque sensor 58
is exposed to a magnetic field that causes a torque in the opposite
direction illustrated in FIGS. 4A and 4B the forces caused by
rotation of coil 66 would be exerted on force sensors 68B and 68C
and little, if any, force would be exerted on force sensors 68A and
68D. Magnetic field torque sensor 58 outputs signals that vary as a
function of the force exerted on each of the force sensors 68. In
some instances, a stronger external magnetic field, such as that
produced by MRI device 16, generates a larger force on force
sensors 68 than a smaller external magnetic field, such as that
produced by telemetry head magnet 46, assuming that the magnetic
field orientation is substantially the same. As will be described
in further detail herein, control module 56 analyzes the signals
output by magnetic field torque sensor 58 to determine whether IMD
26 is exposed to an external magnetic field, such as the static
magnetic field generated by the primary magnet of an MRI
device.
[0051] In one example, each of force sensors 68 may be a strip of
piezoelectric film that generates an electrical signal (e.g.,
charge or voltage) in response to a change in the physical
geometry, e.g., stretching, bending or other physical change,
caused by the pressure or force exerted by the torque of coil 66.
Strips of piezoelectric film may, in some instances, require no
external power in order to function, are lightweight, thin, and
flexible. Additionally, strips of piezoelectric film are also very
sensitive, making them suitable for detecting very low-level
mechanical signals. In other examples, however, force sensors 68
may include other types of sensors or combinations of sensors, such
as sensors that include a membrane or transducer element to detect
physical displacement caused by the torque on coil 66, including
but not limited to MEMS sensors, optical sensors, mechanical
resonance sensors, piezo resistive elements, or the like. Force
sensors 68 may, in some instances, be electrically isolated from
coil 66 via a dielectric material 76. In other instances, coil 66
may be conductor with an outer insulation layer that electrically
isolates coil 66 form force sensors 68.
[0052] In some instances, additional force sensors 68 may be placed
elsewhere along coil 66. In the example of FIGS. 4A and 4B,
additional force sensors 68 may be placed along the portions of
loop that extend in the x-direction. For example, two force sensors
68 may be arranged adjacent to opposite sides of a third portion of
coil 66 extending along the x-axis such that the third portion of
coil 66 along the x-axis is located (or sandwiched) between the two
force sensors and two force sensors may be arranged adjacent to
opposite sides of a fourth portion of coil 66 extending along the
x-axis such that the fourth portion of coil 66 along the x-axis is
located (or sandwiched) between the two force sensors. The third
portion of coil 66 and the fourth portion of coil 66 are located on
opposite sides of the loop.
[0053] Coil 66 and force sensors 68 of torque sensor 58 of FIGS. 4A
and 4B are arranged in a single detection axis. Coil 66 and force
sensors 68 are arranged in the x-y plane to measure the forces
imposed by a torque on coil 66 having an axis of rotation that is
not along the z-axis. The magnitude of the torque exerted on coil
66 (T.sub.1) along the axis corresponding to the direction of the
dipole moment of coil 66 (e.g., the z-axis in the example of FIGS.
4A and 4B) is equal to:
T.sub.1=.mu..sub.3(B.sub.2{circumflex over (x)}-B.sub.1y) (4)
where .mu..sub.1 is equal to the magnitude of the magnetic moment
defined by equation (1). As such, torque sensor 58 having single
coil 66 can only detect forces caused by a torque in two
dimensions.
[0054] In instances in which torque sensor 58 is configured to
detect the forces imposed by a torque in two directions, IMD 26 may
include two torque sensors 58 physically arranged in different
planes within IMD 26 such that the first torque sensor 58 is in a
plane that is not aligned with a plane in which the second torque
sensor 58 is located. In one example, the plane of the first torque
sensor 58 and the plane of the second torque sensor 58 may be
orthogonal to one another. However, in other instances, the plane
of the first torque sensor 58 and the plane of the second torque
sensor 58 may be orthogonal as long as they are not aligned. For
purposes of illustration, however, the first and second torque
sensors 58 will be described herein as being arranged orthogonal to
one another. The second torque sensor 58 is substantially similar
to the first torque sensor having a second coil 66 and force
sensors 68 arranged within a housing 69 as described above with
respect to FIGS. 4A and 4B, but physically arranged such that the
dipole moment of the second torque sensor is in a direction
orthogonal to the dipole moment of the first torque sensor. For
example, if the direction of the dipole moment of the first torque
sensor is along the z-axis (as illustrated in FIGS. 4A and 4B),
then the dipole moment of the second torque sensor would be either
along the x-axis or the y-axis. The magnitude of the torque
(T.sub.2) exerted on a coil 66 of a second torque sensor 58 having
its dipole moment along the x-axis is equal to:
T.sub.2=.mu..sub.1(B.sub.2{circumflex over (z)}-B.sub.3y) (5)
where .mu..sub.2 is equal to the magnitude of the magnetic moment
of coil 66 of the second torque sensor 58 defined by equation
(1).
[0055] Utilizing two torque sensors arranged orthogonal to one
another (or at least arranged such that they are not in parallel
planes) results in at least one of the torque values being nonzero
for a magnetic field having any orientation. As such, the
arrangement of two torque sensors in such a manner provides IMD 26
the ability to detect a magnetic field with any orientation.
[0056] FIGS. 5A and 5B illustrate views of another example torque
sensor 58'. Torque sensor 58' is substantially similar to torque
sensor 58 of FIGS. 4A and 4B, but includes a second coil 66' and
force sensors 68' located in a second detection axis that is
orthogonal to the first detection axis within the same housing 69.
In the example of FIGS. 5A and 5B, the second coil 66' and force
sensors 68' are arranged in the y-z plane. The arrangement of coil
66' and force sensors 68' is substantially similar to that
illustrated in FIGS. 4A and 4B and described in detail above with
respect to coil 66 and force sensors 68.
[0057] Force sensor 68A' is arranged adjacent to a first portion of
coil 66' extending along the y-axis and force sensor 68B' is
arranged adjacent to an opposite side of the first portion of coil
66'. In other words, force sensor 68A' and force sensor 68B' may be
viewed as sandwiching the first portion of coil 66', i.e., the
first portion of coil 66' is located between force sensors 68A' and
68B'. The arrangement also includes force sensors 68C' and 68D'
arranged adjacent to opposite sides of a second portion of coil 66'
extending along the y-axis, such that the second portion of coil
66' is located (or sandwiched) between force sensors 68C' and 68D'.
The first portion of coil 66' and the second portion of coil 66'
are located on opposite sides of the loop.
[0058] The torques on coil 66 and coil 66' are defined by equations
(4) and (5) above, respectively. As described above, arranging
coils 66 and 66' such that they are substantially orthogonal,
torque sensor 58' may detect a magnetic field having any
orientation. Again, however, coils 66 and 66' need not be
orthogonal but should be arranged such that they are not aligned in
the same plane or parallel planes.
[0059] FIG. 6 is a block diagram that illustrates an example
control module 56 of IMD 26 in further detail. Control module 56
includes a processing module 80, memory 82, therapy module 84,
sensing module 86, communication module 88, and field
discrimination module 89.
[0060] Processing module 80 may communicate with memory 82. Memory
82 may include computer-readable instructions that, when executed
by processing module 80 or other component of IMD 26, cause
processing module 80 or other component of IMD 26 to perform the
various functions attributed to them herein. Memory 82 may be any
non-transitory computer-readable storage medium, including any
volatile, non-volatile, magnetic, or electrical media, such as RAM,
ROM, NVRAM, EEPROM, Flash memory, or any other digital media.
[0061] Processing module 80 may also communicate with therapy
module 84 and sensing module 86. Therapy module 84 and sensing
module 86 are electrically coupled to electrodes 38, 40, 42, and 44
of leads 28 and 30. Sensing module 86 is configured to analyze
signals from electrodes 38, 40, 42, and 44 of leads 28 and 30 in
order to monitor electrical activity of heart 32, such as the
depolarization and repolarization of heart 32. Processing module 80
may detect cardiac activity based on signals received from
electrical sensing module 80. In some examples, processing module
80 may detect tachyarrhythmias based on signals received from
sensing module 86, e.g., using any suitable tachyarrhythmia
detection algorithm.
[0062] Processing module 80 may generate EGM waveforms based on the
detected cardiac activity. Processing module 80 may also generate
marker channel data based on the detected cardiac activity. For
example, marker channel data may include data that indicates the
occurrence and timing of sensing, diagnosis, and therapy events
associated with IMD 26. Additionally, marker channel data may
include information regarding the performance or integrity of
components of IMD 26 or leads 28 and 30. Processing module 80 may
store EGM waveforms and marker channel data in memory 82.
Processing module 80 may later retrieve stored EGMs from memory 82,
e.g., upon a request from programmer 22 via communication module
88.
[0063] Therapy module 84 is configured to generate and deliver
therapy, such as electrical stimulation therapy, to heart 32 or
other desired location. Processing module 80 may control therapy
module 84 to deliver electrical stimulation therapy to heart 32
according to one or more therapy programs, which may be stored in
memory 82. For example, processing module 80 may control therapy
module 84 to deliver pacing pulses to heart 32 based on one or more
therapy programs and signals received from sensing module 86.
[0064] Therapy module 84 may also be configured to generate and
deliver cardioversion and/or defibrillation shocks to heart 32 in
addition to or instead of pacing pulses. Processing module 80 may
control therapy module 84 to deliver the cardioversion and
defibrillation pulses to heart 32. For example, in the event that
processing module 80 detects an atrial or ventricular
tachyarrhythmia, processing module 80 may load an
anti-tachyarrhythmia pacing regimen from memory 82, and control
therapy module 84 to implement the anti-tachyarrhythmia pacing
regimen. Therapy module 84 may include a high voltage charge
circuit and a high voltage output circuit when therapy module 84 is
configured to generate and deliver defibrillation pulses to heart
32, e.g., should the ATP therapy not be effective to eliminate the
tachyarrhythmia.
[0065] Communication module 88 includes any suitable hardware,
firmware, software or any combination thereof for communicating
with another device, such as programmer 22 and/or a patient
monitor, e.g., by wireless telemetry. Under the control of
processing module 80, communication module 88 may receive downlink
telemetry from and send uplink telemetry to programmer 22 and/or a
patient monitor with the aid of an antenna (not shown) in IMD 26.
Processing module 80 may provide the data to be uplinked to
programmer 22 and the control signals for a telemetry circuitry
within communication module 88.
[0066] Control module 56 obtains signals from torque sensors and
field strength sensor 60 and processes the signals to detect the
presence of a magnetic field. In the example illustrated in FIG. 6,
control module 56 may receive signals from torque sensor 58A and
58B (collectively "torque sensors 58"), which are two separate
torque sensors physically arranged substantially orthogonal to one
another within IMD 26. Alternatively, control module 56 may receive
signals from torque sensor 58' (illustrated as a dotted line
representative of an alternative arrangement), which is described
in detail with respect to FIGS. 5A and 5B.
[0067] In some examples, IMD 26 may include additional sensors
other than torque sensors 58 and field strength sensor 60, with
which sensing module 86, processing module 80 or field
discrimination module 89 may communicate. For example, IMD 26 may
include one or more of a motion sensor (e.g., an accelerometer or
piezoelectric element), a heart sound sensor, or a pressure sensor
(e.g., a capacitive sensor) that senses intracardiac or other
cardiovascular pressure. The one or more additional sensors may be
located within housing 34, outside of housing 34, attached to one
or more of leads 28 or 30, or wirelessly coupled to control module
56 via communication module 88. In some examples, torque sensors 58
or field strength sensor 60 may be located outside of housing 34,
attached to one or more of leads 28 or 30, or wirelessly coupled to
control module 56 via communication module 88.
[0068] Field discrimination module 89 is in electrical
communication with torque sensors 58, field strength sensor 60, and
processing module 80. Field discrimination module 89 may include
circuits that interface with torque sensors 58 and field strength
sensor 60. For example, field discrimination module 89 may include
circuits that provide current to coils 66 of torque sensors 58.
Field discrimination module 89 may also include amplification
circuits, filtering circuits, and/or other signal conditioning
circuits that process signals received from torque sensors 58 and
field strength sensor 60. In some examples, field discrimination
module 89 may also include circuits that digitize the conditioned
signals and communicate the digitized signals to processing module
80.
[0069] Field discrimination module 89 receives signals from field
strength sensor 60 and determines the strength of the magnetic
field. Field discrimination module 89 also receives signals from
torque sensors 58 and determines whether a torque is exerted on
coils 66 of the respective sensor 58 by an external magnetic field.
As described in detail herein, field discrimination module 89 may
identify the source of the detected magnetic field as either the
primary magnet of MRI device or telemetry head magnet 46 based on
the strength and/or the torques detected using the output of field
strength sensor 60 and torque sensors 58, respectively.
[0070] In one example, field discrimination module 89 may obtain
the signals output by torque sensors 58 and determine whether IMD
26 is exposed to an external magnetic field based on the signals
obtained from torque sensors 58. As described above, a current is
supplied to coils 66 of torque sensors 58 by one of the components
of IMD 26, such as field discrimination module 89, to produce the
internal magnetic field. When patient 10 and IMD 26 are subjected
to an external magnetic field, the external magnetic field and the
internal magnetic field interact by imposing a torque on coils 66
in an attempt to align a magnetic moment of coils 66 with the
external magnetic field. Force sensors 68 of torque sensors 58
generate signals representative of the force imposed on them by the
torque of coils 66.
[0071] Field discrimination module 89 may, for example, receive
signals representative of the force imposed on each of force
sensors 68 by the torque of coils 66. The signals may, for
instance, be voltage signals. Field discrimination module 89 may
analyze the forces imposed on the force sensors 68 to detect the
presence of the external magnetic field. For instance, field
discrimination module 89 may detect the presence of the external
magnetic field when a force is imposed on a pair of force sensors
68 on opposing sides of coil 66 and in opposing directions. For
example, field discrimination module 89 may detect presence of the
external magnetic field when forces that exceed a threshold are
detected on force sensors 68A and 68D at the same time or forces
that exceed a threshold are detected on force sensors 68B and 68C
at the same time. Detecting forces on force sensors 68 on opposing
sides of coil 66 and in opposing directions distinguishes a force
caused by torque versus a force caused by translational motion. In
some instances, field discrimination module 89 may additionally
require that the magnitude of the imposed force detected on force
sensors 68 exceeds a magnitude threshold, thus using the magnitude
of the forces on sensors 68 as a possible discriminator between
smaller external magnetic fields (e.g., telemetry head fields) and
large external magnetic fields (e.g., MRI static magnetic field).
In some instances, torque sensors 58 may include memory and/or
processing circuitry to process the signals of force sensors 68 and
output and indicator as to whether or not a torque is detected.
[0072] The sensitivity of torque sensors 58 may be adjusted such
that only the torque caused by a large magnetic field, such as the
primary magnet of MRI device 16 is detected. The sensitivity of
torque sensors 58 may, for example, be adjusted by adjusting the
number of turns of coils 66, the area of the loop formed by coils
66, the amount of current supplied to coils 66, the threshold
torque value, or the like. For example, increasing the number of
turns of coil 66 increases the sensitivity of torque sensors 58.
Likewise, the magnitude of the current supplied to coil 66 may also
affect the sensitivity of torque sensors 58. The more current
supplied to coil 66, the larger the internal magnetic field and
thus the interaction with the external magnetic field. As such, the
larger the current supplied to coil 66, the more sensitive torque
sensors 58 is. Additionally, the material used as force sensors 68
may further affect the sensitivity. Using a stiffer material as
force sensors 68 require an increased torque to measure the same
amount of force. As such, stiffer material decreases the
sensitivity of torque sensors 58. The magnitude threshold values
utilized by field discrimination module 89 may be selected to
require more or less torque on coil 66, this increasing or
decreasing the sensitivity of torque sensors 58. One or more of
these parameters may be adjusted or selected to provide torque
sensors 58 with the desired sensitivity.
[0073] By adjusting the sensitivity of torque sensors 58 such that
it is capable of detecting torque when IMD 26 is exposed to the
primary magnet of MRI device 16, but not detect when IMD 26 is
exposed to smaller magnetic fields, such as the magnetic field
generated by telemetry head magnet 46, torque sensors 58 may be
utilized as an MRI detector. In other instances, field
discrimination module 89 may use the magnitude of the forces
exerted on force sensors 68 to differentiate between IMD 26 being
exposed to the primary magnet of MRI device 16 or smaller magnetic
fields, such as the magnetic field generated by telemetry head
magnet 46. For example, field discrimination module 89 may compare
the forces exerted on force sensors 68 by coils 66 with respective
threshold values and, detect presence of MRI device 16 when the
magnitude the forces on one of the torque sensors exceeds the
threshold values. However, if forces are present, but the magnitude
of the forces on neither of the torque sensors exceeds the
respective thresholds, field discrimination module 89 detects
presence of telemetry head magnet 46.
[0074] Processing module 80 may transition IMD 26 from operation in
the normal mode to operation in one of the telemetry head mode or
the MRI mode, depending on the source of the magnetic field
indicated by field discrimination module 89. Processing module 80
may operate in the normal mode while no magnetic field is detected.
While operating in the normal mode, processing module 80 may
provide typical sensing, pacing, and defibrillation functions
without preparing for communication with telemetry head 24 or
preparing IMD 26 for entry into an MRI environment. Operation of
processing module 80, however, may change when transitioning IMD 26
from operation in the normal mode to operation in either the
telemetry head mode or the MRI mode.
[0075] Processing module 80 may transition IMD 26 from operation in
the normal mode to operation in the telemetry head mode in response
to indication from field discrimination module 89 that the source
of the magnetic field is telemetry head magnet 46. While in the
telemetry head mode, processing module 80 may control communication
module 88 to communicate with programmer 22 via telemetry head 24,
e.g., download data from programmer 22 and upload data to
programmer 22.
[0076] Processing module 80 may transition IMD 26 from operation in
the normal mode to operation in the MRI mode in response to
indication from field discrimination module 89 that the source of
the magnetic field is the primary magnet of MRI device. While in
the MRI mode, processing module 80 may execute commands that
prepare IMD 26 for exposure to an MRI environment. For example,
processing module 80 may notify an operator, via communication
module 88, that the MRI field has been detected and that IMD 26 is
configured for operation during an MRI scan. In other examples,
processing module 80 may disable telemetry functionality during
operation in the MRI mode. With respect to pacing functionality,
processing module 80 may control therapy module 84 to operate in an
asynchronous mode in which pacing may be provided according to a
set timing, i.e., fixed, predetermined timing, and may not be
responsive to events sensed by sensing module 86 such as sensed
cardiac P or R waves. In other examples, processing module 80 may
control IMD 26 to operate in a sensing only mode in which no pacing
therapy is provided. When therapy module 84 includes defibrillator
functionality, processing module 80 may disable tachycardia
detection and defibrillation in the MRI mode so that any electrical
noise induced in leads 28 or 30 may not be misinterpreted as a
tachycardia event. Processing module 80 may also discontinue
storing EGM waveforms in memory 82 and may disable diagnostic
functions since the gradient and RF fields may corrupt the EGM
waveforms. In some examples, processing module 80 may use other
sensors (e.g., a pressure or acceleration sensor), different sense
circuitry, or different sense algorithms to detect cardiac activity
of the patient. In other examples, processing module 80 may
instruct sensing module 86 to filter out signals induced by the MRI
fields. It is contemplated that processing module 80 may control
sensing module 86 and therapy module 84 according to additional
settings not described herein in order to ensure proper operation
of IMD 26 during an MRI scan.
[0077] In some examples, field discrimination module 89 may include
settings for enabling portions the field discrimination
functionality. For example, field discrimination module 89 may
enable torque sensors 58, e.g., supply current to coil 66 of torque
sensors 58 or provide power to any active components of torque
sensors 58 (such as force sensors 68 in instances in which force
sensors 68 are active sensors), in response to the output of field
strength sensor 60. In particular, field discrimination module 89
provides power to torque sensor in response to detecting a magnetic
field with a strength that exceeds a minimum threshold. The minimum
threshold may be a value indicating a minimum magnetic field
strength which control module 56 may identify as either telemetry
head field or as static MRI field. When the detected magnetic field
is weaker than the lower threshold, control module 56 may operate
IMD 26 in the normal mode. The lower threshold value may be set to
a value that reliably indicates that IMD 26 is exposed to a
magnetic field, such as a reliable indication that telemetry head
magnet 46 is near to IMD 26 or that MRI device 16 is near to IMD
26. In other words, the lower threshold value may be set so that
control module 56 ignores magnetic fields that are weaker than may
be indicative of telemetry head magnet 46 or MRI device 16. The
lower threshold value may be programmed such that control module 56
rejects "noise" or magnetic fields produced by sources other than
telemetry head magnet 46 or MRI device 16. In some examples, the
lower threshold may be set to approximately 1-2 mT. In this manner,
when no magnetic field that exceeds the minimum threshold is
detected, no current is supplied to torque sensor and no power is
provided to any components of torque sensors 58, thereby conserving
power resources of IMD 26. When a magnetic field that exceeds the
threshold is detected, torque sensors 58 may be enabled to measure
the torque imposed on coil 66.
[0078] Field discrimination module 89 may, for example, enable
torque sensors 58 by providing any necessary power to components of
torque sensors 58. Field discrimination module 89 may also enable
torque sensors 58 by providing the current to coil 66 to generate
the internal magnetic field. In one example, the current is
continuously supplied to coil 66 when torque sensors 58 is enabled.
In other examples, field discrimination module 89 may duty cycle
the current provided to coil 66 in order to further conserve power.
For instance, field discrimination module 89 may provide current to
coil 66 every few seconds.
[0079] In some instances, processing module 80 may operate IMD 26
in a generic magnet mode in response to the magnitude of the
magnetic field exceeding the minimum threshold and then transition
to the MRI mode operate IMD 26 in the MRI mode when the source is
identified as the primary magnet of MRI device 16 or the telemetry
head mode when the source is identified as telemetry head magnet 46
based on the output of torque sensor, as described in detail
herein. In one example, the generic magnet mode may be the same as
the telemetry head mode.
[0080] In some examples, processing module 80 may be configured to
indicate, via communication module 88, to an external computing
device when the static MRI field is detected. For example, an
external computing device may include programmer 22, or any other
computing device within the imaging room in which the MRI device is
located. Upon detection of the static MRI field, processing module
80 may indicate, via communication module 88, to the external
computing device that the patient has an IMD that is capable of
detecting the static MRI field and/or that the static MRI field is
detected. The external computing device may then display an
indicator to a clinician, e.g., on a display, that IMD 26 has
detected the MRI device and is prepared for the MRI scan.
[0081] As a further example, upon detection of the static MRI
field, processing module 80 may indicate, via communication module
88, to the external computing device that the static MRI field is
detected. The external computing device may then send an
acknowledgement to IMD 26 in response to the indication received
from communication module 88. In response to receipt of the
acknowledgement, processor 80 may operate IMD 26 in the MRI
mode.
[0082] Although IMD 26 is described above as having one or more
magnetic field torque sensor 58 described herein, the techniques
described herein are not limited to use of such a torque sensor.
Any sensor capable of detecting a torque caused by entering an
environment with a large static magnetic field may be used instead
of the specific torque sensor described herein.
[0083] FIG. 7 is a flow diagram illustrating an example method of
operation of an IMD including a torque sensor in accordance with
this disclosure. Initially, field discrimination module 89 supplies
a current to coils 66 of torque sensors 58 (90). The amplitude of
the current supplied to coils 66 may be selected to provide torque
sensors 58 with the desired sensitivity. In other instances, other
components of control module 56 may supply the current to coils 66
of torque sensors 58.
[0084] Field discrimination module 89 obtains signals output by
force sensors 68 representative of the force detected by force
sensors 68 (92). As described in detail above, force sensors 58 may
be aligned on opposite sides of coils 66 such that there are two
force sensors on each side of coils 66 that sandwich coils 66. When
patient 10 and IMD 26 are subjected to an external magnetic field,
the external magnetic field interacts with an internal magnetic
field generated by the current through the loop thereby imposing a
torque on coils 66 in an attempt to align a magnetic moment of
coils 66 with the external magnetic field. Force sensors 68 of
torque sensors 58 generate signals representative of the force
imposed on them, which are then obtained by field discrimination
module 89.
[0085] Field discrimination module 89 computes a force detected on
each of force sensors 68 by the torque on coils 66 caused by the
external magnetic field using the signals obtained from force
sensors 68 (94). Field discrimination module 89 detects whether
forces exist on force sensors 68 on opposing sides of either of
coils 66 and in opposing directions (95). For example, field
discrimination module 89 may detect whether forces are detected on
force sensors 68A and 68D of torque sensor 68 of FIGS. 4A and 4B or
forces that exceed a threshold are detected on force sensors 68B
and 68C of torque sensor 68 of FIGS. 4A and 4B. When forces do not
exist on force sensors 68 on opposing sides of either of coils 66
and in opposing directions, field discrimination module 89
determines that patient 10 and IMD 26 are not in the presence of
the static MRI field and continues to provide current to coil of
torque sensor 58 (90).
[0086] When forces do not exist on force sensors 68 on opposing
sides of either of coils 66 and in opposing directions, field
discrimination module 89, field discrimination module 89 determines
whether the force on the force detected on force sensors 68 on
opposing sides of either of coils 66 and in opposing directions
exceeds a threshold value (96). When the forces do not exceed the
threshold value, field discrimination module 89 determines that
patient 10 and IMD 26 are not in the presence of the static MRI
field. When the forces do exceed the threshold value, field
discrimination module 89 determines that patient 10 and IMD 26 are
in the presence of the static MRI field (98). Processing module 80
transitions IMD 26 from operation in the normal mode to operation
in the MRI mode in response detecting the presence of the static
MRI field of MRI device 16 (99).
[0087] FIG. 8 is a flow diagram illustrating an example method of
operation of an IMD in accordance with this disclosure. Initially,
field discrimination module 89 obtains signals output by magnetic
field strength sensor 60 representative of a magnitude of a
magnetic field to which IMD 26 exposed (100). Field discrimination
module 89 determines whether the magnitude of the magnetic field is
greater than a minimum threshold (102). If the magnitude is not
greater than the minimum threshold, field discrimination module 89
continues to monitor the output of field strength sensor 60.
[0088] If the magnitude is not greater than the minimum threshold,
field discrimination module 89 enables torque sensors 58 (104). In
the case of the example torque sensors 58 described above with
respect to FIGS. 4A, 4B, 5A, and 5B, field discrimination module 89
may enable torque sensor 58 by supplying a current to coils 66 of
torque sensors 58. In other examples, field discrimination module
89 may also provide power to other components such as active sensor
components used to detect the torque exerted by and external
magnetic field.
[0089] Field discrimination module 89 obtains signals output by
torque sensors 58 (106). In the example torque sensors 58 described
above with respect to FIGS. 4A, 4B, 5A, and 5B, force sensors 68
may be aligned on opposite sides of coils 66 such that there are
two sensors on each side of coils 66 that sandwich coils 66 and
output signals representative of the force detected by force
sensors 68. When patient 10 and IMD 26 are subjected to an external
magnetic field, the external magnetic field interacts with an
internal magnetic field generated by the current through the loop
thereby imposing a torque on coils 66 in an attempt to align a
magnetic moment of coils 66 with the external magnetic field. Force
sensors 68 of torque sensors 58 generate signals representative of
the force imposed on them, which are then obtained by field
discrimination module 89. Other torque sensors may output other
indications of torque.
[0090] Field discrimination module 89 determines whether a detected
torque exceeds a threshold torque value (110). For the example
torque sensors 58 described above with respect to FIGS. 4A, 4B, 5A,
and 5B, field discrimination module 89 may determine whether a
detected torque exceeds a threshold torque value using the
techniques described with respect to blocks 94-96 of FIG. 7.
However, other techniques for determining whether the torque
exceeds a threshold may be utilized depending on the type of torque
sensor used.
[0091] When the detected torque does not exceed the threshold
torque value, field discrimination module 89 determines that
patient 10 and IMD 26 are in the presence of telemetry head magnet
46 (112). Processing module 80 transitions IMD 26 from operation in
the normal mode to operation in the telemetry head mode in response
detecting the presence of the telemetry head magnet 46 (114).
[0092] When the detected torque exceeds the threshold torque value,
field discrimination module 89 determines that patient 10 and IMD
26 are in the presence of the static MRI field (116). Processing
module 80 transitions IMD 26 from operation in the normal mode to
operation in the MRI mode in response detecting the presence of the
static MRI field of MRI device 16 (118). In this manner, IMD 26 may
utilize torque sensors 58 to differentiate between the telemetry
head magnet and the primary magnet of MRI device 16. Additionally,
by only enabling torque sensor 56 when a magnetic field is detected
using the magnetic field strength sensor 60, IMD 26 conserves
energy by only needing to supply a current when a magnetic field is
present.
[0093] FIG. 9 is a flow diagram illustrating another example method
of operation of an IMD in accordance with this disclosure. Field
discrimination module 89 obtains signals output by torque sensors
58 (120). In the example torque sensors 58 described above with
respect to FIGS. 4A, 4B, 5A, and 5B, force sensors 68 may be
aligned on opposite sides of coils 66 such that there are two
sensors on each side of coils 66 that sandwich coils 66 and output
signals representative of the force detected by force sensors 68.
When patient 10 and IMD 26 are subjected to an external magnetic
field, the external magnetic field interacts with an internal
magnetic field generated by the current through the loop thereby
imposing a torque on coils 66 in an attempt to align a magnetic
moment of coils 66 with the external magnetic field. Force sensors
68 of torque sensors 58 generate signals representative of the
force imposed on them, which are then obtained by field
discrimination module 89. Other torque sensors may output other
indications of torque.
[0094] Field discrimination module 89 determines whether a detected
torque exceeds a threshold torque value (122). For the example
torque sensors 58 described above with respect to FIGS. 4A, 4B, 5A,
and 5B, field discrimination module 89 may determine whether a
detected torque exceeds a threshold torque value using the
techniques described with respect to blocks 94-96 of FIG. 7.
However, other techniques for determining whether the torque
exceeds a threshold may be utilized depending on the type of torque
sensor used. When the detected torque does not exceed the threshold
torque value, field discrimination module 89 determines that
patient 10 and IMD 26 are not exposed to the static MRI field and
continues to obtain signals output by torque sensors 58 (120).
[0095] When the detected torque exceeds the threshold torque value,
field discrimination module 89 determines that patient 10 and IMD
26 are in the presence of the static MRI field (124). Processing
module 80 transitions IMD 26 from operation in the normal mode to
operation in the MRI mode in response detecting the presence of the
static MRI field of MRI device 16 (126). In this manner, torque
sensors 58 may be used as a mechanism to detect the primary magnet
of MRI device 16 by setting the thresholds appropriately.
[0096] Although FIGS. 6-9 are described in the context of torque
sensors 58, control module 56 may obtain and analyze signals from
torque sensor 58' or any other torque sensor. Various examples have
been described. These and other examples are within the scope of
the following claims.
* * * * *