Note: Descriptions are shown in the official language in which they were submitted.
- 1 -
PATIENT REFERENCE DEVICE
FIELD
[0001] The present application generally relates to optical navigation
systems used in
surgical operations and, in particular, to a patient reference device to be
attached to the
patient and tracked by an optical navigation system.
BACKGROUND
[0002] In the field of medicine, imaging and image guidance are a
significant
component of clinical care. From diagnosis and monitoring of disease, to
planning of the
surgical approach, to guidance during procedures and follow-up after the
procedure is
complete, imaging and image guidance provides effective and multifaceted
treatment
approaches, for a variety of procedures, including surgery and radiation
therapy. Targeted
stem cell delivery, adaptive chemotherapy regimens, and radiation therapy are
only a few
examples of procedures utilizing imaging guidance in the medical field.
Optical tracking
systems, used during a medical procedure, track the position of a part of the
instrument that is
within line-of-site of the optical tracking camera. These optical tracking
systems also require
a reference to the patient to know where the instrument is relative to the
target (e.g., a
tumour) of the medical procedure, or to accurately assess positioning of
relative parts of
patient anatomy or orthopedic medical devices.
[0003] In some surgeries, a patient reference device that includes an
optically-
trackable component that the navigation system is capable of tracking is
fixedly attached to
the patient. Provided a proper registration process in undertaken, the
navigation system is
then able to determine the position of patient anatomy in its coordinate
space, so that it is able
to track (and display) patient anatomy relative to tracked instruments and
devices by also
tracking the patient reference device.
[0004] In some cases, the patient reference device maybe inadvertently
bumped
during the surgery which can move the patient reference device, cause it to
break, or cause
the bone to which it is attached to fracture. If the device moves relative to
the patient, then the
registration is lost and the surgery must either proceed without navigation or
it must be
CA 2958013 2017-10-30
CA 02958013 2017-02-15
- 2 -
stopped to reattach the device and re-perform the registration process. At
worst the movement
of the patient reference device is not noticed and the surgery proceeds using
an inaccurate
registration. Accordingly, it would be advantageous to reduce the likelihood
of loss of
registration and to accurately determine whether re-registration is necessary.
BRIEF SUMMARY
[0005] The present application describes a patient reference device for
tracking
anatomical location of a patient by an optical navigation system during a
surgical procedure.
The patient reference device includes an attachment base having an attachment
mechanism to
secure the attachment base to an anatomical feature of the patient; a
optically-trackable array
including a plurality of fiducials in a fixed geometric pattern to be detected
by the optical
navigation system and having a longitudinally-extending arm to space apart the
fixed
geometric pattern from the anatomical feature, the arm including a connector
to be detachably
secured to the attachment base; an inertial measurement unit in the attachment
base to detect
a change in position of the attachment base and to output a motion signal
representing the
change in position and its magnitude; a logic circuit to receive the motion
signal and to
compare it to a threshold level and, if the motion signal exceeds the
threshold level, to
generate an alarm signal; and an output device to output an alarm in response
to the alarm
signal.
[0006] In another aspect, the present application describes a method of
tracking
patient anatomy during a surgical operation using an optical navigation system
and a patient
reference device, the patient reference device being attached to an anatomical
feature of the
patient, the patient reference device including an attachment base having an
attachment
mechanism to secure the attachment base to the anatomical feature and a
optically-trackable
array including a plurality of fiducials in a fixed geometric pattern to be
detected by the
optical navigation system and having a longitudinally-extending arm to space
apart the fixed
geometric pattern from the anatomical feature, the arm including a connector
to be detachably
secured to the attachment base. The method includes determining, based on
comparing a
threshold level to a motion signal from an inertial measurement unit within
the attachment
base, that the attachment base has changed position, wherein the motion signal
represents the
SMI 408 Rowand LLP 313-
001 I CAP I
CA 02958013 2017-02-15
- 3 -
change in position and its magnitude; based on determining that the attachment
base has
changed position, generating an alarm signal; and outputting, via an output
device in the
attachment base, an alarm in response to the alarm signal.
[0007] In yet a further aspect, the present application describes non-
transitory
computer-readable media storing computer-executable program instructions
which, when
executed, configured a processor and/or logic circuitry to perform the
described methods.
[0008] Other aspects and features of the present application will be
understood by
those of ordinary skill in the art from a review of the following description
of examples in
conjunction with the accompanying figures.
[0009] In the present application, the term "and/or" is intended to cover
all possible
combination and sub-combinations of the listed elements, including any one of
the listed
elements alone, any sub-combination, or all of the elements, and without
necessarily
excluding additional elements.
[0010] In the present application, the phrase "at least one of ...or..." is
intended to
cover any one or more of the listed elements, including any one of the listed
elements alone,
any sub-combination, or all of the elements, without necessarily excluding any
additional
elements, and without necessarily requiring all of the elements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Reference will now be made, by way of example, to the accompanying
drawings which show example embodiments of the present application, and in
which:
[0012] FIG. I diagrammatically illustrates, in perspective view, a
navigation system;
[0013] FIG. 2 shows, in block diagram form, an example of the navigation
system;
[0014] FIG. 3 shows a perspective view of one example embodiment of a multi-
part
patient reference device;
[0015] FIG. 4 shows, diagrammatically, one example embodiment of the
attachment
base;
SMI 408 Rowand LLP 313-
001 ICAP I
CA 02958013 2017-02-15
- 4 -
[0016] FIG. 5 shows another example embodiment of an attachment base;
[0017] FIG. 6 shows an example of a battery housing; and
[0018] FIG. 7 shows, in flowchart form, one example method for tracking
patient
anatomy during a surgical operation.
[0019] Similar reference numerals may have been used in different figures
to denote
similar components.
DESCRIPTION OF EXAMPLE EMBODIMENTS
[0020] Advanced imaging modalities such as Magnetic Resonance Imaging
("MRI")
have led to improved rates and accuracy of detection, diagnosis and staging in
several fields
of medicine including neurology, where imaging of diseases such as brain
cancer, stroke,
Intra-Cerebral Hemorrhage ("ICH"), and neurodegenerative diseases, such as
Parkinson's
and Alzheimer's, are performed. As an imaging modality, MRI enables three-
dimensional
visualization of tissue with high contrast in soft tissue without the use of
ionizing radiation.
This modality is often used in conjunction with other modalities such as
Ultrasound ("US"),
Positron Emission Tomography ("PET") and Computed X-ray Tomography ("CT"), by
examining the same tissue using the different physical principles available
with each
modality. CT is often used to visualize bony structures and blood vessels when
used in
conjunction with an intra-venous agent such as an iodinated contrast agent.
MRI may also be
performed using a similar contrast agent, such as an intra-venous gadolinium-
based contrast
agent which has pharmaco-kinetic properties that enable visualization of
tumors and break-
down of the blood brain barrier. These multi-modality solutions can provide
varying degrees
of contrast between different tissue types, tissue function, and disease
states. Imaging
modalities can be used in isolation, or in combination to better differentiate
and diagnose
disease.
[0021] In the field of medicine, imaging and image guidance are a
significant
component of clinical care. From diagnosis and monitoring of disease, to
planning of the
surgical approach, to guidance during procedures and follow-up after the
procedure is
SMI 408 Rowand LLP 313-
001 I CAP I
CA 02958013 2017-02-15
- 5 -
complete, imaging and image guidance provides effective and multifaceted
treatment
approaches, for a variety of procedures, including surgery and radiation
therapy. Targeted
stem cell delivery, adaptive chemotherapy regimens, and radiation therapy are
only a few
examples of procedures utilizing imaging guidance in the medical field.
Optical tracking
systems, used during a medical procedure, track the position of a part of the
instrument that is
within line-of-site of the optical tracking camera.
[0022] In surgical operations in particular, optical tracking is useful for
displaying a
live real-time image that combines pre-operative scan data with instrument
location. This can
assist, for example, a neurosurgeon in guiding an instrument to a treatment
location within
the brain. An example of an image-guided surgical suite is shown in FIG. 1,
which
diagrammatically illustrates, in perspective view, a navigation system 200,
such as a medical
navigation system. The navigation system 200 is positioned in an operating
room ("OR") to
be used to guide a surgeon in conducting a surgical procedure. In this
example, the
navigation system 200 supports, facilitates, and enhances minimally-invasive
access port
based surgery using a minimally-invasive access port-based surgical procedure.
In this
example, a surgeon 101 conducts a minimally-invasive access port based surgery
on a
subject, such as a patient 102, in an OR environment. The surgery may be a
neurosurgery, as
in this example. In these circumstances, the surgeon 101 is positioned
proximate the head of
the patient 102.
[0023] In addition to the navigation system 200, the operating room may
contain
other equipment, such as surgical tool trays, carts, and booms. Some of this
equipment may
feature surgical lights, oxygen or other gas supplies, anesthesia supplies,
etc., depending on
the nature of the surgery being performed.
[0024] Reference is now made to FIG. 2, which diagrammatically illustrates
an
example of the navigation system 200. The navigation system 200 may include an
equipment
tower 201, a tracking system 213, and at least one display device. e.g., a
primary display
device 211 and a secondary display device 205. The tracking system 213 may
include optical
imaging devices, e.g. cameras. In this example, the tracking system 213
includes two
laterally spaced-apart cameras for stereoscopic vision. The camera may be a
three-
dimensional (3D) optical tracking stereo camera, such as a Northern Digital
Imaging (NDI)
SMI 408 Rowand LLP 313-
001 ICAPI
CA 02958013 2017-02-15
- 6 -
optical tracking stereo camera, by way of example. The navigation system 200
may be used
to track at least one instrument, such as a surgical instrument, e.g., an
access port 206, for
assisting the surgeon 101 during the surgical procedure.
[0025] In some embodiments, the navigation system 200 may further include a
device
positioning unit, also referred to as a drive unit 220, having a robotic arm
202 that supports
an optical device, such as an optical scope 204 or camera. In the cast where
the optical scope
204 includes an image sensor, like a camera, the view may be displayed on one
of the
displays 205, 211 to assist the surgeon 101 in navigation. The view may also
be integrated
with other data, including pre-surgical plan information, pre-surgical imaging
(like MRI,
CAT scan, or ultrasound imaging, for example), and may be registered on the
basis of
registration of the patient in the OR space and registration of the surgical
equipment relative
to the patient, as tracked by the navigation system 200. The navigation system
200 may also
track surgical instruments, like the access port 206 or other tools, in the OR
space and may
map models of those tools to a virtual space to which patient data has been
mapped in order
to render a combined display of the tools and the patient and/or pre-surgical
imaging on the
displays 205, 211.
[0026] The equipment tower 201 may be mountable on a frame, e.g., a rack or
a cart,
and is configured to accommodate at least one of a computer operable by at
least one a set of
instructions, storable in relation to at least one non-transitory memory
device, corresponding
to at least one of planning software, navigation software, and robotic
software, and a power
supply, e.g., an AC adapter power supply.
[0027] In some example surgeries, a patient's head may be retained by a
head holder
217, a craniotomy is performed, a dura flap is formed and retracted, and the
access port 206 is
inserted into the patient's brain. The tracking system 213 tracks and
determines, e.g., in real-
time by way of a set of instructions corresponding to tracking software and
storable in
relation to at least one non-transitory memory device, location data of at
least one OR item,
such as the robotic arm 202 and the at least one instrument, e.g., the access
port 206. The
tracked instrument may include at least one fiducial marker 212 mounted in
fixed relation to
the at least one OR item, e.g., the robotic arm 202 and the at least one
instrument, e.g., the
access port 206.
SMI 408 Rowand LLP 313-
001 I CAP I
CA 02958013 2017-02-15
- 7 -
[0028] The secondary display device 205 may be configured to display real-
time
output from the navigation system 200. The displayed data may include at least
one of an
axial view, a sagittal view, at least one coronal view, and a view oriented
relative to the at
least one instrument, such as perpendicular to a tool tip, in-plane of a tool
shaft, etc. The
display may include multiple views.
[0029] The fiducial marker 212 may be a reflective sphere where the
tracking system
213 is an optical tracking device. In some embodiments, the tracking system
213 may detect
electromagnetic emissions arid the fiducial marker 212 may be an
electromagnetic marker.
The three-dimensional position of the at least one fiducial marker 212 is
determined by the
tracking system 213 which is then able to map the location of the fiducial
marker 212 to a
virtual coordinate space and, thereby, position a model of the instillment to
which the fiducial
marker 212 is attached in the virtual coordinate space. The marker positions
could be tracked
relative to an object in the operating room such as the patient. Other types
of markers that
could be used would be radio frequency ("RF"), electro-magnetic ("EM"), light
emitting
diodes ("LED") (pulsed and un-pulsed), glass spheres, reflective stickers, or
unique structures
and patterns. The RF and EM may have specific signatures for the specific
tools to which
they are attached. The reflective stickers, structures, and patterns, glass
spheres, LEDs may
be detected using optical detectors, while RF and EM may be detected by using
antennas.
[0030] In the case of surgical navigation systems, registration is also
important to
ensure that the location of the patient is determined in terms of its position
in the coordinate
system. Then the system is accurately able to track the location of objects
relative to the
patient. That registration process, in various implementations, can be
performed in relation to
a base reference frame and is performable by various techniques, such as (a)
identifying
features (natural or engineered) on the MRI and CT images and pointing to
those same
features in the live scene using a pointer tool that is tracked by the
tracking system; (b)
tracing a line on the curved profile of the patient's anatomy with a pointer
tool that is tracked
by the tracking system and matching this curved profile to the 3D MRI or CT
volume; (c)
applying a tool of known geometry to the patient's anatomy, where the tool is
trackable by
the tracking system; and (d) using a surface acquisition tool based on
structured light or a 3D
scanner and matching an extracted surface to the 3D MRI or CT volume. As an
example,
registration using fiducial touch-points may include first identifying
fiducial touch-points on
Smi 408 Rowand LLP 313-
001 I CAP I
CA 02958013 2017-02-15
- 8 -
images, then touching the ficlucial touch-points with a tracked instrument and
determining
registration data in relation to reference markers. In another example, the
registration may
involve conducting a surface scan procedure by scanning the patient's anatomy
using a 3D
scanner, extracting the surface data from MRI/CT data, and determining
registration data
points by matching the surface data from the 3D scanner with the surface data
from MRUCT
data. These techniques may be used in tandem to complete a registration. In
some
procedures, an initial registration may be supplemented or refined with
additional registration
operations during the course of a surgery.
[0031] Registration typically includes identifying the location of the
patient anatomy
relative to an optically-tracked patient reference device or marker that can
be tracked by the
navigation system and which is in a fixed position relative to the patient
anatomy of interest.
Generally, this may be accomplished by attaching the patient reference device
to a patient
immobilization frame (such as a clamp for skull fixation in neurosurgery),
which itself is
rigidly attached to the patient. The patient reference device is typically a
unique optical array,
such as a fixed geometric pattern or arrangement of fiducials, that serves as
a reference point
for the navigation system. The registration process links the optically-
detected location of the
patient reference device to the optically-detected location of various
landmarks or known
points on the patient using one or more of the techniques described above by
determining the
three-dimensional location of both in the navigation coordinate system.
[0032] After registration, the patient reference device is used by the
optical navigation
system to pinpoint the location of the patient in the coordinate system so
that it can track the
position of trackable objects relative to the patient.
[0033] Because the patient reference device is typically a physical
structure
protruding outwards and in close proximity to the patient, there is a risk
that the patient
reference device may be bumped or dislodged during the surgical operation. If
this occurs,
the surgical operation may need to be stopped to redo the registration
process. Alternatively,
the surgical operation may be continued without relying on the navigation
system any further.
In some cases, the misalignment may be slight enough not to be noticed by
persons in the
operating room and the procedure might inadvertently be carried out in
reliance on the
navigation system which has now lost registration with the actual anatomical
location of the
SMI 408 Rowand LLP 313-
001 I CAP I
CA 02958013 2017-02-15
- 9 -
patient. The phrase "lost registration", in many embodiments, may refer to a
reduction in the
accuracy of the registration below a defined threshold minimum accuracy.
[0034] Some types of surgeries do not include an equivalent to the head
clamp that
immobilizes the patient's cranium during neurosurgery. For example, in some
orthopedic
surgeries, the patient may be only partly immobilized and portions of the
patient anatomy
may be expected to be manipulable during the surgery. In some such cases, the
patient
reference device may be directly attached to the patient anatomy. For example
in some cases
the patient reference device may be attached to bone using a drill and screws
to secure the
patient reference device in place relative to the patient anatomy.
[0035] Screw-based attachment may not be suitable for some surgeries, such
as, for
example sonic spinal surgeries. In some such cases, attachment of the patient
reference
device to patient anatomy is by way of another attachment mechanism, such as a
mechanical
clamp with jaws that can be secured to a bony structure, adhesive (to bone or
skin), or a pin
or other penetrating device. In some spinal surgeries, the patient reference
device might be
intended to be attached to certain vertebrae that are expected to stay (more
or less) stationary
during the surgery. In some cases, the attachment is to the lumbar vertebrae.
[0036] It will be appreciated that if the attachment mechanism is a clamp,
adhesive or
other such attachment mechanism, as opposed to screws/bolts, then there is a
chance that
bumping of the patient reference device may more easily dislodge or at least
shift the position
of the attachment mechanism, even where the patient reference device itself is
not bent or
broken. This becomes that much more difficult to identify in the case of a
surgical operation
in which the patient anatomy is not fully immobilized. It may be unclear
whether the patient
has moved or whether the patient reference device has moved relative to the
patient. The
latter would necessitate re-attachment and re-registration.
[0037] The present application describes a multi-piece patient reference
device
having an attachment base to be detachably secured to patient anatomical
feature and an
optically-trackable array that is detachably secured to the attachment base.
In some cases, the
optically-trackable array may be attached using a quick-break attachment that
allows the
array to be knocked off relatively easily if bumped so as to ensure that no
bumping forces are
transferred to the attachment base. This helps avoid bumping and dislodgement
or
SMI 408 Ro wand LLP 313-
001 I CAP I
CA 02958013 2017-02-15
- 10 -
disturbance of the attachment base relative to the anatomy, so that the
optically-trackable
array may be easily reattached, via the quick-break attachment, without
necessitating a re-
registration. In some cases, the quick-break attachment is a magnetic coupling
between the
attachment base and the optically-trackable array. The attachment base may
feature a
relatively low profile to ensure that it is unlikely to be bumped
accidentally.
[0038] In some embodiments, the attachment base may include an inertial
measurement unit ("IMU") to detect movement of the attachment base. In some
implementations the inertial measurement unit includes one or more
accelerometers and
gyroscopes. In some embodiments, the IMU includes one or more magnetometers,
which
help with correcting for orientation drift. A typical example IMU may include
three
accelerometers arranged orthogonally to each other for measuring inertial
acceleration, and
three gyroscopes arranged orthogonally to each other to measure rotational
position.
References herein to an IMU include an Attitude and Heading Reference System
(AHRS),
which typically includes an IMU and some on-board processing. The IMU,
together with a
logic circuit for detecting more than a threshold change in IMU measurements,
may allow for
determination of whether the attachment base has moved. The attachment base
may include
an output device that may signal, perhaps visually or audibly, when the
attachment base has
moved. In this manner, if the optically-trackable array is bumped and detached
from the
attachment base, before reattaching it and relying on it without requiring re-
registration, the
surgeon or other operating room personnel can confirm that the attachment base
has not
moved.
[0039] It will be appreciated that the attachment base may move relative to
the patient
anatomy or the patient anatomy may move causing movement of the attachment
base. In
some embodiments, this movement is indistinguishable to the attachment base.
In fact,
during a surgical procedure the patient anatomy may be intentionally moved. In
that case, the
IMU may be "reset" so as to treat the newly-moved stationary position of the
anatomy as the
"zero" location from which future movement will be detected.
[0040] In some cases, the output device may include a visual output, such
as an LED
for example, an auditory output, such as a speaker, or a wireless
communications output to an
external device that will generate a visual or auditory alarm.
SMI 408 Rowand LLP 313-
0011CAPI
- 11 -
[0041] Reference is now made to FIG. 3, which shows a perspective view of
one
example embodiment of a multi-part patient reference device 300. The device
300 includes an
optically-trackable array 302 and an attachment base 304. In this embodiment,
the attachment
base 304 includes a clamp mechanism 306 for securing the attachment base 304
to a bony
structure, such as the spinous process, for example.
[0042] The attachment base 304 further includes a housing 308. The top of
the housing
308 includes a quick-break attachment mechanism 310. The quick-break
attachment mechanism
310 may include any coupling mechanism for attaching and securing the
optically-trackable
array 302 to the attachment base 304 in such a manner that it is secured in
place in a pre-
ordained orientation so that it may only be re-attached in exactly the same
orientation and
position. The quick-break attachment mechanism 310 may include a channel,
slot, or other
protrusion-groove structure to physically orient the optically-trackable array
302 to as to protrude
outwards from the top of the housing 308. The channel, slot, etc., may be
keyed to ensure proper
orientation in a pre-determined position. The quick-break mechanism may
include a magnetic
connection to hold the optically-trackable array 302 in position on the
attachment base 304
unless at least a threshold level of force overcomes the quick-break
connection. The magnetic
connection, which may be implemented as one or more permanent magnets in
either side of the
quick-break attachment mechanism 310, ensures a coupling force acts on the
attachment base
304 and optically-trackable array 302 holding them in alignment and in
connection. The level of
force exerted by the quick-break attachment mechanism 310 is to be sufficient
to ensure the
optically-trackable array 302 is not too easily detached, such as by
gravitational forces or
minimal impact forces, but not so solidly attached that it will not detach in
the case of an impact
force that could risk dislodging the attachment base 304 from patient anatomy.
That is the
detachment force capable of overcoming the quick-break mechanism should be
substantially
lower than the force capable of dislodging the clamp mechanism 306 (or other
attachment
mechanism in other embodiments) from the patient anatomy. The term "quick-
coupling" may be
used interchangeably with "quick-break".
[0043] The optically-trackable array 302 includes a geometric arrangement
of fiducials
312 mounted on a stem 314 or longitudinally-extending arm that protrudes away
from the
attachment base 304. Other arrangements of fiducial 312, whether on a frame
structure or on
another substrate, may be used in other embodiments. The stem 314 functions
CA 2958013 2018-04-09
CA 02958013 2017-02-15
- 12 -
to position the fiducials 312 spaced apart from the anatomy to make them more
consistently
and easily visible to tracking devices, e.g. cameras, of the navigation system
during the
surgical operation. In the case of a spinal surgery, particularly if there is
more than one
patient reference device being used in an operation (e.g. each attached to
different vertebrae),
the horizontally-compact vertically-oriented structure of the patient
reference device 300
improves its usefulness in the surgical suite and reduces the likelihood of it
being accidentally
bumped because it obscures an area of interest. In this regard, it will be
noted that the
example patient reference device 300 is vertically aligned, such that the
clamp mechanism
306, housing 308, and optically-trackable array 302 are all generally aligned
along a common
vertical axis.
[0044] Reference is now made to FIG. 4, which shows, diagrammatically one
example embodiment of the attachment base 304. In this example embodiment, the
attachment base 304 has a housing 308 that includes within it a battery 320,
an IMU 322, a
logic circuit 324 and all output device 326.
[0045] The IMU 322 generates signals, i.e. a motion signal, indicative of
measured
inertial forces on the attachment base 304. Together, the logic circuit 324
and the IMU 322
detect whether the attachment base 304 experiences more than a threshold
change in position
(rotation) or more than a threshold change in inertial acceleration forces
(including
gravitational forces, which could indicate positional change or rotation). The
measured
forces of the IMU 322 result in signals that may be comparted with a threshold
by the logic
circuit 324 and more than a threshold change in the IMU 322 measurements may
trigger
generation of an alarm signal that causes the output device 326 to output an
alarm. Output of
the alarm signal may be referred to as an alarm condition for the patient
reference device. It
will be appreciated that in some embodiments the IMU 322 and the logic circuit
324 may be
considered an integral unit and may be implemented as a single integrated
circuit component.
The setting of a suitable threshold for determining that a detectable change
has occurred may
be implementation specific and may be altered to suit a particular
sensitivity. The threshold
level may be related to the relative positional change that such a movement
would cause in
the position, orientation, etc. of the trackable optical array, and may be set
based on it causing
more than a particular change in the position of the array, such as 0.5%, 1%,
3%, etc., or may
SMI 408 Rowand I,LP 313-
0011CAPI
CA 02958013 2017-02-15
- 13 -
be based on it causing an overall movement of more than a threshold distance
by a point on
the array, such as Imm, 2mm, 5mm, etc.
[0046] The output device 326 may include one or more LEDs or other such
light
output devices for signaling the alarm. In one example implementation, when
the IMU 322
reaches a steady state, i.e. holds a stationary position, for at least a
minimum time (e.g. 20-60
seconds, a few minutes, or longer), a green LED may be illuminated indicating
that the
attachment base 30 is in a stable stationary position. Upon detecting more
than a threshold
amount of movement, the IMU 322 and logic circuit 324 may cause illumination
of the green
LED to cease and may cause illumination of a red LED to indicate that the
attachment base
304 has moved. To ensure the "moved" condition is not missed, in some other
embodiments,
the attachment base 304 may include an input device, such a button, switch,
touch sensitive
area, or other input mechanism (not illustrated) for receiving a reset command
so that the
attachment base 304 continues to display a "moved" red LED condition until it
is manually
reset.
[0047] In some embodiments, the output device 326 may include a speaker or
other
audio output mechanism for emitting an alarm sound in response to the alarm
signal from the
IMU 322 and logic circuit 324. The alarm sound may be a constant tone or
series of tones,
intermittent chirping, or any other audible alarm that will alert personnel in
the operating
room to the fact the attachment base 304 has moved.
[0048] In some embodiments, the attachment base 304 may include both the
audible
alarm and the visible alarm.
[0049] In yet other embodiments, the output device 326 includes a wireless
communication system for transmitting the alarm signal to a remote device,
which then
outputs an alarm. For example, the wireless communication system may include a
WiFi chip,
a BluetoothTM chip, a Near-Field Communications ("NFC") chip, or any other
short-range RF
wireless system for establishing a communications channel with another device.
In another
example, the wireless communication may be by RFID, whether active or passive,
in which
the navigation system polls one or more patient reference devices for
information on the
status of the device, i.e. whether an alarm state is active. If the output
device 326 includes
wireless communication capability, then any applicable "reset" command may be
sent to the
SMI 408 Rowand LLP 313-
0011CAP1
CA 02958013 2017-02-15
- 14 -
attachment base 304 over the communications channel from the remote device to
which the
wireless system is connected in order to cancel or reset the alarm condition.
[0050] Although the present example embodiment shows the attachment
mechanism
to be the clamp mechanism 306, other mechanisms for securing the attachment
base 304 to
patient anatomy may be used in other implementations. The clamp mechanism 306
may be
useful in the case of spinal surgeries since the jaws of the clamp mechanism
306 may grip the
protruding spinous process of a vertebrae. Nevertheless, in some cases
adhesive, bone
screws, or other attachment mechanisms may be considered advantageous in place
of a
physical clamp.
[0051] Reference is now made to Figure 5, which shows another example
embodiment of an attachment base 404 for a patient reference device. In this
example
embodiment, the attachment base 404 is a two-part device that includes a
sensor base 420 and
a detachable battery housing 410. The battery housing 410 is designed to
securely attach to
the top of the sensor base 420. The top of the battery housing 410 includes
one side of the
quick-break attachment mechanism 310 for connecting the optically-trackable
array. The
underside of the battery housing 410 may feature contacts 412, 414 that are
electrically
connected to respective terminals of the battery 320 within the battery
housing 410.
[0052] The sensor base 420 includes the IMU 322, the logic circuit 324 and
the
output device 326. It features an attachment mechanism 430 for securing the
attachment base
404 to patient anatomy. The attachment mechanism 430 is illustrated generally
and may
include various attachments including mechanical clamps, pins, adhesive or
other suitable
attachment means.
[0053] The sensor base 420 includes an external casing with a top side that
features
contact pads 422 and 424 for electrically connecting to contacts 412 and 414,
respectively.
One or both of the contact pads 422, 424 or contacts 412, 414 may include a
mechanical
biasing, e.g. spring loading, to ensure solid contact when connected. The
casings of the
sensor base 420 and battery housing 410 feature a coupling mechanism that
ensures the
casings are securely attached in a fixed alignment and position relative to
each other. In the
present illustration, the coupling mechanism is depicted as a snap-fit
mechanism but other
attachment mechanisms may be used for other implementations.
SmI 408 Rowand LLP 313-
001 I CAP I
CA 02958013 2017-02-15
- 15 -
[0054] One advantage of a two-part attachment base 404 is that the battery
in the
detachable battery housing 410 is separable from the sensor base 420. The
sensor base 402
may contain relatively costly components, but the battery may be largely
disposable. The
sensor base 402 may be sterilized for re-use in subsequent surgical
operations, whereas the
detachable battery housing 410 may be disposed after use, since the battery
may not be easily
sterilized in some cases.
[0055] This example embodiment also shows the sensor base 420 including a
reset
input device 440, which in some examples may include a button or other
manually-activated
input mechanism. The reset input device 440 functions to send a signal to the
IMU 322 and
logic circuit 324 that causes them to start the operation of determining
whether the
attachment base 404 has moved more than a threshold amount based on the
current inertial
measurements. That is, the reset input device 440, when activated, signals
that the
attachment base 404 is in a stationary state and that any subsequent movement
beyond the
threshold level should cause an alarm. If any alarm is currently being output,
then a signal
from the reset input device 440 causes the alarm to cease until the IMU 322
and logic circuit
324 detect another indication of movement beyond the threshold level.
[0056] Another embodiment of an example battery housing 450 is shown in
FIG. 6.
In this embodiment, the battery housing 450 includes additional battery
contacts 452, 454 on
the top of its casing to enable electrical DC power connection to the
optically-trackable array.
The additional battery contacts 452, 454 may be implemented as a part of the
quick-break
attachment mechanism 310 in some embodiments. Battery power may be used by the
optically-trackable array in some implementations to power active fiducials,
e.g. infrared
LED-based fiducials, that emit energy as part of their function in assisting
the navigation
system to uniquely identify and track the optically-trackable array. In some
cases, the active
fiducials may include fiducials that emit light at different wavelengths in
order to be
distinguishable to the navigation system. The fiducials may be configured,
internally or
based on circuit elements in the optically-trackable array, to transmit light
using a defined
pattern or pulse frequency to further enable the navigation system to uniquely
identify each
fiducial. In yet other cases, the optically-trackable array may include logic
circuitry or other
computing elements to enable control of the active fiducials so as to receive
optical
communications from the navigation system and/or to transmit communications to
the
SMI 408 Rowand LLP 313-
001 1CAP I
CA 02958013 2017-02-15
- 16 -
navigation system. Example communications may be receiving, possibly
addressed,
instructions regarding pulse patterns to use, or transmitting status
information, such as battery
level information.
[0057] In yet another embodiment, an example attachment base, in one or two
parts,
may contain the IMU, a battery and a wireless communication system. The
attachment base
may be configured to send IMU data to a navigation system regularly. The
navigation system
determines whether the IMU data indicates movement or not, and the navigation
system
outputs any alarms required as a result of detected movement of the attachment
base.
[0058] Reference is now made to FIG. 7, which shows, in simplified
flowchart form,
one example method 600 for tracking patient anatomy during a surgical
operation. The
method 600 is carried out using a patient reference device, such as the
example patient
reference device 300 (FIG. 3) described above. In the operating room and in
the course of
surgery, the patient reference device 300 may be used to track patient
anatomy. The patient
anatomy may include anatomy that is intended to remain stationary during the
operation, such
as a hip, cranium, portion of the spine, etc., depending on the nature of the
operation. In the
present example, the patient reference device is to be attached to a vertebrae
and, in
particular, to the spinous process of a vertebrae. Accordingly, in operation
602 the patient
reference device is clamped to a vertebrae.
100591 In this example, the patient reference device is capable of
receiving an input to
trigger it to begin monitoring for movement. That is, it does not begin
attempting to detect
movement until instructed. That instruction or signal may be supplied via an
input device,
such a button or the like, that is actuated by personnel after the device is
secured in place on
the patient's anatomy. In some embodiments, that instruction may be
communicated to the
device wirelessly, where the device is equipped with a wireless communication
system and
capable of receiving such an instruction via RF or infrared communications,
for example. In
yet another embodiment, the instruction may be implemented simply as the
supply of power;
that is, attachment of the battery housing to the sensor base is the trigger
for the sensor base
to begin detecting movement. As shown in FIG. 7, the method 600 includes
determining
whether to start monitoring for movement in operation 604.
smi 408 Rowand LLP 313-
0011CAP1
CA 02958013 2017-02-15
- 17 -
[0060] On determining that it is to start monitoring (by way of explicit
instruction or
command, or by way of implicit instruction, such as through supply of battery
power), the
device may then, in some embodiments, record current measurements from the IMU
in
operation 606, for comparison against future measurements. As indicated by
operation 608
the device assesses whether there has been a change greater than a threshold
level. In some
embodiments, the recordal of starting measurements is not performed, as the
1MU and logic
circuitry simply attempt to detect a pseudo-instantaneous change in
measurements that
exceeds the threshold level. On the other hand in some embodiments the
original
measurements may be retained in order to detect relatively slow movements
that, in time,
result in more than a threshold change in position or orientation of the
device.
[00611 If the device determines in operation 608 that the attachment base
has
undergone more than a threshold change in position or orientation, based on a
more than
threshold level change in the measurements of the IMU, then in operation 610
it outputs an
alarm. As described above, the alarm may include a visual alarm, e.g. solid or
flashing
LED(s), an auditory alarm, e.g. speaker emitting tone or chirp, or a wireless
communication
to a remote device that signals the alarm. The alarm may include multiple
types of alarms in
combination in some cases.
[0062] In operation 612, the device determines whether the alarm has been
cancelled
and the device reset to a stationary position. Once that occurs, the process
returns to
operation 606 to monitor for movement.
[0063] In some cases, operation 612 may only involve stopping the alarm,
and the
process may return to operation 604 to await a further input command to re-
start monitoring
for movement. These commands may be input using the same input device or
separate input
devices. For example, a reset button may be pressed once to cancel the alarm
output, but not
restart the monitoring operation. After the device is repositioned and
stationary, the reset
button may be pressed again to trigger restarting of the monitoring operation,
e.g. to progress
from operation 604 to 606.
100641 Certain adaptations and modifications of the described embodiments
can be
made. Therefore, the above discussed embodiments are considered to be
illustrative and not
restrictive.
SMI 408 Rowand LLP 313-
001 I CAP I
