U.S. patent application number 14/350460 was filed with the patent office on 2014-09-11 for medical tracking system comprising two or more communicating sensor devices.
This patent application is currently assigned to Brainlab AG. The applicant listed for this patent is Christian Brack, Ingmar Hook, Timo Neubauer, Stefan Vilsmeier. Invention is credited to Christian Brack, Ingmar Hook, Timo Neubauer, Stefan Vilsmeier.
Application Number | 20140253712 14/350460 |
Document ID | / |
Family ID | 44789485 |
Filed Date | 2014-09-11 |
United States Patent
Application |
20140253712 |
Kind Code |
A1 |
Vilsmeier; Stefan ; et
al. |
September 11, 2014 |
MEDICAL TRACKING SYSTEM COMPRISING TWO OR MORE COMMUNICATING SENSOR
DEVICES
Abstract
A medical tracking system comprising at least two sensor devices
which are independently maneuverable and can be positioned in a
fixed position relative to targets, each sensor device comprising
at least one of an orientation sensor and a position sensor for
respectively determining sensor data, the system further comprising
a control unit configured to receive and combine the at least two
sensor data of the at least two sensor devices in order to
determine a relative position between at least two of the at least
two sensor devices.
Inventors: |
Vilsmeier; Stefan; (Munchen,
DE) ; Neubauer; Timo; (Grasbrunn, DE) ; Brack;
Christian; (Neusass, DE) ; Hook; Ingmar;
(Feldkirchen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Vilsmeier; Stefan
Neubauer; Timo
Brack; Christian
Hook; Ingmar |
Munchen
Grasbrunn
Neusass
Feldkirchen |
|
DE
DE
DE
DE |
|
|
Assignee: |
Brainlab AG
Feldkirchen
DE
|
Family ID: |
44789485 |
Appl. No.: |
14/350460 |
Filed: |
October 13, 2011 |
PCT Filed: |
October 13, 2011 |
PCT NO: |
PCT/EP2011/067940 |
371 Date: |
April 8, 2014 |
Current U.S.
Class: |
348/77 |
Current CPC
Class: |
A61B 2034/2057 20160201;
A61B 2034/2055 20160201; A61B 34/20 20160201; H04N 7/183 20130101;
A61B 2034/2046 20160201 |
Class at
Publication: |
348/77 |
International
Class: |
H04N 7/18 20060101
H04N007/18 |
Claims
1. A medical tracking system comprising at least two sensor devices
which are independently maneuverable and can be positioned in a
fixed position relative to targets, each sensor device comprising a
marker device, an orientation sensor for determining sensor data
and a camera, the system further comprising a control unit
configured to receive and combine the at least two sensor data of
the at least two sensor devices in order to determine a relative
position between at least two of the at least two sensor devices
and configured to identify markers in the output image of the
camera in order to determine the position of the markers.
2. The tracking system of claim 1, wherein the sensor data of a
single sensor device represent insufficient information for
determining the relative position between the at least two sensor
devices.
3. The tracking system of claim 1, wherein the at least two sensor
data respectively are data describing the relative position between
the respective sensor device and a relative position reference.
4. The tracking system of claim 1, wherein the control unit is
located in one of the sensor devices, each sensor device comprises
a control unit or each sensor device comprises a part of the
control unit.
5. (canceled)
6. The tracking system of claim 1, wherein at least one of the
sensor devices comprises an orientation sensor and the control unit
is configured to convert orientation data of an orientation sensor
into a coordinate system determined by a target to which one of the
sensor devices is attached.
7. The tracking system according to claim 1, wherein at least one
of the at least two sensor devices comprises an acceleration
sensor.
8. The tracking system according to claim 1, wherein a sensor
device comprises a distance sensor comprising a laser beam source,
wherein the laser beam is angled compared to the optical axis of
the camera.
9. The tracking system of claim 1, wherein the control unit is
configured to select the function of the sensor device as either
acting as a marker device detector or as a marker device in a step
of the medical navigation workflow.
10. A method of determining a relative position between two sensor
devices of a medical tracking system in a medical workflow, wherein
the sensor devices are independently maneuverable and can be
positioned in a fixed position relative to targets, comprising, in
one step of the workflow, the steps of determining sensor data
comprising at least one of orientation data and position data with
two or more of the sensor devices transferring the sensor data to a
control unit and determining the relative position between two
sensor devices by the control unit by combining the sensor data;
and comprising, in another step of the workflow, the steps of
capturing an image using a camera at a sensor device, identifying
markers in the output image of the camera and determining the
position of the markers.
11. The method of claim 10, wherein each sensor device is attached
to a target and the relative position of the targets is determined
from the relative position of the sensor devices.
12. The method of claim 10, characterized by using a sensor device
comprising a marker device and a position sensor being a marker
device detector as a marker device detector in one step of the
medical navigation workflow for obtaining information for
determining the position of a marker device and using the same
sensor device as a marker device in another step of the medical
navigation workflow.
13. A method for determining a mechanical property of a joint
between two bones, comprising the steps of: positioning a first
sensor device in a fixed position relative to the first bone,
registering the first bone by sampling a plurality of sample points
using a pointer and the first sensor device, positioning a second
sensor device in a fixed position relative to the second bone,
registering the second bone by sampling a plurality of sample
points using a pointer and the second sensor device, optionally
re-positioning the first sensor device in its fixed position
relative to the first bone if the first sensor device was used as a
marker device of the pointer in the previous step, determining at
least one relative position between the first sensor device and the
second sensor device for at least one position of the joint as
claimed in claim 10 and determining the mechanical property of the
joint between the first bone and the second bone from the at least
one relative position between the first sensor device and the
second sensor device.
14. A method for aiding the adjustment an adjustable cutting block
comprising a base and a cutting slot which is adjustable relative
to the base, the base being attached to a bone, comprising the
steps of: positioning a first sensor device in a fixed position
relative to the cutting slot, registering the bone by sampling a
plurality of sample points using a pointer and the first sensor
device such that the initial alignment of the cutting slot relative
to the bone is known, positioning a second sensor device in a fixed
position relative to the base of the cutting block, determining the
relative position between the first sensor device and the second
sensor device as claimed in claim 10 for the initial alignment of
the cutting slot, determining the relative position between the
first sensor device and the second sensor device as claimed in
claim 10 while the cutting slot is adjusted and determining the
current alignment of the cutting slot from the initial alignment of
the cutting slot and the current relative position between the
first sensor device and the second sensor device.
15. A computer program embodied on a non-transitory computer
readable medium which, when running on a computer or when loaded
onto the computer, causes the computer to perform determining
sensor data comprising at least one of orientation data and
position data with two or more of the sensor devices transferring
the sensor data to a control unit and determining the relative
position between two sensor devices by the control unit by
combining the sensor data; and comprising, in another step of the
workflow, the steps of capturing an image using a camera at a
sensor device, identifying markers in the output image of the
camera and determining the position of the markers.
Description
[0001] The present invention relates to a medical tracking system
comprising at least two sensor devices which are independently
maneuverable and can be positioned in a fixed position relative to
targets and a method of determining relative position between two
sensor devices of a medical tracking system.
[0002] For many years, medical tracking systems, which are in
particular a part of a medical or navigation system, are in use
which are based on a tracking device which detects the position of
markers which are attached to objects to be tracked.
[0003] This problem is solved by the subject-matter of any appended
independent claim. Advantages, advantageous features, advantageous
embodiments and advantageous aspects of the present invention are
disclosed in the following and contained in the subject-matter of
the dependent claims. Different advantageous features can be
combined in accordance with the invention as long as technically
sensible and feasible. In particular, a feature of one embodiment
which has the same or similar function of another feature of
another embodiment can be exchanged. In particular, a feature of
one embodiment which supplements a further function to another
embodiment can be added to the other embodiment.
[0004] With a tracking system according to the present invention,
advantageously a bulky and expensive 3D camera which captures
images of marker spheres arranged in a known configuration is not
obligatory. Advantageously, the likelihood of obstruction of an
object to be tracked by a user is reduced. This invention aims at
providing an improved medical tracking system and a method of
determining a relative position between two sensor devices.
[0005] According to the present invention, a medical tracking
system comprises at least two sensor devices which are
independently maneuverable and can be positioned in a fixed
position relative to targets. Each sensor device comprises at least
one of an orientation sensor and a position sensor for respectively
determining sensor data. "Respectively determining" means that at
least two sensor devices each determine sensor data. The system
further comprises a control unit configured to receive and combine
the at least two sensor data of the at least two sensor devices in
order to determine a relative position between at least two of the
at least two sensor devices.
[0006] A fixed position in this document means that two objects
which are in a fixed position have a relative position which does
not change unless this change is explicitly and intentionally
initiated. A fixed position is in particular given if a force or
torque above a predetermined threshold has to be applied in order
to change the position. This threshold might be 10 N or 10 Nm. In
particular, the position of a sensor device remains fixed relative
to a target while the target is registered or two targets are moved
relative to each other as explained below. A fixed position can for
example be achieved by rigidly attaching one object to another. The
term "position" in this document means a spatial location in up to
three (in particular less than three) translational dimensions
and/or an alignment in up to three (in particular less than three)
rotational dimensions. The spatial location can in particular be
described just by a distance (between two objects) or just by the
direction of a vector (which links two objects). The alignment can
in particular be described by just the relative angle of
orientation (between the two objects).
[0007] The orientation sensor determines orientation sensor data
which represent the orientation of the sensor device. This
orientation is preferably determined relative to an in particular
stationary reference, such as a ground-fixed reference system which
can be based on the direction of gravity. The reference system can
therefore also be referred to as an absolute reference system. An
orientation sensor may comprise a gyroscope. A gyroscope is a
device for determining the orientation based on the angular
momentum of a spinning object.
[0008] A position sensor determines position sensor data which
represent the position of an object. Preferably, this position is
given relative to the position sensor and therefore relative to the
sensor device. As an alternative, the position can be determined in
an absolute reference system.
[0009] An optional acceleration sensor of a sensor device
determines acceleration sensor data which represent the
acceleration of the sensor and thus of the sensor device. By
integrating the acceleration over a period of time, a movement of
the sensor device can be calculated. The acceleration sensor data
can be part of the sensor data provided by the sensor device.
[0010] The orientation sensor can determine the orientation sensor
data in up to three rotational dimensions, the position sensor can
determine the position sensor data in up to three rotational and/or
up to three translational dimensions and the acceleration sensor
can determine the acceleration sensor data in up to three
rotational and/or up to three translational dimensions.
[0011] The control unit receives the sensor data from the sensor
devices and combines the received sensor data in order to determine
the relative position between the two sensor devices. If, for
example, the control unit receives orientation sensor data from two
sensor devices in an absolute reference system, the control unit
can calculate the relative orientation between the two sensor
devices.
[0012] The term "combine" means in particular that the respective
sensor data, which in particular respectively are insufficient to
be the sole basis for determining the relative position, of the
respective sensor devices are used together to calculate the
relative position. In particular, the determination (calculation)
is performed by using (combining) at least first sensor data of a
first sensor device and second sensor data of a second sensor
device in order to determine the relative position based on
sufficient sensor data.
[0013] A relative position between two objects means the position
of one of the objects relative to the other object. The relative
position can also be given in up to three spatial dimensions and/or
in up to three rotational dimensions. The relative position can
thus comprise up to six dimensions, wherein there is a parameter
for each dimension. Depending on the application or workflow, the
parameters of less than six dimensions may be required or desired.
So if, for example, the relative position of a plane is to be
determined, only two rotational dimensions and one translational
dimension are required to unambiguously describe the relative
position of the plane. In another example, only one or more of the
rotational dimensions of the relative position are required, for
example for determining, from a plurality of relative positions,
the range of motion of a joint having limited degrees of
freedom.
[0014] Preferably, the sensor data provided by a single sensor
device is not sufficient for determining all parameters for all
desired dimensions of the relative position. In other words, the
sensor data of a single sensor device is not sufficient to
determine the desired number of parameters of the relative
position. In yet other words, the sensor data of a single sensor
device describe insufficient information on the relative position.
The number of parameters which can be determined from the sensor
data of a single sensor device might be less than the desired
number of parameters, or the determination of a parameter might
require more than the information given by the sensor data of a
single sensor device. However, if the sensor data of two or more
sensor devices is combined, the available information (also
referred to as sufficient information) is sufficient to determine
all parameters for all desired dimensions of the relative position.
Preferably, the available information is more than sufficient, such
that the information is overdetermined. In this case, the sensor
data is also understood as representing sufficient information.
This can be used for increasing the quality of the determined
relative position.
[0015] In one embodiment, the control unit is located in one of the
sensor devices. More preferably, two or more, preferably each of
the sensor devices comprises a control unit or at least a part of
the control unit. In this case, calculations, such as of the
relative position, can be performed locally at several or each of
the sensor devices, or some parameters of the relative position are
determined in one sensor device and some parameters of the relative
position are determined in another sensor device. However, the
control unit may also be separate from all sensor devices.
[0016] The sensor data can be transferred wirelessly from a sensor
device to a control unit, for example using a Bluetooth connection,
a WLAN connection or any other suitable, preferably low-range data
connection. If a control unit is comprised in a sensor device, the
control unit can thus receive the sensor data from the other sensor
device(s) wirelessly. The connection between sensors and the
control unit within the same sensor device is preferably a wired
connection.
[0017] According to a preferred implementation of the present
invention, two or more sensor devices can communicate with each
other. The sensor data of the communicating sensor devices are
preferably jointly analyzed to determine the relative position
between two (or more) sensor devices. This is particularly useful
if the sensor data of a single one of the at least two sensor
devices is not sufficient for determining the relative
position.
[0018] A sensor device can be positioned in fixed position relative
to the target, for example by rigidly attaching the sensor device
to a target. A target can be an anatomical structure of a patient
such as a bone, a medical instrument such as a cutting block or a
pointer, or a part of the infrastructure in an operating room such
as an operating table.
[0019] In an embodiment of the present invention, at least one
marker is attached to at least one of the sensor devices. With the
at least one marker, and preferably a plurality of markers making
up a marker device, the position sensor of a sensor device can
easily detect the position of the sensor device carrying the
marker.
[0020] It is the function of a marker to be detected by a marker
detection device (for example, a camera or an ultrasound receiver),
such that its spatial position (i.e. its spatial location and/or
alignment) can be ascertained. The detection device is in
particular part of a navigation system. The markers can be active
markers. An active marker can for example emit electromagnetic
radiation and/or waves, wherein said radiation can be in the
infrared, visible and/or ultraviolet spectral range. The marker can
also however be passive, i.e. can for example reflect
electromagnetic radiation in the infrared, visible and/or
ultraviolet spectral range. To this end, the marker can be provided
with a surface which has corresponding reflective properties. It is
also possible for a marker to reflect and/or emit electromagnetic
radiation and/or waves in the radio frequency range or at
ultrasound wavelengths. A marker preferably has a spherical and/or
spheroid shape and can therefore be referred to as a marker sphere;
markers can also, however, exhibit a cornered--for example,
cubic--shape.
[0021] A marker device can for example be a reference star or a
pointer or one or more (individual) markers in a predetermined
spatial relationship. A marker device comprises one, two, three or
more markers in a predetermined spatial relationship. This
predetermined spatial relationship is in particular known to the
navigation or tracking system and for example stored in a computer
of the navigation or tracking system.
[0022] In one embodiment, at least one of the sensor devices
comprises an orientation sensor and the control unit is configured
to convert orientation data of an orientation sensor into a
coordinate system determined by a target to which one of the sensor
devices is attached. As an example, the target is a bone and the
coordinate system is defined by the bone, for example by the
transversal, longitudinal and sagittal axis. In an exemplary
implementation, two sensor devices, each comprising an orientation
sensor, are rigidly attached to two adjoining bones which are
connected via a joint. The orientation sensor data received from
the first sensor device is then converted into orientation data in
a coordinate system corresponding to the bone to which the second
sensor device is attached. In another exemplary implementation, one
sensor device is attached to a cutting slot of an adjustable
cutting block, the base of the adjustable cutting block being
rigidly attached to a bone. The second sensor device is rigidly
attached to the bone. The orientation sensor data of the first
sensor device is then converted into orientation sensor data given
in a coordinate system defined by the bone.
[0023] A position sensor may comprise a still or video camera, in
particular a camera capturing a 2D or 3D image. By identifying
markers in the output image of the camera, in particular by
applying the laws of perspective projection of objects, the
position of the markers and therefore of a target to which the
markers are attached can be determined. In particular, the known
size of the markers and the effect that objects in the distance
appear smaller than objects close by is used to determine the
distance. As an option, a position sensor may comprise a distance
sensor for determining the distance of an object. The data of the
distance sensor and a camera can be combined, in particular to
support the calculation of the distance from the camera image. A
distortion of a known shape of the marker in the image of the
camera can be used to determine the relative orientation using the
laws of perspective projection.
[0024] In one embodiment, the distance sensor comprises a laser
beam source, wherein the laser beam generated by the laser beam
source is angled compared to the optical axis of the camera. This
means that the distance of the laser beam spot on the object
reflecting the laser beam from the optical axis changes in the
output image of the camera with the distance of the object from the
camera. Preferably, the orientation of the object reflecting the
laser beam is used when the distance is calculated because a tilt
of this object relative to the optical axis changes the distance of
the laser beam spot from the optical axis, while the distance is
not changed. If the object is a sensor device, then preferably the
orientation sensor of the sensor device is used to determine the
orientation, and therefore the tilt, of the sensor device.
[0025] Preferably, the medical tracking system further comprises at
least one display device, in particular for displaying the relative
position between two sensor devices. Further preferably, the
display device is located in a sensor device.
[0026] In a preferred embodiment, a sensor device comprises an
orientation sensor and a position sensor. The sensor device can
then be used in a plurality of tracking applications.
[0027] It is possible to use off-the-shelf (consumer) devices as
sensor devices, such as an iPod touch or an iPhone provided by
Apple Inc.
[0028] In one embodiment, a position sensor is a marker device
detector, at least one sensor device comprises a marker device and
the control unit is configured to select the function of the sensor
device as either acting as a marker device detector or as a marker
device in a step of the medical navigation workflow.
[0029] The present invention further relates to a method of
determining a relative position between two sensor devices of a
medical tracking system. The sensor devices are independently
maneuverable and can be positioned in a fixed position relative to
targets. The method comprises determining sensor data comprising at
least one of orientation data and position data with two or more of
the sensor devices. The method further comprises the step of
transferring the sensor data to a control unit and determining the
relative position between two sensor devices by the control unit by
combining the sensor data.
[0030] The sensor data is in particular determined relative to a
reference, which is also referred to as a relative position
reference. This reference is preferably common to the sensor data
provided by the sensor devices. For example, orientation data
represents the orientation of a sensor device in an in particular
absolute, ground-fixed reference system. The reference might be a
field of force, and may in particular be defined by the direction
of gravity and/or a magnetic field such as the field between the
magnet north and south poles of the earth. By combining the
orientation data of two sensor devices, the control unit can
determine the relative position between the two sensor devices. The
reference can also be an object. Position data may represent the
relative position of a sensor device relative to the reference,
such as a (in particular static) reference object like a marker or
a marker device. The reference object is distinct to the at least
two sensor devices and can be detected by the position sensors of
the at least two sensor devices. With position data representing
the relative positions of two sensor devices to a reference object
being known to the control unit, the control unit can calculate the
relative position between the two sensor devices.
[0031] However, the position data provided by a sensor device can
also be used to determine the position of a marker or a marker
device in a reference system of the sensor device. For example, the
position of a marker device of a pointer can be determined relative
to the sensor device, for example for registering an object to
which the sensor device is attached.
[0032] In addition or as an alternative, the sensor data might
comprise acceleration data representing the acceleration of a
sensor device. By integrating the acceleration over a period of
time, a movement of the sensor device can be calculated. This
movement might be used for determining the relative position
between two sensor devices.
[0033] In a preferred embodiment, each sensor device is attached to
a target, such as an anatomical structure like a bone, a medical
instrument or a part of an operation room infrastructure, and the
relative position of the targets is determined from the relative
position of the sensor devices. The sensor device might also be
integrated into a medical instrument or a part of the operation
room infrastructure
[0034] In one embodiment, a sensor device comprising a marker
device and a position sensor being a marker device detector is used
as a marker device detector in one step of the medical navigation
workflow for obtaining information for determining the position of
a marker device and the same sensor device is used as a marker
device in another step of the medical navigation workflow.
[0035] If the relative position between two sensor devices is
determined repeatedly over time, the relative movement between two
sensor devices can be tracked.
[0036] The present invention further relates to a method for
determining a mechanical property of a joint between two bones,
comprising the steps of: [0037] positioning a first sensor device
in a fixed position relative to the first bone, [0038] registering
the first bone by sampling a plurality of sample points using a
pointer and the first sensor device, [0039] positioning a second
sensor device in a fixed position relative to the second bone,
[0040] registering the second bone by sampling a plurality of
sample points using a pointer and the second sensor device, [0041]
optionally re-positioning the first sensor device in its fixed
position relative to the first bone if the first sensor device was
used as a marker device of the pointer in the previous step, [0042]
determining at least one relative position between the first sensor
device and the second sensor device for at least one position of
the joint as described above and [0043] determining the mechanical
property of the joint between the first bone and the second bone
from the at least one relative position between the first sensor
device and the second sensor device.
[0044] The pointer used for registering the first bone may use the
second sensor device as a marker device. The pointer used for
registering the second bone may use the first sensor device as a
marker device. If the second bone is a bone acting together with a
ball joint, such as the femur or the humerus, then an additional
sample point used for registering the bone can be the center of the
head of the bone. This center is determined by positioning the
first sensor device in a fixed position relative to the bone
forming the other part of the ball joint. The bone is then pivoted
about the ball joint, wherein the second sensor device determines
the relative positions of the first sensor device for a plurality
of positions of the bone. Since the second sensor device moves on a
spherical shell centered about the center of the head of the bone
to be registered, the center of the head can be calculated.
[0045] The mechanical property of the joint is for example the
range of motion, such as the range between full flexion and full
extension, or a lateral tilt between the bones, such as the
varus/valgus angle.
[0046] The present invention further relates to a method for aiding
the adjustment an adjustable cutting block comprising a base and a
cutting slot which is adjustable relative to the base, the base
being attached to a bone, comprising the steps of [0047]
positioning a first sensor device in a fixed position relative to
the cutting slot, [0048] registering the bone by sampling a
plurality of sample points using a pointer and the first sensor
device such that the initial alignment of the cutting slot relative
to the bone is known, [0049] positioning a second sensor device in
a fixed position relative to the base of the cutting block, [0050]
determining the relative position between the first sensor device
and the second sensor device as described above for the initial
alignment of the cutting slot, [0051] determining the relative
position between the first sensor device and the second sensor
device as described above while the cutting slot is adjusted and
[0052] determining the current alignment of the cutting slot from
the initial alignment of the cutting slot and the current relative
position between the first sensor device and the second sensor
device.
[0053] The pointer used for registering the bone may use the one of
the sensor devices as a marker device. If the bone is a bone acting
together with a ball joint, such as the femur or the humerus, then
an additional sample point used for registering the bone can be the
center of the head of the bone. This center is determined by
positioning the second sensor device in a fixed position relative
to the bone forming the other part of the ball joint. The bone is
then pivoted about the ball joint, wherein the first sensor device
determines the relative positions of the second sensor device for a
plurality of positions of the bone. Since the first sensor device
moves on a spherical shell centered about the center of the head of
the bone to be registered, the center of the head can be
calculated.
[0054] The current alignment of the cutting slot can be
continuously compared to a desired alignment, which might be
pre-planned using a 3D scan of the bone and/or the mechanical
property of the bone which is determined as explained above.
[0055] After the cut has been performed using the cutting block,
the cutting surface can be verified by placing a defined surface of
the second sensor device on the cutting surface. Then the relative
position between the first and second sensor device is determined
and the alignment of the cutting surface relative to the bone can
be validated.
[0056] As an option, the at least two sensor devices are brought
into a known relative position between each other, for example by
bringing them in contact, and the at least two sensor devices are
preferably notified about this fact, for example by giving a manual
input to the at least two sensor devices. As an alternative, the
manual input is given to one sensor device which notifies the fact
to at least one other sensor device. The at least two sensor
devices are then in a synchronized state, which means that they
know the relative position between them. The change of the relative
position between the at least two sensor device can then be
tracked, for example from the sensor data.
[0057] As another option, anatomical data from a previous
diagnostic step or other examinations are used to increase the
accuracy of the determined relative position and/or to limit the
degrees of freedom when the relative position is determined. If,
for example, the anatomical data preclude the determined relative
position between the at least two sensor devices, then this may be
indicated and/or the relative position can be determined again. If,
for example, one sensor device is used as a marker device of a
pointer, then implausible relative positions between two sensor
devices can be precluded from the information about the point to be
sampled.
[0058] The method in accordance with the invention is in particular
a data processing method. The data processing method is preferably
performed using technical means, in particular a computer. In
particular, the data processing method is executed by or on the
computer. The computer in particular comprises a processor and a
memory in order to process the data, in particular electronically
and/or optically. The calculating steps described are in particular
performed by a computer. Determining or calculating steps are in
particular steps of determining data within the framework of the
technical data processing method, in particular within the
framework of a program. A computer is in particular any kind of
data processing device, in particular electronic data processing
device. A computer can be a device which is generally thought of as
such, for example desktop PCs, notebooks, netbooks, etc., but can
also be any programmable apparatus, such as for example a mobile
phone or an embedded processor. A computer can in particular
comprise a system (network) of "sub-computers", wherein each
sub-computer represents a computer in its own right. The term of
computer encompasses a cloud computer, in particular a cloud
server. The term of cloud computer encompasses cloud computer
system in particular comprises a system of at least one cloud
computer, in particular plural operatively interconnected cloud
computers such as a server farm. Preferably, the cloud computer is
connected to a wide area network such as the world wide web (WWW).
Such a cloud computer is located in a so-called cloud of computers
which are all connected to the world wide web. Such an
infrastructure is used for cloud computing which describes
computation, software, data access and storage services that do not
require end-user knowledge of physical location and configuration
of the computer that delivers a specific service. In particular,
the term "cloud" is used as a metaphor for the internet (world wide
web). In particular, the cloud provides computing infrastructure as
a service (IaaS). The cloud computer may function as a virtual host
for an operating system and/or data processing application which is
used for executing the inventive method. Preferably, the cloud
computer is an elastic compute cloud (EC2) provided by Amazon Web
Services.TM.. A computer in particular comprises interfaces in
order to receive or output data and/or perform an
analogue-to-digital conversion. The data are in particular data
which represent physical properties and/or are generated from
technical signals. The technical signals are in particular
generated by means of (technical) detection devices (such as for
example devices for detecting marker devices) and/or (technical)
analytical devices (such as for example devices for performing
imaging methods), wherein the technical signals are in particular
electrical or optical signals. The technical signals represent in
particular the data received or outputted by the computer.
[0059] The invention also relates to a program which, when running
on a computer or when loaded onto a computer, causes the computer
to perform one or more or all of the method steps described herein
and/or to a program storage medium on which the program is stored
(in particular in a non-transitory form) and/or to a computer on
which the program is running or into the memory of which the
program is loaded and/or to a signal wave, in particular a digital
signal wave, carrying information which represents the program, in
particular the aforementioned program, which in particular
comprises code means which are adapted to perform any or all of the
method steps described herein.
[0060] Within the framework of the invention, computer program
elements can be embodied by hardware and/or software (this includes
firmware, resident software, micro-code, etc.). Within the
framework of the invention, computer program elements can take the
form of a computer program product which can be embodied by a
computer-usable, in particular computer-readable data storage
medium comprising computer-usable, in particular computer-readable
program instructions, "code" or a "computer program" embodied in
said data storage medium for use on or in connection with the
instruction-executing system. Such a system can be a computer; a
computer can be a data processing device comprising means for
executing the computer program elements and/or the program in
accordance with the invention, in particular a data processing
device comprising a digital processor (central processing
unit--CPU) which executes the computer program elements and
optionally a volatile memory (in particular, a random access
memory--RAM) for storing data used for and/or produced by executing
the computer program elements. Within the framework of the present
invention, a computer-usable, in particular computer-readable data
storage medium can be any data storage medium which can include,
store, communicate, propagate or transport the program for use on
or in connection with the instruction-executing system, apparatus
or device. The computer-usable, in particular computer-readable
data storage medium can for example be, but is not limited to, an
electronic, magnetic, optical, electromagnetic, infrared or
semiconductor system, apparatus or device or a medium of
propagation such as for example the Internet. The computer-usable
or computer-readable data storage medium could even for example be
paper or another suitable medium onto which the program is printed,
since the program could be electronically captured, for example by
optically scanning the paper or other suitable medium, and then
compiled, interpreted or otherwise processed in a suitable manner.
Preferably, the data storage medium is a non-volatile data storage
medium. The computer program product and any software and/or
hardware described here form the various means for performing the
functions of the invention in the example embodiments. The computer
and/or data processing device can in particular include a guidance
information device which includes means for outputting guidance
information. The guidance information can be outputted, for example
to a user, visually by a visual indicating means (for example, a
monitor and/or a lamp) and/or acoustically by an acoustic
indicating means (for example, a loudspeaker and/or a digital
speech output device) and/or tactilely by a tactile indicating
means (for example, a vibrating element or vibration element
incorporated into an instrument).
[0061] The present invention shall be explained in more detail with
reference to the accompanying drawings. The figures show:
[0062] FIG. 1 a schematic structure of a medical tracking
system,
[0063] FIG. 2 a schematic structure of a sensor device,
[0064] FIGS. 3 to 12 visualizations of steps of first medical
navigation workflow, and
[0065] FIGS. 13 to 16 visualizations of steps of a second medical
navigation workflow.
[0066] FIG. 1 schematically shows a medical tracking system, also
referred to as a medical navigation system, comprising two sensor
devices 1 and 2. The structure of the sensor devices 1 and 2 is
shown schematically in FIG. 2.
[0067] In this exemplary example, a sensor device 1, 2 comprises a
processor or central processing unit (CPU) 3 which is connected to
a display 4, the gyroscope 5, two cameras 6 and 7 and a Bluetooth
transceiver 8. The 2D-cameras 6 and 7 are located on opposite sides
of a housing of the sensor device 1, 2. Preferably, camera 6 is
located on the same side as the display 4. The cameras 6 and 7 act
as position sensors. A sensor device 1,2 further comprises an
optional distance sensor 19.
[0068] The gyroscope 5 is configured to determine orientation data
which represent the orientation of the sensor device 1, 2 in three
rotational dimensions in an absolute, ground-fixed reference system
based on the direction of gravity. The gyroscope 5 acts as an
orientation sensor. The processor 3 acts as control unit. This
means that both sensor devices 1, 2 comprise a control unit.
[0069] At least one of the sensor devices 1, 2 comprises optical
markers 9, which in the present case are rectangles or squares. The
markers 9 have the same size and are arranged in a known pattern.
This pattern is preferably three-dimensional, which means that the
markers 9 are preferably arranged in two or more (parallel) planes.
The sizes of some or all of the markers 9 can also be different.
The shape of a sensor device can also be used as a marker.
[0070] FIGS. 3 to 12 show different steps of a first medical
navigation workflow. In the exemplary application of the first
workflow, the properties of a knee joint between a femur F and a
tibia T are determined.
[0071] In the step shown in FIG. 3, an adjustable cutting block 10
is attached to the tibia T. The adjustable cutting block 10
comprises a base 11 and an adjustable cutting slot 12 which is
adjustable relative to the base 11. The first sensor device 1 is
rigidly attached to the cutting slot 12 of the cutting block 10 in
a reproducible position relative to the slot 12. The field of view
of the camera 7 is indicated schematically by the eye symbol.
[0072] In the workflow step shown in FIG. 4, the sensor device 1
acquires the anterioposterior (AP) axis or direction as a property
of the tibia T. The AP direction can be determined automatically,
for example if the patient is lying flat on his back. In this case,
the AP direction can be acquired as being parallel or in a known
relation to gravity.
[0073] In the implementation shown in FIG. 4, the AP direction is
acquired based on manually inputted AP data. In this case, an arrow
virtually representing the AP direction is displayed on the display
4. A user can then input data to align the AP arrow shown on the
display 4 with the actual AP direction of the tibia T. For this
purpose, the AP arrow can be rotated in the display plane, for
example by using buttons (not shown) of the sensor device 1 or by
touching the display 4 if the display 4 is a touch sensitive
display.
[0074] As a preferred option, the AP arrow is overlaid on an image
captured by the camera 7 which is located in the housing of the
sensor device 1 on an opposite side of the display 4. This image
typically shows a part of the tibia, and preferably also a part of
the foot. This overlay leads to an improved accuracy of the
manually inputted AP direction. In addition or as an alternative,
the AP direction can be automatically determined from an image
analysis performed by the CPU 3.
[0075] In general, any property of an anatomical structure can be
acquired by manipulating information, such as an arrow, displayed
on the display of a sensor device.
[0076] In the workflow steps shown in FIGS. 5 and 6, the second
sensor device 2, which comprises markers 9 as explained with
reference to FIG. 2, is rigidly attached to a pointer 13. The
relative position between the markers 9 and the tip of the pointer
13 is known. Additional markers, such as the circles 14, can be
displayed on the display 4 of the sensor device 2. In this workflow
step, the second sensor device 2 acts as a marker device and the
first sensor device 1 acts as a marker device detector. In a
modification of this example, there are no fixed markers 9, but
only markers 14 displayed on the display 4.
[0077] The pointer 13 comprises an adaptor for accommodating a
sensor device 1 or 2 in an unambiguous, reproducible position
relative to its tip. Some or all of the fixed markers 9 may be
located on the pointer 13.
[0078] In the medical workflow, landmarks of the tibia T are
sampled by touching the landmark with the tip of the pointer 13 and
determining the position of the markers 9 and 14. Due to the known
constellation of the markers relative to the tip of the pointer 13,
the position of the tip can be determined from the position of the
markers. The positions of the markers are determined by the sensor
device 1. The camera 7 of the sensor device 1 captures an image
comprising the markers. Due to the known constellation and sizes of
the markers, the CPU 3 of the sensor device 1 can analyze the
output image of the camera 7 in order to detect the markers and
hence the positions of the landmarks in a reference system of the
sensor device 1. The CPU 3 uses the size, the shape and the
relative positions of the markers in the output image of the camera
to determine the position of the tip of the pointer. The position
of the markers may be more accurate by using the distance sensor
19, such as a laser beam generator, to calculate the distance of
the markers from the sensor device.
[0079] A landmark is a defined element of an anatomical body part
which is always identical or recurs with a high degree of
similarity in the same anatomical body part of multiple patients.
Typical landmarks are for example the epicondyles of a femoral bone
or the tips of the transverse processes and/or dorsal process of a
vertebra. The points (main points or auxiliary points) can
represent such landmarks. A landmark which lies on (in particular
on the surface of) a characteristic anatomical structure of the
body part can also represent said structure. The landmark can
represent the anatomical structure as a whole or only a point or
part of it. A landmark can also for example lie on the anatomical
structure, which is in particular a prominent structure. An example
of such an anatomical structure is the posterior aspect of the
iliac crest. Other landmarks include a landmark defined by the rim
of the acetabulum, for instance by the centre of the rim. In
another example, a landmark represents the bottom or deepest point
of an acetabulum, which is derived from a multitude of detection
points. Thus, one landmark can in particular represent a multitude
of detection points. As mentioned above, a landmark can represent
an anatomical characteristic which is defined on the basis of a
characteristic structure of the body part. Additionally, a landmark
can also represent an anatomical characteristic defined by a
relative movement of two body parts, such as the rotational centre
of the femur head when moved relative to the acetabulum.
[0080] A detection point is in particular a point on the surface of
the anatomical structure which is detected, for example by a
pointer.
[0081] In the workflow step shown in FIG. 5, the lateral and medial
malleolus landmarks are determined. In the workflow step shown in
FIG. 6, the proximal endpoint of the tibia mechanical axis is
sampled. With the sampled landmarks and the acquired AP direction,
the tibia T is now registered relative to the sensor device 1. For
the workflow step shown in FIG. 6, the sensor device 1 switches to
the other camera 6, which captures a volume different from the
volume captured by camera 7.
[0082] With the tibia T being registered, the mechanical axis of
the tibia T is known. The reference system of the sensor device 1
is in a known relation to the cutting slot 12. As long as the
adjustment of the cutting slot 12 is not changed compared to the
base 11, then the registration is also known with the base 11 as a
reference.
[0083] In the next workflow steps, the femur F is registered. In
the workflow step shown in FIG. 7, the sensor device 2 is rigidly
attached to an adjustable cutting block 15. A cutting block 15
comprises a base 16 which is rigidly attached to the femur F and a
cutting slot 17 which is adjustable relative to the base 16. The
sensor device 1 is attached to the cutting slot 17.
[0084] In the workflow step shown in FIG. 8, the AP direction of
the femur is acquired. The possibilities for acquiring the AP
direction of the femur F are analog to the possibilities described
for the tibia with reference to FIG. 4, such that a detailed
explanation is omitted.
[0085] In the workflow step shown in FIG. 9, the sensor device 1 is
used in combination with the pointer 13 to sample the distal end
point of the femoral axis.
[0086] In the workflow step shown in FIG. 10, the sensor device 1
is detached from the pointer 13 and rigidly fixed in an absolute
position. For example, the sensor device 1 is rigidly attached to a
tripod or an operation room table, in particular to a rail of the
table. Then, the femur F is pivoted about its head. This means that
the sensor device 2 moves on a spherical shell centered about the
center of the femoral head. Using a camera 6 or 7, the CPU 3 of the
sensor device 2 determines the relative position of the sensor
device 2 by detecting the markers 9 and 14 of the sensor device 1
in analogy to the step described with reference to FIGS. 5, 6 and
9. From the plurality of relative positions P1 to P5 of the sensor
device 2 relative to the sensor device 1 and the known fact that
the sensor device 2 moves on spherical shell about a fixed center,
this center, which is the center of the femoral head, can be
calculated.
[0087] Now that the distal endpoint of the femoral axis, the center
of the femoral head and the AP direction of the femur F are known,
the femur F is registered in a reference system of the sensor
device 2, which is in a fixed relation to a reference system of the
cutting slot 17.
[0088] In the workflow steps shown in FIGS. 9 and 10, the first
sensor device 1 acts as a marker device and the second sensor
device 2 acts as a marker device detector. In general, the function
of a sensor device 1 or 2, that is whether a sensor device acts as
a marker device or a marker detector device, is selected by a CPU 3
based on the currently performed workflow step.
[0089] For the workflow step shown in FIG. 11, the first sensor
device 1 is re-attached to the cutting slot 12 of the cutting block
10 in the same relative position to the cutting slot 12 as in the
workflow steps explained with reference to FIGS. 3 to 6. This means
that, as long as the cutting blocks 10 and 15 are not adjusted, the
sensor device 1 is in a fixed relative and registered position to
the tibia T and the sensor device 2 is in a fixed relative and
registered position to the femur F.
[0090] In the workflow step shown in FIG. 11, a measurement of the
relative position between the two sensor devices 1 and 2 is
performed, including the step of exchanging sensor data and using a
reference. Exchanging means that at least one of the sensor devices
transmits its sensor data, like the orientation data acquired by
its gyroscope 5, to the other sensor device using the Bluetooth
transceivers 8. Preferably, both sensor devices 1 and 2 exchange
their respective orientation data, such that the CPUs 3 of both
sensor devices 1 and 2 know the sensor data, like the orientation
data, of both sensor devices. In this implementation, the gravity
field of the earth acts as a reference for the synchronization.
[0091] In addition or as an alternative, a reference object 18 is
used as a reference. In this implementation, the reference object
18 is imaged by at least one camera 6 or 7 of each sensor device 1
and 2. By image analysis, the relative position of the reference
object 18 relative to the sensor devices 1 and 2 is calculated by
the respective CPU 3. The position data representing the relative
position of the reference object 18 to a sensor device is then
transmitted to the other sensor device using the Bluetooth
transceivers 7. In this implementation, again, the position
information of (just) one sensor device can be transmitted to the
other sensor device, or each sensor device can receive the position
data from the other sensor device.
[0092] After measurement of the relative position, at least one of
the sensor devices 1 or 2 knows the relative position, this means
at least the relative orientation in three-rotational dimensions,
of the other sensor device in its own reference system. The
relative spatial location is not needed in the present workflow,
but may also be determined. Since the tibia T and the femur F are
registered, the sensor device thus also knows the relative position
of the femur F and the tibia T. Preferably, the registration data
representing the relation of the bone and the sensor device is also
transmitted to the other sensor device. This, again, is performed
either in one direction only or both sensor devices transmit the
registration data.
[0093] This approach for determining the relative position between
the two sensor devices can also be used if one of the sensor
devices is used as a marker device detector, such as in the
workflow step shown in FIGS. 5 and 6, either replacing or
supplementing the use of the markers.
[0094] In the workflow step shown in FIG. 12, the tibia T is moved
relative to the femur F using the knee joint. A measurement of the
relative positions between the sensor devices 1 and 2 is performed
in a plurality of positions. For each measurement, the sensor
devices 1 and 2 exchange their orientation data and/or the position
data of the reference object 18 such that at least one of the CPUs
3 can calculate the relative position of the sensor devices 1 and
2, and therefore of the femur F and the tibia T. If one measurement
is taken in full extension and one measurement is taken in full
flexion of the joint, then the range of motion of the knee joint
can be determined. From the relative position, also the varus or
valgus angle can be determined. The values of the range of motion
as well as the varus/valgus value may be shown on the display 4 of
a sensor device, such as depicted in the screenshots in the upper
left of FIG. 12.
[0095] FIGS. 13 to 16 show steps of a second medical workflow.
These steps require the registration of the tibia T and the femur F
as explained above with reference to FIGS. 4 to 6 and 8 to 10, with
the same preconditions that an adjustable cutting block 10 is
attached to the tibia T and an adjustable cutting block 15 is
attached to the femur F. The positional relation between the sensor
device 1 and the cutting slot 12 is known, as is the positional
relation between the sensor device 2 and the cutting slot 17.
[0096] In the workflow step shown in FIG. 13, the sensor device 1
is rigidly attached to the cutting slot 12 and the sensor device 2
is rigidly attached to the base 11 of the cutting block 10. With
the registration of the tibia T in the reference system of the
sensor device 1, and the known relation between the sensor device 1
and the cutting slot 12, the current adjustment of the cutting slot
12 relative to the tibia T can be shown on the display 4 of any of
the sensor devices as indicated in the screenshot shown in the
upper left of FIG. 13.
[0097] A first measurement of the relative position between the
sensor devices 1 and 2 is then performed as explained above with
reference to FIG. 11. If the cutting block 10 is then adjusted, the
relative position between the sensor devices 1 and 2 changes. By
repeatedly measuring the relative position and calculating the
current slot adjustment relative to the tibia T from the relative
position, the cutting slot 12 can be adjusted to a desired setting.
For example, one of the sensor devices 1 and 2 can output
indication information if the current adjustment of the cutting
slot 12 relative to the tibia T equals the desired setting. This
indication information can be of optical, acoustical or tactile
nature.
[0098] In this workflow step, the adjustment of the cutting block
10 is tracked using the sensor device 2 as a reference. If the
sensor device 1 would use gravity as a reference, then any movement
of the tibia T would impair the adjustment of the cutting slot 12.
This is overcome by using the sensor device 2, which is rigidly
attached to the tibia T via the base 11 of the cutting block 10, as
a reference and performing measurements of the relative position by
exchanging the orientation data and/or position data.
[0099] In the optional workflow step shown in FIG. 14, it is
assumed that the cutting process of the tibia T has been performed.
In this workflow step, a defined surface of the sensor device 1 is
laid onto the cut surface of the tibia T. Then, a measurement of
the relative position between the sensor devices 1 and 2 is
performed. From this relative position, the position of the cut
surface relative to the tibia T can be calculated for a
verification step. As indicated in the screenshot in the upper
right in FIG. 14, the actual position of the performed cut is
displayed. By activating the disc symbol in the upper right of the
screenshot, the actual position of the cut surface can be saved for
documentation purposes.
[0100] In the workflow step shown in FIG. 15, the cutting block 15
attached to the femur F is adjusted in analogy to the adjustment
process of the cutting block 10 attached to the tibia T as
described with reference to FIG. 13. However, for the adjustment of
the cutting block 15, the sensor device 1 is rigidly attached to
the base 16 and the sensor device 2 is rigidly attached to the
cutting slot 17 of the cutting block 15.
[0101] In the optional workflow step shown in FIG. 16, a defined
surface of the sensor device 1 is laid onto the cut surface of the
femur F. By measuring the relative position between the sensor
devices 1 and 2, the cutting surface can be verified in analogy to
the process described with reference to FIG. 14. Again, the actual
position of the cut surface can be saved for documentation purposes
by clicking on the disc symbol of the screenshot shown in the upper
left of FIG. 16.
[0102] The desired setting of the cutting slot 12 or 17,
respectively, can be calculated automatically based on a 3D image
dataset representing a 3D image of the tibia or femur,
respectively. In addition or as an alternative, the varus/valgus
value and/or the range of motion acquired in the workflow step
described with reference to FIG. 12 can be used for determining the
desired setting.
[0103] When performing a medical workflow using the medical
tracking system of this exemplary embodiment, the next step of the
workflow is begun once the completion of the previous step is
automatically detected or manually inputted. So the completion is
typically known only to the sensor device which determines the
completion. Thus, this sensor device preferably notifies to the
other sensor device(s) of the tracking system that the next step is
to be performed. This may result in one or more of the sensor
devices to change its function from being a marker device to being
a marker detection device or vice versa. In addition, a sensor
device may display on its display 4 some guidance information on
what to do in the next workflow step, thus leading the operator of
the tracking system through the workflow.
[0104] A sensor device 1, 2 may further comprise an acceleration
sensor (not shown). When the sensor data of the acceleration sensor
is integrated over a period of time, this results in an information
on the change of the position of the sensor device in this period
of time. This information may also be exchanged between the sensor
devices and used for calculating the relative position between the
sensor devices.
[0105] It is to be noted that the methods and workflows described
herein do not relate to or comprise any surgical step. In
particular, attaching a cutting block to a bone and performing a
cut are not part of the present invention. This invention solely
relates to the step of navigating, tracking and verifying by
acquiring and analyzing data.
[0106] Any embodiment described so far may be combined with one or
more features of the following additional embodiments:
EMBODIMENT 1
[0107] A medical tracking system comprising at least one sensor
device (1, 2) which can be positioned in a fixed position relative
to a target (10, 13, 15), the sensor device (1, 2) comprising a
marker device (9, 14) and a marker device detector (6, 7), the
marker device detector (6, 7) being capable of obtaining
information for determining the position of a marker device (9,
14), the system further comprising a control unit (3) configured to
process a medical navigation workflow and to select the function of
the sensor device (1, 2) as either acting as a marker device
detector or as a marker device in a step of the medical navigation
workflow.
EMBODIMENT 2
[0108] The tracking system of embodiment 1, wherein the sensor
device (1, 2) comprises a display (4) for displaying at least a
part (14) of the marker device.
EMBODIMENT 3
[0109] The tracking system of embodiment 1 or 2, wherein the marker
device (9, 14) is an optical marker device and the marker device
detector (6, 7) is a still or video camera.
EMBODIMENT 4
[0110] The tracking system of embodiment 3, wherein the optical
marker device (9, 14) comprises a plurality of squares (9) in a
known configuration.
EMBODIMENT 5
[0111] The tracking system of any one of embodiments 1 to 4,
wherein the tracking system comprises at least two sensor devices
(1, 2), wherein, in a particular step of the medical navigation
workflow, one sensor device (1, 2) acts as a marker device (9, 14)
and another sensor device (1, 2) acts as a marker device detector
(6, 7).
EMBODIMENT 6
[0112] The tracking system of embodiment 5, wherein one of the
sensor devices (1, 2) is positioned in a fixed position relative to
a target (10, 15, F, T) and another sensor device acts as a pointer
(13).
EMBODIMENT 7
[0113] The tracking system of embodiment 5 or 6, wherein the sensor
device acting as a marker device transmits the output data of its
marker device detector, an orientation sensor (5) or an
acceleration sensor as sensor data to the control unit (3), the
sensor device (1, 2) acting as a marker detection device transmits
the output data of its marker detection device (6, 7) as sensor
data to the control unit (3) and the control unit (3) is configured
to receive and combine the sensor data of the sensor devices (1, 2)
in order to determine a relative position between two sensor
devices (1, 2).
EMBODIMENT 8
[0114] The tracking system according to any one of embodiments 1 to
7, wherein a sensor device (1, 2) further comprises an orientation
sensor (5).
EMBODIMENT 9
[0115] A method of medical tracking for supporting a medical
navigation workflow, comprising the steps of using a sensor device
(1, 2) comprising a marker device (9, 14) and a marker device
detector (6, 7) as a marker device detector in one step of the
medical navigation workflow for obtaining information for
determining the position of a marker device (9, 14) and using the
same sensor device (1, 2) as a marker device in another step of the
medical navigation workflow.
EMBODIMENT 10
[0116] The method according to embodiment 9, wherein at least two
sensor devices (1, 2) are used, one of the sensor devices (1, 2)
acting as a marker device of a pointer (13) for pointing at sample
points and another one of the sensor devices (1, 2), being
positioned in a fixed position relative to a target (10, 15, F, T),
acting as a marker device detector for obtaining information for
determining the position of the marker device (9, 14).
EMBODIMENT 11
[0117] The method according to embodiment 10, further comprising
the step of registering the target (10, 15, F, T) by sampling a
plurality of sample points.
EMBODIMENT 12
[0118] The method of embodiment 10 or 11, wherein the sensor device
(1, 2) acting as a marker device and the sensor device (1, 2)
acting as a marker device detector both comprise an orientation
sensor (5) and the orientation sensor data are used when the
position of a marker device is determined
EMBODIMENT 13
[0119] The method of any one of embodiments 9 to 12, further
comprising the steps of [0120] determining sensor data comprising
at least one of orientation data, position data and acceleration
data with two or more of the sensor devices (1, 2) [0121]
transferring the sensor data to a control unit (3) and [0122]
determining the relative position between two sensor devices (1, 2)
by the control unit (3) by combining the sensor data.
EMBODIMENT 14
[0123] The method of any one of embodiment 9 to 13, wherein the
marker detector (6, 7) is a camera and the sensor device (1, 2)
further comprises a display device (4) and is positioned in a fixed
position relative to a bone (F, T), wherein the image captured by
the camera (6, 7) is displayed on the display device (4) and a
characteristic property of the bone (F, T) can be input based on
the camera image on the display device (4).
* * * * *