U.S. patent application number 15/753127 was filed with the patent office on 2019-11-28 for microscope tracking based on video analysis.
The applicant listed for this patent is Brainlab AG. Invention is credited to Sven FLOSSMANN.
Application Number | 20190357982 15/753127 |
Document ID | / |
Family ID | 59761936 |
Filed Date | 2019-11-28 |
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United States Patent
Application |
20190357982 |
Kind Code |
A1 |
FLOSSMANN; Sven |
November 28, 2019 |
Microscope Tracking Based on Video Analysis
Abstract
The present invention relates to a computer-implemented medical
method of determining a spatial position of a medical optical
observation device (1), the method comprising executing, on a
processor of a computer (2), the steps of: --acquiring position
data describing, for a plurality of points in time, the spatial
position of the observation device (1) within a co-ordinate system
of a medical tracking system (3); --determining, based on the
position data, average position data describing an average value
for the position of the observation device (1) within the
co-ordinate system of the medical tracking system (2); --acquiring
image data describing a plurality of images acquired at the
plurality of points in time via a camera (4) assigned to the
observation device (1) and detecting the field of view (5) of the
observation device (1); --determining, based on the image data,
optical flow data describing an optical flow for the plurality of
images; --determining, based on the average position data and the
optical flow data, focal plane position data describing a spatial
position of the focal plane (6) of the observation device (1). The
present invention further relates to a corresponding
computer-program, a corresponding computer storage medium and a
corresponding system for determining the spatial position of a
medical optical observation device.
Inventors: |
FLOSSMANN; Sven;
(Feldkirchen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Brainlab AG |
Munich |
|
DE |
|
|
Family ID: |
59761936 |
Appl. No.: |
15/753127 |
Filed: |
August 24, 2017 |
PCT Filed: |
August 24, 2017 |
PCT NO: |
PCT/EP2017/071276 |
371 Date: |
February 15, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 2034/2051 20160201;
A61B 90/20 20160201; A61B 2034/2055 20160201; A61B 2034/2065
20160201; A61B 2090/373 20160201; A61B 2034/2063 20160201; G06T
2207/30244 20130101; G06T 7/277 20170101; A61B 2090/372 20160201;
A61B 2090/378 20160201; A61B 34/20 20160201; G06T 2207/30004
20130101; A61B 90/37 20160201; A61B 2034/2059 20160201; G06T
2207/10068 20130101; G06T 7/70 20170101; A61B 34/25 20160201; G06T
2207/10056 20130101; A61B 2034/2048 20160201; A61B 2034/2074
20160201 |
International
Class: |
A61B 34/20 20060101
A61B034/20; A61B 90/00 20060101 A61B090/00; A61B 34/00 20060101
A61B034/00; G06T 7/70 20060101 G06T007/70; G06T 7/277 20060101
G06T007/277 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 27, 2016 |
EP |
PCT/EP2016/072930 |
Claims
1.-12. (canceled)
13. A computer-implemented method of determining a spatial position
of a medical optical observation device, the method comprising
executing, on at least one processor, the steps of: acquiring
position data describing, for a plurality of points in time, the
spatial position of the observation device within a co-ordinate
system of a medical tracking system; determining, based on the
position data, average position data describing an average value
for the position of the observation device within the co-ordinate
system of the medical tracking system; acquiring image data
describing a plurality of images acquired at the plurality of
points in time via a camera assigned to the observation device and
detecting the field of view of the observation device; determining,
based on the image data, optical flow data describing an optical
flow for the plurality of images; determining, based on the average
position data and the optical flow data, focal plane position data
describing a spatial position of the focal plane of the observation
device.
14. The method of claim 13, further comprising the step of:
determining, based on the focal plane position data, observation
device position data describing the spatial position of the
observation device within the co-ordinate system of the medical
tracking system.
15. The method of claim 13, wherein the observation device is at
least one of: a medical microscope; a medical endoscope; a medical
exoscope; and head-mounted observation goggles.
16. The method of claim 13, wherein determining optical flow data
involves determining the optical flow for each of the images
acquired, wherein a value of the optical flow of the most recent
image is added to an average value for the optical flow of the
images preceding the most recent image.
17. The method of claim 13, wherein the average value for the
position of the observation device is: an arithmetic average value;
a weighted average value; or an average value obtained from
applying a Kalman-filter.
18. The method of claim 13, wherein the average value for the
optical flow is: an arithmetic average value; a weighted average
value: or an average value obtained from applying a
Kalman-filter.
19. The method of claim 13, wherein the medical tracking system is
at least one of: an active or passive optical tracking system; an
electromagnetic tracking system including at least one field
generator and at least one field sensor; and an ultrasound tracking
system including at least one ultrasound generator and at least one
ultrasound sensor; a mechanical tracking system including at least
one joint position sensor configured to detect a relative position
between two elements connected to each other via a joint,
particularly a ball joint or a rotational joint; and a tracking
system including at least one accelerometer and/or at least one
gyroscope.
20. The method of claim 13, wherein a representation of the focal
plane is presented for display on a display device in its
determined position with respect to an image and/or a
representation of at least one anatomical structure of the
patient.
21. The method of claim 13, wherein the field of view of the
observation device is presented for display on a display device,
being overlaid with an image and/or a representation of at least
one anatomical structure of the patient.
22. The method of claim 13, wherein an image and/or a
representation of at least one anatomical structure of the patient
is projected into the optical path of the observation device.
23. A non-transitory computer readable storage medium storing
computing device instructions executable by a processor to perform
the steps comprising: acquiring position data describing, for a
plurality of points in time, the spatial position of the
observation device within a co-ordinate system of a medical
tracking system; determining, based on the position data, average
position data describing an average value for the position of the
observation device within the co-ordinate system of the medical
tracking system; acquiring image data describing a plurality of
images acquired at the plurality of points in time via a camera
assigned to the observation device and detecting the field of view
of the observation device; determining, based on the image data,
optical flow data describing an optical flow for the plurality of
images; determining, based on the average position data and the
optical flow data, focal plane position data describing a spatial
position of the focal plane of the observation device.
24. A system for determining a spatial position of a medical
optical observation device, comprising: a camera, a medical
tracking system and a computer having at least one processor, the
computer having associated memory and instructions which, when
executed by the at least one processor, causes the at least one
processor to: acquire position data describing, for a plurality of
points in time, the spatial position of the observation device
within a co-ordinate system of a medical tracking system;
determine, based on the position data, average position data
describing an average value for the position of the observation
device within the co-ordinate system of the medical tracking
system; acquire image data describing a plurality of images
acquired at the plurality of points in time via a camera assigned
to the observation device and detecting the field of view of the
observation device; determine, based on the image data, optical
flow data describing an optical flow for the plurality of images;
determine, based on the average position data and the optical flow
data, focal plane position data describing a spatial position of
the focal plane of the observation device.
Description
TECHNICAL FIELD
[0001] The present invention relates to the general technical field
of determining the position of medical optical observation devices
such as medical microscopes during a medical procedure. In
particular, the present invention relates to a computer implemented
method, a computer program and a system for determining the spatial
position of a medical optical observation device.
[0002] In medical procedures such as image-guided surgery (IGS), it
is desirable to know the precise spatial position (including the
spatial location and/or the spatial orientation) of medical
instruments and apparatus with respect to each other and with
respect to anatomical structures of a patient. In regards to
medical optical observation devices such as medical microscopes, it
is desirable to know the precise position of the device relative to
anatomical structures of a patient observed with the device. For
example, medical personnel wishes to associate a visually
identified part of the real body with a specific image feature
representing that part of the real body in order to eventually
determine a location on the specific patient's body part at which a
medical procedure is to be carried out.
[0003] In a more specific application, knowing the precise spatial
relationship between a microscope and the patient allows for:
[0004] visualizing the microscope's focal point on a display of an
IGS system with respect to an image representation or images of
anatomical structures, for example in axial, sagittal and coronal
planes through the anatomy which have been obtained by image
modalities like CT or MR; [0005] superimposing/augmenting the
microscope's field of view with images or representations of
anatomical structures, either on a separate display or by a
semi-transparent projection into the optical path of the
microscope.
[0006] Known solutions for integrating microscopes into an
IGS-environment suggest to calculate the microscope's position
exclusively on tracking data, i.e. on data that is obtained by
determining the spatial position of one or more tracking markers
that are fixedly attached to the microscope. This known approach
may lead to wrong results in determining the microscope's position
with respect to the patient's anatomy, particularly for the reasons
that follow below: [0007] The distance between the microscope focal
plane and the microscope's tracking markers is in many cases rather
big, in most cases between about 300 to 700 mm, wherein the
positional inaccuracies within the focal plane rise with an
increased focal length. [0008] Usually, a microscope's field of
view is, due to the microscope's magnification factor, rather
small, and has for example a diameter between about 20 to 40 mm.
Any tracking inaccuracy is therefore even magnified for the
viewer.
[0009] This may cause the actual position of the focal plane to
deviate from the expected position of the focal plane because of
slight changes of the microscope position, which lie below the
tracking system's detection limit and are therefore not recognized
by the tracking system. Registering the field of view as seen
through the microscope with supplementary image data may therefore
be inaccurate and may lead to an inappropriate augmentation of a
user's view through the microscope.
SUMMARY
[0010] The present invention provides a precise and reliable method
of determining the position of a medical optical observation device
in a medical environment, which in turn allows for an accurate
augmentation of a user's field of view provided by a medical
optical observation device. For reasons of simplicity, the
following specification often refers to a microscope. However, it
should be noted that the present invention can be applied with any
medical optical observation device, including microscopes,
endoscopes, exoscopes or head-mounted goggles.
[0011] The method, the program and the system are defined by the
appended independent claims. 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 wherever
technically expedient and feasible. Specifically, a feature of one
embodiment which has the same or a similar function to another
feature of another embodiment can be exchanged with said other
feature. A feature for an embodiment which adds an additional
function to another embodiment can in particular be added to said
other embodiment.
[0012] A first aspect of the present invention relates to a
computer-implemented medical method of determining a spatial
position of a medical optical observation device, the method
comprising executing, on a processor of a computer, the steps of:
[0013] acquiring position data describing, for a plurality of
points in time, the spatial position of the observation device
within a coordinate system of a medical tracking system; [0014]
determining, based on the position data, average position data
describing an average value for the position of the observation
device within the co-ordinate system of the medical tracking
system; [0015] acquiring image data describing a plurality of
images acquired at the plurality of points in time via a camera
assigned to the observation device and detecting the field of view
of the observation device; [0016] determining, based on the image
data, optical flow data describing an optical flow for the
plurality of images; [0017] determining, based on the average
position data and the optical flow data, focal plane position data
describing a spatial position of the focal plane of the observation
device.
[0018] In other words, the present invention suggests to determine
the spatial position of focal plane of the observation device not
only based on the tracking data obtained from the tracking system
that is assigned to the navigation system, but also on data that is
obtained from the images provided by an optical camera assigned to
the observation device. This camera is adapted to observe the field
of view that is provided by the observation device. In this
respect, it is important to note that the observation device may be
any kind of medical device which receives or transmits
electromagnetic radiation, particularly within the visible range of
light, and which provides a field of view to a user in a direct or
indirect manner. In this context, a direct provision of a field of
view means that the user may use the device in the manner of a
conventional microscope or magnifying glass, with the device
transmitting the electromagnetic radiation to the user's eyes,
wherein an indirect provision means that the device transmits data
describing the received image to a display unit which in turn
displays the corresponding image to the user. In both cases, the
image received by the observation device can be "augmented" with
further visual data, e.g. a registered image overlay.
[0019] According to the present invention, a plurality of (a series
of at least two) subsequent images of the field of view of the
observation device are taken by the camera, wherein for each image
the spatial position of the observation device is determined with
the help of the tracking system. Consequently, the spatial position
of the observation device is known for each image taken. Further,
the spatial position of the focal plane (that includes the focal
point at the center) of the observation device can be calculated
based on the determined position and the adjusted focal length of
the observation device.
[0020] In a further step, an average position of the observation
device is calculated from the plurality of the determined
positions. Additionally, the optical flow of each of the images is
determined from which even small positional changes of the
observation device can be recognized.
[0021] Subsequently, a more accurate spatial position of the focal
plane of the observation device can be calculated based on the
average position of the observation device and the optical flow of
the images.
[0022] According to a further embodiment, the spatial position of
the observation device itself within the co-ordinate system of the
medical tracking unit is finally calculated from the determined
spatial position of the focal plane. Since the calculated position
of the focal plane is not only based on tracking data but also
takes into account an average value for the position of the
observation device and the optical flow of the obtained images, the
position of the observation device can be determined much more
accurately than with known methods that only consider the tracking
data obtained from a tracking system.
[0023] As already indicated above, the medical optical observation
device may be any device which provides a user with an optical
image, and which is provided with a camera recording the
observation device's field of view. The inventive method may
therefore be applied to improve determining the spatial position of
any observation device, but may be in particular be used to improve
determining the spatial position of a medical microscope, a medical
endoscope, a medical exoscope or head-mounted observation goggles.
In recent years, such observation goggles are increasingly used in
various technical fields, including image guided surgery,
particularly in the context of so-called augmented reality. A first
kind of such observation goggles comprise miniaturized displays in
front of the user's eyes, that can display any kind of information.
The goggles are equipped with a position sensor by means of which
the spatial orientation of the user's head is determined, and the
information displayed in front of the user's eyes can be adapted in
accordance with the orientation of the user's head. A second kind
of observation goggles differs from the first kind only in that a
semi-transparent screen is provided, through which the user can see
the surrounding area, but which also serves as a head-up-display in
that additional visual information can be projected into the user's
field of view.
[0024] According to a further embodiment of the present invention,
the optical flow is determined for each one of the acquired images,
wherein an "average optical flow" is calculated for an image series
including each acquired image except for the most recent one. The
value for the optical flow of the most recent image is then added
to the average value for the optical flow for the set of the
preceding images. The spatial position of the focal plane and/or
the observation device is then calculated by taking into account
this combined value for the optical flow.
[0025] The average value for the position of the observation device
and/or the average value for the optical flow may be calculated as
an arithmetic average value calculated from the underlying
individual values. On the other hand, the average value may be a
weighted average value calculated from individual values that each
have been provided with a weighting factor. In particular, the more
recent or later values may be provided with a higher weighting
factor than the less recent ones. It is, however, also conceivable
that the average value is calculated by applying a Kalman-Filter on
the individual values underlying the calculation.
[0026] In an even further embodiment, the tracking system for
determining the spatial position of the observation device is
selected from the group consisting of: [0027] an active or passive
optical tracking system, particularly operating within the range of
IR-light; [0028] an electromagnetic tracking system comprising at
least one field generator and at least one field sensor; and [0029]
an ultrasound tracking system comprising at least one ultrasound
generator and at least one ultrasound sensor; [0030] a mechanical
tracking system comprising at least one joint position sensor
configured to detect a relative position between two elements
connected to each other via a joint, particularly a ball joint or a
rotational joint; and [0031] a tracking system comprising at least
one accelerometer and/or at least one gyroscope.
[0032] With the spatial position of the focal plane/focal point
being determined more accurately, the spatial position of the focal
plane/focal point can be displayed on a display in its determined
position with respect to anatomical structures of the patient. In a
similar manner, the field of view as seen by the observation device
can be also displayed on a display device and may further be
overlaid with an image and/or a representation of at least one
anatomical structure of the patient. Such image can be obtained
from any conceivable imaging modality, such as X-ray, CT, MRI or
ultrasound modality. Further, an anatomical atlas may provide the
display with a registered representation of one or more structures
that can be seen in the image provided by the observation device,
which may also help in identifying structures which are difficult
to identify within the visible range of light. In a quite similar
way, an image and/or a representation of at least one anatomical
structure of the patient can be registered with the device's field
of view, and projected into the optical path of the observation
device. By doing so, the user is provided with additional image
information when looking through the observation device. In this
context, a microscope or head-mounted observation goggles may
comprise a head-up-display that provides additional information to
the user.
[0033] A further aspect of the present invention relates to a
program, which, when running on a computer, causes the computer to
perform the method steps of a method as described above and/or a
computer storage medium on which the program is stored, in
particular in a non-transitory form.
Definitions
[0034] The present invention also relates to a system for
determining a spatial position of a medical optical observation
device, comprising a medical tracking system, a computer on which
the above described program is stored and/or run and an optical
observation device having a camera that observes the device's field
of view.
[0035] The method in accordance with the invention is for example a
computer implemented method. For example, all the steps or merely
some of the steps (i.e. less than the total number of steps) of the
method in accordance with the invention can be executed by a
computer (for example, at least one computer). An embodiment of the
computer implemented method is a use of the computer for performing
a data processing method. An embodiment of the computer implemented
method is a method concerning the operation of the computer such
that the computer is operated to perform one, more or all steps of
the method.
[0036] The computer for example comprises at least one processor
and for example at least one memory in order to (technically)
process the data, for example electronically and/or optically. The
processor being for example made of a substance or composition
which is a semiconductor, for example at least partly n- and/or
p-doped semiconductor, for example at least one of II-, III-, IV-,
V-, VI-semiconductor material, for example (doped) silicon and/or
gallium arsenide. The calculating steps described are for example
performed by a computer. Determining steps or calculating steps are
for example steps of determining data within the framework of the
technical method, for example within the framework of a program. A
computer is for example any kind of data processing device, for
example 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 for example comprise a system (network)
of "sub-computers", wherein each sub-computer represents a computer
in its own right. The term "computer" includes a cloud computer,
for example a cloud server. The term "cloud computer" includes a
cloud computer system which for example comprises a system of at
least one cloud computer and for example a plurality of operatively
interconnected cloud computers such as a server farm. Such a cloud
computer is preferably connected to a wide area network such as the
world wide web (WWW) and 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 which do
not require the end user to know the physical location and/or
configuration of the computer delivering a specific service. For
example, the term "cloud" is used in this respect as a metaphor for
the Internet (world wide web). For example, the cloud provides
computing infrastructure as a service (IaaS). The cloud computer
can function as a virtual host for an operating system and/or data
processing application which is used to execute the method of the
invention. The cloud computer is for example an elastic compute
cloud (EC2) as provided by Amazon Web Services.TM.. A computer for
example comprises interfaces in order to receive or output data
and/or perform an analogue-to-digital conversion. The data are for
example data which represent physical properties and/or which are
generated from technical signals. The technical signals are for
example 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 (medical) imaging methods), wherein the technical
signals are for example electrical or optical signals. The
technical signals for example represent the data received or
outputted by the computer. The computer is preferably operatively
coupled to a display device which allows information outputted by
the computer to be displayed, for example to a user. One example of
a display device is an augmented reality device (also referred to
as augmented reality glasses) which can be used as "goggles" for
navigating. A specific example of such augmented reality glasses is
Google Glass (a trademark of Google, Inc.). An augmented reality
device can be used both to input information into the computer by
user interaction and to display information outputted by the
computer. Another example of a display device would be a standard
computer monitor comprising for example a liquid crystal display
operatively coupled to the computer for receiving display control
data from the computer for generating signals used to display image
information content on the display device. A specific embodiment of
such a computer monitor is a digital lightbox. The monitor may also
be the monitor of a portable, for example handheld, device such as
a smart phone or personal digital assistant or digital media
player.
[0037] The expression "acquiring data" for example encompasses
(within the framework of a computer implemented method) the
scenario in which the data are determined by the computer
implemented method or program. Determining data for example
encompasses measuring physical quantities and transforming the
measured values into data, for example digital data, and/or
computing the data by means of a computer and for example within
the framework of the method in accordance with the invention. The
meaning of "acquiring data" also for example encompasses the
scenario in which the data are received or retrieved by the
computer implemented method or program, for example from another
program, a previous method step or a data storage medium, for
example for further processing by the computer implemented method
or program. Generation of the data to be acquired may but need not
be part of the method in accordance with the invention. The
expression "acquiring data" can therefore also for example mean
waiting to receive data and/or receiving the data. The received
data can for example be inputted via an interface. The expression
"acquiring data" can also mean that the computer implemented method
or program performs steps in order to (actively) receive or
retrieve the data from a data source, for instance a data storage
medium (such as for example a ROM, RAM, database, hard drive,
etc.), or via the interface (for instance, from another computer or
a network). The data acquired by the disclosed method or device,
respectively, may be acquired from a database located in a data
storage device which is operably to a computer for data transfer
between the database and the computer, for example from the
database to the computer. The computer acquires the data for use as
an input for steps of determining data. The determined data can be
output again to the same or another database to be stored for later
use. The database or database used for implementing the disclosed
method can be located on network data storage device or a network
server (for example, a cloud data storage device or a cloud server)
or a local data storage device (such as a mass storage device
operably connected to at least one computer executing the disclosed
method). The data can be made "ready for use" by performing an
additional step before the acquiring step. In accordance with this
additional step, the data are generated in order to be acquired.
The data are for example detected or captured (for example by an
analytical device). Alternatively or additionally, the data are
inputted in accordance with the additional step, for instance via
interfaces. The data generated can for example be inputted (for
instance into the computer). In accordance with the additional step
(which precedes the acquiring step), the data can also be provided
by performing the additional step of storing the data in a data
storage medium (such as for example a ROM, RAM, CD and/or hard
drive), such that they are ready for use within the framework of
the method or program in accordance with the invention. The step of
"acquiring data" can therefore also involve commanding a device to
obtain and/or provide the data to be acquired. In particular, the
acquiring step does not involve an invasive step which would
represent a substantial physical interference with the body,
requiring professional medical expertise to be carried out and
entailing a substantial health risk even when carried out with the
required professional care and expertise. In particular, the step
of acquiring data, for example determining data, does not involve a
surgical step and in particular does not involve a step of treating
a human or animal body using surgery or therapy. In order to
distinguish the different data used by the present method, the data
are denoted (i.e. referred to) as "XY data" and the like and are
defined in terms of the information which they describe, which is
then preferably referred to as "XY information" and the like.
[0038] Image registration is the process of transforming different
sets of data into one co-ordinate system. The data can be multiple
photographs and/or data from different sensors, different times or
different viewpoints. It is used in computer vision, medical
imaging and in compiling and analysing images and data from
satellites. Registration is necessary in order to be able to
compare or integrate the data obtained from these different
measurements.
[0039] The invention also relates to a program which, when running
on 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 comprising said program
storage medium and/or to a (physical, for example electrical, for
example technically generated) signal wave, for example a digital
signal wave, carrying information which represents the program, for
example the aforementioned program, which for example comprises
code means which are adapted to perform any or all of the method
steps described herein.
[0040] The invention also relates to a navigation system for
computer-assisted surgery, comprising:
the computer of the preceding claim, for processing the absolute
point data and the relative point data; a detection device for
detecting the position of the main and auxiliary points in order to
generate the absolute point data and to supply the absolute point
data to the computer; a data interface for receiving the relative
point data and for supplying the relative point data to the
computer; and a user interface for receiving data from the computer
in order to provide information to the user, wherein the received
data are generated by the computer on the basis of the results of
the processing performed by the computer.
[0041] 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, for example computer-readable data storage medium
comprising computer-usable, for example 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, for example a data processing device
comprising a digital processor (central processing unit or CPU)
which executes the computer program elements, and optionally a
volatile memory (for example a random access memory or 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, for example 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, for example 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.
The data storage medium is preferably 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 for example 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 a vibration element
incorporated into an instrument). For the purpose of this document,
a computer is a technical computer which for example comprises
technical, for example tangible components, for example mechanical
and/or electronic components. Any device mentioned as such in this
document is a technical and for example tangible device.
[0042] It is the function of a marker to be detected by a marker
detection device (for example, a camera or an ultrasound receiver
or analytical devices such as CT or MRI devices) in such a way that
its spatial position (i.e. its spatial location and/or alignment)
can be ascertained. The detection device is for example part of a
navigation system. The markers can be active markers. An active
marker can for example emit electromagnetic radiation and/or waves
which can be in the infrared, visible and/or ultraviolet spectral
range. A marker can also however be passive, i.e. can for example
reflect electromagnetic radiation in the infrared, visible and/or
ultraviolet spectral range or can block x-ray radiation. To this
end, the marker can be provided with a surface which has
corresponding reflective properties or can be made of metal in
order to block the x-ray radiation. 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 however
also exhibit a cornered, for example cubic, shape.
[0043] A marker device can for example be a reference star or a
pointer or a single marker or a plurality of (individual) markers
which are then preferably in a predetermined spatial relationship.
A marker device comprises one, two, three or more markers, wherein
two or more such markers are in a predetermined spatial
relationship. This predetermined spatial relationship is for
example known to a navigation system and is for example stored in a
computer of the navigation system.
[0044] In another embodiment, a marker device comprises an optical
pattern, for example on a two-dimensional surface. The optical
pattern might comprise a plurality of geometric shapes like
circles, rectangles and/or triangles. The optical pattern can be
identified in an image captured by a camera, and the position of
the marker device relative to the camera can be determined from the
size of the pattern in the image, the orientation of the pattern in
the image and the distortion of the pattern in the image. This
allows to determine the relative position in up to three rotational
dimensions and up to three translational dimensions from a single
two-dimensional image.
[0045] The position of a marker device can be ascertained, for
example by a medical navigation system. If the marker device is
attached to an object, such as a bone or a medical instrument, the
position of the object can be determined from the position of the
marker device and the relative position between the marker device
and the object. Determining this relative position is also referred
to as registering the marker device and the object. The marker
device or the object can be tracked, which means that the position
of the marker device or the object is ascertained twice or more
over time.
[0046] The present invention is also directed to a navigation
system for computer-assisted surgery. This navigation system
preferably comprises the aforementioned computer for processing the
data provided in accordance with the computer implemented method as
described in any one of the embodiments described herein. The
navigation system preferably comprises a detection device for
detecting the position of detection points which represent the main
points and auxiliary points, in order to generate detection signals
and to supply the generated detection signals to the computer, such
that the computer can determine the absolute main point data and
absolute auxiliary point data on the basis of the detection signals
received. A detection point is for example a point on the surface
of the anatomical structure which is detected, for example by a
pointer. In this way, the absolute point data can be provided to
the computer. The navigation system also preferably comprises a
user interface for receiving the calculation results from the
computer (for example, the position of the main plane, the position
of the auxiliary plane and/or the position of the standard plane).
The user interface provides the received data to the user as
information. Examples of a user interface include a display device
such as a monitor, or a loudspeaker. The user interface can use any
kind of indication signal (for example a visual signal, an audio
signal and/or a vibration signal). One example of a display device
is an augmented reality device (also referred to as augmented
reality glasses) which can be used as so-called "goggles" for
navigating. A specific example of such augmented reality glasses is
Google Glass (a trademark of Google, Inc.). An augmented reality
device can be used both to input information into the computer of
the navigation system by user interaction and to display
information outputted by the computer.
[0047] A navigation system, such as a surgical navigation system,
is understood to mean a system which can comprise: at least one
marker device; a transmitter which emits electromagnetic waves
and/or radiation and/or ultrasound waves; a receiver which receives
electromagnetic waves and/or radiation and/or ultrasound waves; and
an electronic data processing device which is connected to the
receiver and/or the transmitter, wherein the data processing device
(for example, a computer) for example comprises a processor (CPU)
and a working memory and advantageously an indicating device for
issuing an indication signal (for example, a visual indicating
device such as a monitor and/or an audio indicating device such as
a loudspeaker and/or a tactile indicating device such as a
vibrator) and a permanent data memory, wherein the data processing
device processes navigation data forwarded to it by the receiver
and can advantageously output guidance information to a user via
the indicating device. The navigation data can be stored in the
permanent data memory and for example compared with data stored in
said memory beforehand.
[0048] Preferably, atlas data is acquired which describes (for
example defines, more particularly represents and/or is) a general
three-dimensional shape of the anatomical body part. The atlas data
therefore represents an atlas of the anatomical body part. An atlas
typically consists of a plurality of generic models of objects,
wherein the generic models of the objects together form a complex
structure. For example, the atlas constitutes a statistical model
of a patient's body (for example, a part of the body) which has
been generated from anatomic information gathered from a plurality
of human bodies, for example from medical image data containing
images of such human bodies. In principle, the atlas data therefore
represents the result of a statistical analysis of such medical
image data for a plurality of human bodies. This result can be
output as an image--the atlas data therefore contains or is
comparable to medical image data. Such a comparison can be carried
out for example by applying an image fusion algorithm which
conducts an image fusion between the atlas data and the medical
image data. The result of the comparison can be a measure of
similarity between the atlas data and the medical image data. The
atlas data comprises positional information which can be matched
(for example by applying an elastic or rigid image fusion
algorithm) for example to positional information contained in
medical image data so as to for example compare the atlas data to
the medical image data in order to determine the position of
anatomical structures in the medical image data which correspond to
anatomical structures defined by the atlas data.
[0049] The human bodies, the anatomy of which serves as an input
for generating the atlas data, advantageously share a common
feature such as at least one of gender, age, ethnicity, body
measurements (e.g. size and/or mass) and pathologic state. The
anatomic information describes for example the anatomy of the human
bodies and is extracted for example from medical image information
about the human bodies. The atlas of a femur, for example, can
comprise the head, the neck, the body, the greater trochanter, the
lesser trochanter and the lower extremity as objects which together
make up the complete structure. The atlas of a brain, for example,
can comprise the telencephalon, the cerebellum, the diencephalon,
the pons, the mesencephalon and the medulla as the objects which
together make up the complex structure. One application of such an
atlas is in the segmentation of medical images, in which the atlas
is matched to medical image data, and the image data are compared
with the matched atlas in order to assign a point (a pixel or
voxel) of the image data to an object of the matched atlas, thereby
segmenting the image data into objects.
[0050] In the field of medicine, imaging methods (also called
imaging modalities and/or medical imaging modalities) are used to
generate image data (for example, two-dimensional or
three-dimensional image data) of anatomical structures (such as
soft tissues, bones, organs, etc.) of the human body. The term
"medical imaging methods" is understood to mean (advantageously
apparatus-based) imaging methods (for example so-called medical
imaging modalities and/or radiological imaging methods) such as for
instance computed tomography (CT) and cone beam computed tomography
(CBCT, such as volumetric CBCT), x-ray tomography, magnetic
resonance tomography (MRT or MRI), conventional x-ray, sonography
and/or ultrasound examinations, and positron emission tomography.
For example, the medical imaging methods are performed by the
analytical devices. Examples for medical imaging modalities applied
by medical imaging methods are: X-ray radiography, magnetic
resonance imaging, medical ultrasonography or ultrasound,
endoscopy, elastography, tactile imaging, thermography, medical
photography and nuclear medicine functional imaging techniques as
positron emission tomography (PET) and Single-photon emission
computed tomography (SPECT), as mentioned by Wikipedia.
[0051] The image data thus generated is also termed "medical
imaging data". Analytical devices for example are used to generate
the image data in apparatus-based imaging methods. The imaging
methods are for example used for medical diagnostics, to analyse
the anatomical body in order to generate images which are described
by the image data. The imaging methods are also for example used to
detect pathological changes in the human body. However, some of the
changes in the anatomical structure, such as the pathological
changes in the structures (tissue), may not be detectable and for
example may not be visible in the images generated by the imaging
methods. A tumor represents an example of a change in an anatomical
structure. If the tumor grows, it may then be said to represent an
expanded anatomical structure. This expanded anatomical structure
may not be detectable; for example, only a part of the expanded
anatomical structure may be detectable. Primary/high-grade brain
tumors are for example usually visible on MRI scans when contrast
agents are used to infiltrate the tumor. MRI scans represent an
example of an imaging method. In the case of MRI scans of such
brain tumors, the signal enhancement in the MRI images (due to the
contrast agents infiltrating the tumor) is considered to represent
the solid tumor mass. Thus, the tumor is detectable and for example
discernible in the image generated by the imaging method. In
addition to these tumors, referred to as "enhancing" tumors, it is
thought that approximately 10% of brain tumors are not discernible
on a scan and are for example not visible to a user looking at the
images generated by the imaging method.
[0052] Image fusion can be elastic image fusion or rigid image
fusion. In the case of rigid image fusion, the relative position
between the pixels of a 2D image and/or voxels of a 3D image is
fixed, while in the case of elastic image fusion, the relative
positions are allowed to change.
[0053] In this application, the term "image morphing" is also used
as an alternative to the term "elastic image fusion", but with the
same meaning.
[0054] Elastic fusion transformations (for example, elastic image
fusion transformations) are for example designed to enable a
seamless transition from one dataset (for example a first dataset
such as for example a first image) to another dataset (for example
a second dataset such as for example a second image). The
transformation is for example designed such that one of the first
and second datasets (images) is deformed, for example in such a way
that corresponding structures (for example, corresponding image
elements) are arranged at the same position as in the other of the
first and second images. The deformed (transformed) image which is
transformed from one of the first and second images is for example
as similar as possible to the other of the first and second images.
Preferably, (numerical) optimization algorithms are applied in
order to find the transformation which results in an optimum degree
of similarity. The degree of similarity is preferably measured by
way of a measure of similarity (also referred to in the following
as a "similarity measure"). The parameters of the optimization
algorithm are for example vectors of a deformation field. These
vectors are determined by the optimization algorithm in such a way
as to result in an optimum degree of similarity. Thus, the optimum
degree of similarity represents a condition, for example a
constraint, for the optimization algorithm. The bases of the
vectors lie for example at voxel positions of one of the first and
second images which is to be transformed, and the tips of the
vectors lie at the corresponding voxel positions in the transformed
image. A plurality of these vectors is preferably provided, for
instance more than twenty or a hundred or a thousand or ten
thousand, etc. Preferably, there are (other) constraints on the
transformation (deformation), for example in order to avoid
pathological deformations (for instance, all the voxels being
shifted to the same position by the transformation). These
constraints include for example the constraint that the
transformation is regular, which for example means that a Jacobian
determinant calculated from a matrix of the deformation field (for
example, the vector field) is larger than zero, and also the
constraint that the transformed (deformed) image is not
self-intersecting and for example that the transformed (deformed)
image does not comprise faults and/or ruptures. The constraints
include for example the constraint that if a regular grid is
transformed simultaneously with the image and in a corresponding
manner, the grid is not allowed to interfold at any of its
locations. The optimizing problem is for example solved
iteratively, for example by means of an optimization algorithm
which is for example a first-order optimization algorithm, such as
a gradient descent algorithm. Other examples of optimization
algorithms include optimization algorithms which do not use
derivations, such as the downhill simplex algorithm, or algorithms
which use higher-order derivatives such as Newton-like algorithms.
The optimization algorithm preferably performs a local
optimization. If there is a plurality of local optima, global
algorithms such as simulated annealing or generic algorithms can be
used. In the case of linear optimization problems, the simplex
method can for instance be used.
[0055] In the steps of the optimization algorithms, the voxels are
for example shifted by a magnitude in a direction such that the
degree of similarity is increased. This magnitude is preferably
less than a predefined limit, for instance less than one tenth or
one hundredth or one thousandth of the diameter of the image, and
for example about equal to or less than the distance between
neighboring voxels. Large deformations can be implemented, for
example due to a high number of (iteration) steps.
[0056] The determined elastic fusion transformation can for example
be used to determine a degree of similarity (or similarity measure,
see above) between the first and second datasets (first and second
images). To this end, the deviation between the elastic fusion
transformation and an identity transformation is determined. The
degree of deviation can for instance be calculated by determining
the difference between the determinant of the elastic fusion
transformation and the identity transformation. The higher the
deviation, the lower the similarity, hence the degree of deviation
can be used to determine a measure of similarity.
[0057] A measure of similarity can for example be determined on the
basis of a determined correlation between the first and second
datasets.
[0058] In particular, the invention does not involve or in
particular comprise or encompass an invasive step which would
represent a substantial physical interference with the body
requiring professional medical expertise to be carried out and
entailing a substantial health risk even when carried out with the
required professional care and expertise. For example, the
invention does not comprise a step of positioning a medical implant
in order to fasten it to an anatomical structure or a step of
fastening the medical implant to the anatomical structure or a step
of preparing the anatomical structure for having the medical
implant fastened to it. More particularly, the invention does not
involve or in particular comprise or encompass any surgical or
therapeutic activity. The invention is instead directed as
applicable to positioning a tool relative to the medical implant,
which may be outside the patient's body. For this reason alone, no
surgical or therapeutic activity and in particular no surgical or
therapeutic step is necessitated or implied by carrying out the
invention.
BRIEF DESCRIPTION OF DRAWINGS
[0059] In the following, the invention is described with reference
to the enclosed figures which represent preferred embodiments of
the invention. The scope of the invention is however not limited to
the specific features disclosed in the figures which show:
[0060] FIG. 1 an IGS-setup according to the present invention,
employing a tracked microscope;
[0061] FIG. 2 a method according to the present invention.
DETAILED DESCRIPTION
[0062] FIG. 1 shows an IGS-setup that employs a surgical microscope
1 for obtaining images of a patient, in the shown example a
patient's head 9 which contains a specific anatomical structure 8
that is of interest during a surgical procedure. The microscope 1
is mounted on a support arm 12 and is oriented towards the patient
9 in order to have the anatomical structure 8 within the field of
view 5 of the microscope 1. For obtaining focused microscope images
of the structure 8, the focal distance w.sub.d has to be adjusted
such that the structure 8 lies within the focal plane 6.
[0063] Further, the microscope 1 comprises an internal optical
camera 4 that observes the field of view 5 of the microscope 1 and
is adjusted to the focal length w.sub.d, as well.
[0064] Both, respectively, the microscope 1 and the patient 9 are
provided with tracking markers 10 and 11 which can be spatially
determined by means of a tracking system (represented by the
stereoscopic camera array 3). The positional information provided
by the tracking system 3 is processed by a computer 2 thus
comprises a display 7 and is connected to the tracking system (as
indicated by a first double-arrow in FIG. 1).
[0065] For calculating the spatial position of the microscope 1
and/or the spatial position of the focal plane 6, the inventive
system does not only consider the obtained positional data of the
microscope 1 and the structure 8, but also considers the optical
flow of the images provided by camera 4 (which provides computer 2
with camera images and is therefore also connected to computer 2 as
indicated by a second double-arrow). In a specific example, the
system performs a position-determining method as outlined
below:
[0066] At first, the spatial position P.sub.Mi of the microscope is
determined via the tracking system 3 for a plurality of subsequent
points in time (P.sub.M1, P.sub.M2, . . . , P.sub.Mn).
[0067] Additionally, the optical flow F.sub.i for each image of an
image series (I.sub.1, I.sub.2, . . . , I.sub.n) for these points
in time is calculated, for example by using the Lucas-Kanade
method. As the optical flow usually provides several transformation
vectors for different points (V.sub.lik) in the image, an average
over the transformation vectors (F.sub.i=avg.sub.i(V.sub.lik) is
calculated. It is, however, also possible to filter out outlying
transformation vectors which may result from movements of objects
such as surgical instrument within the image, so as to consolidate
different transformation vectors. In case the entire image has
moved uniformly, the optical flow is simply calculated from one
single transformation vector.
[0068] Based on the determined position and on the determined
optical flow, the final position of the focus plane P.sub.Fn can be
calculated as a function of the determined positions and the
determined optical flow, for example by the formula
P.sub.Fn=P.sub.A+F.sub.A+F.sub.n), wherein P.sub.A is an average
value over the determined positions of the microscope, F.sub.A is
an average value over the optical flow determined for the series of
all images except for the most recent one, and F.sub.n is the value
for the optical flow determined for the most recent image.
[0069] Based on the known position of the focus plane P.sub.Fn, the
position of the microscope P'.sub.Mn can finally be calculated.
[0070] FIG. 2 shows the basic steps of the inventive method. Based
on acquired position data, average position data is calculated,
wherein based on image data, optical flow data is calculated. Based
on the calculated average position data and on the calculated
optical flow data, focal plane position data is calculated. Based
on the focal plane position data, it is further possible to finally
calculate the observation device position data.
* * * * *