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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a procedure for the correlation of
different coordinate systems in computer-supported, stereotactic surgery
without the use of additional so-called referencing markers.
In computer-supported, stereotactic surgery it is necessary to correlate
different coordinate systems with each other when diagnostic data
generated prior to surgery by means of an NMR tomograph, for example, is
to be used for optimizing orientation during surgery. This is necessary,
for example, if such pictorial information must be superposed on a image
obtained of the surgical field. The current image of the surgical field
may consist of the field of view seen in a surgical microscope, or of a
monitor image generated with a video camera.
2. Discussion of Prior Art
Normally, the necessary correlation is performed by adopting a referencing
procedure in which so-called referencing markers are measured on a
patient, with the coordinate positions of these markers relative to the
patient's coordinate system and relative to the diagnostic data coordinate
system being known. Such marker measurement can be performed, for example,
using a surgical microscope such as the one disclosed in German patent
application 41 34 481 of the applicants' assignee, corresponding to U.S.
Pat. No. 5,359,417.
As an alternative, the markers can also be measured by means of so-called
laser pointers which are placed on the surgical microscope. The U.S. Pat.
No. 5,279,309 discloses that such markers can be implemented in the form
of miniature transmitters placed on the patient and located via
appropriate detectors.
A disadvantage of all known procedures based on referencing using markers,
however, is that these procedures are relatively time-consuming and must
be repeated if the patient's position may have changed.
Also, it is always necessary to perform the imaging diagnostic procedures
with these markers. This puts the patient under stress if the markers must
be implanted as described, for example, in U.S. Pat. No. 5,178,164.
OBJECT OF THE INVENTION
It is therefore the objective of the present invention to provide a
procedure which makes it possible to correlate the diagnostic data
generated prior to surgery with the current topographical data of the
patient by using a surgical microscope, without the need for measuring the
coordinates or locating separate referencing markers. In particular, it is
intended to improve the stereotactic application possibilities of a
surgical microscope.
This problem is solved by a procedure for correlation of different
coordinate systems in computer-supported stereotactic surgery without use
of additional referencing markers that includes: using a surgical
microscope mounted on a carrier system to obtain partial topographical
information and spatially correlating the partial topographical
information with diagnostic data generated prior to surgery via a
correlation algorithm.
In accordance with the invention, no separate markers are now used to
perform the correlation of different coordinate systems in a
time-consuming referencing procedure. Instead, the surgical microscope
mounted on a suitable carrier system is used directly for the acquisition
of at least partial topographical information of the patient. The partial
topographical information obtained with the surgical microscope is
subsequently digitized and correlated with the diagnostic data records
generated prior to surgery via known algorithms.
Totally different imaging procedures can be used in combination with the
procedure according to the invention to obtain the diagnostic data records
generated prior to surgery. As examples, the neutron magnetic resonance
tomography (NMR), the positron emission tomography (PET), the magnet
enzephalography (MEG) and the single photon emission computer tomography
(SPECT) are specified here as modern diagnostic procedures, which can all
be used on their own or in any combination.
Partial topographical information using the surgical microscope can be
obtained in different ways. A suitable embodiment of the procedure
according to the invention can be selected as a function of the desired
outlay and the specific requirements.
The surgical microscope must be configurated in accordance with the
procedure in question.
The time-consuming referencing procedures using separate referencing
markers and the resulting complex operational procedures including the
related patient stress involved if such markers need to be implanted, are
no longer required.
Furthermore, the virtually automated acquisition of partial topographical
information using the surgical microscope permits fast re-correlation of
the different coordinate systems if the patient's current position or the
position of parts of the patient's body has changed.
DESCRIPTION OF THE DRAWINGS
Further advantages and details of the procedure according to the invention
and different embodiments thereof can be taken from the following
description of examples based on the annexed figures in which:
FIG. 1 shows a block diagram with the most important components required
for performing the procedure according to the invention.
FIG. 2 shows a flow diagram of a first embodiment of the procedure
according to the invention.
FIG. 3a shows a flow diagram of a second embodiment of the procedure
according to the invention.
FIG. 3b shows the contours visible in the field of view of the surgical
microscope which can be used for referencing in a second embodiment of the
procedure according to the invention.
FIG. 4 shows a flow diagram of a third embodiment of the procedure
according to the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The acquisition of at least partial topographical information according to
the invention using a surgical microscope mounted on a motorized carrier
system can be performed in different ways. Different embodiments of the
procedure according to the invention are described in the following on the
basis of FIGS. 2-4.
All described embodiments of the procedure according to the invention have
in common the fundamental system configuration with the necessary basic
components of a fixture suitable for this purpose. The most important
required components are schematically shown in the block diagram of FIG.
1.
For performing the procedure according to the invention, a surgical
microscope (1) is envisaged, this being mounted on a suitable carrier
system (2)--shown only schematically--which in the illustrated example is
motor-operated.
With the help of the carrier system (2), defined positioning in a known
coordinate system of the surgical microscope (1) is possible in up to six
spatial degrees of freedom. The standard degrees of freedom for the
spatial positioning of the surgical microscope are three degrees of
freedom in rotation and three in translation.
A suitable, multi-joint carrier system (2) which is motorized is disclosed
in the German patent application 42 02 922 of the applicants' assignee,
corresponding to U.S. Pat. No. 5,332,181. This comprises amongst others
drives and encoder assigned to the respective joints, so that a central
control unit (3) of the overall system can continuously determine the
coordinate-related positions of the surgical microscope (1) together with
the known geometry data of the carrier system (2) and the surgical
microscope (1).
As an alternative to the known carrier system disclosed in German patent
application 42 02 922, more simply configurated carrier systems can be
used provided they permit defined spatial positioning of the surgical
microscope on them and the acquisition of the respective coordinate
position. It would be feasible, for example, to configurate certain
embodiments of the procedure according to the invention without the drives
in the individual joints and to position the carrier system manually or to
provide an alternative position-reading system.
The surgical microscope (1) used features a generally known optical design
and can also include a superimposing device via which images generated
elsewhere or graphical illustrations can be superimposed on at least one
of the stereoscopic observation beam paths via known beam splitting
devices.
In addition, the surgical microscope (1) includes a position identification
system based on an optical system, which permits active, high-precision
measurement of the field of view plane under observation. For this purpose
it is possible, for example, to integrate a laser triangulation measuring
system in the surgical microscope optics, this measuring system permitting
the precise determination of the coordinates of a point in the field of
view plane.
As regards a preferred, suitable surgical microscope, reference is made
expressly to the surgical microscope disclosed in German patent
application 41 34 481 of the applicant.
As an alternative to a position detection system based on an optical
system, other, preferably also non-tactic position detection systems may
possibly be used according to the invention. The use of 3D ultrasonic
sound digitizers would, for example, be possible.
In addition, a (previously mentioned) central control unit (3) in the form
of a control computer is envisaged. The control unit (3) performs the
entire control work and position detection of the carrier system and also
processes the image information of the diagnostic data records generated
prior to surgery which were digitized and filed in an appropriate image
data base (4).
The central control unit (3) further comprises in input interface (3.1),
e.g. in the form of a keyboard, by means of which the operator can perform
the surgical planning, for example.
An initial example of the procedure according to the invention is now
explained using the flow diagram in FIG. 2, in which the major procedural
steps are listed. The surgical microscope mounted on the motorized carrier
system in an initial embodiment of the procedure according to the
invention is first moved in a defined way over the part of the patient's
body which is of interest and to be subjected to correlation. For this,
the body area in question is first selected and the surgical microscope is
positioned over this area by means of the motorized carrier system.
The field of view plane of the surgical microscope is then moved in a
scanning motion over the body area of interest. The scanning motion can be
achieved by the operator manually controlling the maneuvering of the
surgical microscope mounted on the motorized carrier system. As an
alternative, defined positioning over the area in question can be obtained
by the central control unit with specific, preselected positioning
parameters. Such positioning parameters include, for example, preselection
of the defined scanning range and the scanning speed, etc. During the
scanning motion over the body area of interest, which is to be spatially
correlated with the diagnostic data record generated prior to surgery, the
position detection system of the surgical microscope continually defines
point-by-point that distance between the object surface and the surgical
microscope whose spatial coordinates are known to the central control unit
as a result of the encoder information of the carrier system. In this way
it is possible to record partial topographical information on body areas
of the patient and to file this data in a digitized form. The
topographical information obtained in this way thus consists in the
present example in a three-dimensional surface profile, such as was
generated from the different distances between the object surface and the
surgical microscope over a certain surface area. The partial topographical
information of the object area under observation or of interest thus
obtained with the surgical microscope is subsequently correlated with the
topographical information of the diagnostic data record generated prior to
surgery, which also provides three-dimensional object information. For the
correlation between the measured 3D profile and the diagnostic data record
generated prior to surgery, known correlation algorithms, like the ones
known in photogrammetry are used.
This embodiment of the procedure according to the invention requires
neither separate marker on the patient, nor additional devices on the
surgical microscope, if the previously mentioned surgical microscope of
German patent application 41 34 481 is used, for example. The only demand
on the surgical microscope used is that it must be able to measure the
distance measurement of a point in the field of view and to transfer the
signal to the central control unit.
The use of alternative surgical microscopes is another possibility in this
embodiment of the procedure according to the invention. These surgical
microscopes may, for example, be equipped with an active autofocus system
which permits them to perform the required point-to-point distance
measurement.
When the correlation of the patient's topography with the diagnostic data
generated prior to surgery has been performed, the referencing procedure
is completed and the surgical microscope is moved to the planned starting
point for subsequent surgery.
Another embodiment of the procedure according to the invention for the
correlation of different coordinate systems using a surgical microscope
without the use of additional markers is explained in FIGS. 3a and 3b.
Before the actual surgery, specific anatomical details in the body area of
interest are provided with contours at the central control unit in at
least two images of the diagnostic data record generated prior to surgery,
which correspond to different sectional planes. If brain surgery is
planned, for example, the circumference of the patient's head or the
contour of one ear can be marked as contours in two images. Such modified
images are then digitized and also filed in the image data base.
A modified image, which now only has these contours left on it, is then
projected into the observation optics via a projection device of the
surgical microscope and thus superimposed on the field of view under
observation. Next, the surgical microscope mounted on the carrier system
is shifted manually by the user above the patient's object area of
interest until the contour of the projected, modified image coincides with
the appropriate anatomic detail of the patient in the field of view, or
until the contours coincide. When optimum coincidence has been obtained,
the spatial coordinates of the surgical microscope and the appertaining
field of view orientation and position are picked up by the central
control unit and filed as an initial data record. The determination of the
coordinates of the surgical microscope position including the field of
view is performed in the known way via the central control unit, which
evaluates the coordinate information of the carrier system and the
information of the position detection system.
Manual positioning of the surgical microscope is effected via a control
element operated by the user, this element permitting the surgical
microscope mounted on a motorized carrier system to be controlled in a
defined manner. A handle, similar to a joystick, or the like can, for
example, be used for this purpose.
The second filed and modified image is processed in a completely identical
manner; subsequently the second recorded data record relating to the
determined position of the surgical microscope and the appertaining field
of view orientation and position are also filed.
With two spatial positions of the surgical microscope, including the field
of view orientation and position, being known relative to the contours,
the necessary referencing or correlation of the coordinate system can then
be performed. On completion of correlation by the control unit, the
referencing procedure is finished and the planned starting position for
surgery is assumed as in the previously described embodiment of the
procedure according to the invention.
As an alternative to manual spatial positioning of the surgical microscope
using the control element, this embodiment of the procedure according to
the invention makes it possible to move the surgical microscope mounted on
the motorized carrier system automatically over the object area of
interest. During this process, the object area covered is recorded and
real-time matching procedures are performed with the modified contour
images. When optimum coincidence of the contours in the modified images
and the anatomic details in the field of view has been obtained, the
position of the surgical microscope and the field of view is recorded,
etc., as in the previously described procedure. For this embodiment of the
procedure according to the invention, the field of view must be
continuously recorded during the scanning motion by means of a video
camera, for example. The video camera or other suitable electron-optical
image detectors can be advantageously arranged in a documentation beam
path of the surgical microscope, for example.
FIG. 3b shows a presentation of the display (5) of the central control unit
in which the contour of a specific characteristic anatomic detail (6)--in
this case an ear of the patient--has been marked in a diagnostic image
produced prior to surgery. This modified image is digitized and filed
together with the coordinate data.
In the procedure according to the invention, this image is then projected
into the observation optics of the surgical microscope, and at the same
time the surgical microscope is displaced manually or automatically via
the carrier system until this contour coincides as far as possible with
the actual anatomic detail.
As an alternative to the embodiment of the procedure according to the
invention described last, another embodiment for the collection of partial
topographical information makes it possible with the help of the surgical
microscope to work without the marking of anatomic details of interest and
to measure points in the object area under observation directly using the
surgical microscope if these points can clearly be recognized and
identified both in the field of view and in the corresponding diagnostic
image.
A flow diagram displaying the basic procedural steps of this is shown in
FIG. 4. In this case, at least three characteristic points in a image of
the are first marked by means of the control unit before surgery. It is
necessary, of course, to choose a image of the diagnostic data record
which concerns at least part of the object area also observed subsequently
through the surgical microscope. Then, the surgical microscope mounted on
the carrier system is positioned in space so that the clearly identifiable
points are located in the field of view. By means of the position
detection system of these points are then measured in their coordinates
with the position of the surgical microscope being recorded
simultaneously.
The subsequent correlation with the diagnostic data record generated prior
to surgery is then performed in the known manner.
The identification of the characteristic points can be performed like in
the previously described embodiment by manual manoeuvring of the surgical
microscope over the relevant object area and by appropriate assigning of
these points through the user. As an alternative, an automated procedure
including the automatic recognition of these points is possible again if
the surgical microscope is equipped with a suitable electro-optical image
detector and a motorized carrier system is provided.
The collection of partial topographical information by the embodiment of
the procedure according to the invention described last can be
beneficially used intraoperatively if during brain surgery, for example,
brain shifts occur, necessitating re-referencing of the field of view
under observation to the diagnostic data records generated prior to
surgery.
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Description |
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