Note: Descriptions are shown in the official language in which they were submitted.
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5 WO 96136292 PCTIEP96/02109
Specification
Method and Device for Fixing the Human Head
10
The invention relates to a method and a device for fixing the
human head.
In many branches of human medicine or of medical research,
15 secure fixing of the head of a patient or of a test subject is
necessary. This is of the greatest importance especially in the
field of head surgery and of ear, nose and throat surgery.
Through the use of imaging computer technology in diagnosis
and therapy, the requirements for accuracy and reproducibility
20 have risen, both in the establishment of a spatially defined point
in or on the human head and in the fixing of the head itself.
The most widely known methods for fixing the human head are
briefly described below:
25
a) Fixing the head with adhesive tape:
The head of the patient lies in the rear position on a foam
ring. Adhesive tapes stretched across the forehead and
30 upper and lower jaw fix the head
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5 on to a base. The disadvantages of this are the following
points:
- through the strong pulling of the adhesive tapes,
pressure points, displacements and/or skin
swellings can occur;
10 - once the retaining elements (adhesive tapes) have
been removed, renewed positioning in exactly the
same place is scarcely possible any more, and
this is particularly disadvantageous in stereotactic
operations and in radiotherapy;
15 - the head cannot be fixed sufficiently; the
movement of the head can be restricted too little,
particularly in a sideways direction (towards the
side).
20 b) Fixing the head with a face mask:
The head lies in the rear position in a pre-formed shell
and the face is covered by a mask, which has been
individually prepared previously and is laterally anchored.
25 On the basis of skin displacements on the bones of the
face, however, there is very slight movement between
the face and the mask so that it is not possible to achieve
extremely accurate fixing of the head, the following points
also being negative:
30 - the operation area in the region of the face is not
accessible, since it is largely covered;
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5 - swelling of the skin under the mask which sits
tautly;
- the complete covering of the face is a strain on the
patient;
- high costs and expenditure of time.
10
c) Fixing the head by clamping it;
The head of the patient is clamped by fixing screws from
several sides into a metal ring. The disadvantages of this
15 are:
the operation areas of the head and the back of
the head are largely covered and thus they are not
accessible or only accessible with difficulty;
- high costs of the metal ring;
20 - different positions of the patient for different types
of intervention are only possible to a limited extent;
- displacements of the skin occur frequently.
d) Fixing of the head by screwing down of the skull:
25
The head of the patient is screwed down at a plurality of
points via a metal ring. The disadvantages of this are the
following:
- screwing on to the skull bones represents an
30 invasive method and is thus only possible and
justified in certain indications;
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5 - the psychological strain on the patient is
considerable;
- the method can only be applied to a limited extent
to certain positions of the patient.
10 e) Fixing of the head via the teeth (the so-called Gill
Thomas-Cosman mount as per GB-A-2 213 066);
An impression of the teeth of the upper jaw is here
placed into the mouth (cemented) and tightened via a
15 crossbar on a ring shaped holding device running at nose
height against a support at the back of the head. The
result of this is that the position of the head of the patient
has to be adapted by force, i.e. using considerable force,
to pre-set connection points. Through the necessary
20 cementing onto the teeth of the upper jaw, this device
cannot be used on elderly, toothless patients. In
addition, the following points are disadvantageous:
- different operation areas are not accessible
because of the holding frame which takes up so
25 much space (e.g. in ENT-surgery an endoscope
cannot be led in through the nose);
- the positioning of the head of the patient is
complicated and difficult, thus time consuming and
a great strain on the patient.
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5 - tightening and cementing the impression tray in
the mouth is a strain on the patient, particularly
when freeing the impression;
- the mount is expensive, particularly as ear plugs
are also provided for fixing the head and straps
10 running over the skull cap and these further
restrict the possible regions for operations;
- the patient's head can only be put in a limited
number of positions, since the mounting frame
extends as far as the nape of the neck and this
15 also means that particularly lateral regions of the
back of the head are not accessible.
The purpose underlying the invention, therefore, is to create a
method and a device for fixing the human head which avoids
20 the disadvantages mentioned, is simple in construction and
application and at the same time to a great extent gentle on the
patient; in addition, the device should make possible the exact
application of calibration points (so-called markers) and
maximum accessibility to operation areas.
25
This purpose is fulfilled with a device in accordance with the
features of claim 1 or with a method according to claim 14 or 16.
In addition, an impression tray suitable for this method is
claimed according to claim 17 and an operation simulation
30 method according to claim 23.
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5 In contrast to the devices or methods described initially, on the
device or the method according to the invention the fixing of the
human head is essentially achieved through vacuum forces
which act between the head to be fixed and an impression,
taken individually from the respective person, of the upper jaw
10 or of the so-called hard palate (palatinum durum) and teeth as
far as they are present. Freeing the impression from the upper
jaw or the hard palate of the patient once the investigation or the
treatment is finished, is possible by switching off the vacuum
with very little application of force and is thus very gentle on the
15 patient. The fixing or fastening of the upper jaw impression tray
likewise take place in an especially simple and easily
reproducible way, which is gentle on the patient, via the
application of vacuum.
20 Through this fixing by means of a vacuum, it can be ensured
that, especially with toothless patients (e.g. accident victims)
and even after an impression has been used several times, a
secure connection by vacuum, remaining exactly the same, is
always made possible. As a means of producing the vacuum,
25 simple vacuum pumps with an adjustable level of vacuum
pressure, which may be controlled to monitor secure fixing of
the impression, hose couplings and isolating valves may be
used. To support the vacuum effect, by application of
impression mass to the impression which is in fact
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5 finished, flat hollow spaces or vacuum channels are produced
or, by preference, are already formed in the impression, and a
terminating connector can be inserted in the front upper jaw
region of the impression and of the upper jaw impression tray.
In addition, this system is easy to clean in the sterilizer and the
10 running costs are low since for each individual patient only one
impression from cheap impression material is used, whilst the
remaining components of the fixing mount may be used again
and again.
15 Through the support elements which are in the form of supports
or columns and may be positioned in any place on the base
plate, or through similar base holders with a plurality of swivel
axes or ball ends, the patient's head is practically completely
accessible to the doctor treating him, for any type of
20 intervention. What is essential here, is the slim rod-shaped
design of the support elements which, however, are sufficiently
stable and in contrast to the known massive metal rings can be
positioned at any place on the base plate in such a way that
they do not interfere with the planned intervention and can be
25 set in all co-ordinate axes or degrees of freedom.
Of particular advantage here is a counter-fixing device which is
similarly constructed and thus capable of being positioned in
various ways for the additional securing of the head of the
30 patient, particularly in
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5 regions of the upper head area and the back of the head or in
the shoulder area, the fixing of the head being secured
especially on restless/conscious patients or where there is
greater effect of force on the patient's head such as in working
with bones or cartilage. In addition, this makes possible even
10 distribution of pressure and takes the stress off the patient.
Especially the shoulder fixing device is here of independent
importance since through it, even without a vacuum, fixing of the
patient's head by exercising counter-pressure to the upper jaw
impression can be achieved with a stretching of the throat
15 region. This "stretching" process is particularly suitable for
surgery in the throat region.
What is particularly advantageous, moreover, is the application
of passive or active calibration points, which in modern medicine
20 establish reference points and reference planes on the practical
application of imaging processes such as for example CT
(Computerized Tomography) or MRI (Magnetic Resonance
Imaging). The claimed fixing device, makes it possible, after the
preparation of an impression and the application of a calibration
25 rod to the upper jaw impression tray or to the upper jaw cross-
plate securely connected thereto, to establish calibration points
which can then be used with, or even without, further fixing of
the patient's head in the imaging process (CT or MRI) then as
reference points for further measures such as the
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5 calibration of the patient in preparation for an operation or for
operation simulation. This makes possible a new type of
efficient operation preparation with a simulation of the planned
intervention, since the operation instruments can be pre-set
even without a patient being laid on them, and with the aid of
10 computer-generated virtual patient images, for instance, the
direction of insertion and the length of instruments can be
established, avoiding essential nerve passages or blood vessels
which can be recognized on the computer-generated images.
When the patient is then added and the computer data
15 correlated with the calibration points or reference points, the
operation can then be carried out relatively quickly.
Preferred embodiments, given by way of example, are
described and explained in greater detail below with the aid of
20 the drawing. These show:
Fig. 1 - a device for fixing the head of a patient with a
plurality of support elements, in plan view;
25 Fig. 2 - the device according to Fig. 1, in side view with
the head of the patient shown diagrammatically;
30
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5 Fig. 3 - the device according tot Figs. 1 and 2 in front
elevation looking from the body to the head of a patient
not shown.
Fig. 4 - a preferred connected mount for calibration
10 points in plan view;
Fig. 5 - the mount for calibration points, in side view
looking in the direction of arrow A in Fig. 4.
15 Fig. 6 - a side view similar to Fig. 2, however from the
opposite side, with a base plate with a fixing device
placed on it and a similarly formed counter-fixing device;
Fig. 7 - a fixing device similar to that in Fig. 3, however
20 viewed from the head to the body of the patient;
Fig. 8 - an upper jaw cross-plate in plan view in the
longitudinal axis of the body, with holder rods attached to
it to fix it on to a support element;
25
Fig. 9 - a support element in stand form with a base
holder, a base rod and a holder rod with a hinge joint
which can be centrally locked, in side view;
30
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5 Fig. 10 - a support element as per Fig. 9 with a central
adjusting screw, in front elevation.
Fig. 11 - a support element in the form of a stand as per
Figs. 9 and 10, with base holder, telescopic holder and
10 base rods and ball and socket joints with a central locking
device, in plan view;
Fig. 12 - a mount for calibration points similar to Figs. 4
and 5 with a screw fixing device, transverse distance rod
15 and a lateral distance rod;
Fig. 13 - an upper jaw impression tray, in perspective
view;
20 Fig. 14 - the base plate according to Fig. 1, in outline,
with extension plates in a modular form of construction;
and
Fig. 15 - a preferred counter-fixing device for the
25 shoulder region in side view.
A base plate made of steel, which may be magnetised, and on
to which further plate parts 1' (cf. Fig. 14) can be attached in a
modular form of construction, is connected on its underside via
30 stable connections 2, here only indicated diagrammatically, for
example
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5 bolts, with an operating table. The base plate 1 can be adjusted
to these connections 2 in respect of the operating table in a
horizontal and in a vertical direction and can be twisted to a
certain degree, there being a high degree of security ensured in
each position. On the base plate 1 serving as reference base, a
10 head support ring 3 lies centrally (or a head support adapted to
the shape of the head) and may be moved freely according to
the position of the patient. When the head is laid back, the head
rest ring 3 consists of a slightly compressible hard rubber ring
on which the back of the head is bedded. Here, head rest rings
15 3 of different diameters and different thicknesses are available
for the different sizes of head and different operating positions.
The head rest ring 3 or the shaped head rest are expedient for
the even distribution of pressure and transmission of force from
the head to the base plate 1 when the patient is on his side.
20 They increase the support surface, which results in a reduction
of the surface pressure. The pre-shaped headrest is mainly
used where the patient or the test subject is on his or her side.
To fix the patient's head, a plurality of support elements 4, which
25 may be freely positioned and are in the shape of stands, are
provided here in the corner region of the base plate 1 as force-
transmitting portions of the head holding device. These consist
respectively of a base holder 5,15 and a preferably
30
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5 screwed in base rod 7,17 securely connected thereto, and a
holder rod 8,18 jointed to the latter, the reference number with
the prefix "1" indicating in each case the same constructional
element on the opposite longitudinal centre plane of the base
plate 1. The holder rod 8 or 18 has at its end in each case one
10 fastening place 28 with a screwed locking device 10 for each
end of a central upper jaw cross-plate 27.
The base holder 5,15 has an on/off switch 6,16 for strong
permanent magnets built into the base holder, with which it can
15 be magnetically immovably anchored to any point on the base
plate 1 which is magnetisable (or it can be freed). On an
alternative pneumatic design, 6,16 indicated an actuating valve
to activate a vacuum with which the base holder 5,15 can be
held on to the base plate 1 by suction. On this version, the base
20 plate does not need to be magnetisable, thus a simple plastic
plate can be used which, in addition, means that it can be easily
used on the MRI-scanner. The base holders 5,15 can,
however, also be pushed into corresponding bore holes 12 in
the base plate 1 (cf. Fig. 10).
25
The respective hinge joint 9,19 between the base rod 7,17 and
holder rod 8,18 is fixed by means of a central screwed locking
device 11 and is secured. On the modified version in the form
of a stand, however, with
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5 the same base holder 5,15 according to Figs. 9 to 11 the head if
the patient is supported by telescoping holding tubes 22 as the
base and holder rods 7, 8 and ball and socket joints 23 as the
hinged joint 9. The end of the right or the left holder rod 8,18 in
each case forms a contact point 28 for fastening on to the upper
10 jaw cross-plate 27. This cross-plate 27 is connected to an
upper jaw impression tray 30 filled with an impression mass 31
(cf. Figs. 4 and 13) by means of a connection, especially a
quick-setting adhesive, on its flat side. The ends of the upper
jaw cross-plate 27 (compare Fig. 3) here leave the mouth area
15 of the patient approximately in the region of the corner of the
mouth, however they can also be led towards the nose or
towards the chin. The upper jaw cross-plate 27 can here also
be mounted on one side as a cantilever.
20 The upper jaw cross-plate 27 consists for example of stainless
chromium steel and has a thickness of approximately 2 mm. Its
size and form are variable and can thus be well adapted to the
respective requirements of the operation, for example can also
consist of very strong carbon fibres. In the centre region 29 of
25 the upper jaw cross-plate 27 which runs transversely, a U-
shaped space is cut out in order to lead in a tube, for example,
or to gain space and an overview in the mouth region for
surgery. The ends of the upper jaw plates at the fastening
points 28 are, just like the whole
30
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5 upper jaw cross-plate 27, adapted in size and form, particularly
in their overhang, to meet the requirements of the respective
procedure in the treatment intervention.
In Figs. 2 and 3 the device for fixing a patient's head is shown in
10 operating position. From this it is clear that the support
elements 4 run from the point of introduction of the force on the
upper jaw impression tray 30 like a portal or a bridge to the base
plate 1, and, after the joints 9 or 23 have been stopped, take
over the transmission of force in all directions in a stable
15 fashion. Here, however, the overall structural shape is slim, so
that the operation or treatment area on the head is easily
accessible for the doctor.
On stereotactic operations, however, reference points are
20 essential, the previously described structure of the fixing device
or elements of same also being able to serve as a mount for
calibration points 37 (cf. Figs. 4,5,8 and 12). This so-called
calibration rod consists of a transverse distance rod 33 which is
connected to the upper jaw impression tray 30 so as to be
25 secured against twisting and/or displacement. A lateral distance
rod 34 is fastened on the transverse distance rod 33 by a
screwed or clamping connection 35, 36 so as to be able to be
adjusted and fixed into place. Marker pins serving as calibration
points 37 can either themselves form the calibration points or
30
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5 serve as carriers for markers (e.g. in the form of lead pellets).
However, as reference points or calibration points, other types
of sensors can also be used, for example optical, radioactive or
inductive transmitters. The marker pins can also be attached to
any other point of the mount e.g. to the transverse distance rod
10 33 or to one of the holder rods 8,18 (cf. Fig. 8).
In Figs. 1 - 3 and in Figs. 6 and 7 a counter-fixing device 40 for
the back of the patient's head is shown, such as is expedient
particularly in operations where great force is used on the skull
15 (e.g. chiseling, milling). On an otherwise identical structure with
base holders 5,15, base rods 7,17 and holder rods 8,18 etc., the
counter-fixing device 40 has a plurality of adjusting screws 41
and counter-pressure discs 42 attached thereto. This counter-
fixing device 40 is, however, not absolutely necessary for
20 procedures where no force is used such as radio-therapy, and
thus the head of the patient is held only on the support element
or elements connected to the upper jaw impression tray 30.
In Fig. 15 a shoulder saddle 52 is provided which is adjustable
25 in height as an alternative counter-fixing device 50 and this
allows exact re-positioning. The shoulder saddle 52 is here
mounted on a base rod 51, anchored on the base plate 1 by
means of a plug-in connection 12 so as to be slideable and
rotatable and
30
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5 thus, when it has been placed on the patient's shoulders, an
opposing force to the upper jaw fixing device can be applied and
the spinal column here stretched in the throat region. This
counter-fixing device 50 is thus especially expedient for
procedures in the throat region. Additional counter-fixing
10 devices 50 can also be fixed to the lower jaw in any position.
The upper jaw impression tray 30 is shown together with
connected holder-rods 8 in Fig. 8. A calibration point 37 can be
attached to said holder-rods such that the patient can be
15 scanned with the unit shown here, this unit being held exactly,
and so as to be capable of being re-positioned, by the vacuum
applied to the lower jaw impression tray 30. Then the head of
the patient can be determined by connecting the holder rods 8
with the support elements 4 for the operation, for instance
20 through inserting into a bearing eye 24, shown in the successive
Figs. 9 to 11, through connecting the base holder 5 and
stopping the joints 9 or ball or socket joints 23.
In Fig. 9 to 11 views of the preferred embodiment of the support
25 element 4 are shown, namely in the form of a stand known from
precision engineering, these stands 21 being "lockable" by a
central locking device 20 or being capable of being held rigid in
one position. Here, through the activation of the locking device,
a
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5 piston presses on collet chucks, not shown, in the ball and
socket joints 23 and fixes same. Tightening then occurs under
fluid pressure (especially hydraulic) in the hollow holder tubes
22, such that all the joints 9 or 23 of respectively one support
element 4 are simultaneously stopped or made rigid.
10
In Fig. 13 a perspective view of the upper jaw impression tray
30, with impression mass 31 filled into it is shown for
clarification (indicated by dots.) On this "vacuum kit", a flexible
strip 38, which by preference is stamped out f a thin rubber mat
15 in a U or star-shape, is laid into the impression mass 31 before
the impression of the upper jaw or palate is taken, to create
vacuum channels or pockets into which the vacuum is applied
later. At the same time a connector piece 39 is also formed
such that, once the jaw impression has been removed and the
20 impression mass 31 has hardened, the strips 38 can be pulled
away either in several pieces or in one piece. In this way, flat
pockets or channels are formed in the impression which is
individual for each patient, and these form pressure chambers
towards the upper jaw/palate when the vacuum is applied (cf.
25 Fig. 12) to the upper jaw impression tray 30 via the connector
pieces 39. By monitoring the vacuum (approximately 0.2 atm)
the exact seating of the impression tray 30 and thus the exact
positioning can also be checked. Here standardized
30
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5 impression trays 30 in a plurality of pre-fabricated sizes can also
be used.
What is also of great importance is the possibility shown in Fig.
14 of expanding in modular fashion the base plate 1 with further
10 base plates 1' connected by means of transverse longitudinal or
rotating guides 1 a, 1 b and 1 c. These base plates 1' can, just
like base plate 1, have a large number of push in boreholes 12
arranged in grid form (and/or on the side edges 12') into which
the base holders 5,15, the base rods 7,17 (or 51 in the case of
15 the shoulder counter-fixing device) can be inserted. Here the
base plate 1' can then be moved in the shoulder area together
with the counter-fixing device 50 in respect of the head
longitudinal central plane around the rotatable guide 1c, in order
to give the person carrying out the operation, for example, better
20 access to a certain cervical vertebra. It should be noted that it is
possible to make reference back to the original stereotactic
positioning e.g. by means of the marker pins 37 since the swivel
movement (or even a translatory relative movement) is detected
between the base plates 1 and 1' by scales or angle/length
25 measurement transmitters on the guides 1 a, 1 b, 1 c in all co-
ordinate axes or degrees of freedom and thus the position of the
patient can also be changed.
30
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5 The practical application of the device according to the invention
is now to be described below together with the calibration points
37 shown in Figs. 4, 5, 8 or 12 with the aid of CAS (computer-
assisted surgery): CAS represents a navigational aid during
operations. Before the operation, the patient is scanned using
10 CT or MRI. Then the individual steps are reconstructed
(generated) as a 3D object with corresponding stereotactic
space co-ordinates on the processing computer and transferred
to a display or a monitor in the operating theatre. This virtual
picture is calibrated in the operating theatre to the patient with
15 the aid of a passive mechanical arm coupled to the computer
(e.g. similar to figure 12) and at the end of which a probe is
located. Sensors on each of the 6 rotational axes of the arm
inform the computer of the relative angles of the parts of the arm
to one another, the computer being in the position of calculating
20 the stereotactic co-ordinates of the point of the probe. By
moving through a plurality of points (e.g. anatomical points or
through calibration points that are impenetrable by X-ray - so-
called marker-characterised reference points) on the patient or
on the calibration device and the corresponding correlation to
25 the reconstructed 3D object on the display, it is possible for the
computer to fit this 3D object into this virtual space. The better
the points moved through agree with the points correlated on
the screen, the more exactly the virtual image and the head
30
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5 of the patient agree with one another, which leads to great
accuracy of the system. The person carrying out the operation
can, during the operation, find his bearings with the aid of the
reconstructed 3D object and a plurality of two dimensional
images which always show the point of the probe.
10
The successful application of this method is only guaranteed if
exact fixing of the patient' head and thus of the calibration is
provided. As described initially, known systems are at the
present time not in a position of registering exactly movements
15 made by the patient. Even on a system with active head-
movement registration, fixing in order to control aiming devices
is unavoidable. Thus, at the present time with known fixing
methods, it is necessary before each use of the probe to check
the head position by moving through corresponding calibration
20 points. On each head movement, therefore, subsequent
calibration is necessary. The results are, amongst other things,
considerable lengthening of the operation time. Moreover, a
change of position between checking of the calibration and
application of the probe for planning orientation and navigation
25 can have important consequences for the patient because this
mistake is not detected by the system and thus faulty
interpretation can result. Thus the reliability of the whole system
is limited. For the calibration, a sufficiently large and easily
accessible area of skin
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5 is necessary. This is needed for the marker calibration on which
a plurality of markers is applied to the skin. The surface
calibration, on which the areas of skin serving for the
subsequent calibration may not be displaced by the application
of the mount, severs to improve the marker calibration. By
10 displacing the skin and/or the markers attached to same in
relation to the head, a correlation of the real head of the patient
to the 3D object reconstructed from the CT-data cannot be
carried out with the desired and necessary precision. This is
true both for marker calibration and for surface calibration. With
15 all these known methods, therefore, there was an unsatisfactory
situation.
In contrast with this, in the application of the device or method
according to the invention the following procedure is followed:
20 first of all, an upper jaw impression is taken from the patient by
means of the upper jaw impression tray 30 and the impression
mass 31 filled into same. If this is done shortly before the CT-
scan, then, after the setting of the calibration device 33 to 37
consisting preferably of carbon fibres, the patient can be
25 scanned by CT without the impression tray 30, held only by
vacuum, being removed and without the application of the
additional head mount. Here, the calibration device 33 to 37 is
so adjusted by pushing or swinging the distance rods 33,34 that
the marker pin 37 located on the screwed mount 36
30
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5 (generally pellets made of material that is impenetrable by x-ray
are used) is found in the scanned region. Here no active
holding by the patient is necessary and thus the mouth area is
accessible for insertion of tubes.
10 This kind of reversible fixing of the head in the initial position is
especially sensible with CT-scans for surgery involving soft
parts since these can be displaced depending on the respective
position. It is however often expedient to scan the patient (and
thus the calibration device 33 to 37) fixed in the head support
15 shown in Figs. 1 to 3. A positive side effect of this exact fixing
of the head during the CT-scan is the avoidance of movement
artefacts that often occur. After the CT examination the support
element 4 and the vacuum are released and the impression tray
30 (together with the calibration device 33 to 37) is taken away.
20 This can be stored for a later operation.
Here the following procedure is taken: after the impression tray
30 has been inserted into the mouth area, the latter is
connected with the cross-plate 27 which is in moveable contact
25 with the already-described support elements 4 of the head
mount. Then the impression tray 30 carrying the impression for
the individual patient or a pre-fabricated one is pressed on to
the teeth or on to the hard palate and fixed there by means of a
vacuum. Then, once the operator
30
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5 has convinced himself, by checking the vacuum, of the correct
position of the impression tray 30 and thus also of the
calibration device 33 to 37 connected thereto, the head fixing
mount is fixed by stopping (making rigid) all the hinged
connections 9, 19 between holder rods 8, 18 and base rods 7,
10 17 and by anchoring (activating the magnets or the negative
pressure source by means of switches 6,16) of the base holders
5, 15 on the base plate 1 or 1'.
On the subsequent step of the operation, which can take place
15 over a shorter or longer period of time, the impression tray 30 in
combination with the calibration device 33 to 37 is fitted to the
upper jaw of the patients head in the manner already described
for the CT-scan and fixed onto the base plate 1 through the
application of vacuum to the impression tray 30 as well as
20 stopping the support elements 4 on the base plate 1. Now the
necessary calibration points on the calibration device 33 to 37
for the CAS procedures can be moved through and thus a
correlation be made between the real head of the patient and
the virtual 3D image stored after the scan. What should be
25 particularly stressed is the fact that the calibration points in the
form of marker pins 37 are immovable in relation to the head of
the patient. Through the application of the head-fixing mount in
combination with the calibration device 33 to 37, maximum
accuracy can thus be achieved with stereotactic procedures of
30 this kind.
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5 In conclusion, the advantages of the device according to the
device are summarised:
- exact fixing of the head with space-saving construction;
- maximum freedom of vision and movement in the area of
the operation for the person carrying out the operation;
10 - positioning of the head in variable positions for use in
different kinds of operations;
- no invasive intervention is needed to fix the head;
- no displacements of the skin, and thus of the position,
cased by the mounts;
15 - the possibility of attaching instruments of the most varied
kind, e.g. an endoscope, to the mount as well as its
suitability for virtual 3D endoscopy;
- definition of exact calibration points by the calibration
device attached to the upper jaw or palate which can at
20 the same time be used as a component of the fixing
mount;
- the conditions of the fixing by the base holders which are
freely movable on the base plate are adapted to the
individual features of the patient's head and not the other
25 way round, i.e. the patient's head being forced into the
devices;
- simple handling, which also saves time, through the
application of a vacuum and thus particularly gentle on
the patient and hygienic.
25
