CA2188469A1

CA2188469A1 - Method for making a perfected medical model on the basis of digital image information of a part of the body

Info

Publication number: CA2188469A1
Application number: CA002188469A
Authority: CA
Inventors: Bart Swaelens; Wilfried Vancraen
Original assignee: Individual
Current assignee: Materialise NV
Priority date: 1994-04-19
Filing date: 1995-04-11
Publication date: 1995-10-26
Also published as: US5768134A; ATE169418T1; DE69503893D1; BE1008372A3; DE69503893T2; EP0756735B1; WO1995028688A1; EP0756735A1; AU677906B2; AU2250295A

Abstract

Method for making a perfected medical model on the basis of digital image information of a pan of the body, according to which this image information of a part of the body is convened by means of what is called the rapid prototyping technique and thus with a processing unit (4) and a rapid prototyping machine (5), into a basic model (9) of which at least a pan perfectly shows the positive or negative form of at least a pan of the pan of the body, characterized in that at least a functional element (10) with a useful function is added to the basic model (6) as a function of the digital information and possibly as a function of additional external information.

Description

- 21~
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AMENDED SHEE';
_ _ , ~ethod for ~n~k;n~ a perfected medical model on the basis of diqital imace information of a ~art of the body.

The invention concerns a method for making a p-~f~ct~
medical model on the basis of digit21 image informatlon of a part of the body, according to which this image information of a part of the body is converted, by means 10 of what is called the rapid prototyping technique and thus with a processing unit and a rapid prototyping machine, into a baRic model of which at least a part p~ ct~y shows the positive or negative form of at least a part of the part of the body.
3y rapid prototyping technique should be understood all techniques whereby an object is built layer by layer or point per point by adding or hardening materi~1 (also called free-form manufacturing). The best known 20 techniques of this type are: stereo lithography and related techniques, whereby for example a b2sin with liquid synthetic material is selectively cured 12yer by layer by means of a computer-controlled electromagnetic beam; selective laser sintering, whereby powder particles 25 are sintered by means of an electromagnetic beam or are welded together according to a specific pattern; or fused deposition modelling, whereby a synthetic material is fused and is stacked according to a line pattern.
3 0 ~he digital image inf ormation can be provided by a computer tomography scanner.
~he model produced up to now according to the above-raentioned technique, can be a model which is an exact 218~

2 A~lENoED SHEET
copy of the part of the body, for example a piece of bone, and upon which a surgery operation can be practised, or it can be a prosthesi8 which fit8 perfectly to the part of the body.
However, the model8 produced up to now, including three-dimensional images, do not take advantage of all the information contained in the image information. They form a perfect copy of the part of the body, but they do 10 not contain any additional functional elements.
Functiona' cl ~ ntc, ouch ac an opcning indicating/thG
place and direction for boring, can be added ma~ally, but not as a function of the image information~ At the 15 time when these models are made, the grey v~ue data of the image information are lost. Howev~, these grey value data contain clinical data which ~e important f or the use of the models. Such clin~Ycal data are for example the muscles and tendons wh~!ch have to be taken 20 into account when designing a pro~thesis. These muscles and tendons are visible in th~/images, but not in the three-dimensional model, nor~hén working with segmented contours/6urfaces in CAD-a~ications.
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25 The manipulation of ~figital image data during the preparation of a surc~ry operation, for example, is known as such. It is po,~!sible, for example, to determine the position and dir~tlon of an implant on the images or to simulate surg~ies. However, there is no connection with 30 reality an~by lack of reference, these prepared image data ca,~ot be used in practice. The image information i~used to the full.
A~ for th~ applicaticn ~f d~nt~ Fl~ntc, ~tt ~ ~r have 2188~6g _ 2/1 - ~
AMEN~ED StlEI~
Such models which are exact copies of real structures are for example produced from medical images with the technique disclosed in the article "Integration of 3-D medical imaging and rapid prototyping to create stereolitographic models" from T.M.BARl~ER et al., published in "Australasian Physical ~ EnginPPrin~ Sciences in MPtiil'inP"~ vol. 16, no.
2, June 1993, pages 79-85.
Scanner data are transformed to a suitable format in a computer and the images are processed as a volume of voxels. The object is segmented prior to the meshing of the ob~ect surface and the creation of the stereolithographic model. The obtained model cannot be used for regi~tration, this is finding back a position on the patient.

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copy of thc p~r~ o~ t~Q bcdy, fo~ Qv~ Q ~ pioc~
bone, and upon which a surgery operation~n be practised, or it can be a prosthesis which~perfectly to the part of the body. /~
However, the models pr~ up to now, including three-dimensional ima~do not take advantage of all the information eontained in the image information. They form a pe~fect copy of the part of the body, but they do ~t cont-;n -y ~dditio~ 1 unct~o-~1 ol~ --t~. -Functional elements, such as an opening indicating the place and direction for boring, can be added manually, but not as a function of the image information. At the 15 time when these models are made, the grey value data of the image information are lost. However, these grey value data contain clinical data which are important for the use of the models. Such clinical data are for example the muscles and tendons which have to be taken 20 into account when designing a prosthesis. These muscles and tendons are visible in the images, but not in the three-dimensional model, nor when working with segmented contours/surfaces in CAD-applications.
25 The m ~ ?~lat on of ~7; git~ ge A~ta d~lr;
preparation of a surgery operation, for example~nown as such. It is possible, for example, t~de~ermine the position and direction of an implant~on the images or to simulate surgeries. However, theré is no connection with 30 reality and, by lack of reférence, these prepared image data cannot be used in practice. The image information is not used to the full.
~:for ~h~ ~rr];f~A~inn n~ A~n~l ;mrl~n~c~ P~t1-Qmr1-c h~ve 2188~

~M~MDED StlEE~
How to colour selected elements of a three-dimensional object such as an anatomic model, prepared by irradiation techniques or example by stereolithography, is disclosed in EP-A-O 535 984, but this document does however neither disclose nor suggest to add artificial functional elements to the model for registration ~uL~oses, this is for transposing the pre-surgical planning or simulation to the surgery .

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y of thc paL ~. of the l~Ayr fclr ~mrl ~ c~ u~/
bone, and upon which a surgery operation can~be practised, or it can be a prosthesis which fits pe,~éctly to the part of the body.
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However, the models produced up to now, inc~Yuding three-dimensional images, do not take advant~ge of all the information contained in the image ~formation. They form a perfect copy of the part of v e body, but they do 10 not contain any additional funct,~nal elements.
~, Functional elements, such ~ an opening indicating the place and direction for ~?6ring, can be added manually, but not as a function ,~ the image information. At the 15 time when these mod~s are made, the grey value data of the image inform~ion are lost. However, these grey value data co~in clinical data which are important for the use of/the models. Such clinical data are for example )~e muscles and tendons which have to be taken 20 into af~'count when designing a prosthesis. These muscles ~nd ~endons are visible in the images, but not in the th~ee-dimension.al model, nor when working with segmented d~nto- cJ~-- fac~ ;n r~n ~rPl;r::t;~nc 25 The manipulation of digital image data during the preparation of a surgery operation, for example, is known as such. It is possible, for example, to determine the position and direction of an implant on the images or to simulate surgeries. However, there is no connection with 30 reality and, by lack of reference, these prepared image data cannot be used in practice. The image information is not used to the full.
As for the application of dental implants, attempts have ~188~6~

3 ~ r already been made to use teeth of a provisional prosthesis as a reference. This provisional prosthesis is made on the basis of a mould. Nith a reconstruction by means of computer tomography scanner images on the 5 basis of planes in which the bone is clearly visible, what is called a dental scan, one can see whether the position and the angle of the provisional teeth are correct in relation to the underlying bone, and one can make corrections. However, this is a time-consuming 10 method.
Sometimes, a template is made on the basis of the mould and this template is used during the surgery. Only surface data are used hereby, 80 that part of the lS information of the dental scan remains unused.
Another method consists in making a model of the jaw by means of the rapid prototyping technique and to make a template on the basis of this model which is used during 20 the surgery. The information of the digital image of the teeth (the dental scan) cannot be used either with this method .
The invention aims to remedy these disadvantages and to 25 provide a method for making a perfected medical model on the basis of digital image information of a body part whereby the image information can be optimally used and can be put to use in practice.
30 This aim is reacped according to the invention as at least ~vfunc~ional element with a useful function is added to the basic model, as a function of the digital lnro--~-tion -~i pocc:"ly aC a fll~ce;qn qf ~ ;
axtC~ ," rOr~iqr, 2188~9 AMENDEG SHEE~
image information in the form in which all medical data are visible, this is in the grey value image information, before segmentation, the useful function of the functional element being an indication of a physical parameter, such as a position, a direction, a length or an angle which are important during surgery or the shape of a bone ele~ation.
External information coming from the medical user may be added to the image information, the artificial functional eiement being also as a function of this additional external information.

- 218846~

4 ~ A~ 0 By subsequently converting the image with the additional information in information for the control of a rapid prototyping machine, there i8 a feedback of the medical data to reality and a perf ected model is obtained which 5 does not only have the shape of a certain part of the body, such as a ragged bone shape, and thus provides a perfect reference, but which also contains artificial elements which are added as a function of the image information and of possible new additional information, 10 and which have a useful function.
In a ~- tic~l~r ~ ~imont of t~ invcntion, ~he functional element is added as a function of the digital image information in the form in which all medical data 15 are visible.
Such a form of the image information con6ists of the grey value inf ormation .
In a peculiar embodiment of the invention, the 20 information on the basis of which the functional element i6 determined is processed factually in the perfected model by means of a voxel oriented computer system.
Via contour generation (segmentation/interpolation), one 25 can switch from image processing to for example stereo l ithography .
~1 ~O,y Po~ ~ew information'added from outside to determine ~t~,G h ; ~ to ~ O n the functional element,~must then also be presented as 30 voxels or contours.
The functional element with a useful function can be a shape, a colour or a texture.

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Thi~ ~e~ul f~ .Llon can ~e ~he in~lcatloll uL a pc6~1., a direction, a length or an angle which ar~portant during a surgery, the formatio~ of a poi~ attachment, the formation of a filling for a~ertain defect, a 5 prosthetic function, etc. ~
A useful function can~erf example also be facilitating the identificati~f a model or of model parts for a certain p~ by providing an inscription or a label whi~y not restrict the diagnostic or functional 1 0 q~ ~
The method can be used in numerous applications.
Thus, it can be usefully applied in combination with the 15 already applied computer aided surgery simulation, whereby bone segments are cut and moved at a certain angle and over a certain distance. With the help of the method, templates and jigs can be made which provide a perf ect ref erence on the one hand and indicate angles and 20 movements on the other hand.
The method can also be used for the preparation of tooth implants, whereby the perf ected medical model is a template end the functional element is an opening or 25 notch on the place where drilling is required, or for making a knee prosthesis, whereby the basic model is a metal base which can be joined to a sawn off tibia or femur and whereby the functional elements are orientation pins and/or fastening pins which stand on said base and 30 which position and/or fix a prosthesis. Also an actual prosthesis can be made according to the method, part of which fits perfectly to existing bone and another part of which forms the functional element with a prosthetic f unction .

WO 95128688 2 1 8 8 ~ 7~. _ .

In order to better explain the characteristics of the invention, the following preferred ~ 'i L8 of a method for making a perfected medical model on the basis of digital image inf ormation of a part of the body are given as an example only without being limitative in any way, with reference to the ~ ying drawings, in which:
figure 1 shows a general block diagram of a method for making a perfected medical model according to the invention;
figure 2 schematically shows how a perfected medical model is made on the basis of the image;
figure 3 schematically shows how another form of a perfected medical model is made according to the method of the invention;
figures 4 to 8 schematically show how yet other forms of perfected medical models for other applications can be made according to the invention.
A6 is schematically represented in figure 1, images 3 are made of a part of the body of a patient 1 by means of a computer tomography scanner 2 or any other digital image processing unit such as a Magnetic Resonance Image machine, which thus contain digitized medical inf ormation .
Instead of converting these images in for example a three-dimensional image or a dental scan and subsequently either making a model by means of rapid prototyping or processing the images, the image data will be first ~ ~ " ~

W0 95/28688 2 ~ 8 ~ r~ s .

processed in a processing unit 4, after which a perfected model 6 is made with these processed digitized image dat~
by means of rapid prototyping with a rapid prototyping machine 5. Use can be made for this operation of a 5 vi~ual three-dimensional image 17 or a dental scan 18 which is derived in the usual manner from the images 3.
This three-dimensional image 17 and this dental scan 18 are represented in figure I by means of a dashed line.
10 What is characteristic is that the model 6 can be used in reality on the patient 1 or in other words that the cycle represented in figure 1 is completed. In this figure, everything that is situated under the dashed line 19 represents reality, and everything that is situated above 15 it is immaterial inf ormation .
The processing or preparation includes the manipulation of medical digital image data, possibly with additional digital information from outside, in such a way that an 20 artificial, functional element 10 with a useful function is added to the produced basic model 9.
The processing of existing and possibly new information or the "design" is carried out with a voxel-oriented 25 system in the processing unit 4, i.e. by means of voxels or contours, whereby voxels or groups of voxels are indicated in the images 3. A voxel is a three-dimensional pixel and thus represents a cube. The grey value data of the voxels can be used to obtain still 30 higher resolutions and accuracies. The processing unit 4 which controls the rapid prototyping machine can help during the processing by carrying out operations on these voxels which are standard operations in three-dimensional ~ image processing, such as thresholding ( segmentation on Wo 9sn8688 r~I/DL~
~ ~8 the basis of grey values ), three-dimensional reduction, expansion, region growing, boolean operations such as adding and subtracting, projections, etc.
5 If external techn;cAl elements are added, for example coming from a CAD system, these elements must be represented as voxels or contours as well. This can be easily done by means of cross section and shading ~lgorithms .
After the interactive processing of the image information (for example rotations, translations, etc. ), it is possible to go back to the original CPD data to obtain a higher resolution and accuracy of the functional element.

Figure 2 shows an enlarged representation of one of the images 7 with grey values, derived in the processing unit 4 in the form of voxels from the images 3 of a bone 20 20 produced by the scanner 2. Through processing in the processing unit 4 are made negative images 8 in voxel form which fit perfectly to the images 7 and thus to the bone. Moreover, the image 11 of a functional element 10 is provided in voxel f orm in the images 8 . The im~ges 8 - 25 coincide with a ref erence part which f orms a negative basic model 9 which fits perfectly to the bone, which basic model 9, together with the functional element 10, f orms the perf ected model 6 .
30 In figure 2 is represented by means of a dashed line 21 the boundary between what is reality (underneath it) and what is image inf ormation ( above it ), whereas what is situated above the dashed line 22 is represented enlarged ~nd in voxel form.

wo gs/ts688 2 1 8 8 ~ ~ 9 r~
When providing the image 11 of the functional element 10 in voxel orm, one can take into account all medical information contained in the images 7. Via stereo lithography, the images 8, with on top of them the images 5 11 of the functional element 10, are converted in the three-dimensional, factual, perfected model 6 which can be placed a6 a template on the bone of the patient 1 during a surgery and which f its perf ectly to it . The useful function of the functional element 10 can then be 10 put to use. The information of the scanner 2 and the information of the position and direction of the functional element 10 based upon it, are in this way used to the full and translated into reality.
15 In order to pass from the information of the processing unit 4 to the rapid processing technique, one can proceed as follows:
the information or data set, consisting of voxels and 20 contours, of the processing unit 4 is converted into a set of contours per layer height. This is done by means of a screen which is finer than the screen of the original images 3, since the rapid prototyping techniques have a higher resolution than the scanner 2. In order to 25 obtain this finer screen, use is made of the grey value inf ormation in the images 3 . Thus, a pixel or voxel can partly belong to the perf ected model 6 and partly not .
This ph~n~ ^non is known as partial volume effect. When there are only two materials in one pixel or voxel, a 30 contour line can be calculated in between the pixels by means of interpolation, as described by B. Swaelens and others in "~edical Applications of Rapid Prototyping Techniques ", p . 107-120 of "Proceedings of the Fourth International Conference on Rapid Prototyping, Dayton, W0 95/28688 r~
~ ~ 8~ ~!6 ~ ~

OH, June 14-17, 1993". Said higher resolutlon is important to make the designed model fit well onto the part of the body. Once the contours per layer are calculated, they are interpolated in the third dimension 5 up to the layer height which is suitable f or the rapid prototyping technique. This layer height is usually si~n;f;cAatly lower than the scan distance.
Another method consists in converting the above-mentioned 10 data set into a surface description with for example one of the usual formats such as triangle format (STL). Such descriptions are used to calculate sections which are made by the rapid prototyping machine 5. Here also, it is possible to work with sub-voxel resolution.
According to ~ third method, the medical data or d~gital inform~tion is converted from the processing unit 4 to a CAD system. This is again approached by means of a surface descrlption and by rAlclllat;n~ the sections. It 20 is possible to further add elements in the CAD system, but not as a function of the image information.
The functional element 10 with a useful function can be a shape, a colour, a texture or another characteristic 25 element. The useful function of the element 10 can be the indication of a place where, a direction in which, a length over which or an angle at which one must cut, saw or drill; it can also be a point of attachment, the f il l; ng of an existing def ect, a prosthetic f unction or 30 an iden~; f ;~Arj on.
In the n~ 1, represented in figure 2, the perfected model 6 is a template and the functional element 10 is an opening which indicates the position and direction for wo gs/28688 2 ~ 8 8 4 ~ ~ P.~

the boring bit of a boring machine. The basic model 9 forms a reference part. The thickness of the basic model 9 at the height of the opening determines the depth of hole .

The met~od can be used for the preparation of tooth implants. The position and the orientation of the implants, both in relation to the bone and in rel~tion to the teeth, is very important. First, a dental scan is 10 made. Thanks to computer-aided preparations, the thickness, position, direction and length of an implant can be well planned. By making a template according to the invention as represented in figure 2, it is not only possible to match the planned size and length of the 15 implant in reality, but also directly the position and direction . For we have a ref erence part f ormed by the basic model 9 which fits perfectly to the bone and an element 10 which forms a guide for the boring bit with which the hole for the implant is drilled and which 20 ~ nmin~s the position, direction and depth of said hol e .
Instead of directly making a negative perfected model 6, a positive model 13-14 of the bone can be made in the 25 above-described manner, but containing information regarding the position, direction and depth of the drill hole to be made in the form of protrusions 14 as represented in figure 3. Only afterwards, a basic model 9 i8 made as a reference part, for example manually, with 30 openings as functional elements 10, as a negative mould of the positive model 13-14 as represented in figure 4.
Another application resides in the production of a membrane for bone generation, whereby this membrane can W095/28688 . P.,~
~8~9 form the reference part or basic model 9 and the functional element 10 a notch or incision as represented in figure 5. First, a positive in~ ';ate model 15 is made on the basis of the images 3 of the scanner 2, via 5 stereo lithography, consisting of a basic model 9 and the required bone elevation 16 as a first functional element 10. Whereas, according to known methods, said bone elevation is determined by realising the elevation in reality in a radiographically visible material, prior to 10 the scanning, the elevation is calculated according to the invention by the processing unit 4 and imported in the medical information derived from the grey value data, either departing from an ideal bone shape ~tored in a memory of the processing unit 4 or interactively.
A second functional element 10 can be possibly provided, namely a place indication, for example in the shape of a notch, there where the implant should come. This can be either done through the agency of the user or 20 automatically by means of a computer according to a stored program. In any case, it is preferably provided as a function of the grey value data in a dental scan.
From the intermediate model 15 is made a perfected model 25 6 in the shape of a membrane by making a mould on the basis of the intermediate model 15 and by 6haping a foil in the mould into a membrane. Just as the intermediate model 15, the membrane is provided with a notch as a functional element 10 which has as a function to indicate 30 the place of the implant.
In the case where the implant is provided together with the membrane, ref erence marks or sutures can be provided aa functional elements 10 in the ab~ve-descri~ed manner WO 95128688 2 ~ 8 ~ ~ 6 ~ r~
.

to position the membrane in the space where the bone will grow later.
Another application of the method according to the 5 invention consists in making prostheses.
With a knee prosthesis, the sliding surface of both the femur and the tibia must be replaced by sawing away a piece and by replacing this piece by a prosthesis.
10 Hereby, it is important that the prosthesis fits correctly to the bone, especially on the side of the tibia, since there is only a thin wall of strong cortical bone there to support the prosthesis. When the prosthesis is too large, protruding edges form a problem.

In the first place, an incision is indicated in voxel form in the images 7, there where the tibia or femur should be sawn . A f irst negative model 6 is made in the 20 aboYe-described manners which fits perfectly to the bone 20, but which protrudes all round this bone 20 with an edge which is cut off by said inri ~ion . This edge then forms a functional element 10 which serves as a guide for the saw with which the incision is sawn duriIlg the 25 surgery operation.
The voxels above the incision are removed in the processing unit 4 and a base 12 is designed here as a reference part or basic model 9 upon which orientation 30 pins are provided as functional elements 10 by the - processing unit 4. On the basis of this design is made, for example by means of stereo lithography and casting, a real model 6 which fits correctly to the 1~ ;nin~ part of the bone 20 and which is provided with functional Wo gs/28688 ~ i 9 .

elements 10 which are oriented in the right manner.
The base 12 can be designed such that it penetrates partly in the bone 20, and PCper;Al ly also partly 5 ~uLLuu~d6 the bone on the outside, as represented in figure 8. This largely increases the strength.
On the basis of the negative model 6 which forms the sawing template, and taking into account the thickness of 10 the base and the position of the functional elements 10, a positive model can be made of the prosthesis itself.
One can hereby depart from the real model 6 of the sawing template or pref erably f rom the digital inf ormation thereof in the processing unit 4 and calculate the 15 prosthesis with the latter to finally transform it via rapid prototyping in a real prosthesis. This prosthesis will also be provided ~ith functional elements 10 which are complementary to those provided on the base 12.
20 Instead, a standard prosthesis can be provided on the base 12, whereby the functional elements 10 on the basic model 9 formed by the base 12 need to be provided in this case as a function of complementary elements of the standard prosthesis.
A hip prosthesis can be made in an analogous manner which fits perfectly to the femur shaft on one side and which cont~ins a te--hn;rAl part with functional elements on the other side upon which the artif icial f emur head can be 30 placed. In the images 7 can be indicated the ideal length and the direction.
A prosthesis fitting perfectly to an existlng structure on one side and bearing a technical part on the other 218~69 AMEI\IDE~ SHEE~
side which has a prosthetic function can also be used for dorsal vertebra. Grey value data, for example regarding the position of the nerves, can be used in the processing unit 4 for the design of the prosthesis.
It ic ~lco ~ y pocc~a to de~ign proft~ cc~r~';~
to the invention which are partly or entirely sup~ed by weak parts. Such prostheses are ~example obstructors or "bobbins" which are use~ fill up the 10 nasal cavities and sinuses after t~e and/or bone has been surgically removed. The~ parts can be crushed, and ideally some distan~s kept from the bone parts.
This is possible a~ing to the invention by slightly enlargi~g the~e parts in the processing unit 4 at the 15 stage of ~ image processing. A te~ hn; CA 1 part could pos~y be designed as well onto which can be e.ttached a procthocic such ~c ~ ~Ant-l p.ro~' hA~i~
q;!ho pro~ont invon~inn ;a hy nr~ ----na 1 ;m;t~o~ Lo 20 above-described emhodiments represented in_~ings;
on the contrary, _uch a method f~ng a perf ected medical model on the basi~ital image i~formation of a part of ~can be made in all sorts of varian~ still r~-;ning within the scope of the 25 ~ tion.

Claims

Claims.

1. Method for making a medical model on the basis of digital image information of a part of the body, according to which this image information of a part of the body is converted, by means of what is called the rapid prototyping technique and thus with a processing unit (4) and a rapid prototyping machine (5), into a basic model (9) of which at least a part perfectly shows the positive or negative form of at least a part of the part of the body, characterized in that at least one artificial functional element (10) with a useful function is added to the basic model (6) as a function of the digital image information in the form in which all medical data are visible, this is in the grey value image information, before segmentation, the useful function of the functional element being an indication of a physical parameter, such as a position, a direction, a length or an angle which are important during surgery, or the shape of a bone elevation.

2. Method according to claim 1, characterized in that external information is added to the image information, and the artificial functional element is also as a function of this additional external information.

3. Method according to any of the preceding claims, characterized in that the information, on the basis of which the functional element (10) is determined, isprocessed factually in the perfected model (6) by means of a voxel oriented computer system.

4. Method according to claims 2 and 3, characterized in that the external information added from outside to determine the functional element (10) is also presented as voxels or contours.

5. Method according to any of the preceding claims, characterized in that a functional element (10) is added consisting of a shape, a colour or a texture.

6. Method according to, any of the preceding claims, characterized in that a drilling or sawing template is made with a reference part as a basic model (9) which fitsperfectly to a part of the body part and a guide for the instrument as a functional element (10).

7. Method according to any of the preceding claims, characterized in that it is used for the preparation of tooth implants and in that a basic model (9) is made with a reference part and at least one functional element (10) via a dental scan (18) and simulation in different planes.

8. Method according to any of the preceding claims, characterized in that a membrane for bone generation is formed and an intermediate model (15) is made first consisting of a basic model (9) with a required bone elevation (16) as a functional element (10), determined by means of the grey value images (7), after which, by means of a mould, a metal foil is transformed into a membrane containing the above-mentioned functional element (10).

9. Method according to claim 8 characterized in that a membrane for bone generation is formed and an intermediate model (15) is made first consisting of a basic model (9) with a notch or an incision as a functional element (10) to indicate the place of an implant, after which, by means of a mould, a metal foil is transformed into a membrane containing the above-mentioned functional element(10).

10. Method according to any of the preceding claims, characterized in that a perfected model (6) is made by first making a positive model (13-14) of the structure containing information on a functional element (10) and by subsequently making anegative mould of it.