WO1996010243A1

WO1996010243A1 - Method for the three-dimensional reproduction of anatomical parts and equipment for carrying out said method

Info

Publication number: WO1996010243A1
Application number: PCT/IT1995/000155
Authority: WO
Inventors: Massimo Zanna
Original assignee: Massimo Zanna
Priority date: 1994-09-29
Filing date: 1995-09-26
Publication date: 1996-04-04
Also published as: IT1269404B; ITFI940181A1; AU3577595A; ITFI940181A0

Abstract

A three-dimensional model of an anatomical part is obtained by starting with two-dimensional radiographic CAT scan images on which points of reference are marked and then transferred to a paper support by means of optical scanning. Subsequently, patterns are formed for each image on sheets of transparent material, such as wax, having a thickness equal to that of the CAT scan. Said patterns are then superimposed on one another in the same sequence in which the scan images were taken and each is submitted to a calibrated pressure. The equipment comprises a frame (1) with graduated edges (2) and sliders (6) moveable according to perpendicular axes in order to mark the points of reference as well as a support base (10) for forming the patterns and stacking them under a calibrated pressure.

Description

DESCRIPTION

METHOD EQE THE THREE -DIMENSIONAL REPRODUCTION OF

ANATOMICAL PARTS AND EQUIPMENT FOR CARRYING OUT SAID

METHOD.

F-i .l of the invention

The present invention relates to a method for creating three-dimensional reproductions of human and animal body anatomical parts, such as organs, skeletal and muscular structures and the like, based on images from a usual radiographic CAT test.

More particularly, the invention relates to a method which makes possible the realization of a wax model corresponding to the anatomical part one wishes to reproduce.

The invention, furthermore, relates to equipment for putting said method into practice. Background art

Computerized systems for the creation of three- dimensional visual images by means of processing two- dimensional images obtained from radiographic CAT scans are already known. At an experimental level, robotized equipment and stereolithographic machines designed to be connected to the above-mentioned processing systems to transform three-dimensional visual images of anatomical parts into material models have also been proposed. Given the currently very high costs of the necessary equipment, it is not possible to use these methods routinely or on a large scale. The object of the present invention is to provide a method for the three-dimensional reproduction of anatomical parts on the basis of two-dimensional radiographic images which can be worked at a limited cost and, thus, be suitable for wide use on a large scale. Summary of the invention

The method according to the invention which accomplishes the above mentioned object is characterized by the following steps: - identifying and impressing reference marks on each two-dimensional radiographic image of the anatomical part to be reproduced;

- scanning said marked radiographic images to print them on respective paper supports; - positioning above each of said printed paper supports a sheet of transparent material having the same thickness as the CAT scan and fixing said sheet on said support in correspondence with said reference marks; cutting said sheet of trasnparent material following the contour of the two-dimensional image printed on the paper support in order to obtain a pattern of said image with projecting members on which a hole is formed in correspondence with said refernce marks;

- superimposing said patterns on one another in the same sequence said two-dimensional radiographic images were taken, aligning said holes axially in order to obtain a three-dimensional model of said anatomical part.

Preferably, the sheets of transparent material from which the patterns corresponding to the individual two- dimensional radiographic images are cut are made of wax. Wax proves optimum for its qualities of good transparency and easy cutting as well as because it makes it possible to easily finish the stack of patterns, thus allowing for the duplication of the model in other materials such as resin or plaster with usual techniques of duplication.

A further object of the present invention is to provide easy-to-use and extremely inexpensive equipment for carrying out the method in a practical manner.

The equipment according to the invention comprises: - a frame delimiting a window with graduated edges of dimensions at least equal to those of a radiographic plate, and provided with sliders moveable according to two perpendicular axes having marking means suited to leave a mark on the radiographic plate which can be read by an optical scanner;

- a support base for paper supports on which the marked images from said radiographic plates are printed, above said support base there extending an arm provided with punching means slidable towards and away from said support base and along said arm;

- a stacking plane for the patterns in transparent material to be superimposed on one another according to a pre-established sequence, said plane having reference elements for the correct positioning of said patterns and pressure means for calibrating the thickness of each of said patterns.

Description of the drawings

Further characteristics and advantages of the method and relative equipment according to the present invention will become apparent in the following description of one of its possible embodiments, given as an example and not limitative, with reference to the attached drawings in which: - figure 1 is a perspective view of a frame with sliders for impressing the reference marks on the radiographic plates in conformity with the method according to the present invention;

- figure 2 is a perspective view of a frame with punches for obtaining flat patterns from the marked radiographic plates;

- figure 3 is an exploded perspective view of a stacking plate for stacking and pressing the flat patterns. Rest mode of carrying out the invention

In the present description, the term "reference mark" indicates, as well known to a person skilled in the art, a point of reference conveniently identified on a radiographic image whose relative position with respect to the visualized anatomical part remains constant in all the other CAT scans. That being stated, with reference to figure 1, number 1 indicates a rigid square or rectangular frame delimiting a window 2 having a graduated edge 2a. On two opposite sides of frame 1, two parallel guides are fixed on which two sleeves 4 are slidingly mounted. Each sleeve is fixed to one end of a graduated bar 5 on which a pair of slider 6 are mounted. The sliding of bar 5 along the two parallel guides 3 can be blocked in any position by means of a setscrew 7 provided on at least one of sleeves 4. Similarly, the movement of sliders 6 can be blocked along the graduated bar 5 in any position by means of respective setscrews 8. Each slider 6 holds a marking device 9, formed substantially by a pointed stem, not shown, which by rotation can be moved away from and towards window 2.

In conformity with the method according to the invention, frame 1 holding sliders 6 is positioned above a backlighted panel and the various radiographic images of the anatomical part to be reproduced are positioned one after the other inside window 2 in order to mark on the plate the reference marks selected by the operator according to the form of the anatomical part radiographed. Said marks, after having been selected on one radiographic image, are transferred onto the other images, without any possibility of error, using the graduated scale on edge 2a.

Subsequently, the various tomographic sections marked in the above-mentioned manner are read by a scanner and printed on a sheet of paper or a card, after correction of scale if necessary, with the help of a usual computer. A positive image is thus printed in actual size and comprising also the reference marks. With reference to figure 2, 10 indicates a support base from one side of which a rod 11 rises vertically and holds a horizontal arm 12 extending above support base 10. Two moveable heads 13 forwardly protruding from, and sliding on, arm 12, carry two vertical punches 14 rotatably sliding to and away from base 10.

On support base 10, cards on which the various radiographic images and their reference marks are printed are placed one after another. Each card is fixed to support base 10 by means of pins 14a of punches 14 which have been previously aligned to said marks.

A sheet of pre-calibrated wax is then placed on the card. The wax sheet has the same thickness as the CAT scan (as known, the CAT scan provides two-dimensional images of sections of the anatomical structure obtained with cuts carried out at intervals of 1mm, 1.5mm, 2mm or other thicknesses) . The sheet of wax can then be cut, for example with a surgical knife, following the contour of the image printed on the underlying card which is visible through the layer of transparent wax. In this manner, a three-dimensional pattern of the image printed on the card is obtained consisting of a flat, shaped piece of transparent wax having a thickness equal to the space between one CAT section and the next. Each punch 14 has a tubular element 14b sliding axially and whose free end is sharp so that it can form a hole in the sheet of wax in correspondence with each reference mark. The cut pattern of the printed image has, therefore, a number of projecting members, on which said holes are made, equal to the number of reference marks. After a number of patterns equal to the number of radiographic CAT images available has been formed, the part of figure 2 of the equipment for carrying out the method of the present invention can be transformed into the part illustrated in figure 3 obtained by disassembling vertical rod 11 from support base 10 and reassembling arm 12 in correspondence with one of the two sides of support base 10 suitably designed for such application. More precisely, said side has a central flat projection 10a and two protruding side feet 10b to which arm 12 is fixed. Arm 12, projection 10a and feet 10b, therefore, delimit two slots 15 inside which the two heads 13 of arm 12 are slidably housed. Two pins 16 rise vertically from heads 13 on support base 10, the relative distance of said pins being adjustable, if necessary, by sliding heads 13 inside slots 15. Normally, however, such adjustment is not required since heads 13 have been already correctly positioned on arm 12 when adjusting the position of the punches 14 in the previous configuration of arm 12 shown in figure 2. Additional pairs of pins 17 and 18 extend from support base 10, in particular rising from two intermediate points of the two opposite sides adjacent to the one to which arm 12 is fixed, as well as from the two corners which said sides form with the side of support base 10 opposite that to which arm 12 is fixed. On pins 16, 17 and 18, a plate 19 engages which has two slots 20 for pins 16 and pairs of holes 21 and 22 for pins 17 and 18.

The previously cut patterns are stacked on support base 10 according to the same sequence of the radiographic CAT images and positioned so that said pins 16 engage in the respective holes of each pattern. Thus, it is possible to superimpose all the previously cut patterns with extreme precision and plate 19 functions as a calibrating and pressing element. In order to ensure perfect calibration and control of the thickness of each pattern inserted, two pairs of spacer rings 23 having a thickness equal to that of the CAT section corresponding to that pattern are contemporaneously placed on the two pairs of pins 17 and 18. The subsequent manual pressing (for each pattern inserted) facilitates the adhesion between the various patterns and the control of the total thickness of the model to the millimeter. To facilitate the work of the operator, rings 23 can have different colors according to their thickness.

The raw model obtained by the above-described superimposition of the various layers of wax can be used as it is or can be finished by rounding the edges. It can be duplicated in other materials (resin or plaster) with the usual duplication techniques.

Clearly, though in the present embodiment of the invention it has been envisaged to modify the support base 10 with punches 14 shown in figure 2 in order to obtain a stacking plane for calibrating and pressing the patterns placed thereon, as illustrated in figure 3, the two parts of the equipment fall within the scope of the invention also when realized as independent items. In particular, the stacking plane can comprise a base for supporting the patterns in a stacked relationship and guide means, for example along a side of the base, for the reference elements. The reference elements can be formed by blocks sliding in said guide means to adjust their distance to a required value and pins vertically extending from said blocks for engaging with the holes formed on the projecting members of the patterns.

With the method and equipment according to the invention it is possible to obtain, at very low cost, accurate reproductions of the maxillary or mandibular skeleton (for use in dentistry) , of the whole cranium (for maxillofacial surgery,plastic surgery, otorhinolaryngology and neurosurgery) , or other bone components (for orthopedics and surgery of the hand) , and of various organs (for other branches of surgery) .

The method has proven particularly effective in dental and maxillofacial surgery, particularly in the field of implantology, where the models obtained with this method can be used to produce axially-predetermined surgical stents (with special kits) , stents for shaping access windows in sinus lifting and alveolar nerve transposition operation and stents for taking bone grafts. They can also be used for direct preparation of sub- periosteal implants, pre-operative modelling of osteosynthesis devices and means, preparation of regenerative traction devices for medium and serious bone defects and for complete maxillary reconstructions, programming of osteotomy in pre-implant orthognathic surgery, etc. Variations and/or modifications can be brought to the method for the three-dimensional reproduction of an anatomical part and the equipment for carrying out said method according to the present invention without departing from the scope of the invention itself as specified in the appended claims

Claims

O 96/10243 PCMT95/00155

- 9 - CLAIMS 1. Method for the three-dimensional reproduction of an anatomical part on the basis of two-dimensional images obtained from a radiographic CAT test or equivalent test, characterized by the fact that it comprises the following steps:

- identifying and impressing reference marks on each two-dimensional radiographic image constituting the radiographic test and relative to said anatomical part; - scanning said marked radiographic images to print them on respective paper or card supports;

- positioning above each of said printed paper or card supports a sheet of transparent material having the same thickness as the CAT scan and blocking said sheet on said support in correspondence with said reference marks; cutting said sheet of transparent material following the contour of the two-dimensional image printed on the paper or card support in order to obtain a pattern of said image with projecting members on which a hole is formed in correspondence with said reference marks;

2. Method according to claim 1, wherein the material from which said patterns are cut is wax.

3. Method according to the previous claims wherein each of said patterns is subjected to a calibrated pressure at the time they are superimposed on one another.

4. Equipment for the three-dimensional reproduction of an anatomical part on the basis of two-dimensional images obtained from a radiographic CAT scan or equivalent test which are used to obtain patterns in transparent material of a thickness equal to the space between two subsequent CAT sections, said patterns being then stacked according to the same sequence of the CAT sections to form a model of the anatomical part, characterized by the fact that it comprises: - a frame (1) delimiting a window (2) with graduated edges (2a) of dimensions at least equal to those of a radiographic plate and provided with sliders (6) moveable according to two perpendicular axes holding marking means (9) suited to leave a reference mark on the radiographic plate readable by optical scanning;

- a support base (10) for paper or card supports on which the marked images from said radiographic plates are printed, above said support base there extending an arm

(12) carrying punching means (14) slideable from and towards said support base and along said arm for forming a hole through projecting members of said patterns in correspondance with said reference marks; a stacking plane (10) for said patterns in transparent material to be superimposed on one another according to a pre-established sequence, said plane having reference elements (13,16) for the correct positioning of said patterns and pressure means (19) for controlling the thickness of said patterns by exerting a calibrated pressure on each of them.

5. Equipment according to claim 4, wherein said support base (10) comprises a vertical rod (11) to the end of which said arm (12) is fixed.

6. Equipment according to claims 4 and 5, wherein said slideable punching means (14) comprise a slideable tubular element (14a) with a sharp end.

7. Equipment according to claims 4, 5 and 6, wherein said vertical rod can be disassembled from said support base for paper supports and said arm can be disassembled from said vertical rod, so that said support base for paper supports can be transformed into said stacking plane (10) for patterns in transparent material by applying said arm (12) to one side of the support base designed in such a way that the supports (13) for said slideable punches (14) have the function of said reference elements (13,16) for the correct positioning of said patterns.

8. Equipment according to claim 4, wherein said stacking plane comprises a base (10) for supporting said patterns, said base having guide means (15) for positioning said reference elements (13,16) in correspondance with said reference marks.

9. Equipment according to claim 8, wherein said reference elements are a pair of pins (16) extending vertically from blocks (13) adjustably sliding within said guide means (15) of said base, said pins engaging with the holes formed on the projecting members of said patterns.

10. Equipment according to claims 4 to 8, wherein said pressure means for the stack of patterns comprise guide pins (17,18) rising vertically from said patterns stacking plane, a plate (15) which can be slidingly engaged on said pins as well as spacer rings (23) having the same thickness as the corresponding patterns and engaging on said pins contemporaneously with each pattern, so that a calibrated pressure can be exerted on each of said patterns by said plate for the control of thickness to the millimeter.