CN1303949C - Method for preparing titanium alloy skull repairing body - Google Patents

Abstract

The invention discloses a method for making a titanium alloy cranial prosthetic body, which is applied to the fields of cranial bone repair in neurosurgery and the like. The present invention designs and assembles the prosthesis based on the patient's CT image. After data segmentation of the tomographic image is carried out by a computer stored with general image processing software and reverse design software, the three-dimensional prototype of the patient's head is reconstructed, and the defective part is designed according to the three-dimensional prototype. Restoration, and then use the rapid prototyping system to make the restoration model, and press the titanium mesh plate according to the model to form the final restoration. It is characterized in that the prosthetic model is first made by digital design technology, the special-shaped surface rapid prototyping system is used, and the titanium mesh plate is pressed by the progressive forming method, which avoids springback, fracture, and wrinkles when large-sized parts are pressed by the moldless multi-point technology And other issues. The titanium alloy prosthesis completed by the method of the present invention has high preparation precision, low cost and high speed, and the final prosthesis is in good agreement with the patient's skull, realizing the personalized customization of the cranium prosthesis.

Description

A kind of preparation method of titanium alloy skull prosthesis

technical field

The invention relates to a preparation method of a titanium alloy skull prosthesis, which is mainly used in the fields of cranial bone repair in neurosurgery, medical plastic surgery, cosmetic surgery and the like.

Background technique

Skull repair is a common surgical procedure in neurosurgery, medical plastic surgery, etc. The materials used mainly include: silicone rubber, polymethyl methacrylate (PMMA), good skull ratio and titanium alloy mesh. Among them, titanium alloy stencils have been widely used in clinical applications because of their good biocompatibility, non-toxicity and high strength. However, the current preparation process of titanium metal plate is either difficult to shape, or the production cost is high and the cycle is long, which seriously limits its popularization and application. At present, there are mainly the following three preparation processes:

(1) Manual shaping This is a shaping method commonly used in China. The doctor manually prefabricated the approximate shape of the restoration according to the appearance and shape of the patient's defect site and his own experience. During the operation, he compared it with the exposed skull of the patient, and then manually Repeated modification, and finally disinfection to complete the operation.

(2) Mold pressing This is a shaping method adopted abroad. First, the stamping mold of the restoration is processed by a CNC machine tool, and then the restoration is pressed using the mold on a press, and finally cut and sterilized to complete the operation.

(3) Casting and forming First, the wax model of the restoration is prepared by rapid prototyping technology, and the titanium alloy is cast by the lost-wax casting method, and then the mounting holes and growth holes are drilled on the titanium alloy restoration, and finally the operation is completed by disinfection.

The above three processes have the following problems, which limit the application of titanium metal or affect the quality of surgery:

(1) Manual shaping is labor-intensive and has poor precision. Because the real shape of the skull cannot be obtained in advance, there are blind spots in shaping; Postoperative safety has buried hidden dangers;

(2) Mold pressing is advanced to a certain extent, which reduces the labor intensity of doctors. However, the production cycle is long and the cost is high (generally 100,000 RMB per case in foreign countries). Moreover, after the mold is fixed, it cannot solve the springback problem of the prosthesis after pressing, which will affect the fitting accuracy of the prosthesis.

(3) The casting method solves the problem of the accuracy of the restoration, but the process is complicated and costly. The titanium alloy will be oxidized during the casting process, and the thickness of the restoration should not be too thin, otherwise it cannot be cast.

Due to many problems in traditional restoration methods, it is necessary to find a flexible technology to achieve the purpose of fast and accurate restoration. The patent "a method for preparing a titanium alloy skull prosthesis" (application number: 03156843.2) adopts a CT machine to collect tomographic images of the head, and then inputs the tomographic images into a computer for data processing. The feature of this invention is that it stores general image processing After the computer of the software divides the data of the tomographic image, it reconstructs the three-dimensional restoration of the head defect, and then reads the designed restoration surface into the multi-point forming system and the rapid prototyping system to press the titanium mesh plate and make the restoration thin slice model , and finally the final restoration was formed by fitting and contrasting the cut titanium mesh. The pressing of titanium alloy adopts the method of multi-point forming. Multi-point forming is a new technology for three-dimensional surface forming of sheet metal. The principle is to disperse the traditional overall mold into a series of regularly arranged, height-adjustable basic bodies (or punches). In traditional mold forming, the plate is formed by the mold surface, while in multi-point forming, the required envelope surface (or forming surface) is formed by the basic group of punches. The multi-point forming technology is used to quickly press the restoration, and the flexible characteristics of the moldless multi-point technology can be used to repeatedly press the restoration to solve the springback problem of the restoration.

However, in the actual use process, it is found that the quality of the compressed restoration using the multi-point forming technology is better when forming small-sized parts, but there are the following problems when forming large-sized parts (size greater than 10cm×10cm):

1. When forming large parts, the problem of part springback is more prominent, and it must be pressed repeatedly, which increases the production time.

2. In order to eliminate springback, overpressure is necessary during pressing. If the deformation of the part itself is relatively large, it is easy to cause the breakage of the part.

3. It is difficult to determine the process parameters for eliminating springback overpressure at one time. In practice, the method of pressure test is often used (one-time pressing is difficult to eliminate springback), which not only takes a long time, but also often causes excessive convexity in the middle of the part, wrinkles etc.

4. Due to the fact that multi-point forming is easy to cause stress concentration during the pressing process, it will lead to thinning of the plate and decrease in strength, which will affect the safety of the operation.

Contents of the invention

The present invention aims at the existing technology and the problem that the moldless multi-point forming technology is not suitable for making large parts. On the basis of the patented technology named a titanium alloy skull prosthesis preparation method, application number: 03156843.2, a method is proposed. The preparation method of titanium alloy skull prosthesis, the technical idea is: based on image processing, reverse engineering, incremental forming and rapid prototyping technology to manufacture titanium alloy prosthesis. That is, firstly carry out 3D reconstruction on the computer based on the patient's CT data, design the restoration based on the reconstruction model, and perform simulated assembly to ensure that the appearance of the restoration is beautiful and the edges fit well with the edge of the defect; then the physical model of the restoration is made using rapid prototyping technology According to the physical model, the titanium alloy plate is pressed by progressive forming technology, and the final restoration is obtained after edge trimming.

Refer to Fig. 1 and Fig. 2 for the technical solution of the present invention. The method is to collect head tomographic images by CT machine, and then input the tomographic images into the computer for data processing, and then reconstruct the three-dimensional prosthetic body of the head defect after the data segmentation of the tomographic images is carried out by the computer stored with general image processing software, Then input the STL file of the restoration shell into the rapid prototyping system, use the rapid prototyping technology to make the physical model of the restoration, press the titanium mesh plate according to the physical model, and finally fit the comparison and cut the titanium mesh plate to form the final restoration; the CT image Mimics software system is used for processing, Surfacer software system is used for prosthetic design, and fusion deposition rapid prototyping system is used for prosthetic model production; it is characterized in that the present invention uses special-shaped curved surface rapid prototyping system, and uses progressive forming method to suppress titanium mesh compared with physical model Plate, trimmed to get the final restoration, the steps of the progressive forming method are:

a Wrap the mold with a soft cloth, and seal the titanium alloy plate with a plastic film when pressing the part;

b Select the mold according to the different curvatures of the parts. When forming relatively flat parts, use a large diameter mold, and use a small diameter mold for forming a large arc; first use a large diameter mold to press, and adjust the pressing depth to form different parts In the part of the curvature, the indentation depth of the flat part is small, and the indentation depth of the large part is large;

c. During the pressing process, the titanium alloy plate to be formed is repeatedly compared with the physical model of the restoration made by rapid prototyping technology until the two match.

The invention integrates advanced manufacturing technologies such as computer image processing, reverse engineering, progressive forming and rapid prototyping to jointly complete the production of titanium alloy restorations, ensuring the accuracy and efficiency of each link. Because the adjustment and optimization of the design and manufacturing parameters of the prosthesis of the present invention are all completed in the computer, the flexibility is strong, the cost is low, the speed is fast, and the final prosthesis is of high quality, which solves the problem of rapid shaping of the titanium alloy prosthesis; and ensures Fitting precision, no modeling blind spots, realize the individualization of cranial prosthetics.

Description of drawings:

Fig. 1 block diagram of manufacturing system of titanium alloy prosthesis of the present invention

1 CT machine, 2 storage medium, 3 computer, 4 image processing, 5 restoration design, 6 rapid prototyping system, 7 special-shaped surface rapid prototyping system, 8 fitting comparison, 9 final restoration;

Fig. 2 method flowchart of the present invention;

Fig. 3 Defect images existing in the prior art when the multi-point forming technology is used to press the restoration to form large-sized parts (size greater than 10cm×10cm)

Figure a shows the phenomenon of part fracture, picture b shows the parts after riveting, and picture c shows the phenomenon of excessive convexity and wrinkling,

Figure d shows the springback after one-time forming, and picture e shows the sheet becomes thinner;

Fig. 4 is a diagram of adjusting the position of the skull prototype;

Fig. 5 is the control vertices of the restoration surface;

Figure 6 is the local point cloud extracted when the restoration was designed using the mirror image method, and the peripheral curve is the clipping boundary;

Figure 7 is the local point cloud extracted when using the trend transition method to design the restoration, and the outer curve is the clipping boundary;

Figure 8 is the fit comparison between the restoration shell model and the titanium mesh;

Figure 9 is the final titanium mesh restoration;

Figure 10 shows a good fit between the prosthesis and the patient's skull during the operation.

Detailed ways

Utilize the technology of the present invention, carry out clinical application in Beijing Temple of Heaven Hospital. Patient data collection was completed in Tiantan Hospital Information Center, CT image processing was performed using Mimics software system, prosthetic design was using Surfacer software system, titanium mesh pressing was using special-shaped surface rapid prototyping system, prosthetic model was made using fused deposition rapid prototyping system, and finally The final titanium mesh restoration was formed after fitting, comparison and cutting. The specific steps are as follows:

(1) Firstly, a spiral CT scan is performed on the patient's skull, and the scanning interval is set at 2-3 mm. The present invention sets the spacing of the scanning layers according to the position of the patient's skull defect. If the shape of the defect is complex, such as the temple or the root of the ear, the scanning spacing is set to 2mm. If the shape change of the defect is relatively gentle, the scanning distance is set to 3mm;

(2) The collected CT images are stored in a mobile hard disk or a recordable CD storage medium in the medical digital imaging standard (dicom) file format. The storage format is dicom format; dicom format is a standard file format for medical digital imaging and communication, and dicom format records all information;

(3) Segment the skull data from the CT image, the grayscale threshold range is 1250-4095, the grayscale range is 0-4095, and the tissue expression is delicate; the computer with the general medical image control system software (Mimics) is stored from the storage medium Read in the CT image, segment and extract the skull image; in the segmentation step of the Mimics software, set the minimum gray level of the skull pixel to be 1250, and the maximum gray level to be l, where l is the maximum gray level of the skull in the CT image , usually take l=4095, the segmented skull pixel S is:

S＝{P|1250＜V _P ＜l}

Wherein S is the set of skull pixel points, P is the pixel point, V _P is the gray level of the p pixel point, and l is the maximum gray level of the image;

(4) Reconstruction of the three-dimensional skull prototype based on Mimics software;

According to the three-dimensional area growth step of general medical image control system software (Mimics), first select any pixel point of the skull image after segmentation, then the three-dimensional area connected with this pixel point is all temporarily recorded, and then stored by computer In the usual way, specify the path, file name and storage format of the output file, and the computer with Mimics software will automatically complete the reconstruction of the three-dimensional model of the skull prototype, and the file output format is STL;

(5) Design the restoration of the defect site according to the reconstructed 3D prototype of the skull, the specific method is:

a computer equipped with general surface modeling software (Surfacer), read in the three-dimensional prototype data of the skull;

b adjust the position of the skull prototype;

c. According to the three-dimensional curve generation step of the software, determine the boundary curve of the final restoration at the defect site;

d Utilize the processing technology in the general surface modeling software (Surfacer), that is, the step of software frame selection to extract points, the step of software to obtain point cloud of section, the step of software to generate curve, the step of software to generate surface, after virtual assembly of restoration surface and skull prototype, and then According to the trimming step in the software, trim the curved surface to obtain the final restoration surface, and at the same time, follow the surface offset step in the software to offset the restoration surface by 2 mm to form a shell and store it as an STL file format;

(6) Use the rapid prototyping system to make the restoration shell model. The shell STL file is input to the rapid prototyping system, and the restoration shell model is made by superimposing ABS materials; compared with the restoration model, the titanium alloy restoration is pressed by progressive forming technology. The specific parameters are: the diameter of the ABS material wire is 0.4mm, the material forming temperature is 220°C, the forming room temperature is 70°C, and the temperature is kept for 30 minutes after forming;

Import the restoration shell STL file into the rapid prototyping system to make the restoration shell model. The restoration is pressed from a square blank plate, which must be trimmed to obtain a surgically usable restoration. Since the surface of the restoration has no obvious boundary features that are easy to confirm, and the boundary used for cutting is a space curve, it is difficult to directly cut out the required shape. The present invention satisfactorily solves this problem by adopting the comparison method in kind, and the specific process is as follows:

a. Read the restoration shell file (STL file) into the rapid prototyping system. Rapid prototyping is a new three-dimensional part forming process based on the idea of material accumulation. Layer-by-layer manufacturing to form three-dimensional parts;

b Layer the shell model with a layer thickness of 0.15mm and store it in the cli file format;

cUsing layered files to drive the rapid prototyping control system, superimposed manufacturing layer by layer to form the shell model of the restoration;

The specific steps for pressing the titanium stencil by progressive forming method are as follows:

a In order to protect the surface of the titanium alloy from being scratched, wrap the mold with a soft cloth, and seal the titanium alloy plate with a plastic film when pressing the part.

b. When using progressive forming to press parts, select the mold according to the different curvatures of the parts. When forming relatively flat parts, use a large-diameter mold, and use a small-diameter mold for forming parts with a large radian. The pressing frequency affects the forming efficiency, the higher the frequency, the faster the efficiency, and vice versa.

c. First use a mold with a large diameter to press, and adjust the indentation depth to form parts with different curvatures. The indentation depth of the flat part is small, and the indentation depth of the large arc part is large.

d For parts or parts with larger radians, use small-diameter molds to press, and these parts are mainly concentrated on the top of the forehead and the temple.

During the pressing process, the titanium alloy plate to be formed is repeatedly compared with the physical model of the restoration made by rapid prototyping technology until the two match. The pressing equipment is produced by Swiss Accor (ECKOLD AG) and Wuxi Jinqiu Machinery Co., Ltd. The Swiss Accor equipment is called Universal Forming, and the Wuxi Jinqiu equipment is called a special-shaped surface rapid prototyping machine.

(7) Titanium stencils are pressed using progressive forming technology, and the special-shaped curved surface rapid prototyping machine produced by Wuxi Jinqiu is used as the equipment. Equipment parameters: large mold Φ80mm and small mold Φ40mm, pressing frequency up to 49 Hz; compare the made restoration shell model with the pressed titanium mesh until the two are completely fitted (see Figure 8). Cut the titanium mesh along the border of the prosthetic model to form the final titanium mesh restoration (see Figure 9).

The present invention designs the prosthetic body based on the three-dimensional prototype of the skull, and the key is that the edge of the prosthetic body fits well with the edge of the skull defect. The edge of the restoration should cover 1-1.5 cm around the defect for titanium nail fixation. A good fit can ensure the contact area between the restoration and the skull, increase the success rate of the operation and the postoperative comfort of the patient. According to the defect of the patient's skull, two different design methods are determined:

Method 1: If one side of the patient’s skull is defective and the other side is intact, the mirror image method can be used to design a restoration using the health data of the other side. The steps are:

a The computer equipped with general-purpose surface modeling software (Surfacer) reads in the three-dimensional prototype of the skull;

b Adjust the position of the three-dimensional prototype so that the symmetry plane of the prototype coincides with the YZ coordinate plane, see Figure 4. The specific method is to first select three points on the symmetric plane of the skull to generate plane 1, then generate plane 2 on the YZ coordinate plane, combine the three-dimensional prototype with plane 1, and move the assembly to make plane 1 and plane 1 align according to the alignment steps in the software system. Plane 2 coincides to complete the position adjustment. The adjusted 3D prototype facilitates subsequent data extraction and evaluation of the appearance of the prosthetic surface;

c Mirror copy the skull prototype along the YZ coordinate plane;

d According to the three-dimensional curve generation steps of the software, the points on the edge of the skull defect are sequentially selected with the mouse to generate a spatial closed curve, see Figure 6 for the internal closed curve. Then follow the offset steps of the software to offset the generated closed curve outward by 10mm as the trimming boundary of the restoration, see Figure 6 for the outer closed curve;

e Press the software frame to select the extraction point step, face the defect part to the operator, draw a rectangular frame along the clipping boundary, and cut off the point data outside the frame, see Figure 6;

f According to the step of taking the cross-section point cloud by the software, make a group of parallel cross-sections with the point data extracted in step e along the vertical direction with the craniofacial, the distance between the cross-sections is D=3mm, and extract the cross-section points. For the extracted cross-section points, refer to accompanying drawing 6;

g According to the software generation curve step, use the 3 basic spline curve interpolation section points in general graphics technology to generate a group of section curves, and then follow the software reparameterization step to reparameterize the generated curve group to ensure that all curves have the same control points and orientation;

h According to the steps of generating the surface by the software, use the skin surface in the general graphics technology to interpolate the section curve, and the obtained surface is the restoration surface;

i Virtually assemble the prosthetic surface and the skull prototype, observe whether the fit and appearance of the two meet the design requirements, and at the same time adjust the control vertices of the surface accordingly until a satisfactory shape is achieved, see Figure 5;

j According to the cutting step in the software, use the boundary curve generated in step d to cut off the surface outside the boundary, and the cut surface is the final restoration surface;

Method 2: If the area of the defect is small, or there is no mirror image data for reference, use the method of trend transition to design the restoration. The steps are:

a The computer equipped with general-purpose surface modeling software (Surfacer) reads in the three-dimensional prototype of the skull;

b Adjust the position of the 3D prototype so that the symmetry plane of the model coincides with the YZ coordinate plane, see attached drawing 4. The specific method is to first select three points on the symmetric plane of the skull to generate plane 1, then generate plane 2 on the YZ coordinate plane, combine the three-dimensional prototype with plane 1, and move the assembly to make plane 1 and plane 1 align according to the alignment steps in the software system. Plane 2 coincides to complete the position adjustment;

c According to the three-dimensional curve generation steps of the software, the points on the edge of the skull defect are sequentially selected with the mouse to generate a closed space curve, see Figure 7 for the internal closed curve. Then follow the offset step of the software to offset the generated closed curve outward by 10mm as the trimming boundary of the restoration, see Figure 7 for the outer circle closed curve;

d Press the software to frame the extraction point step, face the defect part to the operator, use the mouse to draw a rectangular frame along the clipping boundary, and cut off the point data outside the frame, see Figure 7. As much point cloud information as possible for reference, the range of the rectangular domain is about 20mm larger than the clipping boundary, see Figure 7;

The remaining steps are the same as the f-j steps of method one.

(8) Fit and compare the restoration shell model and the pressed titanium mesh plate, and cut to form the final restoration;

(9) It is used for clinical operation after disinfection, see Figure 10.

The prosthesis prepared by the invention fits well with the patient's skull, and clinicians comment that the invention shortens operation time, reduces pain of patients, and significantly improves operation quality.

The preparation of the titanium alloy cranial prosthesis was carried out according to the above steps. It took less than 2 hours from obtaining the patient's CT data to prefabricating the titanium alloy prosthesis. The final prosthesis fit very well with the patient's defect during the operation, and the size was appropriate. One operation success. According to the comparison of clinicians, compared with the previous manual shaping method, the appearance is beautiful, no incision is required, the number of titanium nails is reduced, and the overall operation time is shortened because there is no intraoperative shaping time.

The following table is the comparative result of the present invention and main preparation technology at present: Preparation time (hours) cost(RMB) quality Remark hand shaping 5 5000.00 generally Sometimes reshaped during surgery mold pressing 60 100000.00 better lost wax casting 60 50000.00 generally modeless multipoint 6 7000.00 good Good for forming parts with small dimensions this invention 2 7000.00 good

Claims (1)

1. method of making titanium alloy skull repairing body, be to gather the head faultage image by the CT machine, again faultage image is imported and carried out date processing in the computer, faultage image is carried out after data cut apart at the computer of depositing the general image process software, the three-dimensional dummy of reconstructed head defect, then dummy housing stl file is input to rapid prototyping system, adopt rapid shaping technique to make the mock-up of dummy, according to mock-up compacting titanium mesh plate, the contrast of fitting is at last reduced titanium mesh plate and is formed final dummy; Wherein the CT Flame Image Process adopts the Mimics software system, and the Surfacer software system is adopted in the dummy design, and the fusion sediment rapid prototyping system is adopted in the making of dummy model; It is characterized in that, use the abnormal curved surface rapid forming system, adopt progressive molding method compacting titanium mesh plate according to mock-up, obtain final dummy after cutting the limit, the step of progressive molding method is:

A wraps up mould with softish cloth, with plastic sheeting titanium alloy sheet is sealed when compacted part;

B selects mould according to the different curvature of part, adopts the big mould of diameter when the part of shaping relatively flat, and the part that the shaping radian is big adopts the little mould of diameter; At first adopt the big mould compacting of diameter, by regulating the part of different curvature on the compression distance formation of parts, the position compression distance that radian is smooth is little, and the position compression distance that radian is big is big;

The titanium alloy sheet that c is shaped needs in pressing process repeatedly with the mock-up of the dummy that adopts rapid shaping technique to make relatively, fit like a glove until both.

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