Segmentation of retinal blood vessels based on centerline extraction / 生物医学工程学杂志

The precise estimation of blood vessel centerline and width is a prerequisite condition for the quantitative and visualized diagnosis of blood vessel disease in fundus images. In this paper, a retinal blood vessel segmentation algorithm based on centerline extraction is proposed. According to the characteristics of the fundus image and retinal blood vessels, the image is convoluted with the masks of discrete Gaussian partial derivative kernels. The centerline is determined by differential geometric properties of the blood vessels and the width is also calculated. The precision of our method can reach sub-pixel level with a fast computation speed. The experiments on several kinds of fundus images showed that the method worked quickly and accurately.

Research on computer-aided technology of surgical guide for dental implant / 生物医学工程学杂志

The present paper was conducted to a systematic method of surgical guide for dental implant based on computer-aided technology through CT data and dental-cast data. By analyzing the patient's CT data, the implant region was planned using image processing techniques. For the specified implant region, the computer-aided method for the rational allocation of dental implant was addressed in a sense of anatomy. With biomechanical principles as well as aesthetical and functional requirements as preconditions, this method can make full use of bone quantity and quality to produce the optimum implantation axis. The transferring of implant planning to the patient was then realized by registration between CT models and dental-cast models. A case research explained the whole process of the surgical guide. The results validated the correctness and feasibility of this method, which has a great significance to enhance the quality and accuracy of implant surgery.

Realization of algorithm on finishing optimization-tool-path generation for high-speed machining molar crown / 生物医学工程学杂志

Molar crown is very small and has not only thin-wall, but also complex profile, especially, the occlusal surface of each molar crown has many cusps, ridges and fossae being differently distributed. When conventional processing method is used, it is impossible to machine molar prosthesis rapidly and exactly. To enhance machining velocity and improve the surface precision of molar crown, an algorithm of entity rapid offset-based STL format is put forward. By the application of Zigzag toolpath planning and micro-machining cutter, the finishing toolpaths for high speed milling molar prosthesis are generated. In terms of Mikron UCP800 high-speed machine center, the molar all-crown made of alloy aluminum material is successfully machined. The test results show that the algorithm of tool-path generation works fast, the number of toolpaths is small, and the cutter feeds smoothly.

A method of dental arch auto-detection for dental plaster models / 生物医学工程学杂志

The shape of dental arch for orthodontic diagnosis and treatment is of great significance. This paper presents an automated method for detecting the dental arch form. Firstly, 3D teeth data model is retrieved by the 3D-optical measuring system. Secondly, the occlusal plane is computed by interactively picking up four feature points. Thirdly, the feature point set is filtered by the rule and two-step curve fitting method is used to obtain the dental arch form. Finally, some examples are tested in this work and the results demonstrate that the proposed algorithm is effective and feasible.

Establishment of database with standard 3D tooth crowns based on 3DS MAX / 生物医学工程学杂志

The database with standard 3D tooth crowns has laid the groundwork for dental CAD/CAM system. In this paper, we design the standard tooth crowns in 3DS MAX 9.0 and create a database with these models successfully. Firstly, some key lines are collected from standard tooth pictures. Then we use 3DS MAX 9.0 to design the digital tooth model based on these lines. During the design process, it is important to refer to the standard plaster tooth model. After some tests, the standard tooth models designed with this method are accurate and adaptable; furthermore, it is very easy to perform some operations on the models such as deforming and translating. This method provides a new idea to build the database with standard 3D tooth crowns and a basis for dental CAD/CAM system.

Computer aided design and manufacturing of the framework of PFM fixed bridge / 生物医学工程学杂志

We have carried out a research on the method for Computer Aided Design and Manufacturing (CAD/ CAM) of the framework of porcelain-fused-to-metal(PFM) fixed bridge. Taking the missing of the mandibular first molar as an example, firstly, we used ATOS II 3D scanner to collect the 3D data of the abutment teeth and used the acquried data to design the coping crowns. Secondly, the relevant standard bridge was selected from the standard bridges database and was deformed inaccordance to the characteristic of the patient. Then it was set to the correct position between the coping crowns automatically based on the restricting lines and faces. Finally, the connector was designed to connect the coping crowns and the bridge based on the touching area. The final product was manufactured by 3-axis NC milling machine. The results of examination showed that the framework of PFM fixed bridge fitted the abutment teeth very well, and the hardness of the connector and the precision of the whole model were feasible and reasonable. The method of designing and manufacturing the framework of PFM fixed bridge from CAD/CAM is practicable, efficient and accurate. It is also an important part of homemade dental CAD/CAM system.

Research of tool-path generation algorithm for NC machining dental crown restoration / 生物医学工程学杂志

Seeing that the manual method to restore tooth has the disadvantages such as long "lead-time", assurance of quality highly depending on operator's technology, and real-time cure difficulty met by lots of dental patients coming up for tooth restoration, we put forward an algorithm of tool-path generation based on STL data model for roughing dental restoration. The algorithm can reconfigure the STL data of dental crown restoration quickly, can generates the multi-level offset wire-loop by the use of horizontal plane cutting triangle facets; and then on the basis of offset wire-loop, it can plan Zigzag and follow the contour machining tool path. The algorithm has been applied to Dental CAM software, through simulation machining, the result shows that it can not only generate interference-free tool path, but also save a lot of "lead-time" for dental restoration. Accordingly, the algorithm is of great value for reference in clinical application.

Research and application of computer-aided technology in restoration of maxillary defect / 生物医学工程学杂志

This paper presents a new method of designing restoration model of maxillectomy defect through Computer aided technology. Firstly, 3D maxillectomy triangle mesh model is constructed from Helical CT data. Secondly, the triangle mesh model is transformed into initial computer-aided design (CAD) model of maxillectomy through reverse engineering software. Thirdly, the 3D virtual restoration model of maxillary defect is obtained after designing and adjusting the initial CAD model through CAD software according to the patient's practical condition. Therefore, the 3D virtual restoration can be fitted very well with the broken part of maxilla. The exported design data can be manufactured using rapid prototyping technology and foundry technology. Finally, the result proved that this method is effective and feasible.

Computer aided design and manufacture of individual laminate veneer / 生物医学工程学杂志

In view of the instance of a damaged medial incisor, we have introduced a method using computer aided technology to design and manufacture the laminate veneer. Firstly, the data on preparation teeth was retrieved by the 3D-optical measuring system. Secondly, the triangle mesh model of preparation teeth was reconstructed by using the reversion project software. And the 3D model of the laminate veneer was constructed through some operations, such as extracting the edge line of preparation teeth, mirroring the integrity incisor and local freeform transform. The result has proved that the fabrication process is reliable and efficient. The dental restoration quality is steady and precise. The artifical laminate veneer has met the request of esthetical symmetry.

The development of a system for 3D reconstruction from DICOM data and collaborative visualization / 生物医学工程学杂志

Complex surgeries often need multi-disciplinary surgeons to work collaboratively and set synthesized operation plans. Aided by collaboration enabled three dimensional visualization software over network, operation plans can be made more intuitively and accurately. Because different disciplinary surgeons often work at different locations, a distributed collaboration virtue environment over network should be provided. By our knowledge, such a system does not exist yet. Toward this, we implement a platform upon Client/Server architecture over network. The 3D model is reconstructed from CT image data of DICOM format and the resulting mesh is then simplified, using the Visualization Toolkit (VTK). The simplified polygon mesh data is further seamlessly integrated into our 3D graphics system developed with the HOOPS/3DAF for displaying, where the model is converted to the lossless compression stream file format-HSF, which is suited for network transmission. Using this format, a collaboration enabled interactive visualization system is implemented upon Client/Server architecture, developed with HOOPS/NET toolkit. The reconstructed 3D model is clear, and the interactive collaboration with 3D visualization is fairly real-time. We then implemented a platform for developing collaborative surgery simulation software, into which the surgery operation simulation and prosthesis design function can be easily added.

Virtual orientation of the lower and upper jaws model on the position of centric occlusion / 生物医学工程学杂志

The rotation axis equation of the simple articulator is built by the cylinder feature identification, which facilitates the rotation transform of the lower jaw data. Then the collision points and areas on the position of centric occlusion are found to form two collision couples. The virtual orientation of the lower and upper jaws model is realized by collision detection of the collision couples. Consequently the occlusal relation between the lower and upper jaws is established. It sets a good basis for the virtual adjustment of edentulous occlusal surface. The jaw movement of opening and closing in the state of hinge axis is also simulated accordingly.

Research and implement of the primary motion simulation based on virtual articulator / 生物医学工程学杂志

This paper presents our work on the research process of virtual articulator simulation. Firstly, plaster models of upper jaw and low jaw are measured by 3D-optical measuring system and processed to get the available data. Secondly, complex physical modeling of the jaw motion is simplified and decomposed to a series of position transform, such as translation, rotation, etc.. Thirdly, opening/closing movement and laterotrusion is simulated by real-time updating display. Fourthly, the efficient collision detection algorithm is applied to dynamically compute occlusal contact regions and cutaway view. Finally, the current shortage of the virtual articulator simulation is discussed in detail and research prospect is forecasted.

An experimental research on the fabrication of the fused porcelain to CAD/CAM molar crown / 生物医学工程学杂志

This paper introduced the fabrication process of the fused porcelain to molar crown with CAD/CAM technology. Firstly, preparation teeth data was retrieved by the 3D-optical measuring system. Then, we have reconstructed the inner surface designed the outer surface shape with the computer aided design software. Finally, the mini high-speed NC milling machine was used to produce the fused porcelain to CAD/CAM molar crown. The result has proved that the fabrication process is reliable and efficient. The dental restoration quality is steady and precise.

The mechanism and application of the correction for spherical myopia using small beam excimer laser / 生物医学工程学杂志

In the laser ablation refractive surgeries, the corneal ablation model and its realization by laser are difficult to design. They greatly affect the results of those surgeries. This paper firstly presents a mathematical model for corneal ablation to correct the refractive error of spherical myopia, and then gives a technique of planning laser focus positions on cornea to realize the ablation model. Based on the principle of the correction for spherical myopia using small beam laser, our excimer laser corneal surgery system has been able to perform such refractive surgery. Now the corneal surgery system has been applied to clinical practice. Thirty-nine eyes with spherical myopia underwent LASIK using this kind of system. Their refractive states have been greatly improved. Preoperatively, the mean sphere was -5.57+/-2.95 D and the mean uncorrected visual acuity 0.12+/-0.07. One day after surgery, the mean sphere was -0.03+/-0.57 D and the mean uncorrected visual acuity 0.90+/-0.29. One month after surgery, the mean sphere was -0.68+/-0.98 D, and the mean uncorrected visual acuity 1.0+/-0.26.

Research on human eye cornea's mathematical model and application in diopter correction / 生物医学工程学杂志

The excimer laser diopter correction has proven to be efficient and safe. This paper presents the principle of excimer laser refractive surgery. Based on analyzing the mathematics model of the human eye cornea, the authors have proposed a new model which can be used to proceed the myopia, hyperopia, astigmatism diopter correction. Also studied were the excimer laser's ablation mechanism and the flying-spot scanning technology. The research results have been directly applied to Ophthalmic excimer laser system. The correction of diopter is well improved.