| Oral health as a mirror is a reflection of human health. The World Health Organization that oral health is one of the ten human health standard. With the development of China’s socialist material civilization and spiritual civilization, more and more citizens aware of the importance of oral health. China has begun to slowly enter the aging stage, oral disease trends change. The third national oral health survey deciduous teeth of5-year-old children suffering from dental caries disease was66.0%, the middle-aged man suffering from dental caries disease was88.1%, the periodontal healthy rate of14.5%,37.0%rate of tooth loss.; elderly people suffering from dental caries was98.4%, periodontal health was14.1%and86.1%of the rate of tooth loss. This shows that our dental caries incidence is relatively high, affecting people’s normal life, but this kind of disease is early prevention, if early prevention can reduce the incidence of30%, and as long as about10%of the cost of treatment.In the prevention of oral diseases, oral diagnosis is an essential means. With the development of modern medical equipment technology, emerging out of new diagnostic techniques, provides a powerful tool for the diagnosis of oral diseases. In the field of X-ray diagnosis of oral dental machine, dental panoramic machine Dental CT. Wherein oral is most accurate diagnosis of the Dental CT. Dental CT can accurately reflect the oral tissues from the three-dimensional (axial, coronal, and sagittal), and the Dental CT lesions can see dental films and panoramic dental machine can not be found. For most dentists, to obtain high-resolution three-dimensional structure of the image of the Dental CT is the more satisfactory technology for diagnosis and treatment. And Dental CT can also help doctors design preoperative and postoperative scientific evaluation,this has wide application in oral shaping the field of Oral Implantology. Traditional CT radiation dose, large volume, high cost disadvantages limit the application in the field of Oral Medicine. Therefore, low cost, small footprint, low-dose, easy to operate, easy to maintain the advantages of Dental CT gradually replace conventional CT in the field of oral. The Dental CT belongs specialist equipment, the cost is relatively low,. Currently in China has basically only was able to assemble in large cities, large hospitals, is not conducive to raising the level of our primary medical care.Since the end of the20th century in Europe and Japan designed the first Dental CT, dental CT enter a stage of rapid development, began to be widely used in clinical and the foreign Dental CT technology has been relatively mature. Due to the high technical threshold, the domestic market to rely on imports. Domestic research and development of Dental CT started late, and our industrial base is relatively poor, the core components can not keep up the level of foreign Currently only a small number of research units in the development of Dental CT, but the domestic Dental CT has not yet listed.First in theory, Dental CT is a specific application of CBCT. Reconstruction algorithms use more Feldkamp, Davis, Kress cone top trajectory reconstruction methods for single-round FDK algorithm. Because the mathematical theory of the algorithm is relatively simple, the calculation process is relatively simple, easy implementation of the hardware acceleration and parallel computing, mechanical mechanism easy to implement, so that the algorithm to obtain a wide range of applications in CBCT. The Dental CT imaging principle and the principle is somewhat similar to conventional CT imaging, But CBCT the acquired two-dimensional projection data, the corresponding use of a two-dimensional flat panel detector, whereas conventional CT is obtained by one-dimensional data, the corresponding use of the linear detector.In terms of structure, Dental CT has a horizontal, sitting, and standing, no matter what kind of form, contains these three key components of flat panel detector, high voltage generator and rotating mechanical structure, and its scanning mode are unchanging.The design phase of Dental CT complex, which, to obtain precise geometric parameters; cooperative control of the scanning system; flat panel detector calibration; reasonable system debugging four key technical issues that must be addressed.In this paper, the key technical problems in Dental CT system, do the following work:1, the experimental correction of the flat panel detector.The experiments were carried out on the stability of the flat panel detector, linear consistency and SNR correction through experiments in order to ensure the acquisition of the projected image quality of flat panel detector..2, To achieve a flat panel detector, high voltage generator and gantry rotation between the three synchronization control.(1) Flat panel detector control timing analysis. Understand the structure of the flat panel detector imaging principle basis, through experiments, analysis, control the timing of the flat panel detector control interface. Combined with practical application, the selected image acquisition rate of10Hz.. (2) High-voltage generator control sequence, as well as the communication protocol analysis. Application Fluke the Max-ray measurement equipment and oscilloscope to capture the high-voltage output signal, analysis of the X-ray output pulse width and frequency, high-voltage generator to determine the timing control. The use of serial debugging assistant and virtual serial port to the serial signal detection compared to determine the communication protocol of the high-voltage generator..(3)Tablet detection, high-voltage generator and gantry rotation between the three synchronization control.On the basis of the flat panel detector and the high-voltage generator to control the timing analysis and experiment, to achieve a synchronous control of the beam detector image acquisition and high voltage pulse generator..In the the rack rotation of the control in the present design by analyzing and comparing the chosen stepper motor of the cumulative error of0. In order to improve the control accuracy of the stepper motor, stepper motor control using the hard drive to be broken down, by adjusting the frequency to control the speed of the stepper motor. Because the stepper motor for their own reasons, in the process of starting and stopping there will be vibration, smooth motion overshoot phenomenon, which seriously affected the stability of the system and Dental CT imaging quality. In order to achieve a smooth start and stop of the motor, stepper motor start and stop software design uses a stepper motor acceleration and deceleration algorithm. Stepper motor acceleration and deceleration algorithm for linear acceleration and deceleration algorithm, exponential acceleration and deceleration algorithm, subparagraph7S-shaped curve acceleration and deceleration algorithm. Used in this design is the S-shaped curve algorithm, the algorithm is not Break fitting, instead of using the cosine function of the fitting, by the actual application, S-type fitting curve obtained after the correction. In the case of stationary rack control, in order to by grating feedback signal to the the Dental CT rack, flat panel detector and a high voltage generator synchronization control.Finally, on the basis of the above analysis and experimental design, the system control program, and a schematic circuit diagram according to program design and production of the corresponding circuit board. Since the motor is the equipment of high-current, high-voltage generator is a high-pressure equipment, detectors valuables used in the various components of the control interface optocoupler isolation. The design also uses two serial ports for communication, and a serial port for communication and image workstation, a serial port for monitoring parameter settings and status of the high-voltage generator. In order to achieve the coordination of the system scan, designed using the feedback grating angle, read the feedback signal with FPGA. In addition, the system external circuit buttons and display functions for interactive design. Because use FPGA as control core,32-bit processor, the Nios II embedded, which makes significantly improve the control performance of the FPGA, and the FPGA many logic chips can be integrated in the chip, which greatly simplifies the circuit, software design more flexible.The design of control system software contains three parts:FPGA software design contains several important modules, detector timing control, high voltage generator timing, stepper motor acceleration module and Nios II core customization. The stepper motor acceleration and deceleration S-curve algorithm fitting parameters matlab generated and stored in the FPGA generated Rom, the system is running, by values read Rom to change the stepper motor, the number of crossover, in order to achieve the control of motor acceleratio n and deceleration. Nios II software design, set the unique communication protocol of the control system, also need the serial communication module, timer module and button&display module.PC software design, including the preparation of serial communications and serial communication protocol function, for detecting a state of the parameter setting of the high voltage generator and high voltage generator. The PC software design focuses on image acquisition code design, image acquisition detector comes with the development kit, but need to be cut according to the actual needs, such as the acquisition of the choice of image size, the acquisition image preprocessing optionsthe images collected real-time storage, as well as with the control system coordinated operation.After the design is complete, test and debugging, For the experiments of the detector using the control system to obtain the acquisition rate and collected in the different modes of the pulse width, and further corrected in accordance with these controls timing control system software. The stability, linearity, consistency and signal-to-noise ratio of the detector and by experiments conducted experiments correcting. Oscilloscope to capture control of the output pulse analysis system, by serial debugging assistant and virtual the serial detection serial control state, while taking advantage of the X-ray testing equipment detected X-ray source output conditions. The entire system has been reasonable debugging, PC software, image processing and image workstation software integrated, and running well during the experiment.Proceed from each of the key components of the Dental CT, comprehensive analysis and actual experimental operation of the control scheme is designed and produced a corresponding circuit board, and ultimately with the mechanical structure of online debugging, combined with image processing software, the completion of the Dental CT functional prototype system design. The control system in terms of stability, electromagnetic compatibility Fang, still need further experiments. |
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