The Development Of The Control System Of Digital Breast Tomosynthesis

As one of the threats of women’s health, breast cancer killed more than 400000 people every year all over the world. And more than 1200000 women will get breast cancer annually. At the same time the number of patient with breast cancer grows at 2% ～3% per year. The incidence of breast cancer accounts for 7 percent to 10 percent in total malignant tumor. For the past few years the incidence of breast cancer increased year by year in our country, and the age of onset has the youth oriented tendency. The prognosis effect of breast cancer is closely related to the size and the type of the lesion. Small size and early type of the lesion always has a better prognosis effect. Therefore early diagnosis and treatment are quite important for improving the prognosis and reducing the fatality of breast cancer.Breast X-ray imaging is one of the effective ways to detect breast tumors. It’s also the first choice for breast cancer diagnosis. Breast imaging has an important application for the prevention and treatment of breast cancer, especially in early breast cancer. In the recent 40 years, as the development of semiconductor the computing power of computer and the technology of flat panel detector had made great strides. The development of breast X-ray imaging has experienced from Film Mammography (FM), Digital Mammography (DM), Full Field Digital Mammography (FFDM) and Digital Breast Tomosynthesis (DBT).French first used molybdenum target X-ray film for breast imaging in the 1970’s. For its high resolution, this kind of traditional breast imaging was called as the first choice in breast cancer diagnosing. However, the shortcoming of this method is that the image contrast is low when the tumor is closed to the chest or in dense breast. Molybdenum target X-ray film mixed with noises always lead to some missed diagnosis.Nowadays, FFDM is the universal technology, which has solved the problems of limited contrast, low detectivity and high noise in FM. The quality and contrast of images have been improved. At the same time FFDM also reduces the lasting time of examination and the rate of repeat examination. Patients feel more comfortable during the examination compared with FM or DM. The emergence of FFDM improved the image quality of breast X-ray imaging to a certain extent.However, traditional FM, DM and FFDM, are all based on 2D medical image. The features of 2D medical image limit the image quality in dense breasts and lead to overlapped tissues in the breast.Grant invented a new method of X-ray imaging named Digital Tomosynthesis (DTS) in 1972, which was based on the principles of geometry in tomography. This kind of imaging collecting method gets images from limited angle and limited range. Comparing with Computed Tomography (CT), DTS does not need to collect images from 360 angles, and this feature makes DTS more suitable for oral, breast and joint. DBT was developed based on DTS and flat-panel detector technology.The compressed breast and detector are stationary in DBT system. The X-ray tube moves over an arc relative to the pivoting point, which is above the detector surface. With the acquiring several views of the breast from every angle, the computer reconstructs the images into a 3D volume set. DBT technology makes up the shortage of FFDM in dense breast imaging. DBT greatly increases clarity compared to FFDM especially in the imaging of the boundary of tumors and micro calcifications. Because of this, the detection rate of breast cancer is sharply raised.At present, FFDM is the main method in breast X-ray imaging in China. In order to improve the application of DBT and the early diagnosis rate in our country, this development was put forward in this paper.This development began after reading and analyzing a lot of books and literatures. At first, the design of the whole control system was introduced, including the main function and the principle of this system and so on. The second part of this paper described the hardware design of the system, like system power supply, system image chain construction, motor controller, compressor controller, CAN bus and so on. The last part is the software design of the system. This part mainly discussed the initialization of the system on power-on, the control flow and sequence of the expose and compression. More details are as follows:For the hardware part, this DBT control system was composed of high voltage generator, X-ray tube, flat panel detector (FPD), the C-arm motor, TOMO motor, compression motor, linear parallel grids, collimator and so on. For ease of development and administration, this control system was divided into five parts. Any part of them who are related to controllment or communications is used to send or receive the messages through CAN bus.The first part is system power supply. In order to guarantee the other parts of the system work well, the system power supply should be developed firstly. After the assessment of the power consumption of the whole system, the maximum power of the control system was determined to 6500W. The 220V electric power was brought into the control system after isolation, filtering, voltage transformation, rectifying. The voltage output include 220VAC,24VDC and 12VDC. The second part is image chain control part. This part was composed by high voltage generator, X-ray tube, FPD, expose handbrake and so on. All of these components were controlled by image control board. The main function of this part is generating X-ray and acquiring views of the breast. The control chip in this system all chose the ARM chip, which performs well and has rich on-chip resources. To assure the control chip works stably, all the control signals were isolated by optical coupler named PS2801, which is a kind of fast optical coupler with 3kHz work frequency. The third part is motor control part. This part was composed by C-arm motor, TOMO motor, limit switches, electro optical sensors, grating disc and so on. All of these components were controlled by motor control board. The limit switches, electro optical sensor and grating disc were used for precise positioning of the motor. The motor control board’s task is to control the motors operating to the precise position as the orders of the image control board. The fourth part of the hardware design is compression control part. This part was composed by compression motor, pressure sensor, displacement sensor, touch screen, buttons and so on. All of these components were controlled by compression control board. The function of this part is to compress the breast and show the compression data on the screen timely. The last part is CAN bus controller. This part was composed by the CAN bus subsystem on every control board and the CAN bus computer connector. This part provides every component who communicate through CAN bus a unique CAN bus ID and make sure the whole DBT control system could communicate stably and reliably.For the software part, this paper mainly talks about the most important software design which could determine the image quality. This DBT control system can mainly realize acquiring images at normal expose mode and AEC expose mode. Based on these two kinds of acquisition mode, initialization of the system on power-on and compression control, the software design was divided into four parts.The first part is initialization of the system on power-on. The function of this part is to initialize the high voltage generator, FPD, motors and so on, and print the system state on the screens. The second part is acquiring images at normal expose mode. In this part the software should control the high voltage generator, FPD, motors and other components related to acquire the single image at normal expose mode. The third part is acquiring images at AEC expose mode. The function of this part is to realize the acquisition of the several views of the breast from every angle at AEC mode. The last part is compression control. The main idea of this part is compressing the breast properly with the help of buttons, pressure sensor and displacement sensor.After the study of the DBT’s role in breast X-ray imaging and the development status in foreign countries and China, this paper gives a detailed design of DBT control system regarding to hardware and software. Although some achievements had been made, the whole control system should be continued to improve.