Research On Correction Of The Dose’s Instability Of X-ray Industrial CT

CT technology has made significant development in various industries, especially in industry and medicine. In practice, it can not only clearly and accurately reproduct the internal structure of the object, but also give material composition and geometry of the internal details quantitatively. In the X-ray industrial CT system, X-rays emitted from ray source having some volatility, in particular the accelerator ray source device, the single beam dose may fluctuations under the same parameters conditions, which made the acquisition data having a large difference. At the same time, the differences of scintillator response, the differences of the position and installation of detector elements, which make the response inconsistent for the same ray dose. Because of the x-ray dose fluctuation, when it comes to the reconstruction, there will be some artifacts, it not only lessens the signal-noise ratio, but also decreases recognition of the image. Therefore, the instability of ray dose of industrial CT is an important factor restricts the reconstruction quality, and it becomes one of the important issues must be taken into account in CT system.This paper did some research on the instability dose of X-ray CT. Fisrt of all, investigate the causes of dose fluctuation, simulate the affects the instability dose works on image reconstruction, at the same time, simulatie the correction with ratio correction way. Then, designed the correction system. Correction system is seperated from the reconstruction data acquisition module and mounted between the ray source and workpiece, to avoid the problem of shading from workpiece and scatter. At last, did the experiment in the way of ratio correction with real acquisition data.Simulation with the shepp-logan model, get the two-dimensional matrix data obtained by fan beam projection, reconstruction after adding the impact factor, the shadow artifacts can easily be seen. After analyses, reconstruct images after the ratio correction simulation, eliminated the shadow artifacts, improve the peak signal-noise ratio of the image.The design of the dose instability correction system is under the modular design concept, it can be divided into three parts, detection module, logic control module and transmission module. Detection module works with the scintillator detector to convert light energy to electricity, it includes scintillator detector and DDC118 chip. Logic control module use FPGA as control core, it caches the data from DDC118 and send to the transmission module. Transmission module provides the differential hardware interface, transmit the data in differential ways to make sure it is transimitted to computer accurately. The design of the hardware was on Altium Designer, logic control language was writed in VHDL, and compiled, synthesised and simulated on Quartus II software.Testting the correction platform, and correcting the actual CT dose data. The designed system can collect data accurately, the dynamic range of acquisition channel is 30197, meet the requirements of CT system. At the same time, did the dose correction experiment with real data, by comparing the data chart, the data ranges from 17750~17940, decrease to 17800~17850 after correction, and the signal-noise ratio increases from 327 to 367, proving the effectiveness of the dose correction.