| With the development of modern technology level of nuclear medicine, the number of diagnostic radiology examination is increasing every year. At the same time, diagnostic radiology equipment as a public convenience,which use the X-ray to diagnose the disease, also creates additional public ionizing radiation. The medical treatment, health sector, radiation protection and other department concerning problem is how to effectively ensure public safety. Through the relevant national regulations and standards, relevant departments work out the appropriate quality control procedures, testing parameters and technical indicators, and build the foundation for diagnostic equipment of hospitals QA and QC system. Quality control parameters of medical diagnostic X-ray machine include tube current(m A), tube voltage(k V), exposure time(ms), the half-value layer(HVL), Air Kerma and other physical parameters.With the development of diagnostic radiology techniques,the examining method has changed, original regulations, standard become invalid, for example, GB 11755.2-89 " Methods for the measuring of tube current of medical diagnostic X-ray equipment", which force the new norms to be drafted as soon as possible. At the support program of "Medical X-diagnostic equipment measurement standards and traceability system research" of National Science and Technology, the paper is great significance for launching research on the tube current, the tube voltage and other parameters of traceability as well as new testing method. In this paper, using Hall detector combined with high-speed acquisition circuit, non-invasive testing tube current signal of different types of machine, using wavelet algorithms to analysis tube characteristic, which is the first in China to develop accurate tube calculation method of current and exposure time, system repeatability better than 0.5%, the relative error better than ± 1% under standard current source, the relative error less than ± 2% in the actual X-ray high-voltage cable, meanwhile completing the system linearity using PTW dosimeter.Tube voltage as a key parameter of medical diagnostic X-ray machine in quality control, the latest international standards ISO 16526-2011 provides three methods to test it, including interventional resistor divider, semiconductor detectors of multi-channel ratio method and spectroscopy method. Non-invasive method of tube voltage measuring traceability issues can be completed by intervention resistor divider method, which is used in the national measurement standards laboratory department. Channel ratio method has patents at abroad, the core principle of it is the tube voltage associated with the two-channel detector of different thickness filter material, tube voltage can be measured using look-up table method. Spectroscopy method plays an important role in modern nuclear analytical, it expand the application of the radiation field in the medical diagnostic X-ray machine, but not work on the complete application in the key physical parameters calculation in the field of diagnostic X-ray machines. Detection mechanism based on the measurement instrumentation shall have general use, simple considerations. Spectroscopy instruments need to consider the size, price, simple operation and other factors, conventional Na I, HPGe, electric refrigeration Si-PIN, and Cd Zn Te detectors can not effectively meet the above conditions. The effective detection area of Si-PIN less than 1mm2, combined with self-developed ultra-low power consumption, high signal noise charge sensitive amplifier, can complete measurements of spectral data under normal temperature conditions. The energy resolution under 241 Am conditions is up to 4%, Si-PIN is entirely suitable for medical diagnostic X-ray machine of the radiation field measurements.Through the introduction of medical diagnostic X-ray machine works principle and the theory of X-ray generation, the paper analysis mathematical relation between the key physical parameter and the energy fluence, comparative analysis m As, k V, attachment filtering, anode target angle and tube voltage fluctuations on the spectral distribution. Overview the original spectral acquisition method of medical diagnostic X-ray machine, using a computer to carry out semi-empirical model, empirical models and Geant4 Monte Carlo simulation, reference to PTB, NIST and ISO 4037 standards for radiation field conditions, empirical models mainly involve GP,BM,TBC and other mathematical models, compare the results of the model calculations of the energy spectrum, the first half-value layer(HLV1/2),the second half-value layer(HVL1/4),homogenous coefficient, K-line quality, effective energy with graphics and decay curve parameters, lay the foundation for the subsequent instrument unfolding and the spectrum of medical diagnostic X-ray machine for solving the key parameters.In order to analysis the amplitude of Si-PIN semiconductor detector signal, successfully developed a digital spectrum measurement system. Optimization of nuclear pulse signal through theoretical filtering analysis, and according to the signal characteristics of charge sensitive amplifier, the paper carry out the nuclear digital signal cusp molding technology, variable weighting equation convex and concave molding technology and trapezoidal molding technology, use the Simulink toolbox of matlab for algorithm model simulation, complete the related transplants in Xilinx FPGA platform, design the entirety module using modular construction, and test the digital hardware resource and molding effect.The key physical quantities of medical Diagnostic X-ray machine using spectroscopy method to complete non-intervention measure, one of the key technologies involved is the spectral unfolding methods. Using Geant4 Monte Carlo simulation software to build Si-PIN detector model, form the matrix data in the 15-150 ke V range interval 1ke V for the energy response of the detector, focus on the singular value decomposition method, Tikhonov regularization method, Gold method and its corresponding improved method, maximum likelihood(ML) method, maximum a posteriori(MAP) and other numerical methods, firstly use the MSNV and MAP methods in continuous spectrum unfolding, graphical compare different unfolding effects of the methods under the single 100 ke V, and 150 k V continuum spectrum condition, find more suitable solution for the continuous spectrum method. In order to expand unfolding spectra method of medical diagnostic X-ray machine, firstly carry out artificial neural networks and genetic algorithms in the continuous spectrum unfolding. Through the above-mentioned unfolding spectral method comparison, considering the effect of the unfolding spectrum on computing time,computer resource consumption, etc, the Gold improvement methods, MSNV and MAP method was successfully applied to subsequent 80 k V,100 k V and 120 k V unfolding, completed instrument unfolding and used in medical diagnostic X-ray machine for computing tube voltage, half-value layer, Air kerma, the parameter was compared with foreign instrument unfors, dose rate difference was less than 2%. |
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