Study Of Characteristics,Measuring And Protection Of Medical Diagnostic X-ray

Objective: X-ray is widely used in medicine. such as radiotherapy, radiodiagnosis, nuclear medicine and interventional radiology, etc. Comparing to ordinary X-ray, the medical diagnostic X-ray has its own characteristics in quality and quantity, the energy expression, dose measurement, etc. In the application of medical diagnosis, when receiving X-ray irradiation examination, patients should be protected from direct exposure to excess, while minimizing the secondary radiation to the medical staff is important.Methods: Analyzed the energy expression of medical diagnostic X-ray, calculated the ray energy change and the energy spectrum after attenuated by materials, theoretically analyzed and experimentally measured the influence and correction of the response time of ionization chamber dosimeter on the measurement of diagnostic X-ray, calculated and measured the protective effects of several common protective measures.Results:1. Analyze the characteristics and energy expression medical diagnostic X-ray. Derived from the generating of X-ray, X-rays has a continuous energy distribution; analysis the characteristic amounts relate to the quality and quantity, including the tube voltage, the PPV and so on, concluded that the energy has a variety of expressions. According to the specific needs and research conditions, select the appropriate way to describe, include half-value layer, equivalent energy and the average energy, etc. Among them, the energy spectra and average energy is an accurate energy expression of X-ray. X-ray spectroscopy measurements demand specialized equipment, with high requirements. We can use computer simulation to depict the X-ray spectrum, expressing the radiation energy distribution, energy spectrum changes, etc. In the routine monitoring and protective medical applications, the characteristic amounts of X-ray are mainly energy and dose rate.2. According to the interaction of X-rays with matters, separately calculated the ray energy change and the energy spectrum after attenuated by different thickness of aluminum and iron plate attenuation, and calculatedscattered radiation energy spectrum and energy in the 90 degree scattering angle direction, calculated and experimental measureddifferent X-ray attenuation efficiencyon different materials.There are the photoelectric effect and scattering in the interactions of medical diagnostic X-ray and matters. When X-ray transmits substance, the interactions attenuate the intensity and energy of X-ray. After transmitting object, the energy and intensity of single photon reduce; the intensity of generally continuous X-ray becomes low, the average energy becomes higher, and spectrum narrower. Photoelectric absorption effect is the main way substance decays, accompanied by the occurrence of fluorescent effect and Auger effect. Scattering generating between X-rays and matters includes coherent scattering and incoherent scattering. Incoherent scattering is Compton scattering, we can use Compton scattering formula and scattering ratio to calculate the energy and intensity of the scattered ray, resulting in that their intensity and energy were lower than the primary X-ray. The attenuation of various substances acting on X-ray is different, which is related to the density, thickness, shape, etc. Calculate theoretically the effect on the attenuation on X-ray of materials, and measure practical experimental data to verify the theoretical results.3. Analyzed and experimentally measured the influence and correction of response time of dosimeter on the measurement of diagnostic X-ray, and studied the energy response, the directional response and the sensitivity, etc. The response time, energy response and other parameters of different dosimeters are different, the response time of different range of same instruments is different. We should select appropriate measurement dosimeters according to the requirements, if necessary, correct the measurement results. According to the process of dosimeter circuit reading response, simplifying it to the equivalent RC circuit charging process, we can calculate theoretically the response time constant and time resolution correction factor of known dosimeter, measured experimentally to verify the correction result, and then obtain an accurate response time, this method can be used for correcting the measured results in protection evaluation. Medical diagnostic X-ray is mostly medium-energy and low-energy rays. Analyze the requirements for energy response of dosimeters, and make calculations and experimental study of the energy response of different instruments on X-ray measurements.4. Calculated and experimental measured on the protective effects on medical diagnostic X-ray of distance, lead aprons, lead screens, wall(concrete), etc. and propose recommendations about X-ray protection. In the engine room medical diagnostic X-ray passes through the air, the bed, the patient, the walls and shields, process with the absorption and scattering, causing different blocking effects on X-rays owing to different substances. Without shielding measures, under ideal conditions in vacuum the intensity of X-ray is inversely proportional to the square of the distance, in actual situation, the measurement results show that the diagnostic X-ray pass a farther distance in the air, the lower the dose rate is; theoretical calculations and experimental results show: the lead can shield most of X-rays. Put protection recommendations forward: the important parts of body in the lead shielding clothes, in addition to the comprehensive utilization of walls, long distance and other various shielding, can achieve better medical diagnostic X-ray protective effect.Conclusion: Energy spectrum and average energy can be more accurate expression of energy of medical diagnostic X-ray, when no strict requirements, the half-value layer and equivalent energy can also be used for description of X-ray; the response time of the dosimeter has a serious impact on the measurement of dose rate of medical X-ray when the exposure time is very short, the measured value and the true value may differ several times or dozens of times, therefore the time of exposure correction of the measured value is required, in addition exact response time of some instrument is recorded; when using medical diagnostic X-ray to measure, the energy response is an important indicator of a serious impact on the measurement results, the instrument selected to measure should have an appropriate energy response to the measurement target; there are strict requirements to other performance parameter of the dosimeter in the measurement of medical diagnostic X-ray; after the interaction of X-rays and matters, the direct ray, the scattering ray and the transmission ray has a certain relationship, analyzing the changes of the three kinds of rays energy spectrum, calculating and measuring the changes in the intensity of the transmission ray and scattering radiation, lead to the attenuation law of X-rays under the effect of substances, selecting the appropriate shielding material depends on the different attenuation affected by various materials; in the medical diagnostic X-ray protection, the lead is the most important shielding materials, combined with the long distance, walls and other conditions, it can make a better protection from the harmful irradiation of X-rays; when different protection tools used only or used synthetically, the protecting effect is different, using different defense scheme and protection tools synthetically has better result in the protection of the X-ray.This work has important practical significance and provides a basis for the measurement and protection of the medical diagnostic X-ray.