| CT is very expensive and its technology is complicated. In order to ensure its efficient application in the hospital, people must do CT performance testing regularly, then evaluate it according to the corresponding criterion whether the performance of the scanner is qualified or not. Phantom is used to test CT performance. The phantom plays greatly influence on the measurement result, so the quality of phantom is focused by medical unit and technological supervisor office.CT phantom and the CT scanner always develop at the same time, and every revolution of CT promotes the technology development for CT phantom. Foreign study on CT phantom has been almost quite perfect, but domestic study still need to be improved on constantly, the fast popularization of MSCT (multislice CT) and its special scanning mode have brought new challenge to CT phantom nowadays. Compared with conventional scan, MSCT is quite different from MSCT in data acquiring and reconstruction algorithm. Multi-slice images can be obtained when the x-ray tube rotates one rotation, so the phantom must be guaranteed not to be influenced by the adjacent slices in the scanning of MSCT. That is to say, the phantom must have enough length in z axle and uniform homogeneity .Besides, the data acquired in the MSCT scanning is greatly increased; the manual quality assurance (QA) test in traditional method can't meet the requirement of MSCT testing.The MSCT scanning method should be improved from manual testing to auto-testing, which put forward the new acquirement to the design of the CT phantom.The more we focus on the CT QA gradually, the more demands for the phantom are generated., it is impossible for us to import all from foreign countries, the phantom introduced costs great, which limits its popularization in the hospital at the basic level, and prevents the development of the quality assurance work. So the popularization of domestic test phantom lays the foundation of the QA work and establishes the fundamental of remote performance testing of CT.In this paper, methods to CT QA are detailed summarized; various kinds of CT phantom are compared. Basing on the requirement of automatic test of CT, a practical phantom is made, important parameters such as high contrast resolution, slice, uniformity, noise and low contrast resolution, etc have been analyzed and studied. Corresponding testing and evaluating method have been brought forward. The main work finished is as follows:1. Measuring the high contrast resolution of MSCT. With analysis and comparison, considering auto-testing also, MTF method to measure the high contrast resolution of MSCT is adopted. An experimental phantom has been designed and made out; the difference and correspondence between subjective and objective methods to measure the high contrast resolution are studied. The phantom is verified to be feasible by a large number of tests compared with Catphan phantom.2. Measuring CT slice. Using inclined plane method to measure CT slice, we design and make a slice module, through testing, analyze the deficiency of a copy of module and improve it compared with Catphan phantom.3. Measuring and evaluation of the uniformity and noise of MSCT. The z-axis coverage is greatly increased. The signal intensity and noise are different in everyslice because the geometry angle of X ray and efficiency of every detector are different too. A uniformity water module is designed and made; methods to evaluate the slice uniformity and z-axis uniformity are both proposed.4. The research on the low contrast resolution of CT. kinds of methods to measure CT low contrast resolution are analyzed, A alternative method is proposed based on statistics because existing methods are all difficult with materials and difficult in auto-testing. The new method is not only simple, easy to acquire the data but also can give an objective and quantitative description to the low contrast resolution.
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