Abstract: Computed Tomography(CT) image reconstruction playing the core role in CT technique,the performance of reconstruction algorithm is of vital importance to the judgement of accuracy of monitor results．The image of the object is reconstructed from projection data by using algebraic or analytic algorithms．Analytical algorithms are deduced based on rigorous mathematic theories,and have the advantages of fast processing speed．So the analytical algorithms are used widely on CT detection equipment．In the analytic reconstruction algorithms,filter back projection algorithm is the mainstream．The main reason is the filter back projection algorithm has higher operation efficiency,and better reconstructed image quality．It is low cost,easy to realize parallel processing,so it is used in many industrial CT machine．In the process of analytical algorithms,the selection of the filter function playing a decisive role in reconstuction result and efficiency．This paper firstly introduced R-L and S-L filter function,and analyzed their natures．Secondly,it put forward exponential filter function,and analyzed the influence of exponential function in the absence of noise and noise conditions on image reconstruction by adjusting index value of parameter．Lastly, proved by experimental simulation that the exponential filter function can obtain not only better spatial resolution,but also better image properties．

Key words: CT image reconstruction,Filter back projection algorithm,Filter function