We developed an easy method of measuring the presampling modulation transfer function (MTF) using the square wave chart in digital radiography. In this method, the presampling MTF is measured by Fourier transform of image data of the square wave chart. When Fourier analysis of the sampling data of a square wave is carried out, it is generally difficult to find the starting point and terminal point of the periodic data that should be extracted because of an insufficient number of data. To solve this problem, interpolated data were calculated by using a window function of the frequency domain. The aliasing error was avoided using a characteristic such that the square wave has discrete frequency components. The accuracy of this method was investigated by computer simulation study. Actual measurement of the presampling MTF by this method was also performed with a CR system. These studies indicated the effectiveness of our proposed method in terms of accuracy and ease of use.
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