Computation of the MTF with a microdensitometer and a computer on-line system

One of the most popular evaluation methods of radiographic images is the measurement of modulation transfer function (MTF) using the slit method, which is very useful to compare similar characters of film-screen systems. However, it is difficult ot measure the MTF plainly without a loss in accuracy. So, we connected a microdensitometer to the computer and wrote a computer program which was able to measure the MTF automatically. To reduce the fluctuations and uncertainties in the calculated MTF, we examined the process from the film scanning by microdensitometer to the MTF calculating by Fourier transformation. We firmly believe that the linearization process is the most important process to reduce MTF fluctuations. As a result of using the SPLINE function (H D curve approximate expression) in the process of linearization decreases fluctuations and uncertainties of the MTF were able to be when it was included in the manual measurement. We were able to save a great deal of work when we measured the MTF. (author)