抄録
The relationship between the drop at low frequency of the MTF and contrast ratio of the x-ray image intensifier is evaluated. The three samples have the different contrast ratios. It is shown as the function of Pb disc diameter. That relationship is called the disc transfer function (DTF). The DTF can be expressed by two exponential parts. By this it is shown that the flare of the part of the small Pb disc diameter corresponds to the LFD, and the short range effects is especially related to the LFD. Therefore, it is able to be expressed by the simple equation of the relationship between the contrast ratio and the LFD of the XRII. The LFD evaluation which is the difficult measurement can take place the contrast ratio evaluation by several Pb disc diameter which is a simple measurement.
