In this paper, the effects of the transmitted X-ray through the scintillator on the resolution in the scintillator coupled CMOS APS array imager were investigated using a modulation transfer function (MTF). By measuring the system MTF of the detector at each cumulative exposure, we found out that the resolution of the detector was not permanent but changed with the amount of the cumulative exposure into the detector. These measurements were performed under the condition of non-destructive test (NDT). The detector used in this work was two-dimensional array CMOS APS of RadEye1(TM) coupled with Lanex(TM) screen. It was possible to explain the changed MTF with the results of the dark signal increase in the sensor. (C) 2003 Elsevier Ltd. All rights reserved.