An experimental study on the variation of MTF and NPS caused by x-ray beam conditions for three indirect digital radiographic imagers

Digital radiographic X-ray imagers are increasingly used in many clinical areas. So it is important to evaluate the performance of imagers. There is growing consensus in the scientific world that the detective quantum efficiency (DQE) is the best-suited parameter for describing the imaging performance of an X-ray imaging device. DQE is calculated with modulation transfer function (MTF) and noise power spectrum (NPS). As a preliminary study, MTF and NPS of three indirect digital radiographic imagers were measured and analyzed for comparison of imager performance for three imagers. The imagers were evaluated using two standard X-ray beam qualities, RQA5 and RQA9 recommended by an International Electrotechnical Commission (IEC) standard. For MTF and NPS measurement, edge method and two-dimensional Fourier analysis method were adopted each other. In result, the highest MTF is observed in the imager with smallest pixel pitch and preprocessing of raw data among three imagers. There is an obvious MTF difference with preprocessing steps and a little difference between RQA5 and RQA9. NNPS is also affected by preprocessing steps. There are the significant increase of noise at low frequency because of the increase of the multiplicative noise component as exposure increases except CDXI-40G (Canon). The low NPS is relatively caused by high exposure level because of noise conversion process. In comparison, the lowest NPS imager was found. The evaluation of imaging performance using DQE concept will be done as our further study.