Evaluation of the Response of the Modulation Transfer Function to a Computed Radiography Photostimulable Phosphor Imaging Plate for Various Numbers of X-ray Exposures

摘要

The purpose of this project was to analyze the modulation transfer function (MTF) responses to a computed radiography (CR) imaging plate (IP) for various numbers of X-ray exposures and to determine whether or not the MTF response may be used as an indicator of image quality degradation. A measurement facility, which complies with the IEC 62220-1 international standard, has been set up to determine the MTF for computed X-ray detetor systems. The international standard (IEC 62220-1) was demonstrated to allows accurate and reliable measurements of the MTF, and the standardized radiation quality RQA 5 was applied for the measurements. The MTF is the modulation transfer function of the detector. The MTF was obtained from the images that were exposed using an opaque tungsten edge test device (2-mm thick). The presampled MTFs were deduced from the acquired images by using fast Fourier transform analysis techniques, andthe results suggested that a processing with MATLAB could be used to compute the MTF with confidence. To determine this, an Agfa MD CR cassette containing the photostimulable phosphor (PSP) imaging plate (IP) was used to obtain the MTF curve after calculating the line spread function (LSF) curve by calculating and differentiating the edge spread function (ESF) from the edge image. The results of MTF measurements will be presented. No distinctive changes were observed in the 50% MTF, which showed images for numbers of exposures less than 20,000. Also, the 10% MTF maintained a fixed pattern without a change in the image quality. In contrast, the study showed an irregularly shaped deteriorated image quality for the 50% and the 10% MTFs for numbers of exposures 20,000. In conclusion, the results of this examination may be used as a baseline for evaluating an image quality system and the imaging characteristics by using MTF measurement.