The resolution properties of an imaging system are commonly described by its modulation transfer function. The slit and edge methods are the two most commonly used and accepted techniques for measuring the MTF. The use of a slit requires very precise fabrication and alignment of the device in the radiation beam, a high radiation exposure to allow sufficient transmission through the narrow slit (aperture 10 mu m). We took notice of the slit aperture and a new slit device with slightly wider aperture (40 mu m) was made for the im-provement of the conventional slit device. The aim of this work was to show the properties such as the X-ray tube loading, the alignment and the MTF using the new slit device with slightly wider aperture. Imaging plates in the CR system were employed in this measurement.
The use of the 40 mu m aperture slit device can decrease one-fourth of the X-ray tube loading compared to the conventional device. The use of the 40 mu m aperture slit device can improve the alignment for the slit device rotation and the incidence Xray offset. The MTF using the 40 mu m aperture slit device is higher than that using the conventional device. The maximum difference was 0.025 (at 1.3 cycles/mm). The exposure condition of the 40 mu m aperture slit device is near to clinical conditions and the MTF indicates the resolution property under clinical conditions.
Our results showed that the use of 40 mu m aperture slit device allows easy acquisition of a slit image on the detector without precise alignment and ensures an appropriate MTF for the CR system under near-clinical exposure conditions.