Comparison of the imaging physics performance of a prototype flat panel detector with a 400 speed screen-film system

The performance of a digital radiography system that included a prototype flat panel detector (StingRay) was compared with a 400 speed screen-film system. The flat panel detector consisted of a 500 μm thick CsI scintillator with an image matrix size of 3k². The limiting spatial resolution of screen-film (∼4 line pairs/mm) was superior to that of the flat panel detector (∼2.5 line pairs/mm). The digital detector had an excellent linearity response (r² = 0.997), a dynamic range of 20,000:1, and saturated at a radiation exposure of 60 mR. At exposures > 50 μR, the flat panel noise performance was dominated by quantum mottle. For radiation exposure level which produce film densities of ∼1.8, the low contrast performance of the flat panel detector was similar to that of the screen-film system. Changes in radiation exposure, however, significantly affected the performance of the flat panel detector, whereas the performance of screen-film was constant at film densities between 1.5 and 2.5. The digital imaging system produced images for review in ∼13 seconds, which is much faster than the minimum 90 second processing time of film. Raw image data sets acquired using the digital detector showed four individual sub-panels, an artifact that can be eliminated by processing. The flat panel detector investigated in this work offers a wide dynamic range, excellent linearity performance and the rapid availability of digital images. The digital detector will also permit a reduction in radiation exposure where the detection task is relatively easy, or when the radiation to the patient is of specific concern.