Relative speeds of Kodak computed radiography phosphors and screen-film systems

Relative mAs values required to generate a constant plate readout signal for the Kodak Ektascan general purpose (GP-25) and high resolution (HR) photostimulable phosphors were measured as a function of x-ray beam quality and for a range of representative x-ray examinations. The signal intensity was determined from the exposure index (EI) generated during the read out of uniformly exposed phosphor imaging plates. These data were compared to the corresponding relative mAs values required to produce a constant film density of Lanex screen-film combinations with nominal speeds of 40, 400, and 600. The relative detection performance of the photostimulable phosphors generally decreased with increasing kVp and beam filtration. The relative response of GP-25 phosphors was independent of examination type, and modified by approximately 10% when scattered radiation was present. The HR phosphor was more efficient than a Lanex Single Fine extremity screen used with an EM-1 film. These relative response data will be useful for selecting the x-ray technique factors which minimize patient dose in x-ray examinations performed with photostimulable phosphors.