The relationship between pixel value and beam quality in photostimulable phosphor imaging.

Direct digital capture systems are relatively new in diagnostic imaging. Full utilization of these devices requires a thorough understanding of the image formation process. The conversion of x-ray photon energy to a digital pixel value in a commercially available photostimulable phosphor (PSP) imaging system is investigated in this paper. Pixel values measured at 16 different combinations of 4 x-ray beam peak voltages (60, 80, 100, and 120 kVp) and 4 beam qualities are reported. At 60 and 80 kVp exposures were made at 2.58 x 10(-7) C/kg (1 mR); at 100 and 120 kVp exposures were made at 5.16 x 10(-7) C/kg (2 mR). Analysis of variance was used to determine the statistical significance of the relationship between pixel value and beam quality for a given kVp and exposure. A computer model accounting for x-ray spectral effects that accurately predicts pixel value is presented. Calculated pixel value agree within 5.0% of measured values over the range of beam energies, exposures, and qualities.