Screen film systems

Screen-Film Systems. According to Ludwig (5), crucial to the application of x-ray phosphors for intensifying screens is the efficiency with which the incident x-ray energy is converted to useful light energy as given by the expression ... 

The overall efficiency of given x-ray screen is given by equation 3. Screen speed, however, also depends on the film Interaction steps nt nt2 shown In Fiaure 1. In practice it is best to determine the overall speed, S, of the screen-film system (26) using the expression ... 

Fig. 1.4. (a) Characteristic (H and D) curve of a mam-mographic screen-film system. Optical density (OD) of the processed film is plotted versus the log of the relative X-ray exposure to the fluorescent intensifying screen, (b) Characteristic response of a detector designed for digital mammography (from Pisano et al. 2004. With permission)... 

Fig. 1.7. MTF of a modern screen-film system (after Bunch Fig. 1.8. Illustrating the concept of aliasing (from Pisano 1997) and of a typical detector used in digital mammography et al. 2004. With permission)...

Fig. 2.19. Dependence of DQE on exposure to detector for a screen-film system (Bunch 1999), a flat panel detector and a CR system (Data from Monnin 2007)...

Examples of characteristic curves of mammo-graphic screen-film systems are shown in Fig. 5.1. These curves can be well-modeled by... 

Sangway PC, Stapleton RE (1977) X-ray-emission spectra of LaOBn Tm and its impact on screen-film system-desigrL J Electnochem Soc 124 C110... 

Modem NDT film systems (with Pb screens) are very linear X-ray detectors. This is shown in fig.l for different NDT film systems and a X-ray tube at 160 kV. Note that for histoncal reasons the film response curve is often plotted as film density versus log (radiation dose), which hides this linear relationship. The film density is the difference between the measured optical film density and the fog density Db of the film base. 

Sample MTFs of several commerdal digital mammography systems are compared with the MTF of a modern screen-film mammography system in Fig. 2.16. As will be discussed here, factors additional to the dd aperture, d, also affect the MTF of detectors used for digital mammography. In some cases, these cause the ordering of the curves not to corrdate with the dd sizes. 

Fig. 2.18. Spatial-frequency dependent DQE of screen-film mammography and some digital mammography systems (Data on GE systems from Ghetti et al. (2008), Fuji and Anrad systems from Rivetti et al. (2006), Selenia from Laz-ZARiA et al. (2007), Sectra from Monnin et al..(2007) and screen-film from Bunch (1999)...

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