Energy imparted to fluorescent screens from primary and scattered radiation. Variations with atomic composition and screen thickness

Abstract

The effects of thickness and atomic composition of fluorescent screens on the impartation of primary and scattered radiation is analysed. Different fluorescent screens give rise to different quotients epsilon p/epsilon s of energy imparted from primary and scattered radiation respectively, due to their variation in atomic composition and thickness. The image contrast in a given radiation field therefore varies with the choice of screen. Energy imparted by primary and scattered radiation in different fluorescent screens has been calculated as a function of tube voltage using a simple analytical model. Comparison of the results for fluorescent screens of different thicknesses with hypothetical screens with both negligible and total absorption has been made. From the results it is evident that the image contrast increases with increased detector thickness if scattered radiation is present. The trends found in the calculations have been confirmed by measurements of the energy imparted from scattered and primary radiation for a number of fluorescent screens including both commercial and specially made screens. Differences in the ratio epsilon p/epsilon s of up to 50% have been measured, and differences reported by other authors are discussed. Their use of detectors with different response to scattered and primary radiation may explain the discrepancies found.

Modeling granular phosphor screens by Monte Carlo methods

“…The x-ray detection and imaging performance of phosphor screens are affected by intrinsic physical properties, related to x-ray and light photon transport through the material. These properties have been previously investigated by experimental, [5][6][7][8][9][10][11] theoretical, [11][12][13][14][15] and Monte Carlo methods, [16][17][18][19][20][21][22] and have been taken into account in the design of commercial imaging systems. [23][24][25] Phosphor screens have been previously 12,14,15,[26][27][28][29][30] modelled as a series of superimposed x-ray absorbing, light creating, and light attenuating elementary thin layers within the framework of cascaded linear systems analysis.…”

Image Quality in Mammography with Special Reference to Anti-Scatter Grids and the Magnification Technique

“…The scatter reductions obtained by stationary and moving grids, an air gap and a scanning beam are compared in Table 1. The contrast for a 100 urn thick tin foil is shown as is the ratio of the scatter degradation factors with scatter reduction, SDF g , and without scatter reduction, SDF (10,31,35).…”

“…Fig. 13 shows that the scatter to primary ratio increases with increasing tube potential within the potential interval investigated (22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36) when no grid is employed. Using a grid, the scatter to primary ratio is more or less constant with tube potential.…”

“…Ratios of imparted energies due to scattered and primary radiation Scattered radiation determines the contrast C of an image according to the relation (31,35,42):…”

Investigation of optical and imaging characteristics of fluorescent screens for use in digital imaging detectors suitable for telemedicine

“…Τα απεικονιστικά χαρακτηριστικά και η απόδοση της ανίχνευσης των ακτίνων-Χ των φθοριζουσών οθονών εξαρτώνται άμεσα, τόσο από τις φυσικές ιδιότητες, όσο και από τις ιδιότητες δομής των υλικών. Οι προαναφερθείσες ιδιότητες, οι οποίες έχουν μελετηθεί με πειραματικές διατάξεις (Alig and Bloom 1977, Venema 1979, Dick and Motz 1981a, Dick and Motz 1981b, Derenzo et al 1990, Ginzburg and Dick 1993, Van Eijk 2001, αναλυτικά μοντέλα (Venema 1979, Chan and Doi 1983a, Nielsen and Carlson 1984, Nishikawa and Yaffe 1990 καθώς κι από μοντέλα με τεχνικές Monte Carlo (Raeside 1976, Rubinstein 1981, Kalender 1981, Aerts et al 1982, Chan and Doi 1983b, Morin 1988, Andreo 1991, λαμβάνονται υπόψη στο σχεδίασμά και στην κατασκευή εμπορικών απεικονιστικών συστημάτων. Παρόλα αυτά η αναζήτηση για το ιδανικό φθορίζον υλικό, που θα συνδυάζει τα βέλτιστα απεικονιστικά χαρακτηριστικά, απόδοση φωταύγειας και προσιτό κόστος, εξακολουθεί να αποτελεί σημαντική παράμετρο στο σχεδίασμά σύγχρονων απεικονιστικών συστημάτων.…”