Modeling quantum noise of phosphors used in medical X-ray imaging detectors

The noise properties of the granular phosphor screens, which are utilized i n X-ray imaging detectors, are studied in terms of the quantum noise transf er function (QNTF). An analytical model, taking into account the effect of characteristic X-rays reabsorption within the phosphor material and the opt ical properties of the phosphor, was developed. The optical properties of t he phosphor material required by the model were obtained from literature, e xcept for the optical diffusion length to (sigma) that was determined by da ta fitting and was found to be 26 cm(2)/g. The deviation between theoretica l and experimental data is sigma depended. Specifically for sigma = 26 cm(2 )/g and sigma = 25 cm(2)/g the respective deviations between experimental a nd predicted results were 0.698% and -1.597%. However for relative differen ces in sigma more than 15% from the value 26 cm(2)/g, the corresponding dev iations exceed by 6 times the value of 0.698%. The model was tested via com parison to experimental results obtained by a set of Y2O3:Eu3+ phosphor scr eens prepared by sedimentation. The model may be used to evaluate the effec t of screen thickness and irradiation geometry on quantum noise of phosphor materials for transmission and reflection mode. (C) 1999 Published by Else vier Science B.V. All rights reserved.