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Thick phosphor screens for on‐line portal imaging
Author(s) -
Wowk B.,
Shalev S.
Publication year - 1994
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.597209
Subject(s) - phosphor , optical transfer function , optics , materials science , image resolution , reflector (photography) , optoelectronics , physics , light source
Gd 2 O 2 S phosphor screens between 250 and 1000 mg/cm 2 thick were evaluated for use in megavoltage imaging systems. The phosphor layers were placed on brass plates ranging from 1 to 5 mm thick, each with and without an optical back reflector (white paint). Light output and spatial resolution were measured at 6‐ and 23‐MV x‐ray energies. Light output was found to increase linearly with phosphor thickness up to 500 mg/cm 2 , reaching a plateau at 1000 mg/cm 2 . Spatial resolution [modulation transfer function (MTF)] decreased exponentially with phosphor thickness up to 750 mg/cm 2 , where a minimum was reached. The variation of MTF with phosphor thickness was found to obey a simple empirical relation.