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Development of high quantum efficiency flat panel detectors for portal imaging: Intrinsic spatial resolution
Author(s) -
Pang G.,
Rowlands J. A.
Publication year - 2002
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 - 10.1118/1.1507779
Subject(s) - detective quantum efficiency , optical transfer function , optics , quantum efficiency , detector , flat panel , flat panel detector , image resolution , x ray detector , photon , image quality , dark current , optoelectronics , physics , materials science , energy conversion efficiency , photon counting , computer science , artificial intelligence , image (mathematics)
Recently developed flat panel detectors have been proven to have a much better image quality than conventional electronic portal imaging devices (EPIDs). They are, however, not yet the ideal systems for portal imaging application due to the low x‐ray absorption, i.e., low quantum efficiency (QE), which is typically on the order of 2–4 % as compared to the theoretical limit of 100%. The QE of current flat panel systems can be improved by significantly increasing the thickness of the energy conversion layer (i.e., amorphous selenium or phosphor screen). This, however, will be at the expense of a decrease in spatial resolution mainly due to x‐ray scatter in the conversion layer (and also the spread of optical photons in the case of phosphor screen). In this paper, we investigate theoretically the intrinsic spatial resolution of a high QE flat panel detector with a new energy conversion layer that is much denser and thicker than that of current flat panel systems. The modulation transfer function (MTF) of the system is calculated based on a theoretical model using a novel approach, which uses an analytical expression for absorbed dose. It is found that if appropriate materials are used for the conversion layer, then the intrinsic MTF of the high QE flat panel is better than that of current EPIDs, and in addition they have a high QE (e.g., ∼60%). Some general rules for the design of the conversion layer to achieve both high QE and high resolution as well as high DQE are also discussed.