Two possible imaging geometries for a VEPID system are depicted. The setup in (a), which is used for phosphor screens, is a conventional forward-reflecting geometry with the mirror, lens, and camera on the opposite side of the screen as the linac and the source and lens placed equidistant from the screen. For thick clear scintillators, one requires a back-reflecting geometry that is shown in (b), with the mirror, lens, and camera on the same side of the scintillator as the linac and the lens placed closer to the screen relative to the source by a factor equal to the scintillator refractive index.
(a) The raw TSC image of a pediatric chest phantom contains systematic artifacts due to the presence of crystal imperfections dispersed across the imaging field. A simple flat-field correction was sufficient to remove almost all of these artifacts. The flat-field-corrected image of the pediatric chest phantom is provided in (b).
The MTF measured for the prototype TSC is plotted along with the component MTFs due to the CsI(Tl) screen and the lens-camera system. The geometric loss in MTF was determined from the theoretically expected and measured MTF curves for the TSC. Also plotted are the MTF curves for a Lanex Fast-B phosphor screen with and without the effect of optical spread (Ref. 30), and the MTF for the Siemens BEAMVIEW.
The NPS for the TSC is plotted in comparison with that measured for the original Siemens BEAMVIEW, as well as for the BEAMVIEW with our high-end Video-optics V1519 Plumbicon camera system. The spectra have been normalized to reflect the same image dose .
The DQE measured for the prototype TSC is plotted along with that measured for the original Siemens BEAMVIEW, measurements reported for a prototype indirect-detection/a-Si flat-panel EPID (Ref. 30), a prototype direct-detection/a-Se flat-panel EPID (Ref. 19), and Kodak XV-Omat film ( brass build-up) (Ref. 31).
The above images of an anthropomorphic chest phantom were acquired with (a) Siemens BEAMVIEW , (b) TSC , (c) TSC , and (d) TSC .
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