The ghost images, i.e., latent image that is unerasable with visible light (LIunVL) and reappearing image appeared on
computed radiography (CR) plates were completely erased by simultaneous exposing them to filtered ultraviolet light
and visible light. Three different types of CR plates (Agfa, Kodak, and Fuji) were irradiated with 50 kV X-ray beams in
the dose range 8.1 mGy to 8.0 Gy, and then conventionally erased for 2 h with visible light. The remaining LIunVL
could be erased by repeating 6 h simultaneous exposures to filtered ultraviolet light and visible light. After the sixth
round of exposure, all the LIunVL in the three types of CR plates were erased to the same level as in an unirradiated
plate and no latent images reappeared after storage at 0°C for 14 days. The absorption spectra of deep centers were
specified using polychromatic ultraviolet light from a deep-ultraviolet lamp. It was found that deep centers showed a
dominant peak in the absorption spectra at around 324 nm for the Agfa and Kodak plates, and at around 320 nm for the
Fuji plate, in each case followed by a few small peaks. After completely erasing CR plates, these peaks were no longer
observed.
In Storage Phosphor (SP) used for Computed Radiography (CR), the quite stable latent image remains due to impurities
and the lattice imperfections by the existence of trapped electron and hole. The quite stable latent image appears again
(Ghosting image) by the passage of time etc, is recognized as image, and becomes an artifact in a clinical CR image.
This study verified the influence of Ghosting image on a clinical image by a physical characteristic and the subjective
evaluation, and examined the method to delete this artifact by the exposure of ultraviolet light as a method of improving
image. As a result, Ghosting image can be confirmed by the dose used by the clinical diagnosis study, and it is taken as
deterioration of the granularity on a physical characteristic. The decrease of the granularity of about 15% (by winner
spectrum) was admitted by the frequency band of 2cycle/mm in SP that had been used for a long term.
As the method of improving these, Ghosting image was erased with the ultraviolet light lamp with the peak
wavelength at 310nm, and has band from 290 nm to 320 nm, and is useful for the improvement of the image quality.
In this study, we examine the influence of Ghosting image on a clinical image, and report on the method to delete
them by the exposure to ultraviolet light radiation for the image quality improvement plan that uses the x-ray used for
usual clinical diagnosis study.
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