THEORY GUIDE Radiography Theory
10DEC05
TG4825-1
Page
18 of 120
When a STORAGE PHOSPHOR SCREEN is exposed to X-rays:
• special PHOSPHOR on the SCREEN absorbs the radiation in degrees of intensity
determined the body part and the type of SCREEN:
– soft body tissues absorb a small quantity of radiation - these areas are indicated in the
X-ray image by mid-range values
– bone tissues absorb most of the radiation - these areas are indicated in the X-ray
image by light values
– X-rays that do not hit any obstructions are indicated in the X-ray image by dark values
– High Resolution SCREENS absorb less energy than General Purpose SCREENS
• SCREEN has a latent image in the areas that were exposed to the radiation. The quantity
of stored energy or charge on the SCREEN is proportional to the quantity of
X-ray energy absorbed by the SCREEN.
Characteristics of the
STORAGE PHOSPHOR
SCREEN
Description
X-ray absorption About 50% of the X-ray energy is released in the form of
fluorescence when the SCREEN is exposed. The X-ray energy
remaining makes the latent image on the SCREEN.
Photostimulable
luminescence
When the charged PHOSPHOR on the SCREEN is stimulated by
light, the PHOSPHOR releases or discharges blue light proportional
to the energy the PHOSPHOR has stored.
Fading The latent image fades with time, but it is possible to read data from
the SCREEN for a number of days after scanning.
Residual image After a SCREEN is erased by exposing it to light, it keeps some
charge from the latent image. This charge does not make the
SCREEN less effective when it is used again.
To Next Page
Loading...
Need help?
General
