THEORY GUIDE Radiography Theory
10DEC05
TG4825-1
Page
19 of 120
Stimulating the PHOSPHOR
It is necessary to stimulate the PHOSPHOR in the SCREEN to read the latent image. The
following components of the CR systems provide this function:
• light source:
– exposes the SCREEN with high-intensity light that stimulates the electrons and causes
the electrons to be luminescent
– laser beam moves from one side of the SCREEN to the other to expose the image
• DEFLECTOR:
– moves the laser beam across the SCREEN and then back to the starting position. At
the same time, the SCREEN moves perpendicular to the scanning direction of the
laser beam.
– is continually monitored and adjusted to check that the scanning operation is correct
and has a continual speed
• scanning optics:
– focuses and shapes the laser beam, keeping the speed and angle of the beam the
same when it moves across the SCREEN
– angle of a laser beam determines the size, shape, and speed of the beam. An
example is the beam of a flashlight moving across a flat surface from one edge to the
center and to the other edge.
Signal accumulation Signals can accumulate on SCREENS that are not used for more
than 24 hours. Erasing these SCREENS decreases the residual
image to the optimum range for using the SCREEN again. Failure to
erase these signals can result in artifacts.
Long life The photostimulable luminescent quality of the SCREEN does not
decrease with time. The life of a SCREEN can be decreased by
damage to the material.
Characteristics of the
STORAGE PHOSPHOR
SCREEN
Description
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