Light is then converted into an electrical charge by - correct answer ✔CCD
or CMOS devices, or photodetectors such as amorphous silicon photodiode
arrays (last chapter)
Charge-Coupled Devices CCDs - correct answer ✔The oldest indirect-
conversion DR system
X-ray photons interact with a scintillation material and this signal is coupled or
linked by lenses or fiber optics, which act like. - correct answer ✔cameras
These "cameras" - correct answer ✔reduce the size of the projected visible
light image and transfer the image to one or more small (2 to 4 cm2) CCDs,
which convert the light into an electrical charge.
The electrical change are stored - correct answer ✔in a sequential pattern
and released line by line and sent to an analog-to-digital converter.
, CCD-based detectors require - correct answer ✔optical coupling and image
size reduction, they are widely available and relatively low in cost.
A CCD is made up of - correct answer ✔photosensitive receptor and
electronics embedded in a substrate material in a silicon chip.
•Incident light from a scintillator strikes the detector, and electron-hole pairs
are produced in the silicon.
The amount of electron-hole pairs is related to the - correct answer ✔amount
of light absorbed.
The electrons inside the CCD are held - correct answer ✔by electrostatic
forces in the array until the charge is read out to form the image
The detector element (del) contains three electrodes that hold the electrons in
an electrical potential well - correct answer ✔The dels are formed by voltage
gates that , at readout, are opened and closed like gates to allow the flow of
electrons.
To collect the charge on the silicon chips, the voltage sign is changed on the
electrodes within each del, moving the electrons by rows down the columns
until the readout row is reached.
This is commonly known as the bucket brigade scheme.
It is not practical to manufacture a CCD chip larger than - correct answer ✔5
cm x 5 cm.
Most range from 2 to 4 cm
The image must be matched to the size of the CCD.
CCD technology uses lenses or fiberoptics so that the image matches the
receptor size
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