CCD/CMOS (TFT) EXAM QUESTIONS
AND ANSWERS RATED A.
What are some flat panel artifacts that can occur with TFT systems?
Dead pixels, Gain calibration/Flat Field Correction, Image lag
Manufacturers make efforts to maintain a standard of less than what %
defective pixels?
0.1%-0.2%
What is used to correct flaws in the detector, such as dead pixels?
Gain calibration/ Flat field correction. This removes the potential of having
that artifact interfere with diagnosis. It removes the densities on the image by
creating a mask of those defects.
If an image is taken before the detector releases all of the signal from the
previous image, a faint image of the previous exposure may be visible.
What is this error called?
Image lag, it is almost a double exposure of sorts
What does CCD stand for?
Charge-Coupled device
What happens to x-rays before they reach the CCD?
X-ray photons interact with a scintillation material in the CCD chip. The light is
then converted to an electrical charge. The light is then transmitted by lenses
or fiberoptics to the CCD.
How do CCD's work?
The light is sent to one or more small capacitors that convert it into an
electrical charge. This charge is stored in a sequential pattern (in a matrix)
and released line by line and sent to an ADC.
, What is the release of the electrical charge line by line called?
It is known as the bucket brigade.
What is the purpose of a capacitor?
It stores energy
What is the purpose of a scintillator?
It releases light when struck by photons.
What focuses light onto the CCD chip?
Lenses or fiberobtics
Why is the efficiency of the transportation of light to the CCD chip
important?
Because of the noise created. The more light that is sent to the chip without
creation of noise, the more efficient the system is.
The design of the optics is also crucial in imaging performance, why?
Issues arise with geometric distortion such as light scattering or lens/optic
flaws.
What does the amount of electrons produced relative to the incident light
from the scintillator known as?
The quantum efficiency of the CCD. Not the same as DQE, but quantum
efficiency is part of the total DQE.
What does quantum efficiency represent?
It represents the absolute efficiency of the light collection and signal created
by the chip.
Does quantum efficiency affect DQE?
Yes
What is DQE?
AND ANSWERS RATED A.
What are some flat panel artifacts that can occur with TFT systems?
Dead pixels, Gain calibration/Flat Field Correction, Image lag
Manufacturers make efforts to maintain a standard of less than what %
defective pixels?
0.1%-0.2%
What is used to correct flaws in the detector, such as dead pixels?
Gain calibration/ Flat field correction. This removes the potential of having
that artifact interfere with diagnosis. It removes the densities on the image by
creating a mask of those defects.
If an image is taken before the detector releases all of the signal from the
previous image, a faint image of the previous exposure may be visible.
What is this error called?
Image lag, it is almost a double exposure of sorts
What does CCD stand for?
Charge-Coupled device
What happens to x-rays before they reach the CCD?
X-ray photons interact with a scintillation material in the CCD chip. The light is
then converted to an electrical charge. The light is then transmitted by lenses
or fiberoptics to the CCD.
How do CCD's work?
The light is sent to one or more small capacitors that convert it into an
electrical charge. This charge is stored in a sequential pattern (in a matrix)
and released line by line and sent to an ADC.
, What is the release of the electrical charge line by line called?
It is known as the bucket brigade.
What is the purpose of a capacitor?
It stores energy
What is the purpose of a scintillator?
It releases light when struck by photons.
What focuses light onto the CCD chip?
Lenses or fiberobtics
Why is the efficiency of the transportation of light to the CCD chip
important?
Because of the noise created. The more light that is sent to the chip without
creation of noise, the more efficient the system is.
The design of the optics is also crucial in imaging performance, why?
Issues arise with geometric distortion such as light scattering or lens/optic
flaws.
What does the amount of electrons produced relative to the incident light
from the scintillator known as?
The quantum efficiency of the CCD. Not the same as DQE, but quantum
efficiency is part of the total DQE.
What does quantum efficiency represent?
It represents the absolute efficiency of the light collection and signal created
by the chip.
Does quantum efficiency affect DQE?
Yes
What is DQE?
