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TFT questions and answers verified 2024
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TFT questions and answers verified 2024
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TFT/CCD/CMOSTrue or False. Flat panel detectors contain an active matrix of electronic
components. - correct answer ✔True. TFTs are constructed in layers to
receive the x-ray photons and convert them to electrical charges for storage
and readout.
Describe the 3 layers of a flat panel detector. - correct answer ✔First layer -
the x-ray converter
Second layer - The TFT array
Third layer - Glass substrate
What is another name for the X-ray converter? - correct answer ✔The
absorber
The choice of x-ray absorption material determines whether the detector is a
________or _______ conversion system? - correct answer ✔Direct or
Indirect
Describe the Direct conversion system with TFT plates - correct answer ✔1
step process. X-ray photons are absorbed by the coating material and
immediately converted directly into an electrical signal.
What is the radiation-conversion material or photoconductor, typically made of
with direct conversion systems? - correct answer ✔Typically made of
Amorphous selenium (a-Se). This is the material that absorbs and converts x-
rays into electrons, which are stored in the TFT detectors.
What absorbs x-rays and produces electrical charges? - correct answer ✔A
photoconductor
,More than ___ million pixels can be read and converted to a composite digital
image in less than ___ second with direct TFT plates? - correct answer ✔1
million in 1 second
Describe the Indirect conversion system with TFT plates - correct answer ✔2
step process. X-ray photons are converted to light, then the light photons are
converted to an electrical signal.
In which layer are the x-rays converted into light? - correct answer ✔The
phosphor or scintillation layer
Is the scintillation layer structured or unstructured? - correct answer ✔It can
be either structured or unstructured
What are the two types of phosphor structures? - correct answer ✔Turbid
(unstructured or random) and Needle/Columnar (structured)
What are turbid phosphor composed of? - correct answer ✔Gadolinium
Oxysulfide (Gd2O2S)
What is the disadvantage of the turbid phosphor structure? - correct answer
✔It allows light to escape laterally before reaching the surface. This reduces
the efficiency of the phosphor (DQE) and lowers spatial resolution.
What are the needle/columnar phosphors composed of? - correct answer
✔Cesium Iodide (CsI)
What is the advantage of using structure phosphors over unstructured
phosphors? - correct answer ✔They work as light directing tubes, there is
, greater absorption and less light spread. Structured phosphors result in higher
DQE, and higher spatial resolution.
What is the difference between a direct and indirect detector? - correct
answer ✔Indirect converts x-rays to light before an electircal signal, direct
systems skip this step and convert x-rays directly into electrical signals.
What is the TFT array? - correct answer ✔It is basically the FOV of the
image receptor. The TFT array is divided into square detector elements (DEL)
which are basically just pixels.
True or False. Each DEL has a capacitor to store electrical charges and a
switching transistor for readout. - correct answer ✔True
Is the size of the DEL fixed, or can we change it? - correct answer ✔It is set
during manufacturing, and is therefore fixed.
True or False. Larger DEL results in improved spatial resolution. - correct
answer ✔False, Smaller DEL results in improved spatial resolution, but the fill
factor decreases with smaller DELs and becomes a limitation.
What is the fill factor? - correct answer ✔It is the ratio of the sensitive area to
the entire detector detector area. It is usually a percentage.
Does fill factor affect both spatial resolution and SNR? - correct answer
✔Yes
What is the purpose of the glass substrate layer of a TFT? - correct answer
✔It is the foundation for the TFT array
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