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TFT/CCD/CMOS questions with verified answers graded A+
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TFT/CCD/CMOS questions with verified answers graded A+
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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.
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