TFT, CCD, CMOS UPDATED Exam
Questions and CORRECT Answers
True 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.
Questions and CORRECT Answers
True 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.
