TFT/CCD/CMOS EXAM QUESTIONS AND
ANSWERS
True or false. Flat panel detectors have an active matrix of electronic components. -
ANSWER True. TFTs are built-in layers to accept X-ray photons and convert them
to electrical charges for storing and reading.
Describe the three levels of a flat-panel detector. - ANSWER First layer: the x-ray
converter.
The second layer: the TFT array.
Third layer: Glass substrate.
What's another term for the X-ray converter? - ANSWER The absorber
The type of x-ray absorption material used influences whether the detector is a
________ or _______ conversion system. - ANSWER: Direct or indirect
Describe the direct conversion system using TFT plates - ANSWER 1-step process.
The coating material absorbs X-ray photons and converts them instantaneously into
an electrical signal.
What is the common radiation-conversion material or photoconductor used in
direct conversion systems? - ANSWER Typically composed of amorphous
selenium (a-Se). This is the substance that absorbs and converts X-rays to
electrons, which are then stored in TFT detectors.
What absorbs X-rays and generates electric charges? - Answer: A photoconductor.
, Direct TFT plates can scan and convert more than ___ million pixels into a
composite digital image in less than ___ seconds. - Answer: 1 million in one
second.
Describe the indirect conversion mechanism using TFT plates - ANSWER 2 stage
process. X-ray photons are turned into light, which is then converted into an
electrical signal.
In which layer are X-rays transformed to light? - ANSWER The phosphor, or
scintillation layer
Is the scintillation layer structured or not? - ANSWER It could be structured or
unstructured.
What are the two kinds of phosphor structures? - ANSWER Turbid (unstructured
or random), and Needle/Columnar (structured).
What is turbid phosphor made of? - ANSWER Gadolinium oxysulfide (Gd2O2S).
What are the disadvantages of the turbid phosphor structure? - ANSWER It causes
light to escape laterally before to reaching the surface. This diminishes the
phosphor's efficiency (DQE) and degrades spatial resolution.
What are the needle/columnar phosphors made out of? - ANSWER Cesium iodide
(CsI
What are the benefits of employing structured phosphors versus unstructured
phosphors? - ANSWER They function as light directing tubes, with more
absorption and less light spread. Structured phosphors provide better DQE and
spatial resolution.
ANSWERS
True or false. Flat panel detectors have an active matrix of electronic components. -
ANSWER True. TFTs are built-in layers to accept X-ray photons and convert them
to electrical charges for storing and reading.
Describe the three levels of a flat-panel detector. - ANSWER First layer: the x-ray
converter.
The second layer: the TFT array.
Third layer: Glass substrate.
What's another term for the X-ray converter? - ANSWER The absorber
The type of x-ray absorption material used influences whether the detector is a
________ or _______ conversion system. - ANSWER: Direct or indirect
Describe the direct conversion system using TFT plates - ANSWER 1-step process.
The coating material absorbs X-ray photons and converts them instantaneously into
an electrical signal.
What is the common radiation-conversion material or photoconductor used in
direct conversion systems? - ANSWER Typically composed of amorphous
selenium (a-Se). This is the substance that absorbs and converts X-rays to
electrons, which are then stored in TFT detectors.
What absorbs X-rays and generates electric charges? - Answer: A photoconductor.
, Direct TFT plates can scan and convert more than ___ million pixels into a
composite digital image in less than ___ seconds. - Answer: 1 million in one
second.
Describe the indirect conversion mechanism using TFT plates - ANSWER 2 stage
process. X-ray photons are turned into light, which is then converted into an
electrical signal.
In which layer are X-rays transformed to light? - ANSWER The phosphor, or
scintillation layer
Is the scintillation layer structured or not? - ANSWER It could be structured or
unstructured.
What are the two kinds of phosphor structures? - ANSWER Turbid (unstructured
or random), and Needle/Columnar (structured).
What is turbid phosphor made of? - ANSWER Gadolinium oxysulfide (Gd2O2S).
What are the disadvantages of the turbid phosphor structure? - ANSWER It causes
light to escape laterally before to reaching the surface. This diminishes the
phosphor's efficiency (DQE) and degrades spatial resolution.
What are the needle/columnar phosphors made out of? - ANSWER Cesium iodide
(CsI
What are the benefits of employing structured phosphors versus unstructured
phosphors? - ANSWER They function as light directing tubes, with more
absorption and less light spread. Structured phosphors provide better DQE and
spatial resolution.
