Flat panel detector
Encyclopedia
Flat panel detectors are a class of solid-state
x-ray
imaging
devices similar in principle to the image sensors used in digital photography and video, but due to the impracticability of focusing x-rays, the sensors are hundreds of times larger than those used in digital cameras.
layer of gadolinium oxysulfide
or cesium iodide which converts the x-rays into light. Directly behind the scintillator layer is an amorphous silicon
-on glass detector array manufactured using a process very similar to that used to make LCD
televisions and computer monitors. Like a TFT-LCD display, millions of roughly 0.1 mm pixels each containing a thin-film transistor
form a grid patterned in amorphous silicon on the glass substrate. Unlike an LCD, but similar to a digital camera's image sensor chip, each pixel also contains a photodiode
which generates an electrical signal in proportion to the light produced by the portion of scintillator layer in front of the pixel. The signals from the photodiodes are amplified and encoded by additional electronics positioned at the edges or behind the sensor array in order to produce an accurate and sensitive digital representation of the x-ray image.
and can also be produced in larger sizes.
Solid state (electronics)
Solid-state electronics are those circuits or devices built entirely from solid materials and in which the electrons, or other charge carriers, are confined entirely within the solid material...
x-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
imaging
Medical imaging
Medical imaging is the technique and process used to create images of the human body for clinical purposes or medical science...
devices similar in principle to the image sensors used in digital photography and video, but due to the impracticability of focusing x-rays, the sensors are hundreds of times larger than those used in digital cameras.
Mechanics
X-rays pass through the subject being imaged and strike a scintillatorScintillator
A scintillator is a special material, which exhibits scintillation—the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e., reemit the absorbed energy in the form of light...
layer of gadolinium oxysulfide
Gadolinium oxysulfide
Gadolinium oxysulfide , also called gadolinium sulfoxylate or GOS, is an inorganic compound, a mixed oxide-sulfide of gadolinium. Its CAS number is .-Uses:...
or cesium iodide which converts the x-rays into light. Directly behind the scintillator layer is an amorphous silicon
Amorphous silicon
Amorphous silicon is the non-crystalline allotropic form of silicon. It can be deposited in thin films at low temperatures onto a variety of substrates, offering some unique capabilities for a variety of electronics.-Description:...
-on glass detector array manufactured using a process very similar to that used to make LCD
TFT LCD
Thin film transistor liquid crystal display is a variant of liquid crystal display which uses thin-film transistor technology to improve image quality . TFT LCD is one type of Active matrix LCD, though all LCD-screens are based on TFT active matrix addressing...
televisions and computer monitors. Like a TFT-LCD display, millions of roughly 0.1 mm pixels each containing a thin-film transistor
Thin-film transistor
A thin-film transistor is a special kind of field-effect transistor made by depositing thin films of a semiconductor active layer as well as the dielectric layer and metallic contacts over a supporting substrate. A common substrate is glass, since the primary application of TFTs is in liquid...
form a grid patterned in amorphous silicon on the glass substrate. Unlike an LCD, but similar to a digital camera's image sensor chip, each pixel also contains a photodiode
Photodiode
A photodiode is a type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation.The common, traditional solar cell used to generateelectric solar power is a large area photodiode....
which generates an electrical signal in proportion to the light produced by the portion of scintillator layer in front of the pixel. The signals from the photodiodes are amplified and encoded by additional electronics positioned at the edges or behind the sensor array in order to produce an accurate and sensitive digital representation of the x-ray image.
Advantages
Flat-panel detectors are more sensitive, faster and cheaper than film. Their sensitivity allows a lower dose of radiation for a given picture quality than film. They are lighter, far more durable, smaller in volume, more accurate, and have much less image distortion than image intensification detectorsImage intensifier
An image intensifier tube is a vacuum tube device for increasing the intensity of available light in an optical system to allow use under low light conditions such as at night, to facilitate visual imaging of low-light processes such as fluorescence of materials to X-rays or gamma rays, or for...
and can also be produced in larger sizes.