Digital, PACS, Artifacts. Flashcards
DR utilizes an array of electronic x-ray detectors that take the remnant beam &
convert it to electronic signals to make available to the computer
In DR detectors, the materials used for detecting the x-ray signal and the sensors are
permanently enclosed inside a rigid protective housing
The permanent location of the detectors of a DR system is usually:
usually just below the radiographic tabletop, where the Bucky tray is
The image receptor can vary in:
size. 14 x 14, 14 x 17, or 17 x 17 inches
Electronic direct readout detectors are what differentiate
DR from CR.
Examples of types of collection elements:
Photodiodes
Charge-coupled devices (CCD)
Complementary Metal Oxide Semiconductors (CMOS) or
Thin-film transistors (TFT)
The CCD and photodiode are light sensitive devices that
collect light photons.
The photoconductor utilizes
specialized pixels that convert x-rays into light
The TFT is a charge-sensitive device that
collects electrons and creates the signal.
The DR flat panel image receptor consists of
an array of detectors and thin film transistors (TFT)
Exit radiation interacts with the detector and an electrical charge is created
This charge is stored temporarily in the
transistor (TFT) until ready to be read out.
The pattern of electrical charges is what makes up the
latent image.
There are two types of flat panel detectors utilized:
Direct and Indirect. They differ in how the x-ray exposure is converted to an electric charge
Thin-film transistor (TFT) detector arrays may be used in
both direct and indirect-conversion detectors
X-ray photons are absorbed by a scintillator, which is
a radiation-conversion material
In direct conversion, a scintillator absorbs x-rays and converts them to:
electrons which are stored in the TFT detectors
The TFT absorbs the electrons and does what with them?
generates electrical charges
The scintillator used in direct conversion is:
amorphous selenium
The thin film transistor is an array of:
small pixels which absorb electrons and generates electrical charges.
The thin film transistor reacts like ______ to send the electrical charges to the image processor
a switch
How many pixels can be read and converted to a composite digital image in less than 1 second?
Over 1 million.
Indirect also uses TFT technology
The difference is:
that indirect has a two-step process:
1) x-ray photons are converted to light
2) light photons are converted to an electrical signal
The scintillator in indirect conversion converts X-rays into:
visible light.
The scintillator in indirect conversion is made up of:
Cesium iodide (CsI) Gadolinium - Rare-earth element used in intensifying screens