Ch. 10 Digital Image Receptors Flashcards
two groups of digital receptors are
computed radiography (CR) and direct radiography (DR)
what are the 4 parts of a CR system
- cassette
- photostimulable phosphor plate (PSP)
- plate reader
- computer workstation
what is the backing material of the CR cassette, used to absorb back-scatter
aluminum
what are the layers of the PSP plate
- protective layer
- phosphor layer
- reflective layer
- conductive layer
- support layer
what is the phosphor layer typically made of
barium fluorohalide with europium activator
what are the two types of phosphor layers
turbid or structures
phosphor crystals are randomly distributed
turbid
contains columnar phosphor crystals that resemble needles standing on end, packed tightly together
structured
when the electrons in the phosphor layer are ionized the ejected electrons are trapped in this
conduction band
this is what allows the phosphor to store x-ray energy as the latent image
europium
this detects the light that is released from the PSP during scanning and amplifies the light in the form of an analog image
photodetector
the amplified analog signal is converted to a digital signal by this
ADC
two categories of DR
direct capture and indirect capture
two different form of indirect capture
- CCD/CMOS
- TFT
CCDs are coupled with this
scintillator plate - cesium iodide
what does the scintillator plate act as
phosphor layer of CR - fluoresces when radiated
a sturdy, light-proof container for film. Also a sturdy protective container for the photostimulable phosphor plate in computed radiography
cassette
a light-sensitive semiconducting device that generates an electrical charge when stimulated by light and stores this charge in a capacitor
charge-coupled device (CCD)
a scintillator device made up of a crystalline silicon matrix
complementary metal oxide semiconductor
a digital imaging system that uses a cassette, a photostimulable phosphor plate, a plate reader, and a computer workstation to acquire and display a digital image
computed radiography system
a measurement of the efficiency of an image receptor in converting the x-ray exposure it receives to a quality radiographic image
detective quantum efficiency (DQE)
the physical component consisting of multiple detectors that efficiently absorb the transmitted radiation and accurately convert it to an electrical signal for display on a computer workstation
detector array
the process by which washing works; exposes the film to water that contains less thiosulfate than the film
diffusion
a common computer language that allows different systems of a picture archiving and communication system to communicate with each other
Digital Imaging and Communications in Medicine (DICOM)
a digital imaging system that uses a detector array in place of the Bucky assembly; the imaging-forming radiation is captured and transferred to a computer from the detector array for almost instant viewing at the control panel
direct radiography systems
a measurement of exposure in air, followed by a computation to estimate absorbed dose to the patient
dose area product (DAP)
the range of exposure intensities that an image receptor can respond to and acquire image data
dynamic range
provides a numeric value indicating the level of radiation exposure to the digital image receptor
exposure indicator
the range of exposure values to the image that will produce an acceptable range of densities for diagnostic purposes
exposure latitude
a process in which a computer analyzes the histogram using processing algorithms and compares it to a preestablished histogram specific to the anatomic part being imaged
histogram analysis
the invisible image that exists on the image receptor before it has been processed
latent image
the emission of light from the screen when stimulated by radiation
luminescence
the visible radiographic image on the exposed detector after processing
manifest image
a measure of the ability of the system to preserve signal contrast (display the contrast of anatomic objects varying in size), and the value will be between 0 (no difference in brightness levels) and 1.0 (maximum difference in brightness levels)
modulation transfer function (MTF)
a device that absorbs x-rays and creates electrical charges in proportion to the x-ray exposure received
photoconductor
a device used to sense the light released from the photostimulable phosphor plate during scanning
photodetector
the release of energy from trapped electrons by a laser during the scanning of a photostimulable phosphor plate
photostimulable luminescence
a plate made up of several layers that stores x-ray energy as a latent image for cassette-based digital systems
photostimulable phosphor (PSP) plate
a secure network for transmitting and exchange of patient images and data, display (viewing and workstations), and storage (archive server) systems
Picture Archiving and Communication System (PACS)
a device equipped with a drive system and optical system that converts the stored image on a photostimulable phosphor plate to an electronic signal for display on a computer workstation
plate reader
an electronic system that allows patients’ electronic records (medical information and imaging studies) to be accessed from various workstations within or outside of a facility
teleradiology
electronic components layered onto a glass substate that include the readout, charge collector, and light-sensitive elements
thin-film transistor (TFT)
established values within histogram models that determines what part of the data set should be incorporated into the displayed image
values of interest (VOI)
a material that absorbs x-ray energy and emits visible light in response
x-ray scintillator
the scintillator plate is coupled to CCD using this
fiber-optics or optical lens system
each CMOS detector has this
own amplifier, photodiode, and storage capacitor and surrounded by transistors
what makes CMOS not as good as CCD
not as light sensitive as CCD and doesn’t provide as good resolution as CCD
what makes CMOS better than CCD
more efficient and take much less power
thin-film transistor (TFT) arrays are coupled with this
amorphous silicon which acts as the photodetector
in indirect capture systems this is used to convert radiation into light
scintillator
this type of system is able to reduce resolution loss by cutting out the conversion of radiation to light
direct capture
what do direct capture systems use
TFT arrays with photoconductor made of amorphous selenium
this is what’s able to absorb radiation as an input and create an electric charge as an output in direct capture
amorphous selenium
what is the charge stored in, in direct capture
storage capacitors
during image acquisition the computer creates what is called this
histogram
graphic representation of a given data set
histogram
what does the histogram’s x-axis represent
amount of exposure
what does the histogram’s y-axis represent
how many pixels were radiated for each exposure level
this the imaging plate moving through the reader at a very precise speed
slow scan
this is the actual laser array being cast onto the imaging plate
fast scan
sampling frequency must be at least what of the original bandwidth of the analog signal in order to accurately digitize the signal
2 times
what is the principle of the sample frequency being at least two times the original bandwidth of the analog signal in order to accurately digitize the signal called
Nyquist Theorem
the range of exposure values that a receptor can receive and still produce a diagnostic image
exposure latitude
these are numerical values that represent how much radiation exposure a receptor received
exposure indicator
some DR systems use this as exposure indicators which measures the exposure in air
dose area product (DAP)
for CR systems the imaging plates must be cleaned how often
at least every 3 months
integral part of digital imaging is divided into these 3 sections
- acquisition
- network
- storage
this is a file format that allows for exams from all modalities to be able to be stored and used at any PACS terminal across the network
digital imaging and communication in medicine (DICOM)
