Test 5 Flashcards
(39 cards)
Function of the laser:
Scans the CR imaging plate to release stored energy/latent image during image processing.
- helium neon laser
- solid state laser diode
Function of the photomultiplier tube:
Collects, amplifies and converts light to an electrical signal during CR image processing
Function of the ADC
Digitizes the electrical signal to produce the digital image
Function of the erasure cycle:
CR plate is erased by an intense white light after image processing. Releases any residual stored energy/latent image.
What are the advantages of CR digital imaging systems?
- Compatibility w/ existing X-ray equipment
- wider exposure latitude/dynamic range compared to film/screen imaging
- ideal for use in mobile imaging.
What is the disadvantage of CR digital imaging systems?
Amount of time necessary for processing and image readout
What are the 4 components of the CR reader?
Laser
Photomultiplier/PM tube
Analog to digital converter/ADC
Erasure cycle
what are DR flat panel detectors?
an array of X-ray detectors that receive the exit radiation and convert it into electronic signals processed by a computer. Responsible for integrating the signal storage, readout, and digitizing electronics.
what are fixed detectors?
detectors permanently mounted in the table or upright bucky system that communicate directly with the computer.
what does indirect conversion detectors do?
convert exit radiation first to visible light and then to electrical charges .
- uses cesium iodide scintillator to convert exit radiation into visible light
- layer of amorphous silicon is what converts the visible light into electrical charges.
what does direct conversion detectors do?
converts exit radiation DIRECTLY into electrical charges with faster image reconstruction.
*amorphous selenium coated detectors is what converts the exit radiation directly into electrical charges.
With direct and indirect conversion detectors, what are the jobs of thin-film-transistors and the analog to digital converters (ADC)?
TFT-temporarily stores the electronic charge
ADC-converts varying electrical/analog signals into digital data.
what are the advantages of DR direct digital imaging systems?
- produces higher resolution images faster than CR and film/screen imaging systems
- lower patient exposure and dose.
what are the disadvantages of DR direct digital imaging systems?
- incompatibility with existing X-ray equipment
- expensive
what is the digital image matrix composed of?
rows and columns of pixels (picture element). Each pixel corresponds to a shade of gray representing an area in the patient called a voxel (volume element).
what does bit depth determine and what does it control?
- determines the # of shades of gray the system is capable of displaying in the digital image.
- determines contrast resolution
- controls brightness
define brightness
intensity of light that represents the individual pixels in the image on the monitor
The greater the bit depth of a digital system, the ____________.
the greater the # of shades of gray the system is capable of displaying on the monitor.
-high resolution=improved visibility of tissues with similar densities
what is a histogram?
- graphic display of digital data during image processing
- shows distribution of pixel values
- indicates low, proper or high exposure
what is an algorithm?
mathematical formula applied during digital processing
what is spatial resolution dependent on?
- aquisition pixel size
- digital display pixel size
noise/quantum mottle creates ____ signal and _____noise level in a digital image.
high
low
in the SNR ratio, what represents signal?
of X-ray photons that strike the digital detector
what kind of SNR is desirable in digital imaging?
high signal to low noise level
