Ch. 1 Introduction to digital radiography and PACS Flashcards
What does conventional radiography use in its formation process?
film and intensifying screens
Where in a cassette is the film placed?
on one or between 2 intensifying screens
What do intensifying screens do?
emit light when struck by x-rays
Where does the manifest image appear when using film screen?
on the sheet of film
What type of imaging allows text, photos, drawings, animations, and video to appear on the WWW?
Digital imaging
In medicine, what was one of the first uses of digital imaging?
the introduction of the CT scanner
Who introduced the CT scanner? What year?
Godfrey Hounsfield in the 1970’s
What is the basic definition of digital imaging?
any imaging acquisition process that produces an electronic image that can be viewed and manipulated on a computer
What is the 2nd to the discovery of x-ray?
CT
How long did it take for the earliest CT scanner to acquire a single slice?
several hours
What were the first CT scanners only made to image?
the head
How long did it take for the earliest CT scanner to reconstruct an image?
a few days
When was MRI introduced commercially?
in the early 1980’s
Who wrote a publication about MRI in the late 70’s that spurred on MRI use?
Paul Lauterbur in 1973
What in x-ray progressed exponentially in the 70’s?
fluoroscopy
What made it possible to capture the images digitally in fluoro?
Analog to digital converters
What does ADC stand for?
analog to digital converters
What allowed for the display of the dynamic image on a TV monitor in higher resolution and made it possible to store the frames digitally on a computer?
Plumbicon or Vidicon TV tubes
Who introduced the concept of moving images digitally? When?
Albert Jutras in Canada during his experimentation with teleradiology in the 1950’s
What is teleradiology?
moving images via telephone lines to and from remote locations
What does PACS stand for?
Picture Archiving and Communication System
Who developed the early PACS?
U.S. Military for the VA Administration in the 1980’s
What does PSP stand for?
Photostimulable phosphor
What is PSP image capture?
the digital acquisition modality that uses storage phosphor plates to produce projection images.
What was PSP image capture formerly known as?
computed radiography (CR)
Can PSP imaging be used in standard radiographic rooms just like film/screen?
yes
What equipment is required for PSP imaging?
the PSP and phosphor plates, the readers, the technologist control workstation, and means to view the images (a printer or viewing station)
What are the storage phosphor plates similar to?
our current intensifying screens
What is the biggest difference with a storage phosphor plates and current intensifying screens?
the storage phosphors can store a portion of the incident x-ray energy in traps within the material for later readout.
When was PSP imaging first introduced and by whom?
in the U.S. in 1983 by Fuji Medical Systems of Japan
Why didn’t PSP imaging take off right away?
Because the techs didn’t want to deal with new technology
What does FPD stand for?
Flat Panel Detector
How does a FPD form its image?
it uses an x-ray absorber material coupled to a thin film transistor or a charge coupled device to form the image
What does CCD stand for?
Charge-coupled device
Does FPD, TFT, or CCD need a new room retrofitted to use the system?
yes
How many categories does FPD have? What are they?
2; indirect capture and direct capture
What is indirect capture?
devices absorb x-rays and convert them into light, the light is then collected by an area CCD or thin film transistor array and then converted into an electrical signal that is sent to the computer for processing and viewing
What does TFT stand for?
Thin film transistor
What is direct capture?
the incident x-ray energy is converted directly into an electrical signal, typically using a photoconductor as the x-ray absorber, and send the electrical signal to a TFT and then to an ADC. The ADC signal goes to the computer for processing and viewing.
What does ADC stand for?
analog to digital converters
What does DSA stand for?
digital subtraction angiography
What was the first clinical application for digital images and when was it introduced?
digital subtraction angiography in the early 1970’s
What is better? CCD or TFT?
they are both equally as good as the other
Why do FPD, TFT, and CCD have an advantage over conventional radiography and cassette based PSP systems?
because the processing is done right at the room’s console
How is the latent image formed in conventional radiography?
a film is placed inside a cassete that contains an intensifying screen. when x-ray photons interact with the silver halide grains in the film emulsion, and an electron is ejected from the halide. The electron is attracted to the sensitivity speck. the speck now has a negative charge, and silver ions are attracted to equal out the charge. After chemical processing, the sensitivity specks will be processed into black metallic silver, and the manifest image is formed.
How is the latent image formed in a PSP system?
a photostimulable phosphor plate is placed inside a cassette. Most storage phosphor plates today are made of barium fluorohalide with europium as an activator. x-rays strike the photostimulable phosphor and some light is given off but some of the photon energy is deposited within the phosphor particles to create the latent image.
How is the latent image released from a PSP plate?
focused laser light is scanned over the plate, causing the electrons to return to their original state and emiting light in the process. The light is picked up by a photomultiplier tube or CCD array and converted into an electrical signal. The electrical signal is then sent through an ADC to produce a digital image that can be sent to the tech’s review station.
In FPD the system may be…
cassette based or cassette-less
Where is the image acquisition device for the FPD?
It is either built into the table and/or wall stand or enclosed in a portable device.
What are the acquisition methods for FPD?
indirect or direct capture
What is indirect capture similar to? and why?
PSP systems because the x-ray energy stimulates a scintillator, which gives off light that is detected and turned into an electrical signal.
What is the process for direct capture?
the x-ray energy is detected by a photoconductor that converts it directly into a digital electrical signal.
Exposure latitude in conventional radiography is based on what?
the characteristic response of the film, which is nonlinear.
Acquiring images with digital projection imaging involves…
using a detector that can respond in a linear manner
Why is the dynamic range very wide during digital projection imaging?
because a single detector can be sensitive to a wide range of exposures.
In conventional radiography, radiographic contrast is primarily controlled by…
kVp
With PSP and FPD, radiographic contrast is primarily controlled by…
an image processing look up table
What does LUT stand for?
Look up table
What is a look up table?
a table that maps the image grayscale values into some visible output intensity on a monitor or printed film
In conventional radiography, optical density on film is primarily controlled by…
mAs
For digital imaging, mAs has influence on ____, whereas density is controlled by …
image noise; image processing algorithms (with LUTs)
T or F…PSP and FPD systems can be more sensitive to scatter than screen/film
T
Why are PSP and FPD systems more sensitive to scatter than screen/film?
Because the image acquiring devices are more sensitive to low energy photons
What does DICOM stand for?
Digital imaging and communications in medicine
What is the relationship between PACS and DICOM?
PACS can accept any image that is in the DICOM format
What does PACS serve as?
file room, reading room, duplicator, and courier
What are some different parts of PACS?
reading stations, physician review stations, web-access, technologist quality control stations, administrative stations, archive systems, and many interfaces to various hospital and radiology systems.
In film/screen, what captures, displays, and archives the image? How?
the film; Phosphor crystals embedded in the film are sensitive to x-ray photons and emit light when the photon strikes an area of sensitivity on the phosphor. After radiation exposure, the film has to be developed through the use of chemicals that develop and fix the image to the film so that it can be viewed with a light source.
How is a digital image captured?
By either PSP or FPD. The remnant beam is converted to light then digitized or sent directly to a computer for conversion to a signal displayed on a computer monitor.
T or F? The same factors used in film/screen imaging are used in digital imaging.
T
Film/screen images are recorded in a _____ fashion, whereas digital image capture is ____.
logarithmic; linear
What does it mean to a radiographer when digital image capture is linear?
the digital imaging results in a raw image that captures nearly all of the x-ray photons and uses computer software to subtract density values that are outside the predetermined range of diagnostic values for a particular body part.
In DR, what could improper collimation result in?
an image appearing under or overexposed because the sensitivity of digital systems to scatter. Grid use is more critical to ensure proper image contrast.
Higher grid ratios require…
more accurate grid alignment
How are intensifying screens used to increase the effect of x-ray photons?
By conversion of the photons to light in film/screen imaging
What does the conversion of photons to light in film/screen imaging result in?
different screen speeds.
What body part would a slow screen speed be used for?
extremities
What advantage do slow screen speeds have over higher ones?
they are able to resolve more detail than faster screens, but they use more radiation
What does speed class refer to?
the PSP’s ability to capture the image using certain exposure factors.
