Chapter 21: Computer Radiography (CR) Flashcards
-evolved in 1980s
-uses the technology of storage phosphors
pioneered by Eastman Kodak
Computed Radiography (CR)
Is CR still consider a type of digital?
Yes, because you can still manipulate the image
CR two step process
-acquisition
-image processing and display
associated with photostimulable imaging plates
CR
How is the CR data read?
It is read in a raster pattern, which is a zig-zag pattern
is considered an activator as it maintains the presence of electron holes in the PSP
Europium
Common PSP phosphors
-Barium fluorohalide bromides
-Barium fluorohalide iodides
What is the best answer for the common psp phosphors
Europium doped barium fluorohalide
-reusable plates
-rigid sheet of several layers
-records and transmits image from xray beam
-inserted into cassette
-transferred to reader assembly for processing
photostimulable imaging plates
-more sensitive to scatter both before and after exposure, than radiographic film
-sensitive to low levels of radiation energy
PSP’s
Why can’t cassetee be left in the room
They are too sensitive
best between 35 and 50 kev
-absorb more low energy radiation than radiographic film
- more exposure needed if applied kvp is outside of this range
K-edge attenuation
is a digital radiographic imaging modality that uses a photostimulable storage phosphor
imaging plate (PSP or IP), typically inside
a cassette.
CR
is the method by which the data are collected from the imaging plate
Raster pattern
what type of sampling frequency gives you better detail
Higher sampling frequency
how the laser reads the CR (zig zag pattern)
Raster
What laser erases the image, making the electrons return to a stable state?
white laser
What laser reads the electrons inside the plate?
red laser
which laser involves helium neons helps release phosphor
blue/violet laser
-Electron pattern stored in active layer of exposed IP
-Fluorohalides absorb beam through photoelectric interactions
latent Image production
if you wait to process the image for CR how much energy is lost within 8 hours
latent image will lose approximately 25% of its energy in 8 hours
**important to process cassette shortly after exposures
If you don’t run the cassette immediately what happens to those electrons
Those electrons are going to go back to their normal state
What are the two types of scanning:
fast scan and slow scan
which scan is reading the image (the movement of the laser across the IP)
fast scan
which scan is the plate moving through the reader
slow scan
PM tubes (photomultipler) convert light to what
to analog electronic signal
-PM tubes convert light to analog electronic signal
-Analog electronic signal sent to analog to digital converter
-ADC sends digital data to computer for additional processing
-IP erased via exposure to intense light
Reading CR Data
Determines number of density values
-affects density and contrast of system
Pixel Bit depth
dependent upon sampling frequency and plate size
Matrix size
-raw data located and prepared
-what anatomical part is selected
-orientation of part on IP
-number of projections on IP
preproccessing
image file size affected by
-pixel size
-matrix
-bit depth
CR Image processing
Two step process:
-pre-processing
-post processing
-exposure field recognition (FOV)
-histogram analysis
-grayscale analysis
preproccessing
-frequency processing
-spatial location processing
post processing
with this processing, you can not change it or manipulate it
pre processing
With this processing, you can manipulate the image
post processing
-computer looks at distribution of exposure on plate
-improper placement yields histogram analysis errors
Exposure field recognition
-obtained image data does not match reference histogram
-computer cannot find collimated edges
-prosthetic devices
-abnormal areas of increased or decreased attenuation
histogram analysis errors
for CR what cassette size is the best spacial resolution
Smallest cassette
grid error that occurs with digital image receptor systems when the grid lines are cap-tured and scanned parallel to the scan lines in the imaging plate readers. This error occurs with grids used in a stationary fashion for examinations such as mobile radiography or translateral hip images.
grid lines must be running in the same direction as the movement of the laser beam that is scanning the
imaging plate
Moire effect
math algorithm of how it is read
Nyquist Frequency
how often the lead occurs
grid frequency
what technique is there not enough of if there is quantum noise
mAs
grid artifact is what type of effect
moire
pixel pitch and size is inversely related to:
spatial resolution
Th minimum separation between two objects at which each can be distinguished as two seperate objects in the image;most similar to sharpness of detail
spatial resolution
CANNOT be manipulated after exposure; dependent on image acquisition and display factors which include:
o Pixel size
o Number of pixels
o Pixel density
o Pixel pitch
o Sampling frequency
