Chapter 21: Computer Radiography (CR) Flashcards by Jennifer Gonzalez

-evolved in 1980s
-uses the technology of storage phosphors
pioneered by Eastman Kodak

Computed Radiography (CR)

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Is CR still consider a type of digital?

Yes, because you can still manipulate the image

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CR two step process

-acquisition
-image processing and display

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associated with photostimulable imaging plates

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How is the CR data read?

It is read in a raster pattern, which is a zig-zag pattern

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is considered an activator as it maintains the presence of electron holes in the PSP

Europium

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Common PSP phosphors

-Barium fluorohalide bromides
-Barium fluorohalide iodides

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What is the best answer for the common psp phosphors

Europium doped barium fluorohalide

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-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

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-more sensitive to scatter both before and after exposure, than radiographic film
-sensitive to low levels of radiation energy

PSP’s

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Why can’t cassetee be left in the room

They are too sensitive

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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

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is a digital radiographic imaging modality that uses a photostimulable storage phosphor
imaging plate (PSP or IP), typically inside
a cassette.

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is the method by which the data are collected from the imaging plate

Raster pattern

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what type of sampling frequency gives you better detail

Higher sampling frequency

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how the laser reads the CR (zig zag pattern)

Raster

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What laser erases the image, making the electrons return to a stable state?

white laser

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What laser reads the electrons inside the plate?

red laser

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which laser involves helium neons helps release phosphor

blue/violet laser

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-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