Ch.21 Flashcards by Melissa Unknown

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

Computed Radiography (CR)

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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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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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-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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-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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-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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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 is erasing image, making a stable state again

white laser

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what laser reads the electrons

red laser

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which laser involves helium neons helps release phosphor

blue/violet laser

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-xrays expose cassettes and latent image is stored in IP
-rules of positioning remain the same
-wider exposure latitude than film/screen

Image Acquisition

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-Electron pattern stored in active layer of exposed IP
-Fluorohalides absorb beam through photoelectric interactions

latent Image production

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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

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Two types of scanning:

Fast scan and slow scan

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which scan is reading the image

Fast scan

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Which scan is the plate moving through the reader

Slow Scan

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-trapped eletcrons freed
-electrons move to lower energy state
-light captured by PM tubes
-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

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Determines number of density values
-affects density and contrast of system

Pixel Bit depth

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dependent upon sampling frequency and plate size

Matrix size

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-raw data located and prepared -what anatomical part is selected -orientation of part on IP -number of projections on IP

Preprocessing

image file size affected by

-pixel size -matrix -bit depth

CR Image processing Tow step process:

-pre-processing -post processing

-exposure field recognition -histogram analysis -grayscale analysis

pre processing

-frequency processing -spacial 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

-algorithm that detects edges of exposure versus nonexposure -can sometimes be triggered by prosthetics or implants

Collimator edge identification

-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

clinically irrelevant data not included in image display

Histogram analysis: data clipping

examples of histogram equalization

-normal chest xray -bone enhanced histogram image -soft tissue histogram image

Cr's responce to radiation

linear and nonlimiting

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

This is your phosphor layer

europium flurohalide

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 your :

moire

pixel pitch and size is inversely related to:

spacial resolution

-spacial location processing -frequency processing -egde enhancement -image smoothing -image stitching

post processing

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

spacial resolution

distance between center of one pixel to center of adjacent pixel

pixel pitch -decreased pixel pitch=increased spacial

The ability of the imaging system to distinguish between small objects that attenuate the x-ray beam in a similar manner; improves the visibility of the minimum density differences or shades of gray; most similar to gray scale

Contrast resolution

wider window width =

increased contrast resolution

* Increased bit depth =

increased contrast resolution

Increased dynamic ranges =

increased contrast resolution

Manipulation of image appearance after exposure

post processing

brightness alteration

window level

contrast alteration

window width

ount of luminance or light emission of the display monitor; opposite of density, the term used to describe blackness in film/screen

brightness

what does this do to the pixel value High brightness = high x-ray photon attenuation =

low pixel value

A term used to describe the shades of gray seen in an image. In digital imaging, it is called gray scale and represents the number of different shades that can be stored and displayed on the monitor.

Contrast

The minimum separation between two objects at which each can be distinguished as two separate objects in the image; most similar to film/screen’s sharpness of detail

 Resolution (Spatial)

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

Converts analog signal from the image receptor/detector to a digital signal for computer to manipulate for processing, display, and storage

Analog-to-Digital Converter (ADC)

A continuously varying quantity

analog signal * EX: film/screen systems, x-ray photons, light, electricity are produced in varying quantities, resulting in a continuous wave of varying energies

A series of discrete values (used to determine pixel brightness)

Digital signal Computers use discrete values (0,1)

Automatic image software function that adjusts pixel brightness values or ranges to their expected levels for the anatomy being imaged

Image rescaling

Process that takes place in the computer where the raw digital image data are corrected for flaws that are inherent in the x-ray beam, the elements and electrical circuitry of the particular imaging system, or the physical elements and electrical circuitry of the computer

pre processing

Preset or reference histogram characteristics stored by the computer for each anatomical area and view; used to rescale the image if exposure conditions do not match the “ideal”

Look up Tables

Generated by dividing a scanned area into pixels and determining the signal intensity for each pixel; can be calculated for specific anatomy and procedures.

Histogram

What does the phosphor layer hold

The phosphor layer holds the pho-tostimulable phosphor, which is the active component in the plate.

has a built in picture perfect image that is compared to very important to select the correct body part

histogram

what are examples that would show up white

shielding, bone, soft tissue, air

element of phosphor

Europium doped barium fluorohalide

Histogram Look up table Bit depth

Pre processing

Window leveling Window width Annotation Any manipulation to an image

Post processing

lower atomic number means what about the transmission to ir

more transmission to IR

bone absorbs more so what does that mean about what is being transmitted to IR

less transmission to IR