Ch.21 Flashcards
-evolved in 1980s
-uses the technology of storage phosphors
pioneered by Eastman Kodak
Computed Radiography (CR)
CR two step process
-acquisition
-image processing and display
associated with photostimulable imaging plates
CR
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
-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
-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
-more sensitive to scatter both before and after exposure, than radiographic film
-sensitive to low levels of radiation energy
PSP’s
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 is erasing image, making a stable state again
white laser
what laser reads the electrons
red laser
which laser involves helium neons helps release phosphor
blue/violet laser
-xrays expose cassettes and latent image is stored in IP
-rules of positioning remain the same
-wider exposure latitude than film/screen
Image Acquisition
-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
Two types of scanning:
Fast scan and slow scan
which scan is reading the image
Fast scan
Which scan is the plate moving through the reader
Slow Scan
-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
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
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
