Ch.20 Flashcards
Two types of digital radiography systems
CR and DR
This type of digital radiography deals with photostimuable imaging plates (PSP, IP)
CR
Referred to as flat panel detectors (panels)
DR receptors
This type of digital radiography deals with direct conversion without scintillator and indirect conversion with scintillator
DR
What type of digital radiography system does healthcare reimbursements encourage?
DR
When were the most changes made as far as historical development?
1970s and 1990s
-digital computerization of CT, ultrasound, MRI, Mammo
Requires binary machine language
two symbol alphabet
(0 and 1)
Bit versus byte
8 bits=1 byte
Digital image formation must be converted to digital language
Analog-to- digital conversion
ADC involves two distinct steps
Sampling and qualification
Computer memory and power expressed in total bytes
-megabytes, gigabytes, terabyes
Digital data consists of bit values
Binary digit
Bit strings connected as:
Bytes
made up of pixels and voxels
-field of view (FOV)
-spacial resolution dependent on matrix size
matrix
pixel
picture element
voxel
volume element
is a matrix of picture elements (pixels)
Digital image
An arrangement of cells in rows and columns
-each cell corresponds to a specific locations in the image
Matrix
Holds image in plate
PSP
-holding latent image
latent image
not able to see image
manifest
able to see image
PSP
photo simulator phosphor
what is now applied to all imaging modalities
-visualization of anatomy in multiple planes
-computer manipulation of imaging data through sophisticated post-processing software
-adjusting to image
-pre-processing
-built in
-corrects grays
-can enhance pathologies
Look up table
-determined by the number of pixels in the rows and columns
-expressed by listing the number of pixels in each dimension (length and width)
-256X256, 512X512, 1024X1024
Matrix size
-one individual cell in a matrix
Pixel (picture element)
Three values associated with each pixel:
-two for location (length and width)
-one for level of brightness (of shades of gray)
what does each pixel contain
bits of information
(number of bits per pixel determines the shades of gray demonstrated)
How is spacial resolution affected, the smaller the pixel
The smaller the pixels, the greater the spacial resolution
-2pixels required to image 1lp/mm
how is the image resolution affected with the greater the number of pixels
The greater the number of pixels, the greater the image resolution
Level of gray is a determining factor of the overall image quality
determines contrast resolution
number of bits per pixel determines the shade of gray determined
bit depth
number of gray shades that a pixel can produce
Bit depth
what bit depth does most radiography use?
8,10,12 bit depth
Changing position or orientation of pixels, allows rotation and magnification
Geometric Processing Operations
Calculations applied to small group of pixels
Kernel
-enhancing the edges (making everything look sharp), helps increase contrast
High pass filtering/edge enhancement
smooth, even and removes high frequency noise
low pass filtering/ smoothing
makes edges pop out and bring out fine detail in images
edge enhancements
blur something out in the background
unsharp masking or blurring
read left to right
white to black
histogram
annotation
typing on it (supine, erect, AP, PA)
putting 2-3 images together to create one
Stitching
ex. scoliosis series, long bone studies
what happens to your spacial resolution when your matrix size increases and your pixel size decreases
spacial resolution increases
what happens to your density resolution when the gray scale bit depth increases
density resolution increases
-ability to represent small energy values in data set
Low contrast resolution (LCR)
-CR/DR receptors have excellent LCR
-greater dynamic range (low contrast-more shades of gray)
Types of noise
-electronic (system) noise
-quantum noise
artifact, anything unwanted in image
noise
what type of signal to noise ratio is wanted
high signal , low noise
Measure of how sensitive and accurate incoming data is converted to output viewing
Detective Quantum Efficiency (DQE)
want close to 1 as possible, how efficient it is picking up the radiation hitting the IR
more efficient =less dose to patient
DQE
DQE of 1=
100% or no loss of information
-higher DQE means lower dose
-provides information about exposure to image receptor
-acceptable ranges for best image quality
-calculated using histogram values and pixel values of interest mid points
-varies between vendors
Exposure index (EI)
Responsible for understanding and applying EI values
-assess image quality
-ALARA compliance
calculating how much exposure going on to IR and how much radiation to the pt.
Exposure index (EI)
A type of indirect digital radiography; the radiographer must usually move the detector, that is most often housed in a cassette between image acquisition and display
CR
Imaging system that replace traditional film with a reusable detector
Digital Radiography (DR)
Conversion of incoming xray photons to an electronic signal without scintillation
Direct conversion
The number of shades of gray; ranges from 8 bits to 32 bits.
grayscale bit depth
A two-part process involving a scintillator (which converts incoming x-ray photons to light) and a photodetector (which converts light into an electronic signal).
Indirect Conversion
Amplifies or deletes all but the high frequencies.
High Pass Filtering
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
Amplifies or deletes all but the low frequencies.
low pass filtering
Analog to digital consists of two distinct steps
Sampling and Quantification
During this step the analog voltage values are measured at a chosen sampling frequency on the analog waveform.
sampling
Each sampled piece of analog data is then computed and assigned a discrete analog value,
what is this process called
Quantification
means image sharpness
Spacial resolution
is generated during initial processing from the image data that allows the digital system to find the useful signal by locating the minimum and maximum signal within the anatomical regions of interest in the image.
Histogram
What is noise measures as
signal to noise ratio
-A high SNR indicates little noise in the image. Image noise has an inverse relationship to contrast. Increased noise decreases image contrast
a comparison between the actual exposure and the proper exposure received by the image detector.
Deviation Index (DI)
Describes how much of the patient is imaged in the matrix
Field of view (FOV)
which of CR and DR has less patient dose
DR less exposure to pt.
Requires binary machine language
Two symbol alphabet
need a 0 and 1 to create some image
Direct
no step of light
Indirect
is using light
out of indirect and direct which captures better image
direct captures better quality image because 1 less step
out of CR and DR which has the better image
DR
Analog voltage values are measured at a chose sampling frequency and a analog wavelength
how image is read
Sampling
each sampled piece now gets a value of 0 or a 1
quantification
when you increase sampling what does that do to the quality of the image
increases quality of image
pixel pitch and size is dependent on :
Matrix size and image receptor size
The physical distance between pixels; generally measured from center to center.
pixel pitch
determined number of assigned gray shades to pixel value
Bit Depth
Greater bit depth yields:
greater range of gray shades
Greater bit depth increases:
size of data set and volume of data for image processing
determines number of density values
-affects density and contrast of system
Pixel Bit depth
image file size is affected by:
Pixel size
matrix
bit depth
DICOM
Digital imaging and communications in medicine
-digital standard for imaging
Gray scale bit depth
ranges from 8 to 32
image processing information
-point processing
-local processing
-geometric processing
window leveling
up and down (brightness)
Window width
Left and right (contrast)
adjusting input image with output image
point processing operations
tail or spike in histogram
-Densities outside the imaged anatomy
-background information
-Usually eliminated or will skew the graph
Graphic representation of all of the pixel brightness values
in the image in the order of their brightness
Histogram
what might cause a histogram error
from shielding or prosthesis
under or over exposure conditions compensated for by shifting histogram to align with reference histogram
rescaling
-acquired histogram compared to reference histogram
-produces consistent image appearance regardless of exposure
- dose creep
histogram rescaling
-adjustments to image contrast
-produces contrast look according to reference contrast scale for exam view
Look up table
what color would bone be
high atomic number (white)
-high pass filtering edge enhancement
- low pass filtering/smoothing
-unsharp masking or blurring
- spatial location filtering
local processing operations
Under or over exposure conditions compensated for by shifting histogram to align with reference histogram
Rescaling
