Digital Imaging Flashcards
_____ computers handle data composed of continuous signals (current)
analog
______ computers handle data in definite quantities (discrete numbers)
digital
______ connections are a simultaneous transmission
parallel
______ connections are slower, info is transferred in a sequence
series
Specialized peripheral computer processing units
-use memory to perform simultaneous mathematical calculations in parallel (simultaneously) at high Speeds
array processors
Extracts information without alteration
read memory
Replaces old memory with new information
write memory
Read only memory, basic operating instructions
ROM
Temp storage of info during use
RAM
Primary mathematical methods used to convert data to useful information (images)
Fourier Transmission
process of modifying pixel value by masking image through math calculations- pixel masked with density value, changes image quality
convolution
process of returning pixel values to their original level by a reverse process , info returns altered image to original state
deconvolution
Pixels increase, resolution _______
increases
Digital image qualities data characteristics are measured in:
frequency, contrast, noise
raw data, the measure of the total amount of contrast within image
frequency
high frequency, ______ contrast
high
low frequency, _______ contrast
low
subject contrast is high, data contrast is ______
high
signal to noise ratio- high ratio, _____ noise
little
signal to noise ratio- low ratio, ______ noise
high
high image noise, _______ contrast
low
low image noise, ______ contrast
high
filtering process to suppress frequencies to reassign an average gray scale value to each pixel according to its neighbor’s value
masking
amplifies or deletes higher frequencies- Reduces contrast / removes high frequency noise
low pass filtering
amplifies or deletes all frequencies, but a selected range Isolates data - localization of specific densities eg.) Isotope concentration in NM
band pass filtering
amplifies or deletes all frequencies, but high frequencies- Increases contrast
high pass filtering
window level controls _____
density (midpoint)
window width controls _______
contrast (range of visible densities on both sides of the midpoint/ window level)
progressive scanning
increases resolution by scanning 525 lines in ORDER = 1-2lp/mm
slow scanning
raster pattern- 5-7 lp/mm
pixel modification- gray scale expansion does what?
stretches the gray scale to enhance detail
pixel modification- histogram modification
reassigns pixels to different density values to equalize the number of pixels for each gray scale
digital filtering- masking
filtering process that assigns an average gray scale value for each pixel according to it’s neighbor’s value
Layers of the phosphor imaging plate
protective layer
phosphor layer
support layer
conductor layer
light shielding layer
quantum motle occurs due to what
underexposure (high S number)
The phosphors of a CR imaging plate do what?
stores the energy of exit x-rays until processed
The smallest picture element with one gray scale value
pixel
A histogram of pixel values is used to (3)
determine the level of exposure
determine the level of brightness of pixels in the image
make adjustments in brightness levels to improve image
The process of subtracting an earlier image from a later image
temporal subtraction
Manipulating the gray scale values of pixels in the image is called
Contrast enhancement post processing
Window levels can be adjusted to _____ for air and ______ for bone
-1000, 1000
Image noise makes an image appear
grainy
Regarding data acquisition, as the matrix size increases, data acquisition ______
decreases
as the resolution increases we can acquire less data
Pixel with volume
voxel
Spatial Resolution: Horizontal
Pixels going right to left
Spatial Resolution: Vertical
Pixels going up and down
Ensures that all equipment speaks the same language for output devices
DICOM
Ensures that all equipment speaks the same language for input and output devices
DICOM2
Digital Image display qualities are measured by (3)
density
contrast
resolution
Contrast in digital imaging measures what?
the differences between data values
CR imaging plate: phosphor layer
energizes during exposure- photostimulable phosphors
CR imaging plate: support layer is made of what?
polyester
CR Imaging plate: conductor layer
grounds plate to reduce static discharge- absorbs light to increase sharpness
Smaller the pixel, _______ spatial resolution
greater
Pre-Image processing: Sampling looks at what 2 factors
orientation to plate
number of projections on plate
What type of sampling adjusts the latitude and sensitivity for the image and is used for multi images on one plate
Fuji’s Exposure Data Recognition (automatic)
Adjusts latitude but sensitivity is fixed- image is centered but collimation is not equidistant from plate edges
Semi-automatic sampling
Latitude and sensitivity are fixed, will not correct exposure deficiencies (most like film screen)
Fixed sampling
X-rays are converted to electrical charge directly which is then converted to electrical pulses— then converted to an image matrix
DIRECT digital
TFT used in what?
Direct digital
Collects electric charge until gate is activated and signal is sent pixel by pixel
TFT in direct digital
IR plate holding a charge creates what?
fogging
inadequate exposure causes what?
quantum mottle
IR plate exposed to heat causes what?
heat blur
incorrect preprocessing selection causes what?
histogram error
Advantages of digital (4)
Image manipulation
Image storage
Image retrieval
Transmission of images
Disadvantages of digital
Patient exposure (single exposure)
Cost: Technology & Imaging Plates
Technology errors: Pre-processing selection
Decreased latitude for technical errors: Collimation & Positioning
Range of gray scale values that can be assigned to each pixel the number of signal values that the receptor is capable of capturing.
dynamic range
dynamic range of digital imaging
256 to 4096 shades of gray
Selected ranges of brightness values subtracted from the image producing an image with structures at those values subtracted from the image
image subtraction
Resolution of conventional film radiography
6-10 lp/mm
What is a flat-panel image receptor?
Detector for X-rays
How does the receptor recognize the exposure field?
By the number of electrons in detector element
What does the exposure level control?
Number of electrons, electrical charges collected by detector element
Why is it important to select the correct algorithm for a part?
Incorrect selection leads to information loss
gradation processing
fuji
tonescaling
Kodak
Multiscale image contrast algorithm
Agfa
graphically represent a collection of exposure values extracted from the receptor.
Histogram
must quantize, or turn, that continuous stream of electrons into unique values
ADC
An image is created after…
a histogram of the extracted image data is analyzed using one of two formats:
the greater the number of signal values that a receptor is capable of capturing=
the greater the receptor’s dynamic range.
if an image contains quantum noise is the image over or under exposed?
underexposed
Modifies value of pixel to enhance or suppress a visual image characteristic
Convolution / Deconvolution
Process of modifying pixel value by masking image through math calculations
Convolution
Process of returning pixel values to their original level by a reverse process
Deconvolution
The conversion of a radiographic image (film) post chemical processing
Image Digitalization
indirect conversion- CR or DDR?
Computed Radiography
Direct conversion- CR or DDR?
Direct digital radiography
casette based digital image receptors:
PSP photostimuable storage phosphor
Cassette-less digital image receptors:
-PSP photostimulable storage phosphor
-Flat Panel
-CCD (charge coupled device)
which company invented computed radiography?
FUJI
Which company uses photostimulable plates and a laser reader for their CR devices?
FUJI
Which company uses silicon flat panel and TFT’s for their CR devices?
Phillips, GE, Siemens
Which company use rare earth intensifying screens ans CCD’s for their CR devices?
SwissRay
What is the measure of data quality?
Contrast, frequency, noise
What are the qualities of a display image?
Brightness, contrast, resolution
What is frequency data?
Raw data; measure of total amount of contrast within the image
What is contrast?
Measure of differences between data values
High subject contrast =
=high data contrast
What is noise?
Random background information that does not contribute to image quality
What is the relationship between noise and contrast?
Inverse relationship, high noise decreases contrast
What is density/contrast?
Controlled by varying numerical values of each pixel
What is the human visual range for shades of gray?
32 or less shades of gray
What is the photon beam range for shades of gray?
1,000 shades
What is the contrast resolution for digital detectors?
Sensitive to almost 1,000 shades, greater contrast resolution
What is Window Level?
Density levels
What is Window Width?
Contrast levels
What are the factors to evaluate digital images?
Brightness, contrast, image blur, exposure indicator, image noise
What is Image Brightness in a digital image equivalent to?
Opposite density in an analog image
How is Contrast determined?
By the differences in adjacent densities within an image
What is Bone Gray Scale used for?
To visualize bony trabeculae by manipulating the digital image characteristic of contrast
What is Soft Tissue Gray Scale used for?
To enhance the difference between adjacent densities and see muscle, organs and fatty patterns better
What causes image blur in flat panel detectors?
Larger DELs.
How does increasing SID affect image blur?
Decreases blur.
How does increasing OID affect image blur?
Increases blur.
What are the factors that contribute to geometric unsharpness?
Focal spot size, SID, OID.
An image receptor’s ability to respond to exposure
dynamic range
the range of under- or overexposure that
can occur in producing an acceptable image
exposure latitude
