Unit One: CR Flashcards
Digital Imaging
Any image acquisition process that produces an electronic image that can be viewed and manipulated on a computer
Teleradiology
Moving images via telephone lines to an from remote locations
Early PACS developed by _____ to send images between VA hospitals.
Military
What year did the military develop PACS?
1980s
Where and when did the teleradiology concept begin?
Canada in the 1950s
Primary advantage of digital imaging
Increased contrast resolution
Increased contrast resolution
Increased ability to distinguish between and to image similar tissues as being separate and having different shades of gray
How many levels of gray is CR capable of producing?
10,000
Advantages of Digital Imaging
PACS and Informatics
Image archive and retrieval
Post processing/image manipulation
Teleradiology
Share images/reports
Electronic medical record
Reduced patient turn around time
No film, darkrooms, processing chemicals
Modular Transfer Function (MTF)
ARRT DEFINITION
The ability of an imaging system to preserve signal contrast as a function of spatial resolution
Modular Transfer Function (MTF)
BRIAN DEFINITION
How accurately a system converts the x-ray inputs signal into a useful output image
Spatial Resolution and MTF have what type of relationship?
Direct
Objects with higher spatial frequency are (more difficult/easier) to image than those with lower spatial frequency
More difficult
Detective Quantum Efficiency (DQE)
A measure of x-ray absorption efficiency of the IR
Imaging plate layers
- Protective layer
- Phosphor layer
- Reflective layer
- Conductive layer
- Support layer
- Light shielding layer
- Backing layer
Protective layer
A very thin, tough, clear plastic for protection of the phosphor layer
Phosphor layer
A layer of photostimulable phosphor that “traps” electrons during exposure.
Reflective Layer
Sends light in a forward direction, towards the photodetector when released in the cassette reader
Conductive layer
Absorbs and reduces static electricity
Support layer
Semi-rigid material that gives the imaging sheet some strength
Light shielding layer
Serves to protect the imaging plate from light leaks, which can erase or degrade the image that is stored within the phosphors
Backing layer
Soft polymer that protects the back of the cassette
Europium
An activator that is responsible for electrons being trapped in the metastable state
Histogram
A graphical display of the pixel intensity distribution for a digital image
Histogram Analysis
Identifies the useful pixels “values of interest” which are used for processing
Rescaling
Adjusts the pixel values to fit the normal histogram of the body part and adjust for small exposure errors
Lookup Table
Used to give the image just the right amount of brightness and contrast
Bit depth
The number of gray each pixel is capable of displaying.
The number of bits per pixel.
Dynamic range
What the system is capable of
Dose creep
Overexposure of patients due to the ability of the software to make corrections
Exposure latitude
The amount of exposure error that still results in a quality image at an appropriate dose
Window width
Used to adjust the contrast of an image
Window level
Used to adjust where on the scale the window level is set (brightness of an image)
Annotation
Allows text to be added to an image
Image flip
Allows for flipping of an image for proper interpretation
Image Inversion
Allows for the changing of the image from negative (bone is white) to positive (bone is dark)
Magnification
Used to better view smaller objects in an image
Edge Enhancement
Increases the contrast along the edge of a structure through a software function
Smoothing
A function to suppress noise that results from averaging of the frequency of each pixel with surrounding pixel values to remove high-frequency noise
Equalization
Software function that allows underexposed areas (light areas) to be made darker and overexposed areas (dark areas) to be made lighter.
Region of interest
A quantitative function of digital imaging that allows for the pixel value of a selected area of interest to be calculated
What was first gen digital radiography?
Computed Radiography
Contrast Resolution
The smallest exposure change or signal difference that can be detected by the IR. Directly related to Dynamic Range.
Control of Contrast Resolution
The number of shades of gray a digital image can display is controlled by bit depth and dynamic range of the pixels.
Scale of contrast on digital images is also ‘predetermined’ by you when ______
when you select a thumbnail of the anatomy
This predetermined contrast is adjusted by a
Histogram
Each pixel contains bits of information, and the gray level is determined by ___
How many photons struck the imaging plate in that particular location
Spatial Resolution
Refers to the amount of detail present in any image
Thinner phosphor layer = ______ SR
Higher
What contributes to SR in CR?
Sampling frequency of the laser and the pixel size of the display monitor
A thinner diameter laser = _____ sampling frequency
Higher
How is SR measured?
Lp/mm
Nyquist Theorem
States that when sampling a signal, the sampling frequency must be greater than twice the bandwidth of the input signal so that the reconstruction of the original image will be nearly perfect
Thinner laser = ____ SR
Higher
Dynamic Range underexposure and overexposure
50% under
200% over
Exposure Latitude
The amount of exposure error that still results in a quality image at an appropriate dose
Exposure Index
Radiation exposure to an IP that is given in numerical values
Objects with higher SR are more difficult to image than those with lower SR
DQE from highest to lowest
DR, CR, Film
Detective Quantum Efficiency (DQE)
How efficiently a system converts the x-ray input signal into a useful output image
Higher DQE receptors require _____ x-rays to produce an image. This translates to _____ pt. dose
Less
Less
If FOV remains constant and the size of the matrix is increased, pixel size and pitch will _____, which _____ SR
Decrease
Increase
How is pixel pitch measured?
Center to center
How is pixel size measured?
Edge to edge
What is the size of the matrix determined by?
The number of pixels
Smaller pixels = _____ matrix = _____ SR
Larger
Improved
As the matrix in the monitor remains the same, the pixel size must _____ to fit into the matrix
Decrease
Always use the smallest cassette size (FOV) possible for the ________ SR
Greatest
A thinner diameter laser will create a
Higher sampling frequency
A thinner laser will create a _____ number of samples/information/data
Greater
What are CR system speeds a reflection of?
The amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser.
The amount of photostimulable luminescence given off by the IP is determined by
The speed at which the plate is scanned by the laser source (alters speed class)
The wider the laser, the faster the speed class.
The thicker the phosphor later, the faster the speed class
The slower the speed class, the greater the amount of radiation required.
Generally, a higher laser speed, or speed class, will result in _____ ____ due to greater light spread.
Less SR
The wider the laser, the _____ the speed class, due to more light being released from the PSP during processing. This will _____ SR due to a greater light spread.
Faster
Decrease
The thicker the phosphor layer, the ____ the speed class due to more light being released from the PSP. This will ____ SR due to greater light spread.
Faster
Decrease
A thicker phosphor layer is more efficient at absorbing radiation so _____ is required
Less radiation
