CR & DR Flashcards
WHAT IS DIGITAL IMAGING?
Acquisition of images to a computer rather than to film.
HOW IS DATA STORED USING DR?
Pixels/voxels
WHAT IS A BYTE?
Represents one character, digit or value.
Computers understand 0 or 1
1 Byte = 8 Bits
1 Kilobyte = 1024 Bytes
1 Megabyte = 1 Million Bytes
1 Gigabyte = 1 Billion Bytes
WHAT IS A PIXEL?
Arranged in a matrix
CR is at least 512 x 512
More modern systems are at least 1024 x 1024
4096 x 4096 is being developed
WHAT IS A VOXEL?
Product of the pixel area and slice thickness
WHAT IS THE DIGITAL GRAYSCALE?
Bit depth = shades of grey in the image
8 Bit = 256
10 Bit = 1024
12 Bit = 4096
Increase in Bits = an increase in shades of grey
WHAT IS A CCD?
Charged Couple Device
Used in indirect digital conversion
Converts light into electric signal
Involves image stitching pixels
WHAT ARE DIGITAL DETECTORS MADE FROM?
Amorphous Silicone (a-Si)
This converts x-rays into light photons
WHAT IS A TFT?
Thin Film Transistor
Converts light captured within the pixels into an electric signal
WHAT IS a-SE
Amorphous Selenium
Converts X-rays to a hole pair electron
Electron is driven into a pixel where TFT converts it into an electric signal
Temperature dependent (not too hot and not too cold
Sharper image due to no phosphor = no light scattering
WHAT IS CAD?
Computer Aided Detection
Picking up what we may miss by eye
Available in Mamo and developing in other clinical processes
WHAT ARE THE COMMON PRESET DIGITAL FUNCTIONS?
Pre-set processing algorithms
Brightness and contrast controls
Annotation
Rotation/Flip/Zoom
Shuttering
Measurements
Magnification
WHAT IS CR?
Techniques capturing images using storage phosphors within imaging plate
Phosphors cause the release of energy when exposed to infrared light.
Photo-stimulable luminescence occurs
WHAT IS PHOTO-STIMULABLE LUMINESCENCE?
Energy stored in the form of light
Intensity is proportional to number of x-ray photons absorbed by storage phosphor
EQUIPMENT INVOLVED IN THE USE OF CR
X-ray unit
Phosphor Cassette
Cassette reader
Review work station (monitor)
STRUCTURE OF THE IMAGING PLATE
210 micrometer phosphor layer
Phosphor layer is made of barium Flurohalide
Within the phosphor layer there are conduction and valance bands along with F traps
Light Reflection layer
Conductive Crystal layer reducing electrostatic charges, absorbs light increasing sharpness
Light shielding layer made of carbon
Barcode label providing serial number
WHAT ARE THE SEQUENCE OF EVENTS IN THE USE OF CR?
Barium flurohalide compounds are energised and release electrons when exposed to x-rays
Electron are trapped in F centres
After exposure to laser electrons are released from the F centres
Electrons are energised and emit light photons within 7 milliseconds
Light is detected by photomultiplier converting the signal into a time series
The signal is amplified and converted to a digital signal used ACD converter
Exposure to visible light erases the cassette
WHAT IS AN EXPOSURE INDICATOR?
Number displayed indicating exposure to the imaging plate
WHAT ARE THE DIFFERENT TYPES OF EXPOSURE INDICATORS?
KODAK - Exposure index (EI)
Every 300=change in exposure X2
AGFA - Log Median Value (LgM)
Every 0.3=change in exposure X2
Fuji - Sensitivity Number (S)
Every 100=2 X exposure
CR CHARACTERISTIC CURVE
Very wide latitude
Less radiograph repeats
WHAT ARE THE ISSUES RELATED TO USING DR?
Poor technique
Lack of understanding if exposure values
Using incorrect exposure factors
What is QDE/DQE?
Quantum Detector Efficiency
Measure of efficiency of converting x-rays to useful image signal
Higher QDE = Lower patient Dose
Advantages of CR
Can salvage up to 500% over exposure and 80% under exposure
Reduction in exposure factors without loss of image quality
Ability to view the same image in more than one place
Allow post processing features
Not as expensive as DR
Used with present X-ray equipment
