Transcript DIGITAL RADIOGRAPHY - Montgomery College

DIGITAL RADIOGRAPHY
Digital Fluoroscopy
• Input phosphoroutput phosphor
electronic signal beam splitter video
signal  TV monitor
• Video signal is a voltage signal which
varies continuously 
• ADC (Analog Digital Converter) converts
analog to digital
What are some negatives of
conventional (film) radiography?
• Difficult to image both soft tissue and bony
structures in same image
• Difficult to differentiate between the subtle
differences of soft tissues (shades of gray---long
contrast, low contrast)
• Unable to gather quantitative info about
attenuation characteristics of anatomy
• Image is processed permanent as is
• Amount of time needed to process
• Archiving/storage/ acquisition issues
Similarities between CR and film
radiography
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Same x-ray tube and generator
Still select optimum kVp and mAs
Accurate positioning
Use cassette or image receptor
There is still a latent image which can be
processed into a manifest image
DIFFERENCES
• Imaging plate rather than intensifying
screen/film
• Photostimulable phosphor-europium
activated barium fluorohalide phosphor
• 200 screen speed equivalent
• Phosphors absorb photons
• Capable of wider latitudes = better
visualization of soft tissues and bone
DIFFERENCES CONT.
• Film made of minute strands of black
metallic silver
• Digital image = rows and columns called a
matrix
MATRIX, PIXEL AND VOXEL
• Matrix made up of pixels ( picture element)
• Pixels = x-ray intensity at that location and given
a numeric value for the shade of gray
• Voxel represent the volume of tissue of the
patient
• Matrix preferred size – 2048 x2048 or
4, 194,304 pixels
• Larger matrix = more pixels and pixels are
smaller
IMAGE ACQUISITION
• Exit(remnant radiation) IP photons
absorbed photoelectrically by phosphor
LATENT IMAGE
• Exposed IP reader unit (digitizer)
scanned to release energy as light 
photomultiplier tube (PMT) collects,
amplifies and converts light to electronic
signal to ADC manifest image
• Manifest image is a matrix composed of
pixels with assigned brightness levels
• IP scanned again with intense light to
erase plate
• 10,000 readings
Histograms/window or index
levels/algorithms
• Histogram-graphic display of digital data
– Used to evaluate adequacy of IP to x-rays
– PMT needs to be adjusted to compensate for errors
• Window/index levels –
• Algorithms – math formulas needed to formulate
image construction based on anatomy imaged
– Radiographer must indicate correct procedure so the
correct algorithms are used.
IP or IR
IR/IP
• List some characteristics of an IP
• What speed film screen system is
associated with a typical IP?
• How does this affect technique?
DR
• DIRECT READOUT DIGITAL
RADIOGRAPHY
• FLAT PANEL DIRECT CAPTURE
DETECTOR
• CHARACTERISTICS?
• COMPARE INDIRECT CONVERSION TO
DIRECT
Post processing
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Subtraction
Contrast enhancement
Edge enhancement
Black and white reversal
Compensate for errors
Misc.
• Resolution =2.5 line pairs per millimeter
• Window level = adjusts image brightness
• Window width = adjusts radiographic
contrast
• Quantum mottle
• Artifacts
• Scatter
• PACS
• HIS
• RIS