DIGITAL RADIOGRAPHY

Digital Fluoroscopy

• Input phosphoroutput 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

• 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

• 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