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DIGITAL RADIOGRAPHY PowerPoint PPT Presentation


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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.

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DIGITAL RADIOGRAPHY

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Digital radiography l.jpg

DIGITAL RADIOGRAPHY


Digital fluoroscopy l.jpg

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 l.jpg

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 l.jpg

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 l.jpg

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


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DIFFERENCES CONT.

  • Film made of minute strands of black metallic silver

  • Digital image = rows and columns called a matrix


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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


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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


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  • Manifest image is a matrix composed of pixels with assigned brightness levels

  • IP scanned again with intense light to erase plate

  • 10,000 readings


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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 l.jpg

IP or IR


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IR/IP

  • List some characteristics of an IP

  • What speed film screen system is associated with a typical IP?

  • How does this affect technique?


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DR

  • DIRECT READOUT DIGITAL RADIOGRAPHY

  • FLAT PANEL DIRECT CAPTURE DETECTOR

  • CHARACTERISTICS?

  • COMPARE INDIRECT CONVERSION TO DIRECT


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Post processing

  • Subtraction

  • Contrast enhancement

  • Edge enhancement

  • Black and white reversal

  • Compensate for errors


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Misc.

  • Resolution =2.5 line pairs per millimeter

  • Window level = adjusts image brightness

  • Window width = adjusts radiographic contrast

  • Quantum mottle

  • Artifacts

  • Scatter


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  • PACS

  • HIS

  • RIS


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