2 Digital FluoroscopyInput phosphoroutput phosphor electronic signal beam splitter video signal TV monitorVideo signal is a voltage signal which varies continuously ADC (Analog Digital Converter) converts analog to digital
3 What are some negatives of conventional (film) radiography? Difficult to image both soft tissue and bony structures in same imageDifficult 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 anatomyImage is processed permanent as isAmount of time needed to processArchiving/storage/ acquisition issues
4 Similarities between CR and film radiography Same x-ray tube and generatorStill select optimum kVp and mAsAccurate positioningUse cassette or image receptorThere is still a latent image which can be processed into a manifest image
5 DIFFERENCES Imaging plate rather than intensifying screen/film Photostimulable phosphor-europium activated barium fluorohalide phosphor200 screen speed equivalentPhosphors absorb photonsCapable of wider latitudes = better visualization of soft tissues and bone
6 DIFFERENCES CONT. Film made of minute strands of black metallic silver Digital image = rows and columns called a matrix
7 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 grayVoxel represent the volume of tissue of the patientMatrix preferred size – 2048 x2048 or4, 194,304 pixelsLarger matrix = more pixels and pixels are smaller
8 IMAGE ACQUISITIONExit(remnant radiation) IP photons absorbed photoelectrically by phosphor LATENT IMAGEExposed 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
9 Manifest image is a matrix composed of pixels with assigned brightness levels IP scanned again with intense light to erase plate10,000 readings
10 Histograms/window or index levels/algorithms Histogram-graphic display of digital dataUsed to evaluate adequacy of IP to x-raysPMT needs to be adjusted to compensate for errorsWindow/index levels –Algorithms – math formulas needed to formulate image construction based on anatomy imagedRadiographer must indicate correct procedure so the correct algorithms are used.
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