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DIGITAL IMAGING

DIGITAL IMAGING. DIGITAL IMAGING. TERMINOLOGY. Film digitizer Digital radiography Digital fluoroscopy Dynamic range Matrix Pixel Imaging plate Histogram Algorithms Window level Window width TFT CCD. Post-processing image enhancement Latitude Analog Digital Image acquisition

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DIGITAL IMAGING

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  1. DIGITAL IMAGING

  2. DIGITAL IMAGING

  3. TERMINOLOGY • Film digitizer • Digital radiography • Digital fluoroscopy • Dynamic range • Matrix • Pixel • Imaging plate • Histogram • Algorithms • Window level • Window width • TFT • CCD • Post-processing image enhancement • Latitude • Analog • Digital • Image acquisition • Image processing • Image display • Raster pattern • Laser • Photomultiplier tube • a-Selenium • ADC

  4. ANALOG VS. DIGITAL

  5. ANALOG VS. DIGITAL

  6. SIMILARITIES AND DIFFERENCES FILM-SCREEN IMAGING DIGITAL & CR IMAGING • Need to select exposure factors • Accurate positioning • Use of accessory devices • IR receives radiation after passing thru patient • Latent image is produced and enhanced by the use of phosphorescence • Latent image is chemically processed • Limited dynamic range (30:1) • No post processing possible • Storage and retrieval issues • Need to select exposure factors • Accurate positioning • Use of accessory devices • IR receives radiation after passing thru patient • Latent image is produced (CR) and enhanced by the use of phosphorescence • Wide dynamic rage (1000:1) • Post Processing Enhancement is possible • Processing time reduced • Storage and retrieval easier

  7. COMPUTED RADIOGRAPHY

  8. IMAGING PLATE Protective layer: Thin clear plastic that protects the phosphor layer Phosphor layer: this active layer contains the photo-stimuable-phosphor (barium fluorohalide phosphors) that react to x-ray exposure Reflective layer: reflects light forward when the plate is in the reader Conductive layer: absorbs the electrons released during exposure and reduces static electricity Color layer: absorbs stimulating light but reflects emitted light Support layer: semi- rigid layer that provides support Barcode label: allows technologist to use patient/exam identifying information

  9. PSP IMAGING PLATE(CR)

  10. CR Phosphor Plates ABSORPTION EMISSION LASER STIMULATION ELECTRON TRAP ELECTRON TRAP X-RAY LIGHT

  11. LATENT IMAGE (CR) • Formed by x-ray interaction with PSP • Ionizes phosphors, releasing electrons • Electrons trapped in crystal lattice of phosphor • Latent image is formed • Remains until processed by a reader • But does begin to decay so must be “read” in a timely fashion

  12. IMAGE PROCESSING

  13. IMAGE PROCESSING • PSP plate exposed to radiation • Electrons are trapped in phosphor layer • Plate is exposed to a red laser light • As electrons are released, a blue light is emitted • Blue light is captured and recorded by PMT • Image is sent to monitor for display • PSP plate is exposed to intense white light for erasure

  14. IMAGE PROCESSING

  15. IMAGE DISPLAY

  16. Computed Radiography

  17. CR Imaging-Image Acquisition

  18. DIRECT DIGITAL IMAGING

  19. TYPES OF DIRECT DIGITAL IMAGING

  20. DIRECT DIGITAL IMAGING

  21. DIRECT DIGITAL IMAGING Flat panel detector consists of plate covered with amorphous selenium (a-Selenium). This material absorbs x-rays and converts them to electrons. These electrons are stored in the TFT

  22. DIRECT DIGITAL IMAGING

  23. TECHNIQUE CONSIDERATIONS • kVp Dependent, need mAs to saturate optimally • Now COMPUTER controls CONTRAST • Higher kVp to stimulate electron traps

  24. 80 kVp 200mAs 10 mAs 80 kVp Note Quantum Mottle

  25. Histograms are used to plot density of data, and often for density estimation: estimating the probability density function of the underlying variable. The total area of a histogram used for probability density is always normalized to 1. If the length of the intervals on the x-axis are all 1, then a histogram is identical to a relative frequency plot. For x-ray purposes, a histogram tells how often a certain degree of gray is seen in the image.

  26. To Produce Quality Images For Film/Screen Radiography or Digital/CR Radiography: The same rules, theories, and laws still apply and can not be overlookedSID, Inverse Square Law, Beam Alignment, Tube-Part-Film Alignment, Collimation, Grid, Exposure Factors: kVp, mAs, Patient Positioning

  27. Quality Images Patient positioning • Accounts for 85% of the total number of repeat exposures. • Has a direct affect on exposure technique.

  28. COLLIMATION CRITICAL • As the computer reads the density value of each pixel- it is averaged into the total • Close collimation= Better contrast • Bad collimation= more grays and less detail

  29. NEXT WEEK……….

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