Digital Radiography


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Presentation for a Radiographic Exposure class.

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  • Digital Radiography

    1. 3. <ul><li>Computed radiography (CR) which is cassette based. </li></ul><ul><li>Direct Digital Radiography (DR) which is cassette-less. </li></ul><ul><ul><li>Charge-coupled Devices </li></ul></ul><ul><ul><li>Indirect Conversion </li></ul></ul><ul><ul><li>Direct Conversion </li></ul></ul>
    2. 4. <ul><li>Uses photostimulable storage phosphor imaging plates </li></ul><ul><li>Uses existing tube equipment setup </li></ul><ul><li>Needs special cassettes </li></ul><ul><li>Uses a special cassette reader </li></ul><ul><li>Has a computer workstation, viewing station, and if hard copies are needed, a printer </li></ul>
    3. 5. <ul><li>Protective layer </li></ul><ul><ul><li>Insulates IP from handling trauma </li></ul></ul><ul><li>Phosphor layer </li></ul><ul><ul><li>Holds the photostimulable phosphor </li></ul></ul><ul><li>Support layer made of polyester </li></ul><ul><ul><li>The base on which the other layers are coated </li></ul></ul><ul><li>Conductor layer </li></ul><ul><ul><li>Grounds the IP eliminating electrostatic problems </li></ul></ul><ul><li>Light shield layer </li></ul><ul><ul><li>Prevents light from erasing data on the IP </li></ul></ul>
    4. 8. <ul><li>Is a cassette-less system </li></ul><ul><li>Uses a flat panel detector, or a charge-coupled device connected to a computer </li></ul><ul><li>Needs new equipment installation. </li></ul>
    5. 9. <ul><li>This is one type of indirect DR </li></ul><ul><li>It uses Gadolinium Oxysulfide as its X-ray scintillator </li></ul><ul><li>It uses optical lenses to input the light from the scintillator screen onto the CCD </li></ul>
    6. 10. <ul><li>Uses Cesium Iodide or Gadolinium Oxysulfide as the X-ray scintillator </li></ul><ul><li>Uses an amorphous Silicon photodiode to capture light and convert it into an electrical signal </li></ul>
    7. 11. <ul><li>This is a portion of an X-ray detector’s a-Si thin film transistor. </li></ul>
    8. 12. <ul><li>Uses a micro-plated electrode </li></ul><ul><li>Uses an amorphous Selenium photoconductor </li></ul><ul><li>Uses a hydrogenated amorphous silicon (a-Si:H) thin film transistor </li></ul>
    9. 13. <ul><li>Image Processing </li></ul><ul><li>Toleration of Overexposure </li></ul><ul><li>Sensitivity </li></ul><ul><li>Data Clipping </li></ul><ul><li>Spatial Frequency Processing </li></ul><ul><ul><li>Edge enhancement </li></ul></ul><ul><ul><li>Image blurring </li></ul></ul><ul><li>Collimator Edge Identification </li></ul>
    10. 14. <ul><li>A histogram is generated by dividing a scanned area into pixels and determining the signal intensity for each pixel </li></ul><ul><li>The histogram will be compared to the look-up table </li></ul>
    11. 15. <ul><li>CR and DR Imaging plates do not have the typical D log E curve, rather they have a straight line characteristic curve </li></ul><ul><li>The processing computer compares the image receiver data to the look-up table, and is able to compensate for overexposure </li></ul><ul><li>This opens the door for ALARA violations if a tech is purposely setting higher than necessary techniques </li></ul>
    12. 16. <ul><li>Manufacturers have designated a means to ensure adequate IP exposure levels </li></ul><ul><li>The unit of measurement differs from manufacturer to manufacturer </li></ul><ul><li>Fuji uses an S# and a S# of 200 equals 1mR of exposure </li></ul><ul><li>Kodak’s system is the exposure index and 2000 equals 1mR of exposure </li></ul><ul><li>Agfa uses a log median exposure (LgM) and a speed class </li></ul>
    13. 17. <ul><li>In most cases, the IP has more information stored on it than the display system allows </li></ul><ul><li>Exposure data that falls above and below useful levels can be left out </li></ul><ul><li>Also, data which the system deems as clinically irrelevant can be left out </li></ul>
    14. 18. <ul><li>EDGE ENHANCEMENT </li></ul><ul><li>IMAGE BLURRING </li></ul><ul><li>At times, a post-processing algorithm can be used on high noise images to blur the mottled noise into the background. </li></ul>
    15. 19. <ul><li>Artifacts unique to CR / DR can occur during Acquisition, Post-Acquisition, or Display </li></ul><ul><li>This is an example of an image taken with an Agfa cassette backwards. </li></ul>
    16. 20. <ul><li>Phantom images can result from incomplete IP erasure </li></ul><ul><li>Scratches from damaged plates </li></ul><ul><li>Light spots caused by dust </li></ul><ul><li>Fogging due to CR plates being more sensitive to scatter than film </li></ul><ul><li>Quantum mottle </li></ul><ul><li>Heat blur </li></ul><ul><li>Dropout artifacts </li></ul>
    17. 21. <ul><li>Algorithm artifacts </li></ul><ul><li>Dropout artifacts from laser imaging and other laser artifacts </li></ul><ul><li>Histogram errors </li></ul>
    18. 22. <ul><li>Density / Brightness adjustments </li></ul><ul><li>Contrast window width adjustments </li></ul><ul><li>Electronic magnification adjustments </li></ul><ul><li>Image enhancement artifacts </li></ul>