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Our Goal

*. Our Goal. Obtain the best possible image. *. Best Possible Image?. What is our goal?. *. A Diagnostic Image Using the Least Radiation. A prettier picture does not provide benefit to our patient Prettier pictures often involve additional radiation. Contrast.

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Our Goal

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  1. * Our Goal • Obtain the best possible image

  2. * Best Possible Image? • What is our goal?

  3. * A Diagnostic Image Using the Least Radiation • A prettier picture does not provide benefit to our patient • Prettier pictures often involve additional radiation

  4. Contrast • difference in density between areas on radiograph • Your ability to see contrast depends on • Subject contrast • Contrast sensitivity of receptor • Scatter radiation • Monitor / Viewing conditions

  5. * Subject Contrast • difference in x-ray intensity transmitted through various parts of subject • Depends on • thickness difference • density difference • atomic number difference • radiation beam energy

  6. Subject Contrast & Radiation Quality * • high energy beam = lower subject contrast • long scale contrast (less difference between areas receiving varying amounts of radiation) • low energy beam = high subject contrast • short scale contrast (more black & white; more difference between areas receiving varying amounts of radiation) • low energy beam increases patient dose

  7. Photon Phates * • Nothing • Photon passes unmolested • Absorbed • completely removed from beam • ceases to exist • Scattered • change in direction • no useful information carried • source of noise X

  8. Primary vs Scatter • Primary = Good photon • Scatter = Bad photon Focal Spot “Good” photon Patient “Bad” photon X Receptor

  9. Image Noise Caution! Image Noise

  10. Noise • covers valid information with distracting or obscuring garbage

  11. Image Noise • covers valid information with distracting or obscuring garbage Caution! Image Noise

  12. Another Example

  13. Painting Image One Dot at a Time

  14. Noise makes it hard to see low contrast differences

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