Week 10 Physics Review 36

Week 10 Physics Review 36 - X-ray Physics Review for 8th Q...

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X-ray Physics Review for 8th Q There are some key x-ray physics principals that will greatly impact image quality. Geometric Image Sharpness is impacted by Focal Spot Size Source to Image Distance Object to Image Distance Patient Motion Screen Speed
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Focal Spot Size Selection The x-ray beam is more tightly focused when the small focal spot is selected. The edge sharpness is improved because of less shadow or penumbra .
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Small Focal Spot Advantages Reduced penumbra OFD can be increased with minimal loss of detail. Disadvantages Lower mA selection due to tube heating Longer exposure times that can cause patient motion
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Screen and Film Speed The type of film and materials used in the screens will determine the speed of the film & screen combination. Small phosphors in the screens and grain in the film will produce sharper images.
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Screen and Film Speed Speed is determined by the system’s RSV or Relative Speed Value. High RSV needs less radiation but have lower recorded detail.
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SID and Sharpness Longer SID= Less Unsharpness
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The image taken with the small focal spot was better than the large focal spot. The small focal spot will help compensate for increased OFD.
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Motion If the patient moves or fails to hold their breath, the image will be blurry. Large patient may need to have films taken with the large focal spot.
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Modern High Frequency Units Located behind shielded barrier. High Frequency Generators allow much faster exposure times and reduced exposure compared to standard single phase machines.
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High Frequency Units Patient exposure is reduced 35%. The mAs can be
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Week 10 Physics Review 36 - X-ray Physics Review for 8th Q...

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