Tuesday, March 19, 2013

CR Quality Control #5 - Sharpness

This test ensures the display and image processing systems are operating within normal specifications.  This test should be performed monthly or after servicing of the CR reader.

Procedure:
  1. Erase your dedicated test IP
  2. Place a lead apron on the floor of your x-ray room (use same room that baseline image was performed in)
  3. Place test IP on lead apron
  4. Place phantom on cassette (same orientation as baseline image)
  5. Raise the x-ray tube to maximum height, center, and open collimation about 1" past edges of test IP
  6. Use the same technical factors that produced the baseline image (check monthly log for exposure factors) and make an exposure
  7. Annotate exposure indicator number and which CR reader was used
  8. Compare the line pairs/mm on the new image to that of the baseline phantom image

According to the user manual for this phantom, the copper filter within this phantom produces a large amount of scatter which will reduce the actual visibility of detail in our test image, so it shouldn't be used to determine system resolution.  My hospital will need a stand-alone line-pair resolution test pattern for that determination, so check your manual to see if the same is true of your phantom.

When at all possible, use the magnification tool for each workstation to compare the new image to the baseline.  Record any variances, and if a moire pattern is observed, you may need to repeat your phantom exposure prior to recording your observations.



Note: the image on my blog is dramatically reduced in resolution compared to that visible by the radiologist's monitor in the reading room.


Other posts in this series:

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