Thursday, March 21, 2013

CR Quality Control #6 - Shading Correction

This test checks to see if the CR scanning laser has uniform intensity across the entire image plate.  It should be performed monthly, or after service to the CR reader's light guide and/or optics.  While this test can be visibly inspected on digital monitors, it can only be quantitatively performed using hard-copy dry laser film with a densitometer.

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. Print a hard-copy of the phantom image
  9. Measure the optical density of the middle measuring point and document
  10. Measure the optical density of the outer-lying points and document
 

The acceptable variance in optical density of the outer two measuring points (compared to the center) is +/- 10%.  If measurements exceed this variance, repeat the test.  Call a service engineer if still outside acceptable standards.


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