Two primary things can cause the exposure indicator to vary during regular operating procedures; the photomultiplier tube can be out of specifications as well as the exposure output of the x-ray tube. In order to identify early variances, we must perform monthly tests to ensure proper calibration.
Supplies needed:
The exposure indicator should match or be very close to that of the baseline reading. If it does not match, you need to calculate the percentage of difference. Acceptable variation is +/- 20%. Use this formula to calculate:
If results are outside 20% variation, repeat the exposure. If the second exposure is outside variation, there could possibly be a problem with the generator or the CR reader which would warrant a service call. Once the problem has been identified and corrected, a new baseline must be established, and monthly testing needs to continue with comparisons to the new baseline. Note the new exposure indicator and date on the image and in the QC log.
Note - "exposure indicator" refers to a general term that varies between manufacturer (S#, EI, LgM, etc.)
CR Quality Control #1 - Screen Cleaning
CR Quality Control #2 - Creating a Baseline Phantom Image
CR Quality Control #3 - Exposure Indicator Calibration
CR Quality Control #4 - Contrast Evaluation
CR Quality Control #5 - Sharpness
CR Quality Control #6 - Shading Correction
CR Quality Control #7 - Laser Jitter
CR Quality Control #8 - Image Artifacts and Noise
CR Quality Control #9 - Exposure Linearity
CR Quality Control #10 - Residual Image Testing
Supplies needed:
- Test phantom
- Lead apron
- Monthly log of prior tests
- Most recent baseline exposure (see "Creating a Baseline Phantom Image")
- Erase your dedicated test IP
- Place a lead apron on the floor of your x-ray room (use same room that baseline image was performed in)
- Place test IP on lead apron
- Place phantom on cassette (same orientation as baseline image)
- Raise the x-ray tube to maximum height, center, and open collimation about 1" past edges of test IP
- Use the same technical factors that produced the baseline image (check monthly log for exposure factors) and make an exposure
- Annotate exposure indicator number and which CR reader was used
- Compare to baseline exposure indicator number
The exposure indicator should match or be very close to that of the baseline reading. If it does not match, you need to calculate the percentage of difference. Acceptable variation is +/- 20%. Use this formula to calculate:
If results are outside 20% variation, repeat the exposure. If the second exposure is outside variation, there could possibly be a problem with the generator or the CR reader which would warrant a service call. Once the problem has been identified and corrected, a new baseline must be established, and monthly testing needs to continue with comparisons to the new baseline. Note the new exposure indicator and date on the image and in the QC log.
Note - "exposure indicator" refers to a general term that varies between manufacturer (S#, EI, LgM, etc.)
Other posts in this series:
CR Quality Control #1 - Screen Cleaning
CR Quality Control #2 - Creating a Baseline Phantom Image
CR Quality Control #3 - Exposure Indicator Calibration
CR Quality Control #4 - Contrast Evaluation
CR Quality Control #5 - Sharpness
CR Quality Control #6 - Shading Correction
CR Quality Control #7 - Laser Jitter
CR Quality Control #8 - Image Artifacts and Noise
CR Quality Control #9 - Exposure Linearity
CR Quality Control #10 - Residual Image Testing
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