CR Quality Control #2 - Creating a Baseline Phantom Image

Before you begin your routine monthly/semi-annual/annual radiographic equipment testing, you need to have a baseline image to compare it to.  The idea is that when you perform your actual tests in the future, you will not be able to tell whether or not your results are good or bad without having something to reference.  This method provides the measurable standard for calculations that will need to be performed later during testing.

We use one phantom with multiple test tools within it at the place I work now.  Select a medium-range kVp (I use 80 kVp).  You will also need an x-ray room with relatively low mA stations, a lead apron, and some kind of log to record your results in.  The vendor we purchased our phantom from provided us with a log.  We also took a brand new 14x17 cassette out of circulation and only use it for QC testing to reduce variability (and keep it with your phantom).

Procedure:

1. Erase your test CR cassette before any exposures are made.
2. Raise your x-ray tube to its maximum height and keep it above the floor (not directly over the table).
3. Place a lead apron on the floor directly under your central ray.
4. Place your CR cassette on top of the lead apron (without a grid cap).
5. Place your phantom on top of the cassette - make sure to orient the top of the phantom to the top of the cassette and keep this orientation for all future testing.
6. Center your x-ray beam to the phantom and cassette, leaving about one inch of light field outside the borders and onto the lead apron.
7. Select 80 kVp and 100 mA.  Try also setting 0.10 seconds and make an exposure.
8. Process the image and note the exposure indicator (S#, Exposure Index, or LgM)
9. If needed, adjust the time station so that you achieve an optimum exposure indicator number (*see note for proper levels of exposure indicator numbers)
10. Once you have the disired technical factors, annotate the date, exposure factors, and "baseline image" and send to PACS - your PACS administrator can create a folder for QC images 
11. Create an individual baseline image for each CR reader and log results.

*When attempting to expose your baseline image for optimum exposure indicator, you may need to consult the manufacturer guidelines or your physicist.  As a starting point, you can use the following:  

• S# = 200... if you double your time (or overall mAs), you will half your S#
• Exposure Index (EI) = 1800... if you double your time (or overall mAs), you will add 300 to your EI
• LgM = 2.1... if you double your time (or overall mAs), you will add 0.3 to your LgM

The Baseline exposure log should include the following information that will be referred to for later testing:

• Room number (that the test exposures are made in)
• SID
• Image plate identification number
• kVp
• mA
• time station
• Target exposure indicator number (this is your baseline S#, EI, or LgM)
• CR reader (number your readers if you have not already done so)

Keep your logs, test cassette and phantom/s in a safe place away from your other equipment to minimize risk of circulation with other supplies.  Next, we'll get into some of the monthly tests.

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