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Facility Scorecard Article Posted to the FDA Mammography Website 9/27/06

Establishing and/or Changing the Phantom Image Test
Operating Levels

Objective: The objective of this article is to provide help to facilities that perform screen-film (S-F) mammography for initially establishing the operating levels for their phantom image test and for changing the operating levels in a “for cause” situation.

Note: The following suggestions apply to facilities using S-F mammography units. For full-field digital mammography (FFDM) units, facilities should refer to the unit’s quality control manual.

Establishing operating levels for the first time

Prior to performing mammography with new equipment for the first time, your medical physicist (MP) must evaluate your mammography unit and film processor. During or immediately following the mammography equipment evaluation, when the mammography unit and processor are operating under optimal conditions, your MP should be able to assist you in establishing baseline operating levels for the background density on your phantom images. He/she may recommend an exposure technique that will result in:

  • a background density of 1.80 or higher, and
  • a density difference (contrast) with which you can expect to get a minimum of 0.40 under optimized technique factors and processing conditions.

Typically, most current mammography S-F combinations are designed to produce a density difference value of approximately 0.50 or higher when the background density is approximately 1.80. If the density difference value on your phantom image is below 0.40, you should contact your MP regarding how to proceed. Using these baseline values will help in optimizing the image quality of your mammogram films. Additionally, it is also helpful to determine baseline values from phantom images produced over a five-day period; that will help stabilize the operational levels. An average of the values from the five phantom images should produce the most appropriate operating limits.

Once you start performing mammography after setting your baseline operating levels for background density and density difference, you should ask your lead interpreting physician whether the density and contrast of the mammograms are acceptable. If the interpreting physician feels the mammograms are of adequate quality, your operating levels are sufficient and you should continue to use them. However, if your lead interpreting physician recommends changes, you may want to contact your MP for help in determining new operating levels.

Changing operating levels for background density and density difference

Once you have set your operating levels, you should keep them the same unless your lead interpreting physician suggests changes to achieve a difference in density or contrast. Any significant changes occurring in the equipment might also require you to reevaluate the operating levels. Some examples that would lead you to consider reestablishing your existing operating levels are:

  • Lead interpreting physician decision to increase clinical image optical density
  • The replacement of the mammography x-ray unit or film processor
  • Changes in manufacturer or type of film, screen, or processing chemistry

Note: You should not reestablish the operating levels on the recommendation of processor maintenance personnel without consulting with your MP, as the MP is responsible for the technical quality of the image.

Before considering a change in operating levels due to replacement of the mammography x-ray unit or the film processor, consult with your MP about keeping the same operating levels. A small change in system settings, such as the density control, may allow you to continue to use your present operating levels. If your MP recommends new operating levels, inform your lead interpreting physician of the change. If new operating levels are established, ask him/her whether the new levels are producing an acceptable density and contrast for quality mammograms.

If you change the manufacturer or type of film, screen, and/or processor chemistry, you may need to set new operating levels. If you are considering a change in film or screens, you should contact your MP before making the change. During your discussion, your MP may recommend a change in operating levels for your new S-F combination that will work better with a higher background density and density difference. As mentioned earlier, you should always notify your lead interpreting physician about any intended change(s), and immediately following a change, confer with your interpreting physician regarding the quality of the mammograms.

Cautions about changing operating levels

You should not “automatically” change operating levels when problems arise with any of your mammography equipment. If the background density or the density difference start to fluctuate or drift toward or exceed the operating level action limits, contact your MP for help in determining the source of this change. If the change is caused by a problem with a component of your imaging system, you need to fix the problem so that your facility can perform high quality mammography. Adjusting or repairing equipment is a much better approach than frequent changes in the operating levels to accommodate a problem that could adversely affect the quality your facility’s mammograms. When you consider changing operating levels, you should be sure that the change is best for quality mammograms.

The following Question was submitted to the ACR on 2/21/06:

Prompted by a facility question of how & when to re-establish phantom aims, my question to the ACR:  I have not been able to find guidance on establishing new aims for phantom controls in neither the ACR manual or the FDA Regs.  I can find reasons why to establish new Phantom aims but not how.  Some facilities are doing multiple day averages and some are taking the 1st phantom as their new aims.  Can you help? 

ACR Response:

Email response from:

Diane A. Zawacki, R.T.(R)(M)(QM)

American College of Radiology

Program Specialist

Breast Imaging Accreditation

Phone: (800) 227-6440 ext. 4948

Fax: (703) 648-9176

 

Neither the ACR nor FDA have guidance on "re-establishing" phantom aims.  The ACR frequently receives telephone calls from technologists regarding this very same issue.  We think the technologists are confusing this with re-establishing processor QC operating levels.

 

The ACR follows the information provided in the FDA's Policy Guidance Help System.  Please share this information with your facilities.  They will be most interested in #4 and #12 below.

 

From the Policy Guidance Help System:

Citation:

900.12(e)(2)(i),(ii),(iii),(iv):

 

Question 4:  Under what circumstances should I establish a new baseline optical density (OD) operating level?

 

A new baseline OD operating level may need to be established when switching to a new type of film or if the AEC density selector settings in the mammographic unit have been re-calibrated during servicing of the unit.  Before changing operating levels, check that there isn't an underlying problem that needs to be corrected.  A new level may be established if the interpreting physician(s) has/have made an intentional decision to modify background optical densities of the clinical images.  For example, many facilities are choosing to increase film density to take advantage of the film's increased contrast at higher ODs.

 

Question 12:  If the optical density (OD) for the weekly phantom test falls below 1.20  (and/or changes by more than ± 0.20 from the established operating level), must the unit be recalibrated or can we adjust the density setting to obtain a 1.20 OD?

 

If the OD at the center of the phantom image falls below the required minimum of 1.20 (and/or changes by more than ± 0.20 from the established operating level), the facility should follow pathway A, B, or C; below, based on the situation at the facility:

 

  1. If the film is of a different type (e.g., switch from Min-R 2000 to Min-R E) from the previous week's passing test, the facility should establish new phantom QC operating levels.

  2. If the film emulsion batch is unchanged from the previous week's passing test:

  1. Ensure that the phantom is exposed using typical clinical conditions and that the position of the phantom and, where appropriate, the position of the AEC detector have not changed from that used for prior images.

  2. Reevaluate the daily processor performance and make sure the processor is properly optimized according to the film manufacturer's specifications.

  3. If the facility has been tracking mAs, check the function of the mammography unit by comparing the mammography unit's current mAs output with values obtained for previous phantom images.  If the mAs has changed by more than 15%, and the facility has been using the same kVp, the same mammography unit density setting, and the processor is operating within its action limits, then the medical physicist should be called to check the entire imaging chain, including the mammography unit.  If the mAs has not changed by more than 15% then proceed with step 4.   If the facility has not been tracking mAs, the facility should consult with its medical physicist for what to do next.

  4. If no problems are found in steps 2 and 3, adjust the density control setting to obtain an optical density of at least 1.20 at the center of the phantom image (or obtain an optical density within ± 0.20 of the established operating level).

  5. Adjust the density control setting used clinically to be consistent with the changes made in step 4.

  1. If the film is of the same type but of a different emulsion batch from the previous week's passing test, the facility should follow the steps as described in B 1 through 5.

 

If the optical density again falls below 1.20 (and/or changes by more than ± 0.20 from the established operating level) the next time the weekly phantom test is performed, the facility should follow the appropriate pathway (based on the film emulsion used) from the following three options:

 

a. If film of a different type (e.g., switch from Min-R 2000 to Min-R E) is used, the facility should establish new phantom QC operating levels.

 

b. If film of the same emulsion batch is used (assuming the same kVp and mammography unit density settings are used, and the processor is operating within its action limits), the facility should consult with its physicist and check the entire imaging chain before performing mammograms. 

 

c. If film of the same type (but not of the same emulsion batch) is used, the facility should repeat steps B 1 through 5. 

       

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