AEC Performance Quality Control Test

Questions Key Words/Related Topics

Citation:

900.12(e)(5)(i)(A)(B)(C): Annual quality control tests. Facilities with screen-film systems shall perform the following quality control tests at least annually:

(i) Automatic exposure control performance.

(A) The AEC shall be capable of maintaining film optical density within ±0.30 of the mean optical density when thickness of a homogeneous material is varied over a range of 2 to 6 cm and the kVp is varied appropriately for such thicknesses over the kVp range used clinically in the facility. If this requirement cannot be met, a technique chart shall be developed showing appropriate techniques (kVp and density control settings) for different breast thicknesses and compositions that must be used so that optical densities within ±0.30 of the average under phototimed conditions can be produced.

(B) After October 28, 2002, the AEC shall be capable of maintaining film optical density (OD) within ±0.15 of the mean optical density when thickness of a homogeneous material is varied over a range of 2 to 6 cm and the kVp is varied appropriately for such thicknesses over the kVp range used clinically in the facility.

Discussion:

Question 1: If the AEC fails, can a facility use manual techniques until the unit is fixed? Would it require the physicist to come and recheck it or if the repairman did so would that be satisfactory?

Question 2: Do units with multiple AEC detectors have to have each detector tested individually?

Question 3: The regulations in 900.12(e)(5)(i) require that an x-ray unit pass an annual test for AEC performance over a range of 2 to 6 cm thick absorbers. If a unit is used clinically at combinations of kVp and filtration that include tissue thicknesses outside the 2 to 6 cm range, must it meet the AEC performance requirements at the thicknesses where it operates and must it be tested at those technique factors under the annual quality control requirements?

Question 4: During the annual physics survey, must AEC performance be tested for all equipment configurations used clinically by the facility or can it be limited to the contact configuration? What action limits apply?

Question 1: If the AEC fails, can a facility use manual techniques until the unit is fixed? Would it require the physicist to come and recheck it or if the repairman did so would that be satisfactory?

The answer to the first question is yes. According to 900.12(e)(5)(i)(A), if the physicist (or the facility) learns that the AEC cannot perform as required, the facility should first attempt to correct the problem by adjusting the density settings on the AEC. If that is unsuccessful, the facility may use manual mode technique charts. Manual mode would also be acceptable under the complete failure situation raised by the question. Hence, the facility can use manual techniques for 30 days while the non-functioning AEC is being repaired and can continue to use the unit on patients during this period.

Regarding the second question, because the AEC is considered to be a major component of the mammography unit, the physicist must recheck the unit after the problem has been corrected in accordance with 900.12(e)(10).

Question 2: Do units with multiple AEC detectors have to have each detector tested individually?

Where a mammography unit has multiple AEC detectors designed to function independently, each detector must be tested separately (e.g., different AEC detectors for the different size cassette holders or more than one independently selectable AEC detector in a single cassette holder). Where a mammography unit has multiple AEC detectors designed to function as a single unit, the AEC detector unit must be tested. For example, a single detector that can be moved to different positions needs to have the detector tested at only one of those positions. A system with three fixed detectors, each of which can be selected individually, needs to have all three detectors tested. A large field detector that automatically selects its active area needs to be tested only as a single detector.

Question 3: The regulations in 900.12(e)(5)(i) require that an x-ray unit pass an annual test for AEC performance over a range of 2 to 6 cm thick absorbers. If a unit is used clinically at combinations of kVp and filtration that include tissue thicknesses outside the 2 to 6 cm range, must it meet the AEC performance requirements at the thicknesses where it operates and must it be tested at those technique factors under the annual quality control requirements?

No, the unit is not required to meet the AEC performance specification outside the 2 to 6 cm range and the physicist is not required to test the AEC performance requirements for thicknesses outside this range during the annual survey. However, we strongly recommend that in addition to the required testing in the 2 to 6 cm range, the unit also be tested at all clinically used thicknesses outside this range and that the action limits specified in the regulations be applied to the extended test. If the unit cannot meet these action limits outside the 2-6 cm range, FDA recommends that a technique chart be developed showing appropriate techniques (kVp and density control settings) for the different breast thicknesses and compositions so that optical densities within +/- 0.30 (+/- 0.15 after October 28, 2002) of the average under phototimed conditions can be produced.

NOTE: After October 28, 2002, the technique charts referred to in the preceding paragraph may be used only for thicknesses outside the 2-6 cm range. For use of technique charts within the 2-6 cm range, see use of manual techniques when the AEC fails.

You should note that under the Equipment Evaluation outlined in 900.12(e)(10), an evaluation of the AEC under all conditions of use is required, not merely recommended. This is because 900.12(e)(10) mandates conformance with all pertinent aspects of 900.12(b) and (e). Under 900.12(b)(10), the AEC is required to be "operable" under "configurations provided." In this context, "operable," as applied to the AEC means that it must meet the density and reproducibility requirements of (e)(5)(i) within the range of 2 to 6 cm. If designed to operate outside that range, the unit must meet the manufacturer’s specifications over such additional ranges.

Question 4: During the annual physics survey, must AEC performance be tested for all equipment configurations used clinically by the facility or can it be limited to the contact configuration? What action limits apply?

During the annual physics survey, AEC performance in the contact configuration must be tested. The medical physicist does not have to test the other clinically used equipment configurations during the annual physics survey, see guidance on determining AEC performance during equipment evaluations. In the contact configuration, the action limit requires maintenance of the film optical density (OD) over the 2-6 cm thickness range within +/- 0.30 OD (+/- 0.15 OD after October 28, 2002) of the mean.

Key Words:

Screen-Film System

Annual Tests

Automatic Exposure Control

Automatic Exposure Control (AEC)

Mammography Equipment Evaluations