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.