Automatic Exposure Control (AEC) Performance Testing – Annual Physics Survey and Mammography Equipment Evaluation
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.
(C) The optical density of the film in the center of the phantom image shall not be less than 1.20.
900.12(b)(10)(i),(ii)(A)(B),(iii): Automatic Exposure Control.
(i) Each screen-film system shall provide an AEC mode that is operable in all combinations of equipment configuration provided, e.g., grid, nongrid; magnification, nonmagnification; and various target-filter combinations.
(ii) The positioning or selection of the detector shall permit flexibility in the placement of the detector under the target tissue.
(A) The size and available positions of the detector shall be clearly indicated at the X-ray input surface of the breast compression paddle.
(B) The selected position of the detector shall be clearly indicated.
(iii) The system shall provide means for the operator to vary the selected optical density from the normal (zero) setting.
- What is meant by the terms “AEC”, “AEC mode”, “mean optical density”, and “configuration”?
- Can we continue to use technique charts?
- During the annual physics survey, how must the medical physicist test AEC performance and what action limits apply?
- During the mammography equipment evaluation, must the medical physicist test the AEC performance in all equipment configurations used clinically by the facility or can it be limited to the contact configuration? What action limits apply?
- Must medical physicists test all AEC detectors for AEC performance in mammography units with multiple AEC detectors and can the testing procedures be modified if the detectors are in the same cassette holder (bucky)?
- If the AEC performance test fails, does that automatically mean that the AEC is the cause of the failure?
- For purposes of AEC testing, are different image receptor sizes considered different “configurations”?
- The regulations in 900.12(e)(5)(i) require that an x-ray unit pass an annual test for AEC performance using 2, 4, and 6 centimeter thicknesses of a homogeneous material. If a unit is used clinically at combinations of kVp and filtration that include 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? What about AEC performance testing during a mammography equipment evaluation?
- A facility only performs screening mammography and never performs any magnification studies. Must the medical physicist test the AEC in the magnification configuration, even though the unit won’t be used in that configuration by that facility?
- A facility’s x-ray unit has a single AEC detector that may be moved to any of three positions along the chest wall to nipple midline of the breast. It cannot be placed under all areas of the breast. Would this meet the intent of the regulation?
- On the facility’s x-ray unit, the indication of the detector size and position options is projected onto the input surface of the compression paddle. However, when the paddle is moved up and down, the indicated detector size does not change with distance. Is this an acceptable indication under 900.12(b)(10)(ii)(A)?
- A facility’s unit indicates the selected position of the detector by the relative position of the adjustment lever located on one side of the unit and is only visible from that side of the unit. Does this meet the regulation?
- The position of the AEC detector is indicated by a knob under the bucky that can be felt but not seen. Does this satisfy the requirement of being "clearly indicated"?
- How much variability from the "normal" optical density setting must the system provide?
- Do all possible positions of the AEC detector have to be indicated on the compression paddle?
- The position of the AEC detector is infinitely variable over the entire area of the image receptor. How can the position of such a detector be identified on the compression paddle?
- Do paddles designed to be smaller than the full size of the image receptor have to display the AEC detector position and size?
- If the AEC performance is found to be outside the action limit during physicist testing, can a facility adjust the density control settings or 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?