When the mammography unit is initially placed in service or if the entire compression system is replaced, the medical physicist must perform the compression paddle deflection test as part of the mammography equipment evaluation. This test should also be performed periodically throughout the life of the unit or when an old full field compression paddle is replaced with a new one. Periodic testing and testing of a new full field compression paddle may be done by a radiologic technologist or other qualified person but should be performed in consultation with the medical physicist. The frequency of periodic testing should be established with reference to the manufacturer’s maintenance-specifications and the use considerations (wear and tear) unique to the facility. If the excessive deflection of the compression paddle is identified during a mammography equipment evaluation, it must be repaired before the paddle is used on patients. If the facility identifies the problem at any other time, it should be repaired as soon as possible because this problem may compromise clinical image quality. Manufacturers may specify procedures and frequency for testing the compression paddles in their maintenance instructions and adherence to these recommendations should normally be adequate; however the responsibility for compliance still remains with the facility.
One acceptable method for performing the compression paddle deflection test is:
- If the mammographic unit does not have a read-out of compression force, cover the bucky with a towel and place a bathroom scale on the towel.
- In order to prevent measuring deflection of the image receptor support (bucky) or the scale, place a support plate on top of the scale or directly on the towel if a scale is not used. The support plate should be made of a rigid material (e.g., acrylic sheet) that is large enough to completely cover either the scale or bucky.
- Place the test object on the support plate with its base along the chest wall edge of the compression plate. Examples of test objects include: compressible foam materials (e.g. T-200 Minicel foam (10 X 18 cm for the 18 X 24 cm paddle and 14 X 22 cm for the 24 X 30 cm paddle, thickness of 4 to 6 cm) or tennis or rubber balls taped together in the shape of an equilateral triangle (3 balls for the 18 X 24 cm paddle and 6 balls for the 24 X 30 cm paddle)
- Apply a compression force of 111 newtons (25 pounds).
- Measure the distance of each corner of the paddle from the support plate.
- Subtract the smallest distance from the largest distance to determine the deflection. The difference must be 1.0 cm or less to pass the test.
Paddles designed not to be flat and parallel to the breast support table during compression should not be evaluated using the procedure described above, but rather must meet the manufacturer’s design specifications and maintenance requirements.