Since 1983 we have been evaluating the image quality of mammography films by using a "phantom".  A phantom is a plastic block that attenuates the x-ray beam in the same way as a typical human breast.  Test objects of different sizes and shapes are embedded in the block. The test objects represent malignancies or breast structures: micro-calcifications, fibrils, ductal structures, and tumor-like masses.

In 1988 a phantom became available that allowed quantification of an image, based on the test objects observed in an image of the phantom.  We found over 35% of the mammography machines we tested in 1988 failed to image the minimum number of test objects that the American College of Radiology had specified for their mammography accreditation program.

A state law passed in 1989 that required mammography machines to be designed specifically for mammography. Several machines designed for general radiographic work were put out of the mammography business at that time. Steady improvement in phantom image quality was noticed (see graph below). In 1993 rules that required quality control testing of the mammography system, supervision of the program, and set standards for operators of the equipment took effect. Since that time, the phantom image fails in only about 1% of the machines that are tested.

Graph timeline:
1989 - state mammography law passes requiring special machines for mammography
1991 - annual inspections of mammography facilities begin
1992 - Michigan receives media attention for mammography program
1993 - administrative rules on mammography take effect