Method and apparatus for using film density measurements of a radiograph to monitor the reproducibility of X-ray exposure parameters of a mammography unit

Apparatus for using optical densities of a film to measure at least one of a set of exposure parameters of an x-ray beam produced by a mammography unit to create a radiographic image of a breast phantom on a first area of said film, said exposure parameters comprising kilovoltage peak, half value layer and milliampere seconds, said apparatus comprising:

• a mammography beam quality phantom exposed simultaneously with said breast phantom by said x-ray beam to create a radiographic image of said mammography beam quality phantom on a second area of said film;
• said mammography beam quality phantom comprising a body having a first section and a second section, wherein said first section is formed from a first material having a first thickness and said second section is formed from a second material having a second thickness, wherein said first and second materials and said first and second thicknesses are selected so that said first and second sections have different x-ray attenuation properties wherein said different x-ray attenuation properties cause an x-ray beam from a single x-ray beam exposure transmitted through said first and second sections to produce on said film a first optical density for said first section and a second optical density for said second section, wherein a comparison of the measured values of said first and second optical densities, adjusted for the effect of film processing, results in an optical density difference, which difference is reflective of at least one of said set of exposure parameters.

A method for using optical densities of a control film and a test film to monitor a mammography system for changes in x-ray exposure parameters used to radiograph a breast phantom, said mammography system comprising a mammography x-ray unit having an automatic exposure control sensor, film screen cassette combination and an automatic film processor, comprising the steps of:

• generating a control film comprising the steps of:
• positioning said breast phantom over said automatic exposure control sensor of said mammography unit;
• providing a mammography beam quality phantom positioned away from said automatic exposure control sensor;
• shielding a first portion of the test film along one edge of the film from x-ray energy used for imaging the breast phantom;
• radiographing both phantoms simultaneously with a single x-ray exposure from said mammography unit operated at a preset kilovoltage peak, automatic exposure control setting, and known target-filter combination;
• exposing said shielded edge of the control film with visible light from a sensitometer to create a stepwise density pattern having calibrated and numbered steps;
• and
• processing the control film in a film processor to develop images of the breast phantom, the mammography beam quality phantom and the sensitometric pattern;
• generating a test film comprising the steps of:
• positioning said breast phantom over said automatic exposure control sensor of said mammography unit;
• providing a mammography beam quality phantom positioned away from said automatic exposure control sensor;
• shielding a first portion of the test film along one edge of the film from x-ray energy used for imaging the breast phantom;
• radiographing both phantoms simultaneously with a single x-ray exposure from said mammography system operated at a preset kilovoltage peak, automatic exposure control setting, and known target-filter combination;
• exposing said shielded edge of the test film with visible light from a sensitometer to create a stepwise density pattern having calibrated and numbered steps;
• and
• processing the test film in a film processor to develop images of the breast phantom, the mammography beam quality phantom and the sensitometric pattern;
• measuring optical densities of the images of the breast phantom and the mammography beam quality phantom on the test and control films;
• measuring optical densities of the sensitometric patterns on the test and control films;
• adjusting the optical densities of the images of the breast phantom and mammography beam quality phantom of the test film for differences in film processing in relation to the optical density values of similarly numbered density positions of the sensitometric patterns of the test and control films;
• and
• detecting changes in the exposure parameters of the mammography system by comparing the adjusted optical densities of the breast phantom and mammography beam quality phantom on the test film with the control film.