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

• US 5,844,965 A
• Filed: 10/27/1997
• Issued: 12/01/1998
• Est. Priority Date: 11/24/1989
• Status: Expired due to Fees

• Current Assignee: Thomas Jefferson University (Main Line Health System)
• Original Assignee: Thomas Jefferson University (Main Line Health System)
• Inventors: Galkin, Benjamin M.
• Primary Examiner(s): WONG, DON KITSUN
• Application Number:
  US08/968,792
• Time in Patent Office: 400 Days
• Field of Search: 378/207
• US Class Current: 378/207
• CPC Class Codes: A61B 6/583 using calibration phantoms
• CPC Class Codes: G03D 13/007 Processing control, e.g. test strip, timing devices
• CPC Class Codes: H05G 1/26 Measuring, controlling or protecting measuring X-ray radiation G01T

Abstract

Apparatus and methods for using film density measurements of a radiograph to monitor the reproducibility of x-ray exposure parameters used by a mammography unit to make the radiograph are disclosed. Radiographic images of a breast phantom and a novel mammography beam quality phantom are formed simultaneously on a film using a single x-ray exposure. The mammography beam quality phantom comprises at least a first section and a second section formed from materials having different x-ray attenuation properties and thicknesses. For any combination of x-ray exposure parameters useful for film mammography, including the parameters of kilovoltage peak, dose, and half value layer, the material from which the first section is formed is selected so that the optical density produced by the first section of the mammography beam quality phantom is greater than the optical density produced by the breast phantom. The material from which the second section is formed is selected so that the optical density produced by the second section of the mammography beam quality phantom is less than the optical density produced by the breast phantom. The difference in optical density between the first and second sections of the mammography beam quality phantom, adjusted for the effect of film processing, is calibrated in terms of exposure parameters. Thus, the film density measurements of a radiographic image of a mammography beam quality phantom can be used to monitor the reproducibility of x-ray exposure parameters of a mammography unit in making repeat radiographs of a breast phantom.

Claims

1. A mammography beam quality phantom for use in monitoring mammographic kilovoltage peak, said phantom comprising:

a first portion formed from a first material having a first total linear attenuation coefficient; and

a second portion formed from a second material having a second total linear attenuation coefficient, wherein the selection of said first and second materials causes the difference in optical density of the images formed by said first and second portions to change in a known manner in relation to kilovoltage peak useful in mammography when the optical densities are corrected for the effects of film processing.

2. The phantom of claim 1, wherein said first and second portions have first and second thicknesses.

3. The phantom of claim 2, wherein said first and second thicknesses are selected so that the optical densities of the images formed by each of said first and second portions bracket the range of optical densities of the image of a breast phantom.

4. The phantom of claim 1, further comprising a third portion formed from a third material having a third attenuation coefficient.

5. A mammography beam quality phantom for use in measuring kilovoltage peak of an x-ray beam produced by a mammography unit to create a radiographic image of a breast phantom on a film, wherein said mammography beam quality phantom comprises a body having a first section and a second section, wherein said first section is formed from a first material and has 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 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 kilovoltage peak.

6. The mammography beam quality phantom of claim 5, further comprising a third section for use in place of said breast phantom.

7. The mammography beam quality phantom of claim 5 wherein image quality test objects are contained in one or more sections.

8. A mammography beam quality phantom for use in measuring half value layer of an x-ray beam produced by a mammography unit to create a radiographic image of a breast phantom on a film, wherein said mammography beam quality phantom comprises a body having a first section and a second section, wherein said first section is formed from a first material and has 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 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 half value layer.

9. The mammography beam quality phantom of claim 8, further comprising a third section for use in place of said breast phantom.

10. The mammography beam quality of claim 8, further comprising image quality test objects.

11. 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.

12. 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.