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Mammographic X-Ray Instrument Calibration Range
Data acquisition system for NIST mammographic x-ray instrument calibration range.
The Ionizing Radiation Division in the Physics Laboratory established a national standard for radiation exposure from x-ray beams used in mammography and operates a facility for calibration of exposure meters in these beams. One of the critical parameters in mammographic procedures is the x-ray exposure to the breast. The exposure, directly related to the radiation dose to the breast, should be kept to a minimum while maintaining adequate diagnostic quality in the recorded image. Inspectors of the mammography facilities need radiation exposure measuring instruments that have accurate calibrations, traceable to national standards, for x-ray beams that are found in practice. Although NIST has developed and maintained national x-ray exposure standards and has participated in international comparisons of these standards over many decades, these traditional standards have been for filtered beams from x-ray machines with tungsten anodes. The machines used in mammography have molybdenum, or more recently rhodium, anodes so as to produce filtered x-ray spectra much more optimally tailored for high image quality with low exposure. Due to significant differences in x-ray spectra from machines with tungsten anodes and those from molybdenum or rhodium anodes, it was decided that traceability to the national standard for mammography should be available through calibrations in molybdenum or rhodium generated beam qualities. The NIST standard mammography x-ray range was developed in collaboration with the Center for Devices and Radiological Health of the FDA. NIST can provide 17 beam qualities for x rays from molybdenum and rhodium anodes (see Table VIII.7), which span those needed for instrument calibration and proficiency tests in this important area. The standard has been disseminated to secondary calibration laboratories, to inspectors, to the medical physics community and to instrument manufacturers. The accuracy of all radiation exposure measurements in approximately 11,000 U.S. mammography facilities will now trace back to the NIST standard. The NIST national standard for mammography has been directly compared to other NIST primary x-ray standards and has been compared internationally at mammographic energies. For information about the Mammography Quality Standards Act (MQSA) see FDA/CDRH's online publication of Mammography Matters.
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Inquiries or comments:
s.seltzer@nist.govOnline: September 1997 - Last update: June 2003 |
