New NIST Facility Will Improve Accuracy of Radiation Measurements in Mammography

Women undergoing mammography exams at accredited U.S. facilities soon will have much improved assurance of receiving proper X-ray exposures thanks to a new radiation standard and instrument calibration facility at the Commerce Department's National Institute of Standards and Technology in Gaithersburg, Md.

This new NIST facility will allow the operators and inspectors of more than 10,000 U.S. mammography centers to trace the accuracy of their X-ray exposure measurements to the primary mammography X-ray standards at NIST. "One of the critical parameters in mammographic procedures is the X-ray exposure to the breast," explains Michelle Johnson, a physicist in NIST's Ionizing Radiation Division. "The radiation exposure to the breast should be kept to a minimum while ensuring adequate diagnostic quality in the recorded image."

Johnson, along with colleagues Paul Lamperti, Julian Sparrow and Manfred Osti, developed the new calibration facility, which makes NIST only the second national standards laboratory in the world to provide primary standards for mammography.

The calibration facility was established to assist the U.S. Food and Drug Administration implement the Mammography Quality Standards Act of 1992. This law requires the FDA to set up a certification and inspection program for all U.S. mammography clinics. The instruments used by the FDA inspectors to measure the X-ray exposure from the clinical units will be calibrated using standards traceable to the new NIST reference X-ray beams.

For many decades NIST has maintained national standards for medical diagnostic X-ray beams generated by tungsten-anode machines. NIST now can meet important needs in measurement quality that are specific to mammography units, nearly all of which generate X-ray beams from molybdenum or rhodium anodes, with added filtration to improve the beam characteristics. These dedicated mammography X-ray units produce a higher image quality with a lower radiation dose to the breast. The new reference X-ray beams available at NIST include anode and filter combinations of molybdenum and rhodium, and cover the range of beam qualities used in mammography clinics.

The primary standard that defines and measures the reference X-ray beams will be used to establish the calibration factor for each radiation measuring instrument sent to NIST for calibration in this new specialized facility. Anyone wanting to calibrate an X-ray exposure measuring instrument for mammography beams may send the instrument to NIST. Typical users of this service are expected to be secondary calibration laboratories, inspectors of mammography units and instrument manufacturers. The new facility will begin performing calibrations in early 1996.

For further information on the new facility, contact Michelle Johnson, C229 Radiation Physics Building, NIST, Gaithersburg, Md. 20899-0001, (301) 975-2014.

A non-regulatory agency of the Commerce Department's Technology Administration, NIST promotes U.S. economic growth by working with industry to develop and apply technology, measurements and standards.