The mammography quality standards act (MQSA) was established in 1994 and commit all mammography facilities in the United States to be accredited by an approved body and undergo annual inspections by state or federal inspectors. The Food and Drug Administration (FDA) is responsible for implementing MQSA and to develop national mammography regulations.

On October 19, 2001, Philips Medical Systems completed an acquisition strategy through its purchase of Marconi Medical Systems.
The History of Marconi Medical Systems
2001 Royal Philips Electronics and Marconi plc announced that Philips has agreed to acquire Marconi Medical Systems for $1.1 billion.
2000 Marconi introduces Infinite Detector Technology for Mx8000 multislice CT scanner, which acquires an unprecedented 16 simultaneous slices with sub-millimeter isotropic accuracy.
1999 At RSNA, Picker International unveils the new Marconi Medical Systems name and corporate vision.
1998 Picker International acquires the Computed Tomography Division of Elscint Ltd, immediately positioning Picker at the forefront of major global CT suppliers.
1986 Picker produces the industry's first 1.0T MR imager.
1981 Picker is sold to General Electric Co. Ltd. of England (GEC). Picker merged with Cambridge Instruments, GEC Medical, and American Optical to form Picker International.
1967 The name changed from Picker x-ray to Picker Corporation. Picker acquired Dunlee.
1946 The Dunlee Corporation started in Chicago by Dunmore Dunk and Zed. J. Atlee to meet demand for quality x-ray tubes and special purpose tubes.
1915 James Picker Company formed in New York City offering sales and service of x-ray equipment, film and accessories.

Mass is the quantity of matter, the unit is kilogram (kg).

The mass number is the total number of protons and neutrons (also total nucleon) in the nucleus.

See also Atomic Mass Unit, Atomic Mass.

A match describes an activity loss in perfusion and ventilation scintigraphy.