Michael Danos, 77, a theoretical physicist who invented and patented medical imaging devices, died Aug. 30 at Georgetown University Hospital after a stroke. He lived in Washington.

For 40 years before his federal retirement in 1994, Dr. Danos was a physicist at the National Institute of Standards and Technology and its predecessor agency, the National Bureau of Standards.

He held eight patents in electronics and medical instrumentation, and he was author of five books and more than 160 scientific papers.

Since 1990, he had been a visiting scholar at the University of Chicago.

Dr. Danos was born in Riga, Latvia. His homeland was occupied initially by the Soviet Union and then by Germany during World War II.

He avoided conscription by the Latvian, Soviet and German armies and he studied electrical engineering in Riga and later Dresden, Germany, during the war.

After the war, while living in a displacement camp in Hannover, Germany, he received a master's degree in electrical engineering at the University of Hannover. He received a doctorate in physics at the University of Heidelberg.

He then came to the United States, and from 1952 to 1954, he was a postdoctoral research associate at Columbia University. In 1954 he moved to Washington and joined the staff of what then was the National Bureau of Standards.

In the 1970s and 1980s, Dr. Danos's work included relativistic heavy ions.

This work became an important element in the development of the billion-dollar heavy-ion collider being commissioned at Brookhaven National Laboratory on Long Island, N.Y.

In the early 1990s, while on the staff at the National Institute of Standards and Technology, Dr. Danos founded Rayex Co. in Gaithersburg, where he developed high-power X-ray tubes for medical imaging and industrial radiology.

His marriages to Helga Danos and Victoria Danos ended in divorce.

Survivors include his wife, Sheila Fitzpatrick of Washington and Chicago; two daughters from his first marriage, Johanna Danos of Ellicott City and Tamara Danos of Costa Mesa, Calif.; a son of his second marriage, Arpad Danos of Chicago; two brothers; and two grandchildren.