Slice of History: CT Scanner Invented: Nov. 25, 1975

The U.S. government awards a patent for a device that allows doctors, for the first time, to see cross-sections of tissue and organs inside the human body.

The inventor of the machine, known as a CT scanner—short for computerized tomography—is Robert Ledley, a biomedical researcher at Georgetown University and one of the first scientists to see the true potential of computers for  medical diagnosis.

Ledley's first love was physics, but he had become a dentist at his father's insistence that he go into a more secure line of work. He combined the two, applying mathematics to the emerging field of dental prosthetics. His research gained national attention, including an AP story about him headlined, "Mathematics Used to Keep False Teeth in Place."

The real turning point in his career, however, came after the Korean War when Ledley began working at the National Bureau of Standards in Washington D.C. At the same time, his wife Terry became a programmer for that agency's new electronic computer.

It was Ledley's introduction to the world of computers and he soon realized how important a role they could play in diagnosing medical problems.

By the mid-1950s, he had become an engineering professor at George Washington University and began teaching one of the first courses in computer programming. In 1970, he moved to Georgetown University where he became increasingly interested in developing a device that would use computer technology to let doctors see inside a body without needing to open it up.

A British researcher, Godfrey Hounsfield, had created a scanner that could look inside a person's head; Ledley believed he could make one that could scan the entire body.

Working with a young machinist, Ledley designed his scanner, then had the parts taken to a local car dealership where they were dressed up with a fresh coat of paint.  Once all the pieces were put together in a basement laboratory at Georgetown, he began testing the scanner on a human skull filled with fresh calf brains.

Within a month, doctors used the machine to save the life of a four-year-old boy who had been brought into the emergency room after a weekend fall off his bike. The CT scanner was able to spot bleeding in the boy's brain; if the doctors had waited until Monday to treat him, he likely would have died.

The Journal of the American Medical Association described Ledley's invention as a "remarkable and fundamentally new technique." Not surprisingly, other hospitals wanted their own scanners and, in response, Ledley started a company that built and sold them for 300,000. Not long after being awarded the patent, he sold his company to Pfizer.

With his CT scanner widely acknowledged as one of the 20th century's major advances in medical diagnosis and treatment, Ledley was inducted into the National Inventors Hall of Fame in 1990. Seven years later, President Bill Clinton awarded him the National Medal of Technology and Innovation.

Robert Ledley died of Alzheimer's disease in July, 2012.  His prototype for the first CT scanner is in the Smithsonian.

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