Robert S. Ledley Biography (1926-)

Biophysicist and physiologist

Few scientists are talented enough to span more than one discipline, especially fields as diverse as medicine and mathematics. But Robert S. Ledley has done just that, with results that have revolutionized the way medical diagnosisis done.

Ledley was born in New York City in 1926, and earned a doctorate in dental surgery (D.D.S.) from New York University at the age of 22. One year later he earned a master’s degree in mathematical physics from Columbia University. After brief service in the U.S. Army, Ledley worked at the National Bureau of Standards and at Johns Hopkins University before becoming professor of physiology and biophysics and of radiology at the Georgetown University Medical School in 1970.

Ledley is credited with establishing the field of medical informatics,in which computers and other information technologies aid physicians in thediagnosis and treatment of patients. This foundations of this field lie in the 1959 paper of Ledley and Lee B. Lusted, "Reasoning Foundations of Medical Diagnosis," and in Ledley’s 1965 book Use of Computers in Biology and Medicine.

Ledley pioneered the use of medical databases in the 1960s, compiling with Margaret O. Dayhoff a list of all known sequences of proteins and nucleic acids. He also devised methods and instruments, including a motorized microscope with pattern recognition capabilities, that made it possible to scan chromosomes for abnormalities that cause Down’s syndrome and other disorders.

But Ledley’s most important invention was that of the automatic computed transverse axial (ACTA) scanner in the early 1970s. Building on work developed independently by South African physicist Allan M. Cormack and British engineerSir Godfrey Hounsfield, Ledley built a scanner that was capable of making cross-sectional images of any part of the human body. Such scanners have revolutionized the fields of radiology and medical imaging. The ACTA scanner set thecourse for modern computerized tomography (CT) machines.

Computerized tomography uses an array of detectors to collect information from beams of x-rays (in the case of medicine) that have passed through an object, such as a portion of a human body. These beams crisscross and scatter in many directions, and the information collected is then used by a computer to reconstruct the internal structures. The three-dimensional image is then displayed on a two-dimensional display device like a television or a photographicfilm. CT thus presents a nonintrusive way of seeing internal structures, andit can help locate tumors, hemorrhages, and infections without the need for exploratory surgery. CT has also proved useful in geophysics, where it is an important tool for investigating the deep structure of the Earth, and in atmospheric physics, where it can be used to map the liquid contents of clouds.

Computerized tomography relies heavily on complex mathematics and sophisticated computer algorithms in order to process the x-ray scattering results in areasonable amount of time. The prototype of Ledley’s original ACTA scanner isnow on display at the Smithsonian Institute in Washington, D.C.

Ledley holds over 60 patents, and was inducted into the National Inventors Hall of Fame in 1990. He was honored with the National Medal of Technology in 1997. Besides his professorship he is Director of the Medical and Biophysics Division in Georgetown University’s department of biophysics, and is editor-in-chief of four scientific journals.

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