NEW YORK — Robert S. Ledley, a dentist turned biomedical researcher and computing trailblazer who invented the first CT scanner capable of producing cross-sectional images of any part of the human body, died Tuesday in Kensington, Md. He was 86.
The cause was Alzheimer’s disease, his son Fred said.
Nearly every field of medicine has been affected by the whole-body CT scanner, short for computerized tomography. ‘‘Many of the CT scanners we see in hospitals are based on the Ledley design,’’ said Joseph A. November, a professor of history at the University of South Carolina, who is writing a biography of Dr. Ledley.
Before the advent of CT scanning in the early 1970s, radiologists had limited tools. CT scanning gave them not only a far higher resolution than traditional X-rays, but also three-dimensional, cross-sectional images to work with, significantly reducing the need for exploratory surgery and its attendant risks. It also changed the way physicians follow cancers and their response to therapy.
Dr. Ledley was an early advocate of computer-based medical diagnostics, a half-century before medical residents began punching patients’ symptoms into online programs.
In 1959, he published a paper in the journal Science, ‘‘Reasoning Foundations of Medical Diagnosis.’’ It had broad impact in the medical field.
‘‘In the summer before I started medical school, I read that paper, and it was eye-opening,’’ said Dr. Alan N. Schechter, chief of the molecular medicine branch at the National Institutes of Health and a longtime colleague of Dr. Ledley’s. ‘‘The idea that computers could assist physicians in diagnosis and choice of therapy was a totally new understanding of the process of medical diagnosis.’’
Robert Steven Ledley was born in Flushing, Queens, N.Y. His father, Joseph, was an accountant; his mother, Kate, was a teacher. He attended the Horace Mann School and studied physics at Columbia. He hoped to pursue a career in physics, but his parents, worried about the scarcity of jobs in the field, urged him to become a dentist.
‘’His family said he could study physics as long as he also became a licensed dentist, so he could always make a living doing dentistry,’’ November said.
After receiving his DDS from New York University in 1948, Dr. Ledley enrolled as a graduate student at Columbia to study physics. He received his master’s degree in physics in 1950. His professors included Nobel Prize winners Enrico Fermi, Hans Bethe, and I.I. Rabi. ‘‘Rabi joked that Ledley was the only physicist who could pull a man’s tooth,’’ November said.
The year before, he had married Terry Wachtell, a music major at Queens College. At his urging, she switched to math, earned a master’s degree in the subject, and became a mathematics teacher.
In 1951, during the Korean War, Dr. Ledley was in the US Army Dental Corps, assigned to a research unit at Walter Reed Army Medical Center in Washington, where he worked on improving prosthetic dental devices.
Dr. Ledley set out to optimize the fitting of dentures by determining the mean slope of each tooth relative to the surface of the piece of food being chewed. His work, which married dentistry and physics, attracted national attention. An article by the Associated Press carried the headline ‘‘Mathematics Used to Keep False Teeth in Place.’’
After his discharge from the Army, he went to work in Washington at the National Bureau of Standards’ Dental Materials Section, where he also helped his wife get a job, as a programmer on the Standards Eastern Automatic Computer, or SEAC. It was she who introduced him to computers.
Fascinated by the machine, he learned to program the computer by studying the manuals and programs — punched out on long strips of paper tape — that his wife brought home. Before long, Dr. Ledley was working directly with the SEAC and focusing on the role that computers might play in solving biomedical problems.
‘‘I had previously realized that although, conceptually, physics equations could be written to describe any biomedical phenomenon, such equations would be so complex that they could not feasibly be solved in closed form,’’ he said in a 1990 talk. ‘‘Thus SEAC would be my panacea, because the equations would become tractable to numerical methods of solution.’’
In 1956, Dr. Ledley was hired as an assistant professor of electrical engineering at the George Washington University School of Engineering and Applied Science. That year, he began to collaborate with Lee B. Lusted, a radiologist and electrical engineer, on developing ways to teach physicians and biomedical researchers to use electronic digital computers in their work.
In 1960, Dr. Ledley founded the National Biomedical Research Foundation, a nonprofit organization dedicated to promoting the use of computing methods among biomedical scientists.
In addition to his son Fred, Dr. Ledley, who lived in Laurel, Md., leaves his wife; another son, Gary; and four grandchildren.
Dr. Ledley began his work on CT scanning in 1973. Building on earlier work by Sir Godfrey Hounsfield, a British engineer and Nobel Prize winner whose scanner could be used only on patients’ heads, Dr. Ledley assembled a group at Georgetown to build the Automatic Computerized Transverse Axial, or ACTA, scanner, which could scan the entire body.
‘’He’s best known for the CT scanner, but that was a natural outgrowth of a career of working in the field of pattern recognition, image analysis, and applications of computers to medicine,’’ Fred Ledley said.
In 1974, Dr. Ledley established the Digital Information Science Corp., selling the machines for $300,000 each. The next year, soon after obtaining the patent for the ACTA scanner, he sold his company to Pfizer, which briefly dominated the medical imaging market before losing ground to General Electric and Siemens.
Dr. Ledley was inducted into the National Inventors Hall of Fame in 1990 and awarded the National Medal of Technology and Innovation by President Clinton in 1997. The original prototype of the ACTA scanner is at the Smithsonian Institution.