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
on 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 Mr. 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.
Mr. Ledley was an early advocate of computer-based medical
diagnostics. In 1959, he published a paper in the journal Science
titled "Reasoning Foundations of Medical Diagnosis." It had a 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 Mr. Ledley's.
Robert Steven Ledley was born on June 28, 1926, 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 University. Mr. Ledley 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.
After receiving his DDS from New York University in 1948, Mr.
Ledley enrolled as a graduate student at Columbia to study physics.
He received his master's degree in physics in 1950.
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, Mr. Ledley was in the Army Dental
Corps, assigned to a research unit at Walter Reed Army Medical
Center in Washington.
Mr. 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. …