Dr. Mansfield, who grew up in a London slum and was told by a school guidance counselor that he had no future in science, was a printer’s apprentice before his curiosity and determination led him to a life in science.
In the 1970s, he devised methods to produce three-dimensional images from MRI machines that allowed physicians to peer into the inner workings of the body in real time.
Before noninvasive MRI machines came into widespread use in the 1980s, patients often underwent potentially dangerous X-ray examinations or had tissue surgically removed for study. Dr. Mansfield volunteered to be the first person to undergo an MRI scan to prove its effectiveness and safety.
“His work is correctly credited with changing the face of modern medicine,” Colin Blakemore, then the chief executive of Britain’s Medical Research Council, said in 2003.
By the time Dr. Mansfield was awarded the 2003 Nobel Prize in physiology or medicine, which he shared with the U.S. scientist Paul Lauterbur, millions of MRI scans were being conducted each year on patients around the world.
The science behind MRI has been known since the 1940s, when physicists discovered that the nuclei in certain atoms spin in predictable ways when subjected to a magnetic field. The nuclei also gain energy when exposed to radio waves. When the radio waves are turned off, the nuclei continue to emit radio signals that can be measured and used to identify different atomic structures.
Dr. Mansfield had focused his early research on using those principles to identify objects beneath the Earth’s surface. But in the early 1970s, he learned that Lauterbur, then at the State University of New York at Stony Brook, had used MRI techniques to produce two-dimensional images.
By measuring signals from hydrogen atoms, Lauterbur was able to draw a visual distinction between ordinary water and “heavy water,” which has a different atomic structure. He later produced internal images of living clams and mice.
Dr. Mansfield built on Lauterbur’s discoveries, using mathematical methods to develop fast, efficient ways to transform the magnetically charged atomic radio signals into three-dimensional images. In time, MRI scans could be used to identify different tissues and organs throughout the body, becoming immensely important in medicine.
“Most people don’t think about where MRI scanners come from,” Dr. Mansfield told Britain’s Daily Mirror newspaper in 2009. “But I feel very pleased and proud when I receive letters from patients, thanking me for saving their lives.”
Peter Mansfield was born Oct. 9, 1933, in London. His father was a gas fitter, his mother a waitress. The family often lived in poverty.
Because of German air raids on London during World War II, Dr. Mansfield was evacuated three times and spent part of the war years with a family in Devonshire. He compiled a collection of fragments from German rockets — “I knew all about rockets from the wrong end,” he said. But the boy received little academic encouragement and left school at 15 to become a printer’s apprentice.
He attended night school and at 18 found a job with the rocket propulsion department of Britain’s Supply Ministry. After serving two years in the British army, he received a scholarship and studied physics at what was then Queen Mary College at the University of London. He received a bachelor’s degree in 1959 and a doctorate in 1962.
Dr. Mansfield spent two years as a postdoctoral fellow at the University of Illinois at Urbana-Champaign before joining the University of Nottingham faculty in 1964. He retired in 1994 but continued to work at his laboratory for many years after.
He held patents on several key parts of the MRI machine, which made him well off. He was knighted in 1993 and published an autobiography, “The Long Road to Stockholm,” in 2013.
Survivors include his wife of 54 years, the former Jane Kibble; two daughters; and four grandchildren.
Soon after it was announced that Dr. Mansfield and Lauterbur had won the Nobel Prize, another early MRI researcher, Raymond Damadian, took out full-page advertisements in The Washington Post and the New York Times headlined "The Shameful Wrong That Must Be Righted."
Damadian, the founder of a U.S. company that produces MRI machines, complained that his contributions had been slighted and charged the Nobel committee with an "inexcusable disregard for the truth."
Most experts accused Damadian of sour grapes and said the modern MRI grew directly out of the discoveries of Lauterbur and Dr. Mansfield.
“In my opinion, Paul Lauterbur and Peter Mansfield deserve the Nobel Prize,” Alex Pines, a scientist at the University of California at Berkeley, told The Post in 2003. “In a leap of creative genius, they came up with the gradient imaging methodology that forms the basis for what today is known as MRI.”