Dr. Mansfield was awarded the Nobel Prize in Physiology or Medicine in 2003, along with Paul C. Lauterbur, a professor at the University of Illinois at Urbana-Champaign. The two had worked independent of each other in studying magnetic resonance imaging.
Their research proceeded from an understanding that the nuclei of most atoms act as tiny magnets that line up when placed in a magnetic field. If the field is set at a specific strength, the atoms can absorb and emit radio waves.
Scientists initially used the technique, called nuclear magnetic resonance, or N.M.R., to study atoms and molecules, deducing properties from the emitted waves. In his early research, Dr. Mansfield developed N.M.R. techniques to study crystals.
Later, in 1972, as he worked to refine and sharpen N.M.R. data, he had a conversation with two colleagues about what applications such advances might lead to. He soon realized that if an object were placed in a nonuniform magnetic field — one that is stronger at one end than the other — scientists might be able to piece together a three-dimensional image of its atomic structure.
When Dr. Mansfield presented this research at a scientific conference the next year, an audience member asked him how his work compared to findings by Dr. Lauterbur that had been recently published in the journal Nature. Dr. Mansfield said he was not aware of that work.
Both scientists had developed techniques for turning N.M.R. data into images — Dr. Lauterbur while he was at the State University of New York at Stony Brook.
When N.M.R. imaging became common for medical use, the name was changed to magnetic resonance imaging; the word “nuclear” was dropped for fear that patients might think radioactive elements were being used.
Dr. Mansfield built a prototype of a magnetic resonance imaging machine in 1978, and he volunteered to be the first person to be enclosed in it and scanned, even though some scientists worried that its nonuniform magnetic field could induce cardiac fibrillation.
“He was the guinea pig,” said Richard Bowtell, a professor at Nottingham, who had been one of Dr. Mansfield’s graduate students. “He went into the scanner. There was the worry it would knock him dead.”
Dr. Mansfield’s own calculations indicated no danger.
“In fact, the scan went well, and after fifty minutes and sweltering heat, I got out of the machine dripping like a wet rag,” he wrote in his 2013 autobiography, “The Long Road to Stockholm: The Story of M.R.I.”
Dr. Mansfield went on to seek faster scans that could capture the beating of a heart. He developed a technique called echo-planar imaging, which could assemble an image in less than a second instead of minutes or hours.
His techniques enabled scientists to take a rapid-fire succession of images that tracked the movement of internal organs. That led to another advance called functional M.R.I., which depicts activity in the brain.
“He worked on it for 10 years before it took off,” Dr. Bowtell said. “He was very driven. He was very able to follow an idea in the face of adversity.”
Peter Mansfield was born in London on Oct. 9, 1933. Partly because of a reorganization of the British school system, he did not finish high school.
A guidance counselor asked him what he wanted to do. “Well, actually, I wouldn’t mind being a scientist,” Dr. Mansfield recalled saying. The counselor, incredulous, suggested that he seek a more practical vocation.
At 15, he became a printer’s apprentice and took classes five evenings a week to complete his secondary education. In the newspaper one day, he read an article about how someone had achieved his schoolboy dream of becoming a rocketeer. Intrigued, he wrote to the newspaper asking how he might become a rocketeer, too. He was advised to send an application to the government.
Impressed with him, officials at the government’s Rocket Propulsion Department hired him to be an assistant. He resigned his printer apprenticeship.
That job was interrupted by two years of military service. Then, at 23, he entered Queen Mary College at the University of London. He completed his undergraduate degree in 1959 and then a doctoral degree in physics, also at Queen Mary, in 1962. During college, his interest shifted from rockets to physics and nuclear magnetic resonance.
He worked with Dr. Slichter for two years at the University of Illinois before obtaining a faculty position at the University of Nottingham in 1964. He was a fellow of the Royal Society, London, and knighted by Queen Elizabeth II in 1993.
Survivors include his wife, Jean; two daughters, Sarah and Gillian; and four grandchildren.
After Dr. Mansfield received the Nobel Prize, Dr. Slichter reminded him that no award, no matter how prestigious, could compare to the satisfaction of advancing medicine and saving lives. Dr. Slichter told him, “What you’ve done is much more important than a Nobel.”
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