Physics first, medicine later
Magnetic resonance imaging did not begin as a medical project. It grew from nuclear magnetic resonance (NMR), a property of atomic nuclei in a magnetic field. Certain nuclei, such as hydrogen, behave like tiny magnets. Placed in a strong field and struck with radio waves of a particular frequency, they absorb energy and then release a signal. Isidor Rabi studied related effects in beams in the 1930s, and in 1946 Felix Bloch at Stanford and Edward Purcell at Harvard independently detected NMR in bulk materials. They shared the 1952 Nobel Prize in Physics. For years afterward, NMR was mainly a tool for chemists studying molecules.
Toward the body
Because the human body is mostly water and fat, it contains abundant hydrogen, so NMR signals can in principle come from almost anywhere in it. Two problems stood between the laboratory technique and a picture. First, a plain NMR measurement gives a signal from the whole sample, with no location. Second, someone had to show the signal carried medical information.
In 1971 Raymond Damadian, a physician at the State University of New York in Brooklyn, reported in the journal Science that the relaxation times of NMR signals differed between some tumor tissue and normal tissue in rats. This suggested NMR could separate healthy from abnormal tissue. Damadian later patented a scanning concept and in 1977 his group produced a human chest image using a hand-built machine nicknamed “Indomitable.” It collected data point by point and was very slow.
Making an image
The problem of location was solved by varying the magnetic field across the sample. In 1973 Paul Lauterbur, a chemist at Stony Brook, published in Nature a method using field gradients, which made the signal’s frequency depend on position. He called it zeugmatography, from a Greek word for joining together, and showed images of small test objects. Peter Mansfield at the University of Nottingham independently developed gradient methods and mathematical tools, then proposed echo-planar imaging in the late 1970s, a way to collect data much faster. Other groups also contributed, such as researchers at Aberdeen who built early whole-body scanners around 1980, and later developers of improved techniques like Fourier-based reconstruction by Richard Ernst, who received a Nobel Prize in Chemistry in 1991 for related NMR work.
From prototype to hospital
Early human scans in the late 1970s took many minutes and were noisy. During the 1980s, superconducting magnets, better radio coils and faster electronic computers allowed useful clinical images, and commercial scanners were installed in hospitals. The name changed too. “Nuclear” was dropped from the title, in part because it frightened the public, though no ionizing radiation is involved. The technique is the same, and “magnetic resonance” remains the core of the name.
Over time, new pulse sequences allowed a range of contrasts: images that emphasize fat, water, blood flow or fluid. Functional MRI, developed in the early 1990s, tracks changes related to blood oxygenation and is widely used in brain research.
The credit dispute
The 2003 Nobel Prize in Physiology or Medicine went to Paul Lauterbur and Peter Mansfield. Damadian was not included, and he publicly protested, placing advertisements in major newspapers. Supporters argue that his tumor findings and early scanner showed the medical promise of NMR and that he deserved recognition. Others note that Lauterbur and Mansfield provided the gradient methods that made practical imaging possible, which Damadian’s technique lacked. The Nobel Committee did not explain its selection beyond its citation. A fair summary is that MRI had several contributors, each of whom supplied a different necessary ingredient.
Strengths and cautions
MRI gives detailed images of soft tissue, including brain, spinal cord, muscles and joints, with no ionizing radiation. Its limits include cost, long scan times compared with CT, and the need to screen patients for metal and some implantable devices because of the strong magnetic field. This article is history, not advice about whether any individual should have a scan.
What the story shows
MRI is a clear example of basic physics becoming medicine decades later. No one in the 1940s was thinking of scanners. It also shows that large inventions usually have several parents, and that prizes tend to compress a longer record into a few names.