The history of magnetic resonance imaging (MRI) includes the work of many researchers who contributed to the discovery of nuclear magnetic resonance (NMR) and described the underlying physics of magnetic resonance imaging, starting early in the twentieth century. MR imaging was invented by Paul C. Lauterbur who developed a mechanism to encode spatial information into an NMR signal using magnetic field gradients in September 1971; he published the theory behind it in March 1973. The factors leading to image contrast (differences in tissue relaxation time values) had been described nearly 20 years earlier by physician and scientist Erik Odeblad and Gunnar Lindström. Among many other researchers in the late 1970s and 1980s, Peter Mansfield further refined the techniques used in MR image acquisition and processing, and in 2003 he and Lauterbur were awarded the Nobel Prize in Physiology or Medicine for their contributions to the development of MRI. The first clinical MRI scanners were installed in the early 1980s and significant development of the technology followed in the decades since, leading to its widespread use in medicine today.
Nuclear magnetic resonance
In 1950, spin echoes and free induction decay were first detected by Erwin Hahn and in 1952, Herman Carr produced a one-dimensional NMR spectrum as reported in his Harvard PhD thesis.
The next step (from spectra to imaging) was proposed by Vladislav Ivanov in Soviet Union, who filed in 1960 a patent application for a Magnetic Resonance Imaging device. Ivanov's main contribution was the idea of using magnetic field gradient, combined with a selective frequency excitation/readout, to encode the spatial coordinates. In modern terms, it was only proton-density (not relaxation times) imaging, which was also slow, since only one gradient direction was used at a time and the imaging had to be done slice-by-slice. Nevertheless, it was a true magnetic resonance imaging procedure. Originally rejected as "improbable", Ivanov's application was finally approved in 1984 (with the original priority date).
Relaxation times and early development of MRI
By 1959, Jay Singer had studied blood flow by NMR relaxation time measurements of blood in living humans. Such measurements were not introduced into common medical practice until the mid-1980s, although a patent for a whole-body NMR machine to measure blood flow in the human body was filed by Alexander Ganssen in early 1967.
In the 1960s, the results of work on relaxation, diffusion, and chemical exchange of water in cells and tissues of various types appeared in the scientific literature. In 1967, Ligon reported the measurement of NMR relaxation of water in the arms of living human subjects. In 1968, Jackson and Langham published the first NMR signals from a living animal, an anesthetized rat.
In the 1970s, it was realized that the relaxation times are key determinants of contrast in MRI and can be used to detect and differentiate a range of pathologies. A number of research groups had showed that early cancer cells tended to exhibit longer relaxation times than their corresponding normal cells and as such stimulated initial interest in the idea of detecting cancer with NMR. These early groups include Damadian, Hazlewood and Chang and several others. This also initiated a program to catalog the relaxation times of a wide range of biological tissues, which became one of the main motivations for the development of MRI.
In a March 1971 paper in the journal Science, Raymond Damadian, an Armenian-American doctor and professor at the Downstate Medical Center State University of New York (SUNY), reported that tumors and normal tissue can be distinguished in vivo by NMR. Damadian's initial methods were flawed for practical use, relying on a point-by-point scan of the entire body and using relaxation rates, which turned out not to be an effective indicator of cancerous tissue. While researching the analytical properties of magnetic resonance, Damadian created a hypothetical magnetic resonance cancer-detecting machine in 1972. He patented such a machine, on February 5, 1974. Lawrence Bennett and Dr. Irwin Weisman also found in 1972 that neoplasms display different relaxation times than corresponding normal tissue. Zenuemon Abe and his colleagues applied the patent for a targeted NMR scanner, in 1973. They published this technique in 1974. Damadian claims to have invented the MRI.
The U.S. National Science Foundation notes "The patent included the idea of using NMR to 'scan' the human body to locate cancerous tissue." However, it did not describe a method for generating pictures from such a scan or precisely how such a scan might be done.