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History of magnetic resonance imaging
This section aims to pay tribute to the people who have made the modality of MRI possible, to whom we are greatly indebted.
Magnets were first discovered by the Romans more than 2000 years ago. Over the years, the understanding of the magnet has increased and many applications have developed.
The history of Nuclear Magnetic Resonance (NMR), now known as MRI, begins with a French mathematician Jean Baptiste Joseph Fourier (1768–1830) who developed a mathematical method to analyze the heat transfer between solid bodies. Later this discovery made rapid processing of phase and frequency signals possible in NMR.
The unit strength of a magnetic field is the Tesla (1 Tesla = 1 Newton/Ampere-meter) and is named after Serbian-born inventor Nikola Tesla (1856–1943) who discovered the rotating magnetic field.
An Irish physicist, Sir Joseph Larmor (1857–1942) discovered a way to calculate the rate at which energy is radiated by an accelerated electron. He also explained the splitting of spectrum lines by a magnetic field. He is famous in the field of NMR for the so-called larmor equation, which states that the frequency of precession of the nuclear magnetic moment (ω) is directly proportional to the product of the magnetic field strength (B0) and the gyromagnetic ratio (γ ): ω = γB0.
An Austrian, Isidor Rabi (1898–1988) working in the Department of Physics at Columbia University in New York discovered a way to detect and measure single states of rotation of atoms and molecules. He also succeeded in determining the magnetic moments of the nuclei. For his discoveries, he was awarded the Nobel Prize in Physics in 1944.
In the 1940s, Felix Bloch working at Stanford University and Edward Purcell from Harvard University independent of each other, described a physicochemical phenomenon which was based on the magnetic properties of certain nuclei in the periodic system. They found that when certain nuclei were placed in a magnetic field they absorbed energy in the electromagnetic spectrum and re-emitted this energy when they returned to their original state. The strength of the magnetic field and the radiofrequency matched each other according to the Larmor relationship. For this discovery, Bloch and Purcell were awarded with the Nobel Prize for Physics in 1952.
In 1971, Raymond Damadian from Downstate Medical Center in New York measured T1 and T2 relaxation times of normal and cancerous rat tissues and found that normal tissue had shorter relaxation times than the tumour tissue.
In 1974, Paul C. Lauterbur, a professor of chemistry and radiology at New York University and Peter Mansfield from the department of physics at the Nottingham University England independent of each other, described the use of magnetic field gradients for spatial localization of NMR signals. These discoveries led to the foundation for Magnetic Resonance Imaging (MRI). For this discovery, Lauterbur and Mansfield were awarded with the nobel prize for physiology or medicine in 2003.
In 1975, a Swiss physical chemist Richard Ernst described the use of Fourier transform of phase and frequency encoding to reconstruct 2D images. For this discovery he was awarded with the nobel prize for chemistry in 1991.
Later in 1975, Peter Mansfield and Andrew Maudsley proposed a line scan technique, which led to the first cross sectional imaging of human anatomy (cross section through a finger). In 1978, Hugh Clow and Ian R. Young worked at a British company called EMI, created the first transverse NMR image through a human head.