History of MRI.gif (3225 bytes)

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felix_bloch.gif (19652 bytes)Magnetic resonance imaging (MRI) has become the primary technique throughout the body in the routine diagnosis of many disease processes, replacing and sometimes surpassing computed tomography (CT). MRI has particular advantages in that it is non-invasive, using non-ionising radiation, and has a high soft-tissue resolution and discrimination in any imaging plane. It may also provide both morphological and functional information. The resultant MR image is based on multiple tissue parameters any of which can modify tissue contrast. In its development, MRI has incorporated a multidisciplinary team of radiologists, technicians, clinicians and scientists who have made, and are continuing to make, combined efforts in further extending the clinical usefulness and effectiveness of this technique.
The first successful nuclear magnetic resonance (NMR) experiment was made in 1946 independently by two scientists in the United States.

raymond_damadian.gif (87155 bytes)Interestingly, Dr Isidor Rabi, an American physicist who was awarded the Nobel Prize for Physics in 1944 for his invention of the atomic and molecular beam magnetic resonance method of observing atomic spectra, came across the NMR experiment in the late 1930's but considered it to be an artefact of his apparatus and disregarded its importance.
During the 50's and 60's NMR spectroscopy became a widely used technique for the non-destructive analysis of small samples. Many of its applications were at the microscopic level using small (a few centimetres) bore high field magnets.
In the late 60's and early 70's Raymond Damadian, an American medical doctor at the State University of New York in Brooklyn, demonstrated that a NMR tissue parameter (termed T1 relaxation time) of tumour samples, measured in vitro, was significantly higher than normal tissue.

edward_purcell.gif (74344 bytes)Felix Bloch, working at Stanford University, and Edward Purcell, from Harvard University, found that when certain nuclei were placed in a magnetic field they absorbed energy in the radiofrequency range of the electromagnetic spectrum, and re-emitted this energy when the nuclei transferred to their original state. The strength of the magnetic field and the radiofrequency matched each other as earlier demonstrated by Sir Joseph Larmor (Irish physicist 1857-1942) and is known as the Larmor relationship (i.e., the angular frequency of precession of the nuclear spins being proportional to the strength of the magnetic field). This phenomenon was termed NMR as follows:
"Nuclear" as only the nuclei of certain atoms reacted in that way;
"Magnetic" as a magnetic field was required;
"Resonance" because of the direct frequency dependence of the magnetic and radiofrequency fields.

With this discovery NMR spectroscopy was born and soon became an important analytical method in the study of the composition of chemical compounds. For this discovery Bloch and Purcell were awarded the Nobel Prize for Physics in 1952.
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paul_lauterbur.gif (57314 bytes)Although not confirmed by other workers, Damadian intended to use this and other NMR tissue parameters not for imaging but for tissue characterisation (i.e., separating benign from malignant tissue). This has remained the Holy Grail of NMR yet to be achieved due mainly to the heterogeneity of tissue. Damadian is a controversial figure in NMR circles not least for his exuberant behaviour at conferences. Although criticism has been levelled at his scientific acumen it should not overshadow the fact that his description of relaxation time changes in cancer tissue was one of the main impetuses for the introduction of NMR into medicine.
On the 16th March 1973 a short paper was published in Nature entitled "Image formation by induced local interaction; examples employing magnetic resonance". The author was Paul Lauterbur, a Professor of Chemistry at the State University of New York at Stony Brook.

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