Magnetic Resonance Imaging (MRI) devices stand at the pinnacle of contemporary medical technology. These highly intricate machines utilise an amalgamation of quantum physics, high-tech imaging software, Fourier transform mathematics, and superconductive magnets. The influential American physicist of Galician descent, Isidor Rabi, made a ground-breaking discovery of Nuclear Magnetic Resonance (NMR) in 1944, which led him to win the distinguished Nobel Prize in Physics.
Rabi discovered that the atomic nuclei of specific elements, like select versions of hydrogen, carbon, and phosphorus functioned much like bar magnets. In a natural state, these magnetic directions are chaotically aligned in every direction, thereby neutralising each other. In a high-powered magnetic field, however, these molecular ‘bar magnets’ consistently align in a single direction.
When these aligned nuclei are exposed to a radio pulse at a specifically selected frequency, their orientation changes and moves away from the magnetic field’s direction. Each type of nuclei aligns with a different radio frequency under a specific magnetic field. For instance, hydrogen nuclei might respond by twisting at 300MHz, while carbon would do so at 75MHz. When each radio pulse ceases, the nuclei ‘sigh’ and undergo relaxation to realign with the magnetic field. In actuality, this sigh corresponds to a diminishing spiral movement that creates a discernible electric signal. Consequently, NMR technology is regularly utilised in identifying the components of a chemical mixture.
Robert Gibillard put forth a theory on how one can detect the spatial positions of magnetic nuclei across a gradient of magnetic field in his 1952 PhD dissertation at ENS Paris. Paul Lauterbur, an associate professor at Stony Brook in New York, recognised the potential of Gibillard’s discovery to develop biological tissue maps two decades later.
Diffuse biological tissues generate different ‘sighs’; for instance, magnetic hydrogen in fatty tissues might relax more quickly than that within a blood vessel. Utilising the NMR device of his chemistry department overnight, Lauterbur built the world’s first MRI machine. His findings were forwarded to the Nature journal, whose editors quickly shot it down for images being too vague. Subsequently, Peter Mansfield, a physicist at the University of Nottingham, significantly expanded Lauterbur’s work by using Fourier analysis on the output signals to exponentially speed up image production.
Lauterbur sought to secure a patent for his findings, but Stony Brook chose not to finance the patent’s associated expenses, thinking the work was not worthwhile enough. Mansfield nevertheless convinced the University of Nottingham to register patents, earning significant royalties from the commercialisation of MRI machines.
Both Lauterbur and Mansfield were bestowed with the Nobel Prize for Medicine jointly in the year 2003. The magnetic power produced by an MRI machine is often as potent as those employed by electromagnetic cranes in metal scrapyards. Primarily composed of niobium-titanium, the magnets inside an MRI machine account for 80 per cent of the compound’s global usage.
The metals transform into superconductors when chilled to -273 degrees. At these frigid temperatures, an electric current can perpetually create magnetism without depleting power. Comparable technologies are employed in charged particle accelerators, notably the large hadron collider at CERN, allowing the generation of incredibly potent magnetic fields, without overheating the necessary electrical cables. However, the cooling of these magnets to render them superconductors takes a few days, so MRI magnets are left switched on indefinitely.
The intensity of an MRI machine’s magnetic field commonly ranges between one to two tesla. The term tesla has no affiliation with Elon Musk but is in honour of Nikola Tesla, the individual who led the way in electrical and magnetic research.
The French Alternative Energies and Atomic Energy Commission (CEA) revealed the world’s inaugural 11.7 tesla MRI machine last month, after 25 years of extensive R&D. The machine was procured for €70 million, with €50 million accounting for the cost of the magnet assembly alone.
In contrast to the 1mm resolution seen in other top-range commercial machines, this pioneering device can produce human brain images down to a resolution of 0.2 of a millimetre. Notably, it has the capacity to identify atomic components like sodium, phosphorus, and fluorine, capabilities beyond other machines available, thereby potentially advancing our comprehension of brain biochemistry.
This highly precise anatomical data should, for instance, enhance the diagnosis and treatment of neurodegenerative conditions like Alzheimer’s and Parkinson’s disease.
The evolution of MRI technology is not yet complete. There are ongoing efforts in Germany from industrial researchers, who started work on a 14-tesla machine in 2013. Similar projects are also in progress in Korea and the United States.