The MRI (Magnetic resonance imaging) scan is a medical imaging procedure that uses a magnetic field and radio waves to take pictures of our body’s interior. It is mainly used to investigate or diagnose the conditions that affect soft tissue such as tumors or brain disorders. The MRI scanner is a complicated piece of equipment that is expensive to use and found only in specialized centers. Although Raymond Vahan Damadian (1936) is credited with the idea of turning nuclear magnetic resonance to look inside the human body, it was Paul Lauterbur (1929-2007) and Peter Mansfield (1933) who carried out the work most strongly linked to Magnetic resonance imaging (MRI) technology. The technique makes use of hydrogen atoms resonating when bombarded with magnetic energy. MRI provides three dimensional images without harmful radiation and offers more detail than older techniques.
While training as a doctor in New York, Damadian started investigating living cells with a nuclear magnetic resonance machine. In 1971 he found that the signals carried on for longer with cells from tumors than from healthy ones. But the methods used at this time were neither effective nor practical although Damadian received a patent for such a machine to be used by doctors to pick up cancer cells in 1974.
The real shift came when Lauterbur, a U.S, chemist, introduced gradients to the magnetic field so that the origin of radio waves from the nuclei of the scanned object could be worked out. Through this he created the first MRI images in two and here dimensions. Mansfield, a physicist from England, came up with a mathematical technique that would speed up scanning and make clearer images. Damadian went on to build the full body MRI machine in 1977 and he produced the first full MRI scan of the heart, lungs, and chest wall of his skinny graduate student, Larry Minkoff – although in a very different way to modern imaging.
Working of an MRI machine
The key components of an MRI machine are magnet, radio waves, gradient, and a super advanced computer. We all know that human bodies are made up of 60% water, and water is magnetic. Each of the billons of water molecules inside us consists of an oxygen atom bonded to two hydrogen atoms that are called as H2O. Small parts of the hydrogen atoms act as tiny magnets and are very sensitive to magnetic fields. The first step in taking an MRI scan is to use a big magnet to produce a unified magnetic field around the patient. The gradient adjusts the magnetic field into smaller sections of different magnetic strengths to isolate our body parts. Take brain as an example, normally the water molecules inside us are arranged randomly. But when we lie inside the magnetic field, most of our water molecules move at the same rhythm or frequency as the magnetic field. The ones that don’t move along the magnetic field are called low energy water molecules. To create an image of a body part, the machine focuses on the low energy molecules. The radio waves move at the same rhythm or frequency as the magnetic fields in an MRI machine.
By sending radio waves that match or resonate with the magnetic field, the low energy water molecules absorb the energy they need to move alongside the magnetic field. When the machine stops emitting radio waves, the water molecules that had just moved along the magnetic field release the energy they had absorbed and go back to their position. This movement is detected by the MRI machine and the signal is sent to a powerful computer which uses imaging software to translate the information into an image of the body. By taking images of the body in each section of the magnetic field the machine produces a final three dimensional image of the organ which doctors can analyze to make a diagnosis.
“Medicine is a science of uncertainty and an art of probability”. –William Osler