What is MRI and How Does it Work
Water is critically important for MRI
MRI works because the single largest constituent of the human body - about 75% - is water. A molecule of water (H2O) is composed of two hydrogen (H) atoms and one oxygen (O) atom. The inner core (nucleus) of each hydrogen atom consists of a single proton. Under normal conditions, these protons are constantly spinning, which envelopes them within a tiny magnetic field.
Normally, this intrinsic magnetic field is randomly orientated (i.e. has no particular overall direction). Placing a person inside an MRI scanner, which is essentially a very large powerful magnet, makes the protons in their body line up either with or against the direction of the scanner's own strong magnetic field
MRI uses radiowaves
To make an image, short bursts - or pulses - of radiowaves are directed at the area being examined through a special antenna (called a coil). This knocks the protons off-balance, causing them to flip their orientation.
Water content differs in healthy and diseased tissue
The intensity of the MR signal from a particular body tissue is related to the density of protons in the tissue, and therefore to the water content of the tissue. The more water a tissue contains, the stronger its MR signal and the better the resulting image, which is why human bodies are ideal candidates for MRI scanning. Different tissues contain variable amounts of water, and diseased or damaged tissue usually contains more water than healthy tissue. In MS, the focus of interest is the brain and spinal cord (called the central nervous system, or CNS). Lesions in the CNS have a higher than normal water content.
