If you have ever suffered from intractable low back pain, you are probably familiar with an MRI (magnetic resonance imaging) machine. The knocking and shaking inside the machine can be legendary, and the images immensely valuable. This diagnostic tool seems to be a key factor in the expanding understanding of the inner workings of the human body.
Behind all those loud noises and clear pictures, there is a beautiful piece of engineering from the magnets to the MRI cooling system. But how, exactly, does it work?
Magnets and Radios
The MRI scanner uses radio waves and a strong magnetic field to produce images. The magnets are responsible for the loud noises in the machine, and they are also the reason why you are asked to remove any metal from your body before receiving an MRI.
The scanner itself does not expose the person to any sort of radiation, rather it generates a powerful magnetic field around the person. Radio waves are directed at the body through the magnetic field. The combination of these technologies allows the machine to produce detailed pictures of soft tissue structures in the body. This is why an MRI can be so effective in diagnosing sports-related injuries.
MRI technology takes advantage of the high water content of the human body. The hydrogen atoms in water molecules (H2O) become aligned in a magnetic field. As the scanner applies a strong magnetic field, the spinning of all the hydrogen atoms in the body aligns.
The radio waves in the scanner vary the magnetic field. The hydrogen atoms then absorb the energy from the varied magnetic field and the spins change direction. As the magnetic field is turned off, the atoms gradually return to their original spins. This process, called precession, produces a radio signal that the machine can measure and render into an image.
Every type of tissue in the body has a different rate for the hydrogen atoms to return to their original spin. This variation is what allows the images from the scanner to distinguish between different types of tissue. The variable spin rate is part of what produces the clear and fascinating images associated with MRI scans.
In addition to standard MRI scans, there are also Diffusion MRIs and Functional MRIs available. Diffusion MRI measures the rate at which water diffuses through tissues. Functional MRI (fMRI) measures the rate of blood flow to different areas of the brain.
MRI technology continues to evolve and produce fascinating images. Inside the metal, magnets, and MRI cooling system is a beautiful piece of science and engineering.