Magnetic Resonance Imaging

Magnetic Resonance Imaging (MRI)

Another powerful imaging technique is Magnetic Resonance Imaging (MRI). MRI is one of the most important ways we see details of tissues inside the body. Unlike CT scans, MRIs can show both how tissues look as well as how they function. There are estimated to be more than 25 000 scanners in use worldwide.

History

In the 1930s, Felix Bloch and Edward Purcell discovered nuclear magnetic resonance (NMR). They worked at different American universities. But they were both able to show how magnetic fields and radio pulses can cause atoms to give off tiny radio signals. And by detecting these radio signals, you can create an image. This makes it possible to look inside objects without taking them apart or destroying them.

In the early stage of MRI many people did experiments. Herman Carr produced the first one-dimensional MRI image in 1952. In 1972, the physicist Peter Mansfield found a way to make images clearer. He also found a way to reduce scanning time from hours to minutes. In 1974, Paul Lauterbur created the first sectional images of a mouse. On July 3, 1977, Raymond Damadian, Larry Minkoff and Michael Goldsmith performed the first full body scan. In 2003, Lauterbur and Mansfield won the Nobel Prize in Physiology or Medicine for their contributions to MRI technology.

How it Works

MRI scanners use strong magnetic fields and radio waves to form images of the body. Over half your body is made of water. Each water molecule (H₂O) contains two hydrogen atoms and one oxygen atom. The magnet in an MRI scanner causes the nuclei of the two hydrogen atoms to line up. Next, short pulses of radio signals cause the nuclei go back to their original positions. When this happens the nuclei emit weak radio signals that are detected by a receiver. The receiver sends the information to a computer. The computer then creates an image. MRI images capture a lot of details and can be colour-enhanced so that the various parts stand out even more.

Uses

Like CT scans, MRI scans are used to detect structural problems, such as tumours, blood clots, or damage caused by accidents and disease. One unique type of MRI is a Functional MRI (fMRI). An fMRI measures changes in blood flow within the brain. This technique allows doctors to visualize the living brain and observe changes to the brain as it undergoes different functions. CT scanners tend to be used more than MRI machines because they are less expensive to buy. However, as the price of MRI machines comes down, they will likely get used more often.

Did you know? 

Since the introduction of fMRI in 1990, more information about the brain has been collected than in the previous 100 years!

Benefits & Risks

The greatest benefits of MRI machines are that they do not use x-rays. X-rays can be damaging to tissues and cause cancer). MRI machines are also better than CT scanners for taking images of soft tissues, like tumours. Unfortunately, MRI scans are slow. It can take anywhere from 10 minutes to an hour to produce an image! The machines can also be scary for patients who are claustrophobic (afraid of small, enclosed spaces).