MRI scanner

Magnetic resonance imaging

An imaging technique where protons get in a spin

Magnetic resonance imaging (MRI) is well-suited to visualising soft tissues such as the brain. It relies on the magnetic properties of atoms to produce images.

An MRI scanner is a large cylinder containing an extremely powerful magnet. When a patient lies inside the scanner, the magnetic field it produces causes the protons in atomic nuclei to align themselves with it. The scanner then transmits radio waves through the body, making the protons alter their alignment. This causes the nuclei to produce tiny rotating magnetic fields that can be detected and recorded by the scanner to construct the image. Researchers use MRI to look at the structure of the brains (both living and dead) of humans and animals. In 2007, neuroscientists used it to scan the brains of two stroke patients who died about 150 years ago.

More recently, researchers transplanted human cells into the brains of rats to help them recover from stroke and used MRI to detect the structural changes caused by the transplanted cells. Doctors use MRI to visualise the changes that occur in a wide variety of neurological diseases, including Alzheimer’s disease, epilepsy and multiple sclerosis. In Alzheimer’s disease, certain parts of the brain begin to shrink many years before symptoms appear. MRI scans can detect this shrinkage, which is important because early detection can lead to earlier treatment. In addition, the method is used to diagnose brain tumours and to determine exactly where they are so they can be surgically removed.

Lead image:

An MRI scanner.

Matthias Weinberger/Flickr CC BY NC ND


About this resource

This resource was first published in ‘Inside the Brain’ in January 2013 and reviewed and updated in November 2017.

Inside the Brain
Education levels:
16–19, Continuing professional development