How Does an MRI Work?

MRIs work by aligning the magnetic spin of the hydrogen molecules in the body. CREDIT: Image courtesy of MGH-UCLA Human Connectome Project. View full size image

We’ve come a long way since Pavlov and Freud, but scoping out the human brain is still a tricky business. Luckily, technology is on our side, and in recent years researchers have found some clever techniques for taking a peek inside humanity’s great "black box" without jostling the goods.

Among these, Magnetic Resonance Imaging (MRI) is one of the most popular. The non-invasive machine works on the principle that your body (brain included) consists largely of water, which in turn is made up of oxygen and hydrogen molecules. The hydrogen molecules have a magnetic spin that can be aligned by a strong burst of radio-frequency waves from an MRI machine. Once this is done, a second pulse knocks the hydrogen molecules out of spin alignment. A computer then records how long the atoms of different tissues take to realign themselves.

Different tissues have different molecular alignments, and by exploiting this fact a computer can construct a topographical map of the soft tissue in your brain.

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