Magnetic Resonance ImagingMagnetic Resonance Imaging (MRI) uses a magnet, strong enough to pick up a car, to produce detailed images of your internal organs. Doctors can use MRI to see which parts of the brain are active when you perform certain tasks or feel certain emotions and sensations.
Photograph of an MRI scanning machine
How MRI WorksA large proportion of the human body is made up of fat and water, both of which contain lots of hydrogen atoms. In fact, you are made up of approximately 60% hydrogen atoms. Magnetic Resonance Imaging (MRI) works by measuring the way that these hydrogen atoms absorb and then give off electromagnetic energy. When you have an MRI scan, you lie inside a machine that contains a powerful magnet. The nucleus of a hydrogen atom is like a tiny magnet so, by lying in line with the strong magnetic field inside the scanner, all your hydrogen nuclei line up too – just like a compass needle lining itself up with the Earth’s magnetic field. The scanner also has several electric coils which create variations in the strength of the magnetic field at different points in your body. This means that each hydrogen nucleus experiences a slightly different magnetic field strength, which is important for detecting where exactly they are. A pulse of radio waves is used which gives enough energy to the hydrogen nuclei for them to change direction. When the pulse is switched off the nuclei revert back to their original position and each nucleus gives off energy in the form of a radio wave. The frequency of these waves depends on the strength of the magnetic field where each nucleus is and this means that the scanner can work out the location of each nucleus. The radio waves given off also allow the scanner to work out what type of body tissue the hydrogen nuclei are part of. This information is used to create a map of the different types of tissue in your body. Functional Magnetic Resonance Imaging (fMRI) is a type of MRI that allows you to see which parts of your brain are active when you perform different tasks or feel certain emotions and sensations. Brain activity requires energy and a good supply of oxygen-rich blood. The scanner can see the increase in blood flow to the most active parts of the brain because it can detect the difference between hydrogen nuclei in oxygenated blood and those in de-oxygenated blood. In this way the scanner builds-up a 3D map of which parts of the brain are working particularly hard. fMRI mapping of the brain is used to find out how the brain carries out mental tasks and what parts of the brain are responsible for different brain disorders.
Examples of MRI ScansYou can use MRI scans to see what parts of the brain are active when your subject is doing various different things. Here are examples showing five different stimuli.
MRI scan image highlighting the areas of the brain involved in feeling pain
MRI scan images highlighting the areas of the brain involved in feeling love
MRI scan images highlighting the areas of the brain involved when feeling afraid
MRI scan image highlighting the areas of the brain involved when feeling joyful
MRI scan images highlighting the areas of the brain activated by smell