Magnetic Resonance Imaging
What is MRI?
Magnetic Resonance Imaging (MRI) is a scanning technique which uses strong magnetic fields and radio waves to examine almost any part of the body in great detail, including: the brain, bones, heart and other internal organs. MRI scans have sufficient resolution to show almost all different tissue types and produce 3D scans, click here to find out how. [R1]
Diagram of MRI scanner. Source (National Mag Lab)
Safety
MRI scans are very safe procedures as they don’t use any ionising radiation, such as x-rays (Find out more here). Extensive research has been done on the effects of the strong magnetic fields and radio waves, because we experience large amounts of radio waves in every day life due to mobile phones, radios etc. No risks have currently been identified, as a result, this is one of the safest procedures you can have.
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Some people, however, do find the scanner claustrophobic. As you can see in the image above, you have to lie within an enclosed space. To help with this, patients are often given headphones to listen to music to help them to relax. There are some people who aren’t able to have MRI scans. People with implants, such as a pacemaker, wouldn’t be able to have the scan as the strong magnetic field would interfere with its operation. [R3]
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To compare, for a standard MRI scan, your core body temperature can rise by 0.5°C. For comparison, on average your body would only absorb enough energy to make 0.2 cups of tea!
How does it work?
Your body is composed mostly of water which contains hydrogen and the centre of hydrogen is a proton. Protons behave like very small bar magnets which is a property called magnetic spin. When in a magnetic field, all these spins align so that they point in the same direction - like how a compass would align. Bursts of radio waves (produced by the radio frequency coil) are aimed at parts of the body to be scanned; this gives some of the atoms additional energy which causes their spin to flip to a more excited (higher energy) state. After the radio pulses have stopped, the spin flips back to align with the rest in the magnetic field. This is because it wants to be in the lowest possible energy state. In doing so, the atom emits a bit of energy which is detected by the scanner. This can then be used to obtain the location of the protons in the body. The rate at which the spins return to the aligned state, and the energy of the emitted waves differentiate different types of tissue in the body. [R2] For a more in-depth explanation, click here!
You body only absorbs enough energy to make 0.2 cups of tea!