How do MRI scanners work and what do the different noises/sounds correlate to


Just had one, was in it for an hour and have no idea how it actually gets an image and what the various sounds indicate.

In: 4

An MRI machine is basically a large and extremely powerful magnet. This is why you cannot go into or near an MRI machine if you have (magnetic) metal implants in your body.

When your body is inside the MRI magnet, the strong magnetic field affects the chemical elements that make up your body (because of a quantum mechanical property each element has that is known as ‘spin’). The element hydrogen has especially favorable properties for magnetic resonance, and most MRI scans involve detecting hydrogen specifically. The machine uses radio waves to manipulate the ‘spin’ of the elements in your body. Applying radio waves to the body causes the elements’ ‘spin’ to leave the normal state (called ‘equilibrium’). When the radio waves are turned off, the ‘spins’ naturally return to equilibrium. The process of returning to equilibrium generates signals that can be measured by the MRI instrument. The processing and analysis of these signals leads to the images that your doctor looks at and uses to identify problems or disease.

The loud clicks you hear during the MRI procedure are caused by the physical hardware inside the MRI machine. There are coils of wire inside that carry huge amounts of electrical current; the flow of current through the coils creates additional magnetic fields that serve to manipulate the ‘spins’ in your body. The clicks and thumps are the sound of the coils expanding and contracting and vibrating as huge pulses of current flow through them.

Fun fact: in chemistry and biochemistry (and some other fields), there is an analysis technique known as NMR that functions according to the exact same principles as MRI. However, NMR was in use in research long before MRI was developed, so MRI is basically NMR applied to human beings instead of inanimate samples. Why, then, did MRI get a special name instead of just using the existing name NMR? Well, NMR stands for Nuclear Magnetic Resonance. MRI first came out during the Cold War in the 1970s, and the story is that patients were afraid to undergo any test or procedure that had ‘nuclear’ in its name. So NMR was rebranded MRI to avoid scaring people! (side note – neither NMR nor MRI has anything whatsoever to do with the deadly types of radiation created by nuclear weapons, so both methods are non-invasive and non-destructive.)

MRI = Magnetic Resonance Imaging

it is basically a strong magnetic field that makes the hydrogen atoms align in a certain way, then how they are connected to other atoms can be detected with radiowaves. To make images the magnetic field has to be changed in certain ways, every time the field is changes everything metallic in the machine moves a bit making noises