The document discusses how magnetic resonance imaging (MRI) works by using radio frequency pulses and gradient magnets to manipulate hydrogen protons in the body and produce detailed images. Specifically, it notes that an MRI machine applies an RF pulse tuned to hydrogen which causes protons to absorb energy and spin in a different direction. Gradient magnets then locally alter the magnetic field to provide spatial encoding of the signal emitted as protons return to their natural alignment and release energy, which is picked up by coils and used to construct images.

1. Center for Experimental Mechanics, University of Ljubljana, Slovenia
16
q The alignment of protons.

2. Center for Experimental Mechanics, University of Ljubljana, Slovenia
q The MRI machine applies a RF pulse that is specific only to hydrogen.
q When the pulse is applied, the unmatched protons absorb the energy and spin again
in a different direction.
q The RF pulse forces them to spin at a particular direction.
q The gradient magnets are arranged in such a manner inside the main magnet that
when they’re turned on and off rapidly in a specific manner, they alter the main
magnetic field on a local level.
q When the RF pulse is turned off, the hydrogen protons slowly return to their natural
alignment within the magnetic field and release the energy absorbed from the RF
pulses. When they do this, they give off a signal that the coils pick up and send to the
computer system.
17