ABSTRACT
Hydrogen atoms are at the core of the physics of magnetic resonance imaging
(MRI) used for clinical purposes: hydrogen nuclei are made by single protons
with spinning properties that give the ability to interact with surrounding
inhomogeneous magnetic fields. Each hydrogen nucleus produces its own
magnetic field whose strength and direction can be represented by a vector known
as magnetic dipole moment (MDM). The 1.5 Tesla scanner magnet commonly
used for MRI generates a magnetic field 30,000 times greater than earth’s that
both orients the spin of hydrogen nuclei in the direction of the main magnetic
field, and at the same time leads off the “precession” phase, that is, all hydrogen
nuclei precess at the same frequency, although not at the same phase. The scanner
includes a radio wave emitter that excites hydrogen nuclei by deflecting their spin
along the x-y plane. The radio frequency pulse applied enables hydrogen nuclei
to precess at the same phase. Hydrogen nuclei revert back to their original spin
once the radio wave emission is interrupted, and give back the absorbed energy as
radio waves that are picked up by an antenna. The emitted radio wave signal is
then analyzed and processed.
