What is magnetic resonance imaging (MRI)?
MRI incorporates the use of static and gradient
mag-netic fields with radiofrequency (RF) pulses to produce images of the body.
Magnetic field strengths range from 0.15 to 3.0 tesla (T). The tesla is a
measure of the strength of a magnetic field (1 T = 10,000 gauss). The quality
of the image depends on the strength of the magnetic field.
Hydrogen is the element most commonly used in
MRI. The reasons for this are that hydrogen is the most abun-dant element in
human tissue and it can be magnetized. Atoms, such as hydrogen, with an
unpaired number of protons and/or neutrons respond to, and align themselves
within, the magnetic field of the MRI scanner.
Following placement of the patient within the
cylindri-cal bore of the magnet, a steady state is established in which
hydrogen atoms are in alignment. RF pulses are introduced and deflect the
orientation of the atoms. When the RF pulses are eliminated, the hydrogen atoms
return to their original position of alignment. As these atoms establish a
resting state, the energy emitted is used to produce the resulting image.