Within a magnetic field B0, the sum of spins is a net magnetization aligned with B0. This macroscopic magnetization results from a slight excess of spins in parallel state and a null transverse magnetization due to spins being out of phase.
Precession frequency (Larmor frequency) of protons is proportional to field strength intensity.
A RF pulse that matches the precession frequency affects the spin equilibrium : there is an exchange of energy and a tip down of the net magnetization vector. Flip angle depends on intensity, waveform and duration of RF pulse.
 |
 |
Relaxation is the dynamic physical process in which the system of spins returns to equilibrium. Relaxation can be broken down into:
- Recovery of longitudinal magnetization, aligned with B0, following an exponential curve characterized by time constant T1
- Decay of transverse magnetization, due to spins getting out of phase, according to an exponential curve characterized by time constant T2.
Copyright © 2007 Campus Medica. All rights reserved.
Use of this website signifies your agreement to the Terms of Use and Online Privacy Policy.
Search powered by
Summary