How are various physical interactions IN magnetic resonance imaging classified as a function of time?
The interactions can be group into time-dependent and time-independent interactions as follows: • Time-Independent interactions: • Chemical Shift • Spin-spin coupling or J-coupling • Time-Dependent interactions: • Relaxation (T1 and T2 relaxations) • Chemical Exchange Q) What is Free Induction Decay (FID)? A) FID is a transient response forming the most fundamental form of all signals in MRI system. It arises from the action of a SINGLE PULSE (note that a spin echo is formed by two excitation pulses) on a nuclear spin system. Let us analyze each word separately: Free means that the signal is generated by the FREE PRECESSION of the of the magnetization vector M Induction means that the signal is detected by Faraday electromagnetic induction law (using a coil) Decay means that the signal decreases with time FID is the most basic (or primitive) form transient signal in a spin system. It forms the basis for other forms of MRI signals as mentioned above. The decay time of FID depends on the
