Precession is a wobbling motion that occurs when a spinning object is the subject of an external force. Relevant to MRI, the proton of a hydrogen nucleus spins around its axis giving it an angular moment (quantum mechanics). Through the protons positive charge and its spin it generates a magnetic field and gets a magnetic dipole moment (MDM) parallel to the rotation axis. If placed in a magnetic field the magnetic dipole moment will precess about the direction of the magnetic field with an angular frequency (Larmor frequency). The Larmor equation dictates that the frequency of the precession at higher field strengths is higher.

A rephasing or refocusing occurs when spins return to the same starting phase they had directly after the initial exciting RF pulse. E.g. spin echo sequences use 180° pulses to refocus the spins to generate signal echoes and gradient echo sequences use a refocusing gradient to maximize remaining transverse magnetization.

Relaxation time is a general physics concept for the characteristic time in which a system relaxes under certain changes in external conditions. Relaxometry is the theory of relaxation times (spin lattice (T1) and spin spin relaxation (T2)), and their dependence on physical parameters such as magnetic field strength, molecular structure, temperature, pH, and the presence and type of relaxation agents.

The process of returning out of phase magnetic moments back into phase coherence. Caused either by rapidly reversing a magnetic gradient (Field Echo) or by applying a 180° RF pulse (Spin Echo). In the spin echo pulse sequence this action effectively cancels out the spurious T2* information from the signal.

See also Spin Echo Sequence and Gradient Echo Sequence.

From Esaote S.p.A.; Esaote introduced the S-SCAN at RSNA in November 2007. The S-SCAN is a dedicated joint and spine MR scanner derived from the company's earlier G-SCAN system. Unlike the G-SCAN, neither the patient table nor the magnet can rotate from horizontal to vertical position. The patient table can only moved manually. Improved electronics, new coils for lumbar and cervical spine, new pulse sequences, a modified version of the magnet poles and gradient coils are used with a new software release in the S-SCAN.
Esaote North America is the exclusive U.S. distributor of this MRI device.