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Steady-state free precession imaging

Steady-state free precession (SSFP) imaging is a magnetic resonance imaging (MRI) technique which uses steady states of magnetizations. In general, SSFP MRI sequences are based on a (low flip angle) gradient-echo MRI sequence with a short repetition time which in its generic form has been described as the FLASH MRI technique. While spoiled gradient-echo sequences refer to a steady state of the longitudinal magnetization only, SSFP gradient-echo sequences include transverse coherences (magnetizations) from overlapping multi-order spin echoes and stimulated echoes. This is usually accomplished by refocusing the phase-encoding gradient in each repetition interval in order to keep the phase integral (or gradient moment) constant. Fully balanced SSFP MRI sequences achieve a phase of zero by refocusing all imaging gradients.


Steady-state free precession (SSFP)

States of SSFP is a kind of steady states of magnetizations achieved by a series of radiofrequency (RF) irradiation and natural relaxation behaviors of spins. The influencing factors thus include: the flip angles of RF pulses, repetition time (TR) of pulse repeats, the relaxation time constants including longitudinal (T1) and transverse (T2) ones, plus if gradient moments (i.e. the integral of gradients with time) in one TR are zero, etc.

Gradient moments are zero or not

If, within one TR, either one of the gradient moments of magnetic gradients along three logical directions, including slice selection direction (Gss), phase encoding (Gpe) and readout (Gro), is not zero, then spins along such direction obtain different phases, making the signal intensity (SI) of a single voxel is a vector sum of magnetizations therein. It cause some inevitable loss of SI. Such situations belong to ordinary SSFP imaging, with its commercial names listed below.

Otherwise, if all gradient moments are zero within one TR, i.e. gradients of opposite polarities cancel out, then there are no additional effects on the phase from gradients; that is to say, SI of each voxels is the contributions of a series of RF pulses and relaxation phenomena. See Article Balanced steady-state free precession imaging.

Commercial names for gradient-echo imaging sequences

Gradient Echo Pulse Sequences
Academic Classification Spoiled Gradient Echo Steady-State Free Precession (SSFP) Balanced Steady-State Free Precession (bSSFP)
Ordinary type Turbo type
(Magnetization preparation,
extremely low angle shot, short TR)
FID-like Echo-like
Siemens FLASH
Fast Imaging using Low Angle Shot
Fast Imaging with Steady-state Precession
Reversed FISP
Spoiled GRASS
Gradient Recall Acquisition using Steady States
Steady State Free Precession
Fast Imaging Employing Steady-state Acquisition
Philips T1 FFE
T1-weighted Fast Field Echo
Turbo Field Echo
Fast Field Echo
T2-weighted Fast Field Echo
Balanced Fast Field Echo

See also

  • MRI - Magnetic resonance imaging Animation made by; contents are: spin, spin modification, induction, relaxation and precession, spin echo sequence, gradient echo sequence, inversion recovery sequence
  • MRI

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Steady-state_free_precession_imaging". A list of authors is available in Wikipedia.
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