Steady-state free precession imaging
From Wikipedia, the free encyclopedia
Steady-state free precession (SSFP) imaging is a kind of imaging techniques which uses steady states of magnetizations used in MRI.
Contents |
[edit] Steady-state free precession (SSFP)
States of SSFP is a kind of steady states of magnetizations is 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.
[edit] 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 addition 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.
[edit] 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 |
TurboFLASH Turbo FLASH |
FISP Fast Imaging with Steady-state Precession |
PSIF Reversed FISP |
TrueFISP True FISP |
| GE | SPGR Spoiled GRASS |
FastSPGR Fast SPGR |
GRASS Gradient Recall Acquisition using Steady States |
SSFP Steady State Free Precession |
FIESTA Fast Imaging Employing Steady-state Acquisition |
| Philips | T1 FFE T1-weighted Fast Field Echo |
TFE Turbo Field Echo |
FFE Fast Field Echo |
T2-FFE T2-weighted Fast Field Echo |
b-FFE Balanced Fast Field Echo |
