Fat Suppression
Fat signal causes high signal respiration induced ghosts on T1 weighted images and T2 weighted Turbo Spin Echo images. Basic fat suppression methods are used in different combinations by different equipment so take time to learn how your scanner suppresses fat signal. These notes only give a basic outline.
Fat signal causes high signal respiration induced ghosts on T1 weighted images and T2 weighted Turbo Spin Echo images. Basic fat suppression methods are used in different combinations by different equipment so take time to learn how your scanner suppresses fat signal. These notes only give a basic outline.
- Selective Spectral Saturation
- aka Chemsat, FATSAT, CHESS spectral non spatial selective saturation
- A fat selective excitation pulse is applied to the whole volume, followed by a spoiler gradient , Only water spins contribute signal to the following imaging sequence.
- Usually applied before each excitation pulse (TR x slice)
- Takes 10 - 20 msec per routine
- Fat saturation effect lasts about 100 msec
- Increases SAR
- Sensitive to magnetic field distortions
- Only modifies appearance of Fat other contrasts remain unaltered
- Suitable for use after Gadolinium contrast agents
- More difficult (and slower) to achieve at lower field strengths.
- Binomial Excitation
- aka Water Excitation, Jump Back excitation, 1331 excitation
- Relies on the fat and water spins moving out of phase. A series of broadband low flip pulses are timed to decrease the flip angle of Fat, but increase the flip angle of water spins.
- Fat Suppression by selective excitation of water (WE)
- Less susceptible to magnetic field inhomogeneity than spectral saturation
- Lower SAR loading than FATSAT or STIR
- Fastest fat suppression routine
- STIR
- Short TI (tau) Inversion Recovery
- Fat suppression is based on T1 behaviour and selection of TI
- Reverse T1 contrast plus T2 contrast
- Uniform fat suppression independent of magnetic field inhomogeneity
- Can be implemented at any field strength with equal success
- Works well with many acquisition regimes
- Don't use STIR post Gd contrast
- Higher SAR than FATSAT or Water Excitation
- SPIR
- aka Spectral Inversion Recovery
- Spectrally selective form of STIR
- A spectrally selective pulse is applied (non spatial) with a flip selected between 90 and 180 degrees. After a suitable delay time (TD depending on flip angle) the fat spins have reached Mz=0 and the imaging sequence is run.
- Compatible with Gadolinium contrast
- Less susceptible to magnetic field inhomogoneities
- Must be applied at for each excitation routine (TR x slice)
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