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Improving MRI contrast : Imaging water and fat

Improving MRI contrast : Imaging water and fat

by Denis Hoa

Learning objectives

After reading this chapter, you should be able:

  • To present the different fat signal suppression techniques
  • Describe the advantages and disadvantages of STIR sequences, fat saturation, selective excitation of water
  • Specify the different families of contrast agents
    • Explain their action on relaxation time and contrast
    • List their contraindications and main indications
  • Explain magnetization transfer and how it can improve background suppression

Key points

Water and Fat

Technique Principles Advantages Disavantages

 

STIR


Inversion-recovery with TI adapted to suppress the fat signal (according to its T1)

Usually combined with fast spin echo sequences

Good fat signal suppression

Low dependency on magnetic field heterogeneities

Not specific to tissue but to T1 (fat, hematoma, lesion enhanced by Gadolinium…)

(Long acquisition times in standard STIR)

 

Fat Saturation


Selective RF pulse centered on the resonance frequency of fat + spoiler gradients

+/- selective inversion associated with adapted TI

Fat suppression after Gadolinium injection

Fat selective

No modification in the contrast of the other tissues


Requires homogenous field: less effective in wide FOV or if there are magnetic susceptibility artifacts

SAR increased

TR and acquisition time increased

 

Selective excitation


Combination of RF pulses at intervals adapted to water/fat dephasing to separate magnetization of the water and fat

Only the water supplies the signal

Less sensitive to field heterogeneities

Faster

Efficacy increased if the pulse sequence is more complex




The longer the preparation, the longer the acquisition time

References

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