学習目的

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

キーポイント

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

参照

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  6. Gandhi, Brown. MR contrast agents for liver imaging: what, when, how. Radiographics. 2006 Nov-Dec;26(6):1621-36.
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  8. Sadowski, Bennett. Nephrogenic Systemic Fibrosis: Risk Factors and Incidence Estimation. Radiology. 2007 Jan 31.