Improving MRI contrast: Imaging water and fat

  • Antoine Micheau, MD , Denis Hoa, MD
    • Antoine Micheau, MD : IMAIOS, 2 All Charles R. Darwin, Island Hall 2 34170 Castelnau Le Lez
    • Denis Hoa, MD : IMAIOS, 2 All Charles R. Darwin, Island Hall 2 34170 Castelnau Le Lez
  • Thursday, November 24, 2022
  • ISBN 978-1847537768

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

TechniquePrinciplesAdvantagesDisavantages
STIRInversion-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 SaturationSelective 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 excitationCombination 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

 

Contrast agents

Contrast agentPrinciplesAdvantages / ApplicationsContraindications / Adverse effects

Gadolinium
chelates

T1 reduction +++
T2 reduction		Enhanced T1
Perfusion imaging Well toterated		Allergy, pregnancy
Renal / liver failure : Nephrogenic systemic fibrosis

SPIO
USPIO

Superparamagnetic iron oxides : T2* effectSPIO : liver 
USPIO : ganglion		 
Manganese chelatesT1 effectLiver imaging 

 

Magnetization transfer:

  • RF pulse offset in relation to the resonance peak of water
  • Saturation of protons with restricted mobility (brain, muscle, liver)
  • Drop in signal due to exchanges between free and bound protons
  • Does not affect fluids (LCR, blood, urine) containing no bound protons

References

  1. Elster. Questions and answers in magnetic resonance imaging. 1994:ix, 278 p.
  2. McRobbie. MRI from picture to proton. 2003:xi, 359 p.
  3. NessAiver. All you really need to know about MRI physics. 1997.
  4. Kastler. Comprendre l'IRM. 2006.
  5. de Kerviler, Leroy-Willig. Fat suppression techniques in MRI: an update. Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie. 1998;52(2):69-75.
  6. Gandhi, Brown. MR contrast agents for liver imaging: what, when, how. Radiographics. 2006 Nov-Dec;26(6):1621-36.
  7. Lin and Brown. MR contrast agents: Physical and pharmacologic basics. J Magn Reson Imaging. 2007 May;25(5):884-99.
  8. Sadowski, Bennett. Nephrogenic Systemic Fibrosis: Risk Factors and Incidence Estimation. Radiology. 2007 Jan 31.
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