Basics of Fat Suppression For Radiographers

Dear Technologist 

Human body is made up of water as the principle component (reason for using  Hydrogen  MRIs of today ). Fat constitutes the Next abundance. Most of our image quality depends on amount of fat  suppression.

Various fat suppression  techniques exist: 

(a)Difference with Water by frequency selection pulse (called CHESS) (Chemical selective suppression pulse) 

(b) Phase contrast techniques( Mechanism like  India Ink artifacts) 

(c)Short tau inversion recovery Technique(STIR)

(d) DIXON(based on chemical  shift and gives 4 images in one acquisition , i.e. water/fat protons in phase, out of phase, water only and fat only)

(e) Hybrid  technique (combining any of those) 

For all practical purposes the usual decision making is between  STIR and SPAIR

Teaching Points by Dr MGK Murthy

STIR (Short Tau Inversion Recovery Technique ) 

(a) complete sequence   (b) suppresses  all tissues including fat (or near fat resonance frequency for e.g. Gadolinium enhancing tissue) 

(c)can be used in all magnets including low strength  (d)can be used predominantly to produce T2 like contrast    (e) has Low SNR   (f) can be used over large FOV

SPAIR (Spectral Adiabatic Inversion Recovery)

  (a) can be appended/added  to any sequence   (b) selectively suppresses fat only  (c) High homogeneity of magnet required  hence can be used only for high strength  MRIs(preferably 1.5T and above)  (d)can produce T1/T2 like contrast  (e) has High SNR  (f) best and Must for post contrast  fat  suppression (g) can not be used for large FOV

To summarize wherever feasible and available , SPAIR is the preferred technique , Except if the MRI is low strength or FOV is too large . Please use T1 Fat suppression  in pelvis to  decide Dermoid fat suppression (It may not suppress on T2 Techniques and leads to  confusing diagnosis). Of course 3D fat saturated T1 Weighted Spoiled Gradient echo is ideal for post contrast acquisitions in pelvic imaging.