Reducing Chemical Shift
What can you do to eliminate or reduce the chemical shift artifact?
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Once recognized, chemical shift artifacts can generally be "read around" and should not cause major difficulties in image interpretation. If one is trying to detect subtle abnormalities of the optic nerve or small renal cortical lesion, however, chemical shift artifacts may be of sufficient size to obscure a lesion completely.
One simple way to work around the chemical-shift artifact is to swap the frequency- and phase-encode axes prior to imaging. Doing so will not eliminate the chemical-shift artifact but will rotate it to a different anatomical area. Such a strategy may not be successful, however, since it may cause phase wrap-around or flow-related artifacts to be shifted over the area of interest instead.
A second strategy is to adjust imaging parameters to reduce the size of the artifact. This goal can be accomplished by increasing the total receiver bandwidth (or equivalently, by reducing the field-of-view or increasing the magnitude of the readout gradient).
A final strategy, perhaps the best, is to use some sort of fat suppression technique to reduce the signal from fat and thereby minimize the artifact. Such techniques, including the use of the short TI inversion recovery (STIR) sequence and fat-saturation pulses, are discussed in detail in other Q&A's.
One simple way to work around the chemical-shift artifact is to swap the frequency- and phase-encode axes prior to imaging. Doing so will not eliminate the chemical-shift artifact but will rotate it to a different anatomical area. Such a strategy may not be successful, however, since it may cause phase wrap-around or flow-related artifacts to be shifted over the area of interest instead.
A second strategy is to adjust imaging parameters to reduce the size of the artifact. This goal can be accomplished by increasing the total receiver bandwidth (or equivalently, by reducing the field-of-view or increasing the magnitude of the readout gradient).
A final strategy, perhaps the best, is to use some sort of fat suppression technique to reduce the signal from fat and thereby minimize the artifact. Such techniques, including the use of the short TI inversion recovery (STIR) sequence and fat-saturation pulses, are discussed in detail in other Q&A's.
References
Hood MN, Ho VB, Smirniotopoulos JG, Szumowski J. Chemical shift: the artifact and clinical tool revisited. Radiographics 1999; 19:357-371.
Hood MN, Ho VB, Smirniotopoulos JG, Szumowski J. Chemical shift: the artifact and clinical tool revisited. Radiographics 1999; 19:357-371.
Related Questions
Doesn't the chemical shift between water and fat protons also result in a phase shift between them? If this is so, then why aren't chemical shift artifacts seen in the phase-encode direction also?
What is a chemical-shift artifact?
What is STIR?
Doesn't the chemical shift between water and fat protons also result in a phase shift between them? If this is so, then why aren't chemical shift artifacts seen in the phase-encode direction also?
What is a chemical-shift artifact?
What is STIR?