STIR or fat sat: which fat suppression to use
Both make fat dark, by different mechanisms, and each one fails in a different place.
STIR
Fat is black. Water is very bright because T1 and T2 effects add together.
The most reliable edema detector: marrow lesions, fractures, infection, muscle injury. Works over large fields of view, off-centre, near metal and at low field.
It nulls by T1, not by chemistry: blood, protein and gadolinium-enhanced tissue can be nulled too. Not for post-contrast imaging. Lower SNR than spectral fat suppression.
Fat-suppressed T2 or PD (spectral, SPAIR, Dixon)
As T2 or PD with fat removed selectively.
Same purpose as STIR with higher SNR and sharper detail; the standard fluid-sensitive sequence in joints, spine and abdomen. Dixon also gives a fat image and a water image from one acquisition.
Spectral methods fail where the field is uneven. Unsuppressed fat at the edge of the image can be mistaken for edema.
This page is one entry from the MRI Technologist Reference
The full reference has 31 protocols, 9 dynamic study timelines, 19 artifacts, 16 scanner problems and 15 safety topics, as a PDF in English and Arabic plus an interactive tool.
Educational reference. It does not replace your site protocols, the radiologist's instructions, the MR safety officer, or the manufacturer's instructions for any implant, device or contrast agent. Parameter values are typical starting points at 1.5 T and must be adapted to the scanner, coil and patient.