Fat suppression failed or suppressed water: causes and fixes
When fat saturation does nothing, or wipes out water instead of fat, the usual cause is the centre frequency or the shim. This is what to check, in order.
Fat suppression suppresses water, or does nothing
The scanner set its centre frequency on the fat peak instead of the water peak. This happens where fat dominates (breast, large patients) and where the field is uneven. Fat sits about 220 Hz below water at 1.5 T and about 440 Hz below at 3 T. Silicone gives a third peak next to fat.
- Open manual prescan and look at the spectrum: two peaks, water on the left, fat on the right in the usual display
- Move the cursor to the water peak and accept
- Repeat the shim with the volume on tissue
- If it still fails, switch to Dixon or STIR
Not a service problem unless fat suppression fails on the phantom.
Fat-suppression failure
Fat stays bright in part of the image, or water is suppressed instead, usually at the edge of the FOV, near air, metal or curved anatomy.
Spectral methods assume fat sits at one exact frequency. Field inhomogeneity shifts that frequency locally, so the pulse misses fat.
- Centre the anatomy at isocentre
- Place the shim volume on tissue and exclude air; repeat the shim
- Switch to STIR or Dixon
- Fill air gaps with pads (neck, between toes) where site practice allows
STIR has lower SNR and cannot be used after contrast. Dixon takes longer and can swap fat and water.
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.