Imaging description

Crescentic foci of increased T2 signal that mimic fluid may be seen at frequency-selective fat-saturated T2-weighted imaging adjacent to the diaphragm, and can be misinterpreted as small pockets of pleural fluid or ascites (Figure 10.1). The artifact is due to failed fat saturation secondary to local field inhomogeneity at the air-tissue interface between the lung and the diaphragm [1].

Importance

Unsuppressed fat may mimic fluid around the diaphragm, and falsely suggest the presence of pleural fluid or ascites.

Typical clinical scenario

This artifact is common, and in one study was seen in 81% (42/52) of unselected consecutive patients undergoing fatsuppressed T2-weighted fast spin-echo MR imaging [1].

Differential diagnosis

The correct diagnosis of failed fat suppression can be made by cross-registration with other sequences. For example, fat will be of high signal on unsuppressed T1-weighted images, while water will be of low signal (Figure 10.2). Another useful clue that is often seen is co-existent failed fat suppression in the subcutaneous tissue related to field inhomogeneities created by surface coil elements (Figure 10.3).