An artefact was observed on postcontrast magnetic resonance imaging (MRI) of the urinary bladder of several small animals; it took the form of a dark layer in the dependent (dorsal) part of the bladder, with a thin hyperintense layer on top of it, and a hypointense signal in the rest of the non-dependent (ventral) part. The MRI database was searched for animals with T 1 -weighted images of the urinary bladder after the injection of gadolinium. Eighteen dogs and three cats were included in the

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... udy. The artefact was observed in 16 of the animals on the postcontrast images but not on the T 1 -weighted and T 2 -weighted precontrast images. A phantom experiment showed that the signal intensity observed on T 1 -weighted images decreased rapidly as the concentration of gadolinium increased from 6·25 mmol/l to 25 mmol/l. It is hypothesised that the early excretion of concentrated gadolinium into the bladder causes the pseudolayering artefact observed, which has also been reported in human patients.