A robust optical respiratory trigger for small rodents in clinical whole-body MR systems.

An increasing number of animal experiments are currently conducted on clinical MR systems. Motion artefacts due to breathing can become quite apparent, in particular with abdominal examinations. These artefacts can be reduced by using a triggered acquisition. However, the built-in detectors in human whole-body scanners are usually not sensitive enough to detect the tiny movements of small rodents. Therefore, a sensitive optical motion detector was developed together with a simple, robust analogue circuit. This circuit converts the original optical signal into an electrical one, compensates slow drifts and offsets, and finally generates a transistor-transistor logic trigger signal as input for the clinical whole-body magnetic resonance scanner. The trigger was successfully applied in mouse experiments.