In vivo measurement of T and T relaxation times in awake pigeon and rat brains at 7T.

Purpose: Establishment of regional longitudinal (T ) and transverse (T ) relaxation times in awake pigeons and rats at 7T field strength. Regional differences in relaxation times between species and between two different pigeon breeds (homing pigeons and Figurita pigeons) were investigated.

Methods: T and T relaxation times were determined for nine functionally equivalent brain regions in awake pigeons and rats using a multiple spin-echo saturation recovery method with variable repetition time and a multi-slice/multi-echo sequence, respectively. Optimized head fixation and habituation protocols were applied to accustom animals to the scanning conditions and to minimize movement.

Results: The habituation protocol successfully limited movement of the awake animals to a negligible minimum, allowing reliable measurement of T and T values within all regions of interest. Significant differences in relaxation times were found between rats and pigeons but not between different pigeon breeds.

Conclusion: The obtained T and T values for awake pigeons and rats and the optimized habituation protocol will augment future MRI studies with awake animals. The differences in relaxation times observed between species underline the importance of the acquisition of T /T values as reference points for specific experiments. Magn Reson Med 79:1090-1100, 2018. © 2017 International Society for Magnetic Resonance in Medicine.