Functional MRI in the rat at 9.4 T and 16.4 T

Functional MRI (fMRI) in animals at high magnetic fields keeps expanding our knowledge about the basics of neural processing but the specificity of the fMRI-signal is still under ongoing investigation. Yet, as the signal to noise ratio in MRI depends linearly on the magnetic field strength and calls for even stronger magnets for the detection of even smaller anatomical details, the relation between the functional MR-response and field strength can only be approximated with complex models. In this study the blood oxygenation dependent (BOLD) effect was measured and compared at 9.4 T and 16.4 T in the same animal with segmented gradient-echo (GE) and spin-echo (SE) echo planar imaging (EPI) sequence using optimal echo times for the respective field. Furthermore, high resolution fMRI acquisition at 16.4 T was performed up to a 50 µm in-plane accuracy and for an 8 s temporal resolution without the use of cryo-coils or coil-arrays