Echo‐planar BOLD fMRI of mice on a narrow‐bore 9.4 T magnet

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Abstract
The feasibility of BOLD fMRI in association with electrical somatosensory stimulation on spontaneously breathing, isoflurane‐anesthetized mice was investigated using spin‐echo, echo‐planar imaging (EPI) on a vertical narrow‐bore 9.4 T magnet. Three experiments were performed to derive an optimal fMRI protocol. In Experiment 1 (n = 9), spin‐echo BOLD responses to 10% CO2 challenge under graded isoflurane (0.25–1.25%) ranged from 10 ± 2% to 3.5 ± 0.9%; the optimal BOLD contrast‐to‐noise ratio peaked at 0.75% isoflurane. In Experiment 2 (n = 6), hindpaw somatosensory stimulations using 1–7 mA under 0.75% isoflurane revealed the optimal BOLD response was at 6 mA. In Experiment 3 (n = 5), BOLD responses to 4 and 6 mA stimulation under 0.75% and 1% isoflurane were evaluated in detail, confirming the optimal conditions in Experiment 2. These results demonstrated that BOLD fMRI using single‐shot, spin‐echo EPI in a mouse somatosensory stimulation model could be routinely performed on high‐field, vertical, narrow‐bore magnets. This protocol might prove useful for fMRI studies of transgenic mice. Magn Reson Med 52:430–434, 2004.