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Abstract
The increasing availability of ultra-high field scanners has led to a growing number
of submillimetre fMRI studies in humans, typically targeting the gray matter at different
cortical depths. In most analyses, the definition of surfaces at different cortical
depths is based on an anatomical image with different contrast and distortions than
the functional images. Here, we introduce a novel sequence providing bias-field corrected
T1-weighted images and T1-maps with distortions that match those of the fMRI data,
with an image acquisition time significantly shorter than standard T1-weighted anatomical
imaging. For 'T1-imaging with 2 3D-EPIs', or T123DEPI, 3D-EPI volumes are acquired
centred at two inversion times. These 3D-EPIs are segmented into half, quarter or
smaller blocks of k-space to allow for optimisation of the inversion times. T1-weighted
images and T1-maps are then generated as for MP2RAGE acquisitions. A range of T123DEPI
data acquired at 7 T is shown with resolutions ranging from 0.7 mm to 1.3 mm isotropic
voxels. Co-registration quality to the mean EPI of matching fMRI timecourses shows
markedly less local deviations compared to co-registration of a standard MP2RAGE to
the same echo planar volume. Thus, the T123DEPI T1-weighted images and T1-maps can
be used to provide cortical surfaces with matched distortions to the functional data
or else to facilitate co-registration between functional and undistorted anatomical
data.