Echo time dependence of laminar BOLD activation at 7 Tesla

Introduction We present a multi-echo fMRI study at 7 T with 0.75 mm isotropic voxels and TEs ranging from 4.8 to 56 ms. This makes it possible to determine T2 at an unprecedented spatial scale making it possible to assess the local influence of myelinisation and vascularisation. As expected [1], the signal superficial to the cortex decays non-mono-exponentially because of a mixed compartment of venous blood (short T2/T2, complex decay pattern) and CSF (long T2/T2). Simultaneously the echo-time dependence of the functional activation in different layers is investigated, where the expectation is that activation in the pial veins will peak at an earlier TE than within GM due to the short T2 of blood at high field strengths [2,3]. It is not to be expected however that after this initial peak the activation will completely disappear because the pial veins are surrounded by CSF and hence there will be a significant extravascular contribution at later TEs.