Purpose Maximization of the BOLD fMRI contrast requires TE of the MR sequence to match the T2* value of the tissue of interest, which is expected to be higher in the fetal brain compared to a child or an adult. Methods T2* values of the cortical plate/cortical grey matter tissue in utero in healthy fetuses from mid-gestation onwards (20–36 GW) were measured using 3D T2* maps calculated from 2D dual-echo T2*-w data corrected for between-slice motion and reconstructed in 1.0 mm3 isotropic resolution from a sequence of multiple time points, together with 1.0 mm3 isotropic resolution T2-w structural data. Results Mean T2* relaxation times of the cortical tissue were about two times higher than previously reported in adults. In a supporting single seed analysis experiment default mode and auditory networks appeared better localized and less noisy while using TE=100 ms versus TE=43 ms. The results of the previous study reporting a trend for T2* values to decrease with fetal age were reproduced and extended to include subjects in earlier gestation (20–26 GW) and cortical tissues. Conclusions The first measurement of T2* values in fetal cortical tissues suggested the appropriate TE range for fetal BOLD fMRI protocol optimization to be 130–190 ms.

Recently, there has been considerable interest, especially for in-utero imaging, in the detection of functional connectivity in subjects whose motion cannot be controlled while in the MRI scanner. These cases require two advances over current studies: 1) multi-echo acquisitions and 2) post processing and reconstruction that can deal with significant between slice motion during multi-slice protocols to allow for the ability to detect temporal correlations introduced by spatial scattering of slices into account. This paper focusses on the estimation of a spatially and temporally regular time series from motion scattered slices of multi-echo fMRI datasets using a full 4D iterative image reconstruction framework. The framework which includes quantitative MRI methods for artifact correction, is evaluated using adult studies with and without motion to both refine parameter settings and evaluate the analysis pipeline. ICA analysis is then applied to the 4D image reconstruction of both adult and in-utero fetal studies where resting state activity is perturbed by motion. Results indicate quantitative improvements in reconstruction quality when compared to the conventional 3D reconstruction approach (using simulated adult data), and demonstrate the ability to detect the default mode network in moving adults and fetuses with single-subject and group analysis.

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