3D in utero quantification of T2* relaxation times in human fetal brain tissues for age optimized structural and functional MRI

Purpose Maximization of the blood oxygen level–dependent (BOLD) functional MRI (fMRI) contrast requires the echo time 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 with the brain of a child or an adult. Methods T2* values of the cortical plate/cortical gray matter tissue in utero in healthy fetuses from mid-gestation onward (20–36 gestational weeks) were measured using 3D T2* maps calculated from 2D dual-echo T2*-weighted 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-weighted structural data. Results Mean T2* relaxation times of the cortical tissue were about twice as high as those reported previously in adults. In a supporting experiment applying single seed analysis, default mode and auditory networks appeared better localized and less noisy while using an echo time of 100 ms versus 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 cortical tissues and subjects in earlier gestation (20–26 gestational weeks). Conclusion The first measurement of T2* values in fetal cortical tissues suggested the appropriate echo time range for fetal BOLD fMRI protocol optimization to be 130–190 ms. Magn Reson Med, 2016. © 2016 International Society for Magnetic Resonance in Medicine.