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

Abstract

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.

Recent advances in the use of MRI to assess early human cortical development

“…Longitudinal studies in this population have demonstrated immature forms of these RSNs in very preterm infants studied as early as 26 weeks PMA [56, 91]. Interestingly, these results demonstrate great similarity to rs-fcMRI results obtained in fetuses scanned at comparable gestational ages [109-114]. These networks gradually mature during the period in which these infants are cared for in the NICU, demonstrating increasing correlation strength and more mature topology at later PMAs.…”

Quantitative Assessment of Normal Fetal Brain Myelination Using Fast Macromolecular Proton Fraction Mapping

“…Comparison between fetal and adult brain data shows that the MPF enables the largest dynamic range of maturation-dependent changes in brain tissues among quantitative MR imaging parameters available in the literature. [19][20][21][22] Particularly, MPF in WM exhibits about a 5-fold increase from the fetus to adult, whereas the relaxation times T1, 19 T2, 19 and T2* 20 and the apparent diffusion coefficient 21,22 are characterized by the 2-to 3-fold ranges of changes. Despite a generally low level, the MPF in the fetal brain demonstrates substantial regional distinctions and different GA dependencies.…”

“…Third, we did not use specialized image-processing procedures intended to mitigate fetal motion but rather relied on repeat data acquisition with subsequent exclusion of corrupted or misreg- istered source images. The combination of MPF mapping with appropriate registration and motion-correction algorithms 20 may improve the performance and success rate of the method in future applications.…”

Neonatal brain injury and aberrant connectivity

“…These include RSNs located in primary motor and sensory cortices (e.g., somatomotor, visual, auditory networks) and those involving association cortices (e.g., default mode, frontoparietal control, dorsal attention networks). Through investigations of preterm infants and complemented by information available from fetal fMRI investigations, early forms of these networks are identifiable as early as 26 weeks' PMA (Blazejewska et al, 2017;Jakab et al, 2014;Schopf et al, 2014;Thomason et al, 2014;Thomason et al, 2015;Thomason et al, 2017). Many networks initially consist of strong interhemispheric correlations between homotopic counterparts, with intrahemispheric correlations quantifiably weaker.…”