Quantifying Myelin Water Fraction in a Guinea Pig Model of Spontaneous Intrauterine Growth Restriction

Abstract

Intrauterine growth restriction (IUGR) is an obstetrical outcome where a fetus has not achieved its genetic potential. A consequence of IUGR is a decrease in brain myelin content. Myelin water imaging (MWI) has previously assessed fetal myelin water fraction (MWF) and can potentially assess myelination changes associated with IUGR. Thus, this study aims to quantify and compare the MWF of non-IUGR and IUGR fetal guinea pigs (GPs) in late gestation. Our sample consisted of 22 pregnant Dunkin-Hartley GPs with 71 fetuses (34 male) [mean {+/-} standard deviation: 60 {+/-} 1.2 days gestation]. Eight SPGR volumes [flip angles (): 2{degrees} - 16{degrees}], and two sets of 8 bSSFP volumes (: 8{degrees} - 64{degrees}), at 0{degrees} and 180{degrees} phase increments were acquired at 3.0 T. MWF maps were generated for each fetal GP brain using multicomponent driven equilibrium single pulse observation of T1/T2 (mcDESPOT). Regions of interest (ROIs) were placed in the fetal corpus callosum (CC), fornix (FOR), and parasagittal white matter (PSW). Linear regression was performed between five fetal IUGR markers [body volume (BV), body-to-pregnancy volume ratio (BPrVR), brain-to-liver VR (BLVR), brain-to-placenta VR (BPlVR), and brain-to-BVR (BBVR)] and MWF for all regions (coefficient of determination, R2). A t-test with a linear mixed model compared the MWF of non-IUGR and IUGR fetal GPs for all three regions ( = 0.05). The MWF values are as follows: (mean {+/-} standard deviation): 0.23 {+/-} 0.02 (fetal CC), 0.19 {+/-} 0.02 (fetal CC - IUGR), 0.31 {+/-} 0.02 (fetal FOR), 0.27 {+/-} 0.01 (fetal FOR - IUGR), 0.28 {+/-} 0.02 (fetal PSW), and 0.24 {+/-} 0.03 (fetal PSW - IUGR). Significant differences in MWF were found between the non-IUGR and IUGR fetuses in every region. In conclusion, the mean MWF of IUGR fetal GPs is significantly lower than non-IUGR fetal GPs.