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

Background: Intrauterine growth restriction (IUGR) is an obstetrical condition 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 been used to assess fetal myelin water fraction (MWF) and might potentially assess myelination changes associated with IUGR. Purpose: To quantify and compare the MWF of non-IUGR and IUGR fetal guinea pigs (GPs) in late gestation. Study Type: Prospective animal model. Animal Model: Dunkin-Hartley GP model of spontaneous IUGR (mean +/- SD: 60 +/- 1.2 days gestation; 19 IUGR, 52 control). Field Strength/Sequence: Eight spoiled gradient-recalled (SPGR) gradient echo volumes (flip angles [alpha]: 2 degrees-16 degrees), and two sets of eight balanced steady-state free precession (bSSFP) gradient echo volumes (alpha: 8 degrees - 64 degrees), at 0 degrees and 180 degrees phase increments, at 3.0 T. Assessment: MWF maps were generated for each fetal GP brain using multicomponent driven equilibrium single pulse observation of T-1/T-2 (mcDESPOT). MWF was quantified in the fetal corpus callosum (CC), fornix (FOR), parasagittal white matter (PSW), and whole fetal brain. Statistical Tests: Linear regression was performed between five fetal IUGR markers (body volume, body-to-pregnancy volume ratio, brain-to-liver volume ratio, brain-to-placenta volume ratio, and brain-to-body volume ratio) and MWF (coefficient of determination, R-2). A t-test with a linear mixed model compared the MWF of non-IUGR and IUGR fetal GPs (significance was determined at alpha < 0.05). Results: The MWF of the control fetuses are (mean +/- SD): 0.23 +/- 0.02 (CC), 0.31 +/- 0.02 (FOR), 0.28 +/- 0.02 (PSW), and 0.20 +/- 0.01 (whole brain). The MWF of the IUGR fetuses are (mean +/- SD): 0.19 +/- 0.02 (CC), 0.27 +/- 0.01 (FOR), 0.24 +/- 0.03 (PSW), and 0.16 +/- 0.01 (whole brain). Significant differences in MWF were found between the non-IUGR and IUGR fetuses in every comparison. Data Conclusion: The mean MWF of IUGR fetal GPs is significantly lower than non-IUGR fetal GPs.