The assessment of fetal growth using blood oxygen level dependent magnetic resonance imaging
Intra uterine growth retardation (IUGR) is a condition which affects babies at birth and has a long term effect on the health of individuals. Identification of IUGR fetuses in need of clinical intervention is complicated by the fact that not all small babies are growth retarded; some are growing normally. It has been suggested that maternal oxygen breathing has the potential to raise the fetal oxygen saturation in utero and that these changes may be observed using magnetic resonance imaging (MRI) by way of the blood oxygen level dependent (BOLD) effect. This would give a measure of oxygen transport by the placenta, an important factor in IUGR. To investigate this hypothesis, transverse relaxation time measurements (T2*) were made in the fetal liver of babies pre and post maternal oxygen breathing. This was carried out using single shot fast spin echo (SSFSE) sequences to localise the organ and double echo gradient echo sequences (DE GRE) to determine T2*. T2* was calculated for maternal air and oxygen breathing to allow the change in T2* (ΔT2*) between the states to be calculated. Fetuses were then classified into clinical groups in order to determine whether IUGR was related to ΔT2* or other MRI parameters. The changes in T2* in the fetal liver on maternal oxygen breathing appear to be inconsistent across the groups imaged. These changes are expected to be small and may be undetectable using the current protocol. While significant relationships between the MRI measurements and fetal physiological parameters have been observed, the hypothesis that ΔT2* of the fetal liver can identify IUGR has not been proven. However, this work has provided future direction for the use of MRI in assessing IUGR.