The investigation of placental relaxation and estimation of placental perfusion using echo-planar magnetic resonance imaging

Abstract

Echo-planar imaging (EPI) is a form of magnetic resonance imaging (MRI) which acquires images in milliseconds rather than ,inutes as with conventional MRI. The images produced using EPI are affected by the physiological environment in which the hydrogen atoms producing the signals are found, a process referred to as relaxation. Also by producing images a matter of milliseconds apart, quantification of perfusion within the tissue being imaged is feasible. The objective of this study was to investigate T1 and T2 relaxation times along with perfusion in placentae from normal pregnancies at different gestations and also to compare these to pregnancies complicated by abnormal placental function. A cross-sectional study of normal and compromised pregnancies from 20 weeks to term and a longitudinal study of normal pregnancy were performed. Placental T1, T2 relaxation times, and perfusion were measured using echo-planar magnetic resonance imaging. Placental T1 and T2 relaxation times decreased in normal pregnancy ( P<0.001). Relaxation times in pregnancies associated with placental pathology appeared to be reduced for that gestation although the numbers were too small to allow any statistical validation. No differences in placental perfusion with gestation or between normal and compromised pregnancy were demonstrated using this technique. This is the first demonstration of placental magnetic resonance relaxation and perfusion measurements in normal pregnancy using echo-planar magnetic resonance imaging. In the future it may be possible to identify compromised pregnancies by differences in placental T1 and T2 relaxation times, using this novel non-invasive technique.