In Vivo Relaxation Time Measurements in the Human Placenta Using Echo Planar Imaging at 0.5 T

This paper presents the first in vivo measurements of the nuclear magnetic resonance relaxation times T 1 and T 2 at 0.5 T in the human placenta from 20 weeks gestational age until term, in both normal and compromised pregnancies. T 1 measurements were performed by using both an inversion recovery sequence and the Look-Locher echo planar imaging (EPI) sequence on a total of 41 women with normal pregnancies and 11 women with compromised pregnancies. T 2 measurements were performed by using a spin-echo EPI sequence on 36 women with normal pregnancies and 14 women with compromised pregnancies. In normal pregnancies, both the T 1 values measured with the inversion recovery sequence and the T 2 values were found to decrease with gestational age, the linear regression results gave T 1=−9.1 t+1538 r 2=0.23 p=0.03 T 2=−4.0 t+338 r 2=0.47 p=4 10 −6 where t is the gestational age in weeks, and T 1 and T 2 are the relaxation times in milliseconds. T 1 values measured very rapidly with the Look-Locher EPI sequence, but, therefore, with a much lower signal-to-noise ratio, showed no significant trends. The T 1 values measured in the abnormal group were significantly lower than those measured in the normal group. Four out of eight patients with compromised pregnancies had placental T 1 values lying outside the 90% confidence limits for the normal population based about the regression line, significantly more than expected by chance ( p = 0.005). Ten out of fourteen of the T 2 measurements in the abnormal group were below the regression line established for the normal group, with 4 lying below the 90% confidence interval, although these trends were only just significant ( p = 0.06 and p = 0.03).