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 T₁ and T₂ at 0.5 T in the human placenta from 20 weeks gestational age until term, in both normal and compromised pregnancies. T₁ 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. T₂ 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 T₁ values measured with the inversion recovery sequence and the T₂ values were found to decrease with gestational age, the linear regression results gave T₁ = - 9.1t + 1538 r² = 0.23 p = 0.03 T₂ = -4.0t + 338 r²=0.47 p=4 10^-6 where t is the gestational age in weeks, and T₁ and T₂ are the relaxation times in milliseconds T₁ 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 T₁ 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 T₁ 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 T₂ 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).