Efficient exchange of oxygen and nutrients across the placenta is vital for a normally grown fetus. When remodelling of maternal arteries does not occur in early pregnancy the result is placental insufficiency, and fetal growth restriction. Previous studies have shown differences in T2 relaxometry and IVIM between normal and FGR placentae. Here we use a combined T2R and IVIM signal model that separates signals from fetal and maternal blood pools over the whole placental volume. We show difference in T2R, ADC, and maternal perfusion fraction, findings in keeping with previous literature and the pathophysiology of placental insufficiency.
Figure 2 shows example parametric maps for two cases of FGR and two control pregnancies. T2 and ADC maps are visually quite similar between control and pathological placenta, whilst volume fractions of fetal (f*) and maternal (v) perfusion are visibly reduced.
Figure 3 shows parametric histograms over the whole placenta for four imaging parameters. ADC distributions in column two are observed to be different between control and FGR placentae with mean ADC 0.0018(0.0002)mm2s-1 for control and ADC=0.0014(0.004)mm2s-1 for FGR2/3 (95% CI: [-0.0004,-0.0004]mm2s-1). Interestingly the FGR case that delivered at term has an ADC closer to the appearance of the control placentae (ADC=0.0017(0.0002) mm2s-1), motivating its removal from the reported FGR statistics. T2 was reduced in FGR (143.7(59)ms normal vs 119.7(68)ms FGR2/3 (95% CI: [-24.9,21.6]ms)). Fetal perfusion fraction (f*) was similar (0.14(0.11) control vs 0.11(0.12) FGR2/3 (95% CI: [-0.034,-0.028])), whilst the maternal perfusion fraction (v) was reduced in FGR (0.24(0.16) control vs 0.17(0.17) FGR2/3 (95% CI: [-0.075,-0.065])).
1. Lawn, J. E. et al. Stillbirths: Where? When? Why? How to make the data count? Lancet (London, England) 377, 1448–63 (2011).
2. Fox, H. & Sebire, N. J. Pathology of the Placenta. (Saunders Elsevier, 2007).
3. Fox, H. THE PATTERN OF VILLOUS VARIABILITY IN THE NORMAL PLACENTA. BJOG An Int. J. Obstet. Gynaecol. 71, 749–758 (1964).
4. Moore, R. J. et al. In vivo intravoxel incoherent motion measurements in the human placenta using echo-planar imaging at 0.5 T. Magn. Reson. Med. 43, 295–302 (2000).
5. Gowland, P. A. et al. In vivo relaxation time measurements in the human placenta using echo planar imaging at 0.5 T. Magn. Reson. Imaging 16, 241–7 (1998).
6. Derwig, I. et al. Association of placental perfusion, as assessed by magnetic resonance imaging and uterine artery Doppler ultrasound, and its relationship to pregnancy outcome. Placenta 34, 885–91 (2013).
7. Derwig, I. et al. Association of placental T2 relaxation times and uterine artery Doppler ultrasound measures of placental blood flow. Placenta 34, 474–9 (2013).
8. Moore, R. J. et al. In utero perfusing fraction maps in normal and growth restricted pregnancy measured using IVIM echo-planar MRI. Placenta 21, 726–32 (2000).
9. Capuani, S. et al. Diffusion and perfusion quantified by Magnetic Resonance Imaging are markers of human placenta development in normal pregnancy. Placenta 58, 33–39 (2017).
10. Melbourne, A. et al. DECIDE: Diffusion-rElaxation Combined Imaging for Detailed Placental Evaluation. ISMRM 25th Annu. Meet. Exhib. (2017).
11. Portnoy, S. et al. Relaxation Properties of Human Umbilical Cord Blood at 1.5 Tesla. Magnetic Resonance in Medicine 77:1678–1690 (2017)
12. Murphy P.J. The fetal circulation. Continuing Education in Anaesthesia Critical Care & Pain, Volume 5, Issue 4, 1 August 2005, Pages 107–112.