Perfusion and apparent oxygenation in the human placenta (PERFOX)

Abstract

Purpose: To study placental function-both perfusion and an oxygenation surrogate ( $T_2^{*}$ )-simultaneously and quantitatively in-vivo.

Methods: Fifteen pregnant women were scanned on a 3T MR scanner. For perfusion measurements, a velocity selective arterial spin labeling preparation module was placed before a multi-echo gradient echo EPI readout to integrate $T_2^{*}$ and perfusion measurements in 1 joint perfusion-oxygenation (PERFOX) acquisition. Joint motion correction and quantification were performed to evaluate changes in $T_2^{*}$ and perfusion over GA.

Results: The optimized integrated PERFOX protocol and post-processing allowed successful visualization and quantification of perfusion and $T_2^{*}$ in all subjects. Areas of high $T_2^{*}$ and high perfusion appear to correspond to placental sub-units and show a systematic offset in location along the maternal-fetal axis. The areas of highest perfusion are consistently closer to the maternal basal plate and the areas of highest $T_2^{*}$ closer to the fetal chorionic plate. Quantitative results show a strong negative correlation of gestational age with $T_2^{*}$ and weak negative correlation with perfusion.

Conclusions: A strength of the joint sequence is that it provides truly simultaneous and co-registered estimates of local $T_2^{*}$ and perfusion, however, to achieve this, the time per slice is prolonged compared to a perfusion only scan which can potentially limit coverage. The achieved interlocking can be particularly useful when quantifying transient physiological effects such as uterine contractions. PERFOX opens a new avenue to elucidate the relationship between maternal supply and oxygen uptake, both of which are central to placental function and dysfunction.

Keywords: Arterial Spin Labeling (ASL); perfusion; placenta; pre-eclampsia; relaxometry; velocity-selective ASL.