Evaluation of the reproducibility and confounders of fair ASL placenta perfusion measurement in normal pregnancies

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Arterial spin labeling (ASL) is a very promising non-invasive MRI technique that quantifies placental perfusion using arterial blood water as an endogenous tracer, but lacks reproducibility and standardization, which limits its use in clinical practice. The objective was to standardize and identify confounders of FAIR ASL in placental perfusion estimation. This was a prospective study at Necker Hospital ( NCT04142606 ). Fetal weight estimation and Doppler measurements were performed, followed by MRI on a 1.5 T scanner. A T2-weighted axial FIESTA placenta-centered slice was performed as a reference. Perfusion data were acquired with a 10 mm axial single slice FAIR-SSFSE, repeated 3 times with variable selective inversion thickness (3, 5 and 7 cm). To assess reproducibility, the sequences were performed twice and perfusion was measured on the whole placenta and in 4 regions of interest (ROI) by two operators. We also studied the impact of maternal age, gestational age at examination or placental location on blood flow measurements. Sixty-two patients with normal pregnancy were included. The respective mean blood flow for the 3, 5 and 7-cm-thick inversion was 238.3 ± 68.0 mL/100 g/min, 156.4 ± 46.5 mL/100 g/min and 121.6 ± 39.7 mL/100 g/min respectively (ANOVA, P < 0.01) this demonstrates the importance of the methodology in this evaluation. The thicker section appeared to be more representative of placental perfusion in agreement with data in the literature. However we did not observe a significant difference when averaging the perfusion of the 4 ROI or the whole placenta ( P = 0.21, P = 0.56 and P = 0.85 respectively). The sequences were repeated twice in 10 patients and were reproducible. There was no significant difference according to maternal age, gestational age at examination and placental location (anterior or posterior). This study evaluated the reproducibility of FAIR ASL for measuring placental perfusion and showed that the selective slab inversion thickness has a significant impact on blood flow measurements. Other potential confounders need to be investigated to enable the application of FAIR ASL in clinical practice. A potential future application of ASL would be to detect placental insufficiency.