Measurement of the Brain Volume/Liver Volume Ratio by Three-Dimensional MRI in Appropriate-for-Gestational Age Fetuses and Those With Fetal Growth Restriction

Background Fetal growth restriction (FGR) is associated with a high fetal brain volume/liver volume (FBV/FLV) ratio. Ultrasound may not always be reliable, which has prompted further investigation of MRI techniques. Purpose To determine the relationship between FBV/FLV ratio, as measured by MRI, and gestational age (GA) in normal fetuses and those with FGR. Study Type Retrospective. Population One hundred and forty seven singleton pregnancies including 105 appropriate-for-gestational age (AGA) fetuses and 42 FGR fetuses. Field Strength/Sequence Three-dimensional fast imaging employing steady-state acquisition at 1.5 T. Assessment The FBV and FLV were measured by three radiologists. The inter- and intraobserver agreements, the correlation between FBV/FLV ratio, and advancing GA were evaluated; the diagnostic value of FBV/FLV ratio was evaluated and compared with head circumference/abdominal circumference (HC/AC) ratio measured by ultrasound. Statistical Tests Intraclass correlation coefficient (ICC) was used to determine inter- and intraobserver agreements. Regression analysis was used to assess the correlation between FBV/FLV ratio and advancing GA. The diagnostic value of the FBV/FLV ratio was examined by the area under the receiver operating characteristic (ROC) curve. Results The inter- and intraobserver agreements were excellent with an interobserver ICC of 0.984 and intra-observer ICCs of 0.989, 0.994, and 0.995. The FBV/FLV ratio in AGA fetuses decreased significantly with advancing GA (Pearson correlation coefficient = -0.844). The FBV/FLV ratio in FGR fetuses was significantly higher than that in AGA fetuses. To identify fetuses at high risk for FGR using the FBV/FLV ratio, the area under the ROC curve was 0.978, with an optimal cut-off value of 4.10. The sensitivity of FBV/FLV ratio in identifying FGR was significantly higher than that of HC/AC ratio (0.929 vs. 0.529). Data Conclusion An inverse correlation exists between FBV/FLV ratio and advancing GA in normal fetuses. A high FBV/FLV ratio may be used to ascertain fetuses at high risk for FGR. Technical Efficacy Stage: 3