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1968. Lung to Liver Signal Intensity Ratio: Establishing a Normogram from Serial Measurements During Pregnancy
Authors * Denotes Presenting Author
  1. Hassan Aboughalia *; University of Washington Medical Center
  2. Manjiri Dighe; University of Washington Medical Center
Objective:
Our study aims to evaluate the role of the liver to lung signal intensity ratio in fetal lung maturity assessment and to investigate its change over time during pregnancy. As a side objective, we are also evaluating whether there is a difference between the ratios obtained from the lower lung versus those obtained from the upper lung.

Materials and Methods:
This is a retrospective study evaluating the lung-to-liver signal intensity ratio in normal fetuses. Sixteen normal subjects were included in our study who were imaged at three time points during pregnancy. Two sets of data were obtained by an attending radiologist with expertise in fetal imaging for more than 10 years and a fellowship-trained body and pediatric radiologist. Using coronal or sagittal single-shot T2-weighted images, three regions of interests were obtained from the liver, lower lung and upper lung obtained using a free-hand tool capturing the largest possible area of the respective area with attention to avoid the large vessels and airways.

Results:
Forty-eight measurements were obtained from the 16 fetuses at 3 time points. The average Liver to lung ratio increased as the pregnancy progressed with an average ratio of 3.9 and 3.9 at less than 20 weeks in the lower lung and upper lung respectively, 4.6 and 4.3 between 20 and 28 weeks in the lower lung and upper lung respectively and 7.7 and 6.8 at greater than 28 weeks in the lower lung and upper lung respectively (Figure 1). Bland-Altman plot showed concordance in the measurements between the two reviewers with a concordance correlation coefficient of 0.98 (95% confidence interval 0.95 to 0.99). Serial measurements of the lung to liver ratio within each patient showed a mean difference of 4 (95% CI 1.991 to 6.047) between the first and the last measurements in the lower lung and 2.89 (95% CI 1.355 to 4.409) in the upper lung.

Conclusion:
Normal lung-to-liver signal intensity ratio is a useful non-invasive tool in fetal lung maturity assessment. This ratio increases over time due to increased lung signal intensity as the pregnancy advances. Extrapolating a normal curve during various gestational age of pregnancy can be of great added value to enhance the performance of MRI in fetal lung maturity assessment.