Comparison of measurements of the transverse diameter and perimeter of the fetal thymus obtained by magnetic resonance and ultrasound imaging

Abstract

Purpose: To compare measurements of the fetal thymus obtained by magnetic resonance imaging (MRI) and ultrasound (US).

Materials and methods: Written informed consent was obtained from the patients that participated in this Institutional Review Board-approved observational study. The study population consisted of 17 pregnant women carrying fetuses between 21 and 34 weeks of gestation with suspected abnormalities. The transverse diameter and perimeter of the thymus were measured in these fetuses at the level of an axial view of the thorax that includes the pulmonary, aorta, and superior vena cava. The degree of agreement between MRI and US measurements was determined using Lin's concordance correlation coefficient and Bland-Altman analysis.

Results: The mean (standard deviation, SD) gestational age at the time of the prenatal evaluation was 28.4 weeks (3.6). The thymus was measured by MRI and US in all cases. Comparison of the measurements from these two imaging modalities demonstrated a relatively good reproducibility with no evidence of systematic error.

Conclusion: MRI and US measurements of the fetal thymus during the second half of pregnancy are comparable. This finding suggests that MRI can become a useful adjuvant to US for assessment of the fetal thymus.