Effect of magnet strength on fetal brain biometry - a single-center retrospective MRI-based cohort study.

Abstract

Abnormal fetal brain measurements might affect clinical management and parental counseling. The effect of between-field-strength differences was not evaluated in quantitative fetal brain imaging until now. Our study aimed to compare fetal brain biometry measurements in 3.0T with 1.5T scanners. A retrospective cohort of 1150 low-risk fetuses scanned between 2012 and 2021, with apparently normal brain anatomy, were retrospectively evaluated for biometric measurements. The cohort included 1.5T (442 fetuses) and 3.0T scans (708 fetuses) of populations with comparable characteristics in the same tertiary medical center. Manually measured biometry included bi-parietal, fronto-occipital and trans-cerebellar diameters, length of the corpus-callosum, vermis height, and width. Measurements were then converted to centiles based on previously reported biometric reference charts. The 1.5T centiles were compared with the 3.0T centiles. No significant differences between centiles of bi-parietal diameter, trans-cerebellar diameter, or length of the corpus callosum between 1.5T and 3.0T scanners were found. Small absolute differences were found in the vermis height, with higher centiles in the 3.0T, compared to the 1.5T scanner (54.6th-centile, vs. 39.0th-centile, p < 0.001); less significant differences were found in vermis width centiles (46.9th-centile vs. 37.5th-centile, p = 0.03). Fronto-occipital diameter was higher in 1.5T than in the 3.0T scanner (66.0th-centile vs. 61.8th-centile, p = 0.02). The increasing use of 3.0T MRI for fetal imaging poses a potential bias when using 1.5T-based charts. We elucidate those biometric measurements are comparable, with relatively small between-field-strength differences, when using manual biometric measurements. Small inter-magnet differences can be related to higher spatial resolution with 3T scanners and may be substantial when evaluating small brain structures, such as the vermis.