UNASSIGNED: Magnetic resonance imaging (MRI) has been used increasingly as an adjunct examination to ultrasound (US) for the evaluation of fetal anomalies. The purpose of this study was to determine whether the accuracy and confidence of diagnosing fetal vertebral anomalies are improved with MRI. We also assessed whether fetal MRI provides additional information when diagnosing fetal vertebral anomalies.
UNASSIGNED: We performed a single-center, retrospective study of 127 pregnant women with fetuses suspected of having vertebral anomalies on US examination; women also underwent fetal MRI scanning. Comparisons of diagnostic accuracy and confidence were made between MRI and US for the identification of fetal vertebral anomalies. We also assessed any additional information provided by MRI. McNemar\'s paired binomial test, chi-square test, or Fisher\'s exact test were used to compare the diagnostic ability between MRI and US. In all cases, postnatal or postmortem imaging findings were used as reference standards.
UNASSIGNED: A total of 127 participants were recruited between December 2015 and January 2021. Fetal vertebral anomalies were detected in 63.8% (81/127) cases and found to be negative in 36.2% (46/127) of cases at follow up. The diagnostic accuracy of vertebral anomalies was 46.9% (38/81) for US and 84.0% (68/81) for MRI [difference, 37.1%; 95% confidence interval (CI): 27% to 48%; P<0.001]. Both MRI and US were concordant and correct in 36.2% (46/127) of fetuses; MRI provided additional information for 16.5% (21/127) of fetuses, and corrected US diagnoses of 36.2% (46/127) of fetuses; both MRI and US were not consistent with postnatal findings in 10.2% (13/127) of fetuses, and the remaining fetus (0.8%, 1/127) was diagnosed correctly using US but failed to be diagnosed by MRI. Diagnoses were reported with high confidence using MRI in 95.3% (121/127) of cases and 73.2% (93/127) using US.
UNASSIGNED: Fetal vertebral MRI improves the accuracy and confidence of diagnosing fetal vertebral anomalies. This finding indicates that fetal MRI supplements the information provided by US and that MRI may be a good complement in selected fetuses, when US can either not achieve a definite diagnosis or there is doubt regarding its reliability. Thus, MRI may be used to inform prenatal counseling and management decisions.

One of the main concerns in fetal MRI is the radiofrequency power that is absorbed both by the mother and the fetus. Passive shimming using high permittivity materials in the form of \"dielectric pads\" has previously been shown to increase the B 1 + efficiency and homogeneity in different applications, while reducing the specific absorption rate (SAR). In this work, we study the effect of optimized dielectric pads for 3 pregnant models.
Pregnant models in the 3rd, 7th, and 9th months of gestation were used for simulations in a birdcage coil at 3T. Dielectric pads were optimized regions of interest (ROI) using previously developed methods for B 1 + efficiency and homogeneity and were designed for 2 ROIs: the entire fetus and the brain of the fetus. The SAR was evaluated in terms of the whole-body SAR, average SAR in the fetus and amniotic fluid, and maximum 10 g-averaged SAR in the mother, fetus, and amniotic fluid.
The optimized dielectric pads increased the transmit efficiency up to 55% and increased the B 1 + homogeneity in almost every tested configuration. The B 1 + -normalized whole-body SAR was reduced by more than 31% for all body models. The B 1 + -normalized local SAR was reduced in most scenarios by up to 62%.
Simulations have shown that optimized high permittivity pads can reduce SAR in pregnant subjects at the 3rd, 7th, and 9th month of gestation, while improving the transmit field homogeneity in the fetus. However, significantly more work is required to demonstrate that fetal imaging is safe under standard operating conditions.