Human fetal anatomy: MR imaging.

Abstract

Twenty-four pregnant women carrying 26 fetuses (two sets of twins) were imaged with magnetic resonance (MR) imaging at 0.35 T following sonographic evaluation. Each study was retrospectively evaluated to determine which of 33 normal fetal structures were visible on the images and which imaging parameters were most useful for depicting fetal anatomy. Fetal motion degraded fetal images in all but two cases, both with oligohydramnios and in the third trimester of gestation. Nevertheless, many fetal structures were identifiable, particularly in the third trimester. Visualization of fetal anatomy improved with intravenous maternal sedation in five cases. Relatively T1-weighted images occasionally offered the advantage of less image degradation owing to fetal motion and improved contrast between different fetal structures. More T2 weighting was believed to be advantageous in one case for outlining the fetal head and in one case for delineation of the brain. In many cases, structures were similarly identifiable (though with different signal intensities) regardless of the parameters selected. The authors conclude that MR imaging of many fetal structures is currently unsatisfactory and is probably of limited value, particularly in the first and second trimesters. However, the relative frequency and detail with which the fetal head and liver can be depicted indicate that these may be areas for further investigation, and the potential utility of imaging fetal fat warrants further investigation.

The use of magnetic resonance imaging for the diagnosis of fetal intracranial anomalies

“…Optimal spatial resolution was accomplished during the third trimester, although in one patient imaging was performed successfully at 25 weeks' gestational age. Consistent with earlier reports [16,18,20], the increased size of the brain and reduced fetal motion in the third trimester enhanced the use of MRI. Adequate sedation was achieved using intramuscular morphine sulfate, although several investigators have used intravenous diazepam [20] or fetal neuromuscular blockade with curare [4,6] or pancuronium bromide [16].…”

“…Although several investigators have suggested that T2-weighted images produce high signal-to-noise ratios [16,17], in this series relative Tl-weighting with short echoes produced clear delineation between brain and cerebrospinal fluid [9,10,18,20]. Using these sequences, fetal motion artifact was reduced [20] and with the scan's capability to image in three orthogonal planes [9,10,20], cystic intracranial lesions such as Dandy-Walker cysts, porencephaly, or hydranencephaly were visualized clearly.…”

“…Images during the third trimester were improved significantly over those obtained at earlier gestational ages [16,18,20]. Optimal spatial resolution was accomplished during the third trimester, although in one patient imaging was performed successfully at 25 weeks' gestational age.…”

“…Using these sequences, fetal motion artifact was reduced [20] and with the scan's capability to image in three orthogonal planes [9,10,20], cystic intracranial lesions such as Dandy-Walker cysts, porencephaly, or hydranencephaly were visualized clearly. Confirming earlier reports, MRI was not adequate for the evaluation of spinal cord pathology associated with the Chiari II malformation [13].…”

Fetal Hydrocephalus Secondary to Intraventricular Hemorrhage Diagnosed by Ultrasonography and in utero Fast Magnetic Resonance Imaging

“…The application of MRI to fetal imaging has been limited because of artifacts resulting from the motion of the fetus. Fetal curarization and/or maternal sedation before the examination is usually needed to eliminate motion artifacts [11][12][13]. However, the recently developed fast scanning techniques provide clear images in single-breath hold without premedication [10,14,15].…”