[Mapping fetal brain development in the second trimester with 7.0T magnetic resonance imaging]

To obtain the three dimensional visualization model with normal measurements of fetal brain in the second trimester and analyze the developmental changes with gestational age (GA), sexual dimorphisms and cerebral asymmetries.The brains of 69 fetal specimens of 12 - 22 weeks GA were scanned by 7.0T magnetic resonance imaging (MRI). The developing structures were analyzed and a three dimensional visualization model was rebuilt with Amira 4.1 software.Most sulci, except for postcentral and intraparietal sulcus, were present until 22 weeks GA. And none developed secondary branches. Laminar organization, described as early as 12 weeks GA, was delineated as layers with different signal intensities and became typical after 16 weeks GA. Basal nuclei was distinctly visible. Brains had different growth rates linearly increasing with GA. But neither sexual dimorphisms nor cerebral asymmetries was detected.The initial developmental stage of fetal brain occurs at 12 - 22 weeks GA. The developing structures may be distinctly visualized on 7.0T post-mortem MRI. And the three dimensional visualization model aids greatly in the precise cognition of immature brain.