The Development Of The Region Of Basal Nuclei In Fetus Using MRI Of High Field

Ultrasonography (US) had proved to be the important method of choice for examination of the fetal brain in utero. However, it had known limitations in conditions such as maternal obesity and oligohydramnios. Magnetic resonance imaging may be the only complementary means available when US findings were inconclusive and inadequate. However, the application of MR imaging in the fetus in utero had been challenging because of fetal motion and altered fetal position. The post-mortem fetal brain MRI was not restricted in scanning field and sequences, so the images were clearer on post-mortem fetal brain MRI than in vivo, researches of post-mortem MRI had confirmed its'value on autopsy and studies of fetal brain development. The development of the region of basal nuclei took an important role during the development of the whole brain. Changes of the region of basal nuclei was obviously as the GA increased, and it was valuable in estimating health status of the brain and diagnosing disorders of development. Up to now, there had been few reports showing this progress on MRI.Objective:To study the developmental process of the region of basal nuclei by 3.0T and 7.0 T MR images of postmortem fetuses.Methods:131 postmortem fetuses of 14 to 40 weeks gestational age (GA) were scanned by 3.0T MR,34 among them of 14～27 weeks GA were chosen and scanned by 7.0T MR. The time when the structures in the region of basal nuclei could be detected and their changes of MR signal intensity were analyzed on MRI of different Tesla.33 postmortem fetuses of 14 to 22 weeks gestational age (GA) were scanned by 7.0T MR, the volume of basal nuclei was then calculated by Amira software. Lastly, the relationship between these values and fetal age was analyzed statically. Results:On 3.0T MRI, the dorsal thalamus could be delineated as early as 14 weeks GA. The germinal matrix, caudate nucleus, and putamen could be visualized as early as 15 weeks GA. The globus pallidus could be described as early as 18 weeks GA, and the internal capsule and external capsule could be shown as early as 20 weeks GA, and the borderline between the medial globus pallidus and the lateral globus pallidus could be detected on T1WI as early as 20 weeks GA. During 15～25 weeks GA, the germinal matrix could be displayed clearly, the signal from the germinal matrix was relatively high on T1WI and low on T2WI, after 25 weeks GA, the germinal matrix degenerated quickly, and the massive germinal matrix could be detected only in three fetus of 26 GA. The signal intensity of the caudate nucleus during 15～30 weeks GA was relatively low on T1WI and high on T2WI, while during 31～40 weeks GA, it was relatively high on T1WI and low on T2WI. The putamen had a relatively high signal intensity on T1WI and low signal intensity on T2WI during 15～17 weeks GA, and its appearance was patchy during 18～25 weeks GA, then it had a relatively low signal intensity on T1WI and high signal intensity on T2WI during 26～30 weeks GA, and during 31～40 weeks GA, its signal intensity was relatively high on T1WI and low on T2WI. The globus pallidus had a relatively high signal intensity on T1WI and low signal intensity on T2WI during 20～40 weeks GA. Compared to the 3.0T MRI, the T2 images of 7.0T MRI were more clear, and most structures in the region of basal nuclei could be clearly displayed as early as 14 weeks GA, such as the germinal matrix, caudate nucleus, the lenticula, dorsal thalamus. The internal capsule and external capsule could be delineated as early as 16 weeks GA, and the ventral posterior nucleus of thalamus and the mediodorsal nucleus of thalamus became distinguishable by a decrease in their signal intensity as early as 16 weeks GA. The claustrum could be delineated as early as 18 weeks GA.The germinal matrix, caudate nucleus, lenticular nucleus, dorsal thalamus could be displayed clearly during 14～22 weeks GA on 7.0T T2WI, the relationship between the volume of the germinal matrix and gestational age was well described by a equation of the straight line, Y=-1.245+0.115X, R2=0.783, p<0.001, the relationship between the volume of the caudate nucleus and gestational age was described by a by a equation of the straight line, Y=-0.707+0.049X, R2=0.848, p<0.001, the relationship between the volume of the lenticular nucleus and gestational age was described by a equation of the straight line, Y=-1.399+0.104X, R2=0.811, p<0.001, and the relationship between the volume of the dorsal thalamus and gestational age was described by a equation of the straight line, Y=-1.244+0.107X, R2=0.909, p< 0.001.Conclusions:3.0T MRI could show the developmental process of the region of basal nuclei well, but the T2 images of 7.0T MRI were comparatively better. The development of the basal nuclei of postmortem fetuses of 14 to 22 weeks gestational age could be displayed clearly and quantified by 7.0T T2WI using Amira software, which is valuable for clinical diagnosis and evaluation of the development of the brain in vivo.