Research on the developmental changes of central nervous system in the fetus using magnetocardiography and magnetoencephalography

为了评估胎儿中枢神经系统的功能发育，我们首先根据胎儿心电图（fMCG）获得的RR间隔数据集分析胎儿心率变异性，记录胎龄为20-40周的无并发症胎儿的fMCG，并应用功率谱分析计算低频段（LF）、高频频段（HF）和LF/HF比的功率。结果表明，随着孕龄的增加，交感神经活动（LF）的强度显著增加，而副交感神经活动（HF）的强度在孕龄期间保持不变。LF/HF比值也随胎龄的增加而增加，表明在妊娠后期交感神经占优势。因此,。由于R波的检出率和时间分辨率非常高，因此被认为是评估胎儿自主神经系统或胎儿健康状况的有效方法。然后，我们尝试测量胎儿大脑的听觉诱发磁场。胎儿脑电图（fMEG）的检测一直被认为是非常困难的，因为fMEG信号的幅度比fMlCG弱得多，几乎在10^<-14>特斯拉的单位水平上，而且由于信号的非周期性，信号平均技术难以应用。为了提高fMEG的记录成功率，我们对SQUID系统的传感器进行了改进，实现了<10 fT/√<Hz>的空间分辨率。在刺激频率为0.5 Hz，刺激时间为8 min的声脉冲（频率为0.5或1KHz，幅度为70-100 dB，宽度为50 msec）刺激下，记录胎儿颅骨部位在母体腹部的fMEG。得到的信号由声脉冲触发平均。采用该方法，新生儿在脉冲后120 msec处检测到脑电信号的峰值，婴儿在脉冲后120和220 msec处检测到两个峰值。然而，即使足月胎儿也没有明显的fMEG峰值。我们认为，需要进一步提高SQUID系统的灵敏度，听觉刺激和记录方法，以及对数据的后处理，以评估胎儿大脑的功能发育或成熟。少

To assess the functional development of fetal central nervous system, we first analyzed heart rate variability in the fetus based on the data set of RR intervals obtained by fetal megnetocardiography (fMCG), fMCG was recorded in uncomplicated fetuses with the gestational age of 20-40 weeks, and power spectral analysis was applied to calculate the power of the low frequency band (LF), high frequency band (HF) and LF/HF ratio. Consequently, it was demonstrated that the power of LF (sympathetic activity) increases significantly with the gestational age although that of HF (parasympathetic activity) remained unchanged during the period. The LF/HF ratio also increases in proportion with the gestational age, indicating sympathetic dominance in later gestation. Thus, .fMCG is recognized as useful methodology to evaluate fetal autonomic nervous system or fetal well-being, as the detection rate of R waves and the time resolution are very high.Then, we attempted to measure auditory evoked magnet … More ic fields of the fetal - brain. The detection of fetal megnetoencephalogram (fMEG) has been considered very hard because the magnitude of fMEG signals is much weaker than that of fMlCG, almost at the level of units of 10^<-14> Tesla, and because signal averaging technique is difficult to apply due to non-cyclic nature of the signals. To improve the success, rate of recording fMEG, we refined the sensors of the SQUID system and realized spatial resolution of <10 fT/√<Hz>. fMEG was recorded over the site of fetal skull on maternal abdomen under stimulation with acoustic pulses (frequency, 0.5 or 1KHz ; magnitude, 70-100 dB ; width, 50 msec) with a stimulus frequency of 0.5 Hz for 8 min. The signals obtained were averaged triggered by the acoustic pulse. With this methodology, a peak of MEG signal was detected at 120 msec after the pulse in neonates immediately after birth, and two peaks were detected at 120 and 220 msec after the pulse in infants. However, no apparent fMEG peaks were determined for fetuses even in full term. We concluded that further improvement of sensitivity of the SQUID system, auditory stimulation and recording methods, and post processing of the'data would be required to assess the functional development or maturation of the fetal brain using fMEG. Less