Systems Engineering, University of Arkansas at Little Rock, 2801 S University Ave, Little Rock, AR 72204, United States.
Graduate Institute of Technology, University of Arkansas at Little Rock, 2801 S University Ave, Little Rock, AR 72204, United States.
Neurosci Lett. 2021 Apr 17;750:135791. doi: 10.1016/j.neulet.2021.135791. Epub 2021 Mar 8.
Investigation of fetal evoked response to auditory or visual stimuli is an important means of understanding the developmental stages and potential problems in prenatal life. It is, however, not without certain imperfections. The biggest challenge with fetal evoked response is its low signal to noise ratio. Under noisy conditions, the detected fetal evoked response should, therefore, be further investigated to confirm that the source of the signal is from fetal brain and is not related to random noise. Existing methods for verification are: (1) visual inspection of magnetic field maps, which requires user intervention and expert knowledge which can be highly subjective; (2) simultaneous ultrasound measurement, which is expensive and technically difficult to manage; and (3) equivalent current dipole fitting, which requires knowledge of the orientation of fetal head and its dimensions that may not be available at all times.
To verify that the detected fetal evoked response signal is originating from the fetal head by using an objective and feasible method that employs magnetic dipole fitting to fetal evoked response.
From raw fetal magnetoencephalography data, the cardiac interference was removed by frequency dependent subtraction. After averaging over stimulus triggers, the resulting signal was taken as the candidate fetal evoked response. The fetal evoked response was investigated for the highest peak in between 0.2-0.5 s, which is the expected latency of the response to the stimulus. The magnetic field at this highest peak was used for magnetic dipole fitting. The validation of peak was based on the closeness of the magnetic dipole fit to vicinity of fetal head location determined by ultrasound and the anatomically reasonable distance from the fetal heart. The methodology was first tested on a sample neonatal data before application to fetal data.
The results of neonatal application confirmed that the source localization by magnetic dipole fitting for the brain produced meaningful results. When applied to fetal data, auditory and visual evoked response was detected in 27 of the 38 recordings. This implied that with our verification method, fetal evoked responses were detected in 71% of fetuses.
Detection rate of the evoked responses were similar to earlier reports where subjective visual inspection or simultaneous ultrasound measurement were used. Our method using magnetic dipole fitting for verification is more feasible and objective compared to the earlier methods.
研究胎儿对听觉或视觉刺激的诱发反应是了解产前生命发育阶段和潜在问题的重要手段。然而，它并非完美无缺。胎儿诱发反应最大的挑战是其信噪比低。因此，在噪声环境下，应进一步研究检测到的胎儿诱发反应，以确认信号源来自胎儿大脑，而与随机噪声无关。现有的验证方法有：（1）磁场图的视觉检查，这需要用户干预和专家知识，可能非常主观；（2）同步超声测量，昂贵且技术上难以管理；（3）等效电流偶极子拟合，需要了解胎儿头部的方向及其尺寸，但并非随时都能获得。
通过使用基于磁偶极子拟合的客观可行的方法，验证检测到的胎儿诱发反应信号源自胎儿头部。
从原始胎儿脑磁图数据中，通过频率相关减法去除心脏干扰。在刺激触发后平均后，将得到的信号作为候选胎儿诱发反应。在 0.2-0.5s 之间寻找最高峰值来研究胎儿诱发反应，这是对刺激反应的预期潜伏期。在该最高峰值处的磁场用于磁偶极子拟合。峰值的验证基于磁偶极子拟合与超声确定的胎儿头部位置的接近程度以及与胎儿心脏的合理距离。该方法首先在新生儿样本数据上进行了测试，然后再应用于胎儿数据。
新生儿应用的结果证实，大脑的磁偶极子拟合源定位产生了有意义的结果。在 38 次记录中，27 次检测到听觉和视觉诱发反应。这意味着，使用我们的验证方法，71%的胎儿可检测到胎儿诱发反应。
与使用主观视觉检查或同步超声测量的早期报告相比，诱发反应的检测率相似。与早期方法相比，我们使用磁偶极子拟合进行验证的方法更可行、更客观。
