Verification of fetal evoked response by magnetic dipole fitting

• Published in: Neuroscience letters 2021-04, Vol.750, p.135791-135791, Article 135791
• Main Authors: Bisgin, Neslihan, Wilson, James D., Eswaran, Hari
• Format: Article
• Language: English
• Subjects: Acoustic Stimulation; Adult; Evoked Potentials; Female; Fetal evoked response (fER); Fetal magnetoencephalography (fMEG); Fetus - physiology; Humans; Infant, Newborn; Magnetic dipole (MD); Magnetoencephalography - methods; Male; Photic Stimulation; Pregnancy; Prenatal Diagnosis - methods; SQUID Array for Reproductive Assessment (SARA)
• ISSN: 0304-3940; 1872-7972
• DOI: 10.1016/j.neulet.2021.135791

[Display omitted] •Fetal evoked response is extracted from a mixture of fetal and maternal signals.•After extracting, the noisy signal needs verification for its source.•We propose a novel method using magnetic dipole fitting to verify the source.•Proposed method is more feasible and objective compared to existing methods.•The method also produces similar success rates for detecting fetal evoked response. 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 wa