Biomedical subjects

James D Wilson

Publications and source records attributed to James D Wilson.

9 recordsLinked to original sources

PubMed2005

Synchronization analysis of the uterine magnetic activity during contractions.

BACKGROUND: Our objective was to quantify and compare the extent of synchronization of the spatial-temporal myometrial activity over the human uterus before and during a contraction using transabdominal magnetomyographic (MMG) recordings. Synchronization can be an important indicator for the quantification of uterine contractions. METHODS: The spatialtermporal myometrial activity recordings were performed using a 151-channel noninvasive magnetic sensor system called SARA. This device covers the entire pregnant abdomen and records the magnetic field corresponding to the electrical activity generated in the uterine myometrium. The data was collected at 250 samples/sec and was resampled with 25 samples/sec and then filtered in the band of 0.1-0.2 Hz to study the primary magnetic activity of the uterus related to contractions. The synchronization between a channel pair was computed. It was inferred from a statistical tendency to maintain a nearly constant phase difference over a given period of time even though the analytic phase of each channel may change markedly during that time frame. The analytic phase was computed after taking Hilbert transform of the magnetic field data. The process was applied on the pairs of magnetic field traces (240 sec length) with a stepping window of 20 sec duration which is long enough to cover two cycle of the lowest frequency of interest (0.1 Hz). The analysis was repeated by stepping the window at 10 sec intervals. The spatial patterns of the synchronization indices covering the anterior transabdominal area were computed. For this, regional coil-pairs were used. For a given coil, the coil pairs were constructed with the surrounding six coils. The synchronization indices were computed for each coil pair, averaged over the 21 coil-pairs and then assigned as the synchronization index to that particular coil. This procedure was tested on six pregnant subjects at the gestational age between 29 and 40 weeks admitted to the hospital for contractions. The RMS magnetic field for each coil was also computed. RESULTS: The results show that the spatial patterns of the synchronization indices change and follow the periodic pattern of the uterine contraction cycle. Spatial patterns of synchronization indices and the RMS magnetic fields show similarities in few window frames and also show large differences in few other windows. For six subjects, the average synchronization indices were: 0.346 +/- 0.068 for the quiescent baseline period and 0.545 +/- 0.022 at the peak of the contraction. DISCUSSION: These results show that synchronization indices and their spatial distributions depict uterine contractions and relaxations.

Action Potentials↗

PubMed2005

Fetal magnetoencephalography--a multimodal approach.

Past studies have shown the feasibility of recording fetal evoked responses to external stimuli using a non-invasive technique called magnetoencephalography (MEG). These studies were all performed using either auditory or visual stimuli and showed a fairly low detection rate for each modality, thus making this technology currently unreliable for fetal clinical applications. This study is based on the hypothesis that a multimodal approach of applying both auditory and visual stimulation paradigms in successive recording sessions could improve the probability of obtaining a fetal evoked response. A total of 34 studies were performed on 11 normal healthy fetuses at different stages of gestation starting as early as 28 weeks with a 151-channel fetal MEG system. The success rate of obtaining a response to either (or both) stimuli from a study at a given gestation age was 91%. All the 11 fetuses showed a response at least once over the gestation period the recordings were performed. A multimodal testing approach can improve the ability of the MEG technique to reliably monitor the functional development of the fetal brain.

Acoustic Stimulation↗

PubMed2004

A simple wavelet-based test for evoked responses.

Statistically valid detection of evoked responses from magnetoencephalographic (MEG) sensors is complicated by temporal autocorrelation. By decorrelating time series and transforming them toward normality, the discrete wavelet transform (DWT) allows the analyst to test for an association between stimulus and sensor time series with appropriate degrees of freedom. Eswaran et al. (Neurosci. Lett. 2002a;331:128-32) used a 151-channel fetal MEG system to obtain serial recordings from 10 pregnant subjects. There were 3-8 recordings per subject. In each recording session, the fetus was stimulated by 500Hz and 1KHz tones with a relative frequency of 80-20%, respectively. In this new analysis of the same data, the fetal MEG signals were compared to two different stimulus waveforms: the frequent tone and the Novel stimulus, defined as a change in pitch. WaveDetect was developed to determine whether there was a significant association between the stimuli and the MEG traces. This test is performed by taking the DWT of each series and then computing the Spearman correlation between the wavelet coefficients for an appropriate scale. A significant response (i.e., correlated stimulus-sensor pair) was detected from each patient. This result suggests that the combination of serial recordings and WaveDetect may ensure reliable detection of auditory evoked responses.

Acoustic Stimulation↗

PubMed2004

Prediction of labor in term and preterm pregnancies using non-invasive magnetomyographic recordings of uterine contractions.

OBJECTIVE: The purpose of this study was to characterize the noninvasive magnetic field recordings of the uterine electrophysiological activity in patients reporting onset of uterine contractions. STUDY DESIGN: Transabdominal magnetomyographic (MMG) recordings were performed with the use of the SARA system's 151 primary magnetic sensors (CTF Systems Inc, Coquitlam, British Columbia, Canada). Eleven term and 4 preterm patients participated in the study. On all patients, cervical dilation and outcomes were recorded. RESULTS: Of 8 patients having a peak MMG activity exceeding 8 pT (pico Tesla), all but 1 delivered within 48 hours of our recordings. Of the 7 patients with peak activity below 8 pT, 5 failed to deliver within 48 hours of the recordings. This observation reflects an increase in the electrophysiologic activity of the myometrium as labor progresses. CONCLUSION: MMG evaluation provides a new noninvasive method for the prediction of labor. Further studies are in progress to determine the temporal relationship of MMG changes with the onset of labor.

Adult↗

PubMed2004

Functional development of the visual system in human fetus using magnetoencephalography.

The development of the human brain in utero is normally regarded as a dynamic process involving mainly structural and quantitative changes in neurons and their distribution. However, it is generally accepted that a parallel development of functional specialization occurs in certain areas of the brain, especially in the primary cortex. Nearly all knowledge of functional fetal brain development has been obtained from various animal studies rather than human studies. These studies show that the primary sensory areas like auditory, visual, and somatosensory cortex show a basic function similar to that of a fully developed brain. It has been specifically shown that the visual system develops during fetal life and becomes functional before birth. Several studies have demonstrated the feasibility of using visual evoked response (VER) recordings on preterm human infants to follow the functional development of the visual system. With the advent of the noninvasive technique of magnetoencephalography (MEG), human fetal VER recordings are now possible thus providing the opportunity to track its functional development with gestation. We present and discuss the results of VER recordings in human fetuses starting at 28 weeks of gestation performed using a 151-channel MEG system.

Evoked Potentials, Visual↗

PubMed2004

Fetal MEG redistribution by projection operators.

The fetal magnetoencephalogram (fMEG) is measured in the presence of large interference from the maternal and fetal magnetocardiograms. This interference can be efficiently attenuated by orthogonal projection of the corresponding spatial vectors. However, the projection operators redistribute the fMEG signal among sensors. Although redistribution can be readily accounted for in the forward solution, visual interpretation of the fMEG signal topography is made difficult. We have devised a general, model-independent method for correction of the redistribution effect that utilizes the assumption that we know in which channels the fMEG should be negligible (such channels are distant from the known fetal head position). In a simplified case where the fMEG can be explained by equivalent current dipoles, the correction can also be obtained from fitting the dipoles to the fMEG signal. The corrected fMEG signal topography then corresponds to the dipole forward solution, but without orthogonal projection. We illustrate the redistribution correction on an example of experimentally measured flash evoked fMEG.

Algorithms↗

PubMed2003

Noninvasive antepartum recording of fetal S-T segment with a newly developed 151-channel magnetic sensor system.

OBJECTIVE: The objective of this study was to evaluate the efficiency of the detection of the S-T segment in the fetal PQRST complex that is recorded in the antepartum period with the use of a newly developed noninvasive 151-channel magnetic sensor array. STUDY DESIGN: One hundred two fetal magnetocardiographic recordings were performed on normal fetuses with gestational ages that ranged from 27.5 to 39.5 weeks. After the removal of the interfering maternal heart signals, the fetal heart data were inspected to detect the presence of P, QRS, and T segments. RESULTS: The QRS complex was detectable in 100%, the P wave was detectable in 95.1%, and the T wave was detectable in 87.3% of the recordings. CONCLUSION: Fetal magnetocardiography was recorded successfully, the QRS complex was observed in all subjects, and the T detection rate increased, with the gestational age reaching a peak of 97%. Further study of the S-T segment through the antepartum period could lead to advances in the detection of fetal jeopardy before labor.

Cardiotocography↗

PubMed2002

Short-term serial magnetoencephalography recordings offetal auditory evoked responses.

The study objective was to determine whether short-term serial magnetoencephalographic (MEG) measurements would increase the odds in favor of obtaining fetal auditory evoked responses in normal fetuses. The recordings were performed in two phases using the newly developed 151-channel fetal MEG system, superconducting quantum interference device array for reproductive assessment. Ten pregnant subjects with gestational ages ranging from 30-35 weeks were recruited to participate. Daily recordings were performed over a minimum of 3 days during 1 week of gestation and repeated in the same subjects between 36 and 40 weeks gestation. In 80% of subjects, auditory evoked responses were detected at least once. In healthy fetuses, serial recordings over a short span of time increased the rate of detecting fetal evoked response.

Evoked Potentials, Auditory↗

PubMed2002

First magnetomyographic recordings of uterine activity with spatial-temporal information with a 151-channel sensor array.

OBJECTIVE: The purpose of this study was to examine the feasibility of recording the spatial-temporal magnetomyographic activity from the pregnant uterus with the use of the newly developed 151-channel noninvasive device, known as the superconducting quantum interference device array for reproductive assessment. STUDY DESIGN: Uterine magnetomyographic signals were recorded from 10 pregnant subjects with the 151-channel sensor array curved to fit the pregnant abdomen. The recording sessions were 16 minutes in length, with a sampling rate of 250 Hz. RESULTS: Uterine activity bursts were successfully recorded with the superconducting quantum interference device array for reproductive assessment system. By obtaining a contour plot of the magnetic field distribution, we were able to localize the areas of activation over the uterus during a contraction. Also, it was possible to calculate the time delay in the propagation of the activity across the uterus. CONCLUSION: Using superconducting quantum interference device array for reproductive assessment system, we have established the feasibility of recording uterine contractile activity with spatial-temporal resolution that is high enough to determine the regions of localized activation and propagation over the uterus.

Female↗