Body Surface Laplacian Mapping of Bioelectrical Activity

Comparison of electrohysterogram signal measured by surface electrodes with different designs: A computational study with dipole band and abdomen models

Non-invasive measurement of uterine activity using electrohysterogram (EHG) surface electrodes has been attempted to monitor uterine contraction. This study aimed to computationally compare the performance of acquiring EHG signals using monopolar electrode and three types of Laplacian concentric ring electrodes (bipolar, quasi-bipolar and tri-polar). With the implementation of dipole band model and abdomen model, the performances of four electrodes in terms of the local sensitivity were quantified by potential attenuation. Furthermore, the effects of fat and muscle thickness on potential attenuation were evaluated using the bipolar and tri-polar electrodes with different radius. The results showed that all the four types of electrodes detected the simulated EHG signals with consistency. That the bipolar and tri-polar electrodes had greater attenuations than the others, and the shorter distance between the origin and location of dipole band at 20 dB attenuation, indicating that they had relatively better local sensitivity. In addition, ANOVA analysis showed that, for all the electrodes with different outer ring radius, the effects of fat and muscle on potential attenuation were significant (all p < 0.01). It is therefore concluded that the bipolar and tri-polar electrodes had higher local sensitivity than the others, indicating that they can be applied to detect EHG effectively.

Recording of electrohysterogram laplacian potential

Preterm birth is the main cause of the neonatal morbidity. Noninvasive recording of uterine myoelectrical activity (electrohysterogram, EHG) could be an alternative to the monitoring of uterine dynamics which are currently based on tocodynamometers (TOCO). The analysis of uterine electromyogram characteristics could help the early diagnosis of preterm birth. Laplacian recordings of other bioelectrical signals have proved to enhance spatial selectivity and to reduce interferences in comparison to monopolar and bipolar surface recordings. The main objective of this paper is to check the feasibility of the noninvasive recording of uterine myoelectrical activity by means of laplacian techniques. Four bipolar EHG signals, discrete laplacian obtained from five monopolar electrodes and the signals picked up by two active concentric-ringed-electrodes were recorded on 5 women with spontaneous or induced labor. Intrauterine pressure (IUP) and TOCO were also simultaneously recorded. To evaluate the uterine contraction detectability of the different noninvasive methods in comparison to IUP the contractions consistency index (CCI) was calculated. Results show that TOCO is less consistent (83%) than most EHG bipolar recording channels (91%, 83%, 87%, and 76%) to detect the uterine contractions identified in IUP. Moreover laplacian EHG signals picked up by ringed-electrodes proved to be as consistent (91%) as the best bipolar recordings in addition to significantly reduce ECG interference.

Mean curvature mapping for detection of corneal shape abnormality

Corneal topography is used to measure the anterior surface of the cornea. It is conventionally represented as radial slope, radial curvature, and elevation. In this paper, we introduce the application of mean curvature mapping as an alternative representation of the corneal topography. The purpose is to improve the detection of keratoconus and other diseases characterized by local increase in corneal curvature. Both simulated keratoconic cornea and real keratoconus data exported from the corneal topography system were analyzed. Four representations of corneal topography were generated and compared. It was found that mean curvature mapping provided the most precise cone location in simulated keratoconus. In both actual and simulated keratoconus cases, the appearance of the cone-like distortion is more consistent on mean curvature maps. Mean curvature mapping may improve the detection and localization of corneal shape abnormalities.

A spline Laplacian ECG estimator in a realistic geometry volume conductor

We have developed a spline-based Laplacian estimator over an arbitrarily shaped surface of a volume conductor and tested its applicability to Laplacian electrocardiogram (ECG) mapping. In the newly developed algorithm, estimation of the parameters associated with the spline Laplacian is formulated by seeking the general inverse of a transfer matrix. Only one spline-parameter needs to be determined through regularization in order to estimate the realistic geometry surface Laplacian from the body surface potentials. It has been demonstrated that the rich knowledge on regularization in the inverse problems can be directly applied to estimate the spline Laplacian ECG (LECG), such as the discrepancy principle. Computer simulations have been conducted to validate the new approach in a spherical volume conductor and test the feasibility of mapping cardiac electrical sources in a realistic geometry heart-torso model. The present results demonstrate that the realistic geometry spline LECG can be estimated conveniently from the body surface potentials, is more robust against measurement noise and has better performance than the conventional five-point local Laplacian estimator.

High-resolution EEG: a new realistic geometry spline Laplacian estimation technique

BACKGROUND

A new realistic geometry (RG) spline Laplacian estimation technique has been developed for high-resolution EEG imaging.

METHODS

Estimation of the parameters associated with the spline Laplacian is formulated by seeking the general inverse of a transfer matrix. The number of spline parameters, which need to be determined through regularization, is reduced to one in the present approach, thus enabling easy implementation of the RG spline Laplacian estimator.

RESULTS

Computer simulation studies have been conducted to test the feasibility of the new approach in a 3-concentric-sphere head model. The new technique has also been applied to human visual evoked potential data with a RG head model.

CONCLUSIONS

The present numerical and experimental results demonstrate the feasibility of the new approach and indicate that the RG spline Laplacian can be estimated easily from the surface potentials and the scalp geometry.

Body surface Laplacian mapping in patients with left or right ventricular bundle branch block

Body surface Laplacian maps (BSLMs) have been previously reported to provide enhanced capability in localizing and resolving multiple spatially separate myocardial events. However, only a few studies have been reported on the clinical applications of BSLM. To test the clinical utility of BSLMs, BSLMs and body surface potential maps (BSPMs) during ventricular depolarization for complete right or left ventricular bundle branch block (CRBBB or CLBBB) were studied in ten patients in each group. As a control group, ten healthy subjects were also studied using the same procedure. One hundred and twenty-eight electrodes were placed uniformly over the entire chest and back of the subjects. BSLMs were computed from recorded potentials, using a numerical algorithm. The BSLMs showed multiple and more localized positive and negative activities compared with the BSPMs. In healthy subjects, the BSLMs showed multiple areas of positive activity overlying the RV, LV, and the RV outflow, and negative activity corresponding to RV free-wall breakthrough and LV anterolateral breakthrough sites, whereas the BSPMs could not separate RV and LV activities. In the patients with CRBBB, the BSLMs showed more localized areas of activity corresponding to the LV apex breakthrough and LV lateral breakthrough, and separated LV lateral and posterior activation. In the patients with CLBBB, the BSLMs showed multiple RV activation, and propagating activation of LV from lateral to posterior. The BSLMs appear to provide enhanced capability in detecting multiple ventricular electrical events associated with normal and abnormal conduction and a more detailed activation sequence of both ventricles in healthy subjects and in the patients with CRBBB and CLBBB. BSLM may provide an important alternative to other imaging modalities in localizing cardiac electrical activity noninvasively.