Effects of Configuration and Dimension of Concentric Ring

Electrodes in EEnG Recording Applications

V. Zena-Giménez, J. Garcia-Casado, G. Prats-Boluda and Y. Ye-Lin

Centro de Investigación e Innovación en Bioingeniería, Universidad Politécnica de Valencia,

Camino de Vera SN, Valencia, Spain

Keywords: Ring Electrode, Non-invasive Myoelectric Recording, Electroenterogram, Intestinal Slow Wave.

Abstract: Implementing Laplacian techniques through ring electrodes in bioelectrical records can improve the signal

quality and spatial resolution in comparison to that obtained with conventional disk electrodes. Different

dimensions of the rings and recording settings in one electrode can facilitate bioelectric mapping, and

provide flexibility to studies in the field of bioelectrical signal recording. A concentric multi-ring electrode

(multi-CRE), flexible, with gel, auto-adhesive, that can be configured for monopolar and bipolar records is

presented in this paper. Simultaneous recording of intestinal myoelectric activity (electroenterogram, EEnG)

by means of multi-CRE and conventional disk electrodes, respiration and electrocardiogram signals were

performed in healthy subjects. The results revealed that the ability to detect intestinal slow waves was

greatly influenced by the ability to reject its main interferences. Regarding the recording configuration, it

can be concluded that the use of flexible concentric electrodes in bipolar configuration improves the quality

of EEnG signals. Regarding to the effect of the electrode size, the middle ring (30 mm) reached a balance

between better performance against respiratory interference of small rings and better response to low

frequency interference of large rings.

1 INTRODUCTION

The following section introduces Laplacian

bioelectrical recordings and concentric electrodes as

method to obtain such recordings in contrast to

conventional recordings with disc electrodes. Also, a

brief introduction to the intestinal myoelectrical

signal, the current state of the art of its recording and

the importance of intestinal slow waves.

1.1 Bioelectrical Laplacian Recordings

Bioelectric signals records are usually performed

with conventional disc electrodes, either monopolar

or bipolar configurations. One disadvantage of these

electrodes is their poor spatial resolution, mainly

caused by the blurring effect due to the different

conductivities of the volume conductor (Bradshaw

et al., 2001; Besio et al., 2004, Boudria et al, 2014).

In this context, the Laplacian potential has been

shown to reduce the smoothing effect caused by the

volume conductor and performs a better spatial

resolution.

Different configurations of the concentric

electrodes have been used to estimate the Laplacian

bioelectric potential in the body surface (Lu y

Tarjan, 1999; Besio et al., 2006, Boudria et al,

2014). However, the electrodes proposed in those

works were implemented on rigid substrates, which

can cause discomfort to the patient since they cannot

properly adapt to the body curvature and also require

external adhesive for fixing to the skin. In this

regard, one of the objectives of this paper is to

analyze the performance of an electrode that not

only permits to directly estimate the Laplacian of the

potential, but also it is comfortable for the patient

and easy to use. Moreover, at it will be detailed later,

the presented electrode admits multiple

configuration of monopolar and bipolar

configuration for different ring sizes.

1.2 Intestinal Myoelectrical Activity

The electroenterogram (EEnG) is the record of the

myoelectric activity of the small intestine, which has

two components: the Slow Wave (SW) and the

Spikes Burst (SB) at low and high frequencies,

respectively. The SW are slow and periodic

Zena-GimÃl’nez V., Garcia-Casado J., Prats-Boluda G. and Ye-Lin Y.

Effects of Conﬁguration and Dimension of Concentric Ring Electrodes in EEnG Recording Applications.

DOI: 10.5220/0006154400320037

In Proceedings of the 10th International Joint Conference on Biomedical Engineering Systems and Technologies (BIOSTEC 2017), pages 32-37

ISBN: 978-989-758-216-5

oscillations that act as pacemakers and determine the

maximum frequency of the SB and hence of

intestinal contractions. Intestinal SW frequency

varies along the small intestine, and can range from

about 12 cpm in the duodenum, and 8 cpm

approximately at ileum. Although SW is always

present, the force of contraction of the small

intestine is directly related to the intensity of SB

(Fleckenstein & Oigaard, 1978; Quigley, 1996;

Vantrappen, 1997).

Few studies of EEnG surface recordings in

humans have been reported (Chen et al., 1993;

Chang et al., 2007; Prats-Boluda et al., 2011). One

reason may be because the EEnG is a very weak

signal and it is greatly affected by physiological

interference such as respiration, affecting mainly the

SW activity, and ECG which overlaps with the

bandwidth of the SB.

Another objective of this paper is to analyze and

study the potential benefits of estimating Laplacian

EEnG signal by using concentric ring electrodes in

different configurations and sizes. The study in this

paper is focused in the SW, which is the component

that has greater amplitude in EEnG surface records,

and due to the fact that abnormal SW patterns are

related with diabetes (Ouyang, 2015) and several

intestinal pathologies, such as mechanical intestinal

obstruction, irritable bowel syndrome, paralytic

ileus, and intestinal ischemia (Quigley, 1996;

Somarajan et al., 2015).

This paper is organized as follows. Section 2

includes the material and methods that describes the

manufactured concentric multi-pole sensor, the

protocol for signal recordings and the signal analysis

that was carried out. Section 3 shows the results

obtained: recorded signals and characteristic

parameters. In section 4 such results are discussed

and compared to previous works. The conclusions of

this work are summarized in section 5.

2 MATERIAL AND METHODS

This section firstly describes the penta-polar

concentric electrode (inner disc and 4 out rings)

which was manufactured and evaluated in this work.

Secondly, the recording protocol which was carried

out to obtain EEnG signals from healthy humans

with the proposed mulitring electrode and with

conventional disc electrodes. Finally, the methods

and parameters used for characterizing the different

EEnG signals and comparison of recording

configuration are presented.

2.1 Multi-ring Concentric Electrode

In this work a concentric multi-ring electrode

(multi-CRE) formed by four concentric hook-shaped

and an inner circular electrode was implemented.

The external diameters of the sensing rings were set

to 20, 30, 40 and 50 with a constant thickness of 2

mm. The diameter of the inner disc diameter was set

to 10 mm.

The flexible electrodes were screen-printed with

a biocompatible Ag/Ag-Cl paste (Gwent

C2130429D3) printed onto a flexible polyester film

(Dupont Melinex ST506) using a high precision

screen stencil printer (AUREL 900). The ink curing

period was 130º C for 10 min.

A double sided layer of biocompatible adhesive

104 µm thick (MacTac TM8710), adapted to

dimension of the rings, was used in order to improve

the electrode-skin adhesion. Therefore, the adhesive

remains between the skin and the polyester film

leaving a small gap in the rings so as to deposit a

conductive gel layer to reduce contact impedance.

The bipolar and monopolar signals derived from

multi rings electrodes are given by:

= MC

n+1

– MC

(1)

Where, MC

n+1

, n=1…4 are the monopolar

concentric biopotentials picked up by each ring;

MC1 is the biopotential picked by the inner disc;

n+1 is the number of ring ranging from 2 to 5.

2.2 Signal Recordings

Ten recording sessions of 60 min were carried out in

healthy human volunteers in fast state (>6h).

Subjects were lying in a supine position inside a

Faraday cage. Firstly, the abdominal body surface

was exfoliated to remove dead skin cells to reduce

contact impedance. The abdominal surface was also

shaved in male subjects.

The conductive gel was placed on the multi-CRE

without removing the adhesive backing, spreading

the gel carefully on all rings. Thereafter, the

adhesive backing was removed and the electrode

placed 2.5 cm below the umbilicus, as shown in

figure 1. Similarly, two monopolar Ag/Ag-Cl disk

electrodes of 8 mm of diameter were placed 2.5 cm

above the umbilicus and separated the same

distance. One bipolar conventional recording of

EEnG was obtained from these electrodes.

The main sources of physiological interference

usually presented in surface EEnG recordings were

also recorded. Such as, ECG which was monitored

by Lead I using disposable electrodes; respiration

Effects of Conﬁguration and Dimension of Concentric Ring Electrodes in EEnG Recording Applications

Figure 1: Multi-ring concentric electrode, conventional

disc electrodes and accelerometer sensor positions.

which was measured with an airflow transducer

(1401G Grass Technologies, Warwick, USA) and

movements which were sensed by a triaxial

accelerometer (ADXL 335, Analog Devices).

A disposable electrode was placed in the left

ankle and used as bioelectric reference, another

electrode was placed on the left hip to be used in the

monopolar measurements.

All signals, except from acceleration, were

amplified and band-pass filtered (0.1 – 100 Hz) by

means of conventional bioamplifiers (P511, Grass

Technologies, Warwick, USA). Signals were

simultaneously recorded at a sampling rate of 1 kHz.

2.3 Signal Analysis

In order to study the effect of the configuration and

of the dimensions of the electrode rings in the

detection of SW of the EEnG, ten signals were

analysed in each session: five monopolar concentric

(MC), four bipolar concentric (BC) and one

conventional bipolar (BIP). The EEnG signals and

respiration signal were low-pass filtered (f

=0.5 Hz)

and resampled at 4 Hz.

The power spectral density (PSD) of these

signals was estimated by means of autoregressive

parametric techniques (AR, order 120). The PSD

was estimated in moving windows of 120s every 15s

of the recorded signals. The dominant frequency

(DF) was calculated in each moving window, being

defined as the frequency of the maximum energy

peak above 6 cpm. On the other hand, signals’

quality, in terms of respiration interference and low

frequency components was also evaluated. For this

purpose, it was calculated the Welch periodogram

for each moving window so as to compute subband

energies. To sum up, the following parameters were

calculated (Garcia-Casado et al., 2014):

 %DF

TFSW

: defined as the ratio of analysed

windows whose DF is inside the typical

frequency range of intestinal SW (8-12 cpm).

 PR

SW/RESP

: defined as the ratio between the

power within the SW frequency range and the

power in the respiratory bandwidth, calculated

as follows:

SW/RESP

ሺ

ሻ

=10· log ൭

Power(EEnG)|

8 cpm

12 cp

Power(EEnG)|

RESP

-1 cp

RESP

+1 cpm

൱

(2)

 PR

SW/LF

: defined as the ratio between the

power within the SW frequency range and the

power in the low frequency bandwidth,

calculated as follows:

SW/LF

ሺ

ሻ

=10· log ൭

Power(EEnG)|

8 cpm

12 cp

Power(EEnG)|

6 cp

8 cpm

൱

(3)

 %DF

: defined as the ratio of analysed

windows whose DF, after discarding peaks on

the low frequency and respiration bandwidth,

is in the range of SW.

3 RESULTS

Figure 2a shows an example of recorded signals.

The amplitudes of the monopolar concentric signals

appear similar. However, the amplitude of bipolar

concentric signals increases as it does the size of the

ring. On the other hand, the ECG interference was

more present in monopolar concentric and

conventional bipolar signals, while the bipolar

concentric was less affected. However, in the BC3 it

was observed a slight increase in this interference.

This work is focussed only on the study of the SW

and the energy of ECG signal is mainly outside the

slow wave frequency range, thus no further study of

this interference was done.

The identification of SW in the time domain was

difficult mainly due to cardiac interference in MC

and BIP records, and to low amplitude in BC

records. The figure 2b shows the PSD of the filtered

records of the signals shown in figure 2a, extending

the analysis window to 120s. It can be observed

more energy in the range of 8-12 cpm (SW

frequency range) in BC records than in MC and BIP.

In table 1 mean and standard deviation values of the

calculated parameters are shown. It can be seen that

mean of %DF

TFSW

was 57.5% (MC1), 61.4% (BC2)

and 50% (BIP). Also, the power ratio of

signal/interference of respiration (PR

SW/RESP

) was

higher for bipolar concentric signals acquired from

smaller rings (6.15 dB in BC1, 5.96 dB in BC2) than

monopolar concentric and conventional bipolar

(4.52 dB and 3.51 dB for MC4 and BIP

respectively). This could also be appreciated in the

PSD (Figure 2b) where the MC and BIP records are

BIODEVICES 2017 - 10th International Conference on Biomedical Electronics and Devices

(a) (b)

Figure 2: (a) Simultaneous recordings: MC1-5 monopolar concentric EEnG; BC1-4 bipolar concentric EEnG; BIP

conventional bipolar EEnG; RESP respiration; ECG electrocardiogram (b) Power spectral density of corresponding

windows of 120s of signal in (a).

more affected by respiratory interference. In

addition, the PSDs and Table 1 reflect that the larger

the ring size, the higher the respiratory interference.

On the other hand, conventional bipolar

recordings were less affected by low frequency

interference; with PR

SW/LF

ratio of 4.63 dB. The

monopolar concentric records showed similar values

for all dimensions of rings (around 3.9 dB); while

bipolar concentric shows that larger diameters result

on smaller low frequency interference (opposite

behavior to that of respiratory interference), with

values from 2.9 to 4.0 dB.

The ability to pick up the SW, once discarded

the PSDs’ peaks associated with main interferences

(respiration and low frequency) was better for

bipolar concentric, with mean values reaching

94.9% (BC2) compared to monopolar concentric and

conventional bipolar (around 89% in all these cases).

4 DISCUSSION

In this work, it was developed a flexible multi-CRE

for surface EEnG recording so as to analyse the

influence of ring dimension and recording

configuration on the sensed signal. The multi-CRE

allows flexibility in order to select the best ring to

pick up the SW component of the EEnG and it can

be easily adapted to determine the optimum

dimension of CRE for surface recording of other

weak bioelectrical signals, such as

electrohysterogram, electromyogram,

electrogastrogram and/or electroencephalogram.

Also, its flexibility permits that this electrode design

can estimate directly the Laplacian of the signal

when performing bipolar recordings with the inner

disc and one of the outer rings. Laplacian

bioelectrical recordings have proven to enhance

spatial resolution (Boudria et al, 2014) which can be

Effects of Conﬁguration and Dimension of Concentric Ring Electrodes in EEnG Recording Applications

Table 1: Results of parameters (mean ± standard deviation) of EEnG signals.

Signal %DF

TFSW

SW/RESP

(dB) PR

SW/LF

(dB) %DF

MC1 57.5±10.1 5.04±3.68 3.75±3.25 89.4±5.1

MC2 57.1±10.4 4.93±3.71 3.90±3.22 89.4±5.4

MC3 56.3±10.2 4.66±3.74 3.82±3.12 88.5±6.1

MC4 55.3±9.6 4.52±4.07 3.85±3.06 89.1±5.8

MC5 54.1±8.5 4.56±3.46 3.97±3.22 87.3±5.5

BC1 60.1±6.5 6.15±3.25 2.90±2.88 92.4±4.3

BC2 61.4±10.1 5.96±4.31 3.54±2.87 94.9±3.7

BC3 52.9±13.1 4.47±4.86 3.77±2.98 92.2±3.8

BC4 54.7±18.1 4.17±6.26 4.00±3.10 92.9±3.3

BIP 50.1±10.2 3.51±3.73 4.63±3.44 88.5±8.8

a key factor for the estimation of propagation

velocity of slow waves that are of critical

importance for analysing motor patterns of the small

intestine (Huizinga et al., 2015). Moreover, this

multi-CRE was developed on a flexible substrate

which allows a better adaptation to the curvature of

the body compared to rigid electrodes (Besio et al.,

2006; Prats-Boluda et al., 2011, Boudria et al, 2014

). Additionally, in contrast to other ring electrodes

implemented of flexible substrates (Garcia-Casado

et al., 2014) no other materials for fixing it to the

skin were required due to self-adhesive

characteristics. This may be useful in long term

recording (> 60 min). Similarly, the electrolytic gel

also improves electrode-skin contact impedance, and

reduces the needs regarding intensity of skin

abrasion in comparison to previous works (Prats-

Boluda et al., 2011; Garcia-Casado et al., 2014).

The bipolar concentric recordings were more

immune to respiratory and ECG interference,

improving the quality of EEnG records, compared to

those of monopolar concentric and conventional

bipolar records. This is in agreement with other

studies carried out using CRE implemented on rigid

and flexible substrate (Prats-Boluda et al., 2011;

Garcia-Casado et al., 2014). This feature facilitates

the detection of the SW component of the EEnG.

Although this work was focused on the analysis of

the low frequency component (SW range), the fact

that bipolar concentric signals are more immune to

the ECG interference, can facilitate the detection of

spike burst at high frequency in future EEnG studies.

As for the MC configuration, similar values of SW

detectability were observed for the five ring sizes.

However, in BC configuration, the slow wave could

be best picked up by the medium rings (BC2, 30

mm), reaching a trade-off between better

performance against respiratory interference of small

rings and the best response of large rings to attenuate

low frequency interferences. Similar size and

configuration of tripolar electrodes was used to

record intestinal SW in previous works, but unlike

them in this work the multi-CRE did not require any

active preamplification circuits (Garcia-Casado

et al., 2014).

5 CONCLUSIONS

A multipole concentric ring electrode, flexible, with

gel, and auto-adhesive, which permits many

different settings of simultaneous recording of

bioelectrical signals has been successfully

developed.

The feasibility to capture intestinal slow waves is

greatly influenced by the ability to reject the main

interferences that affect its recording. It can be

concluded that the use of flexible concentric

electrodes in bipolar concentric configuration

(Laplacian estimation) improves the signal quality of

EEnG compared to monopolar configuration and to

traditional bipolar records with disc electrodes.

Regarding to the effect of the electrode size, the

middle ring (30 mm) reached a balance between

better performance against respiratory interference

of small rings and better response to low frequency

interference of large rings. The use of such kind of

electrodes could bring this technique closer to

clinical applications.

REFERENCES

Besio, W., Aakula, R. and Dai, W. 2004., Comparison of

bipolar vs. tripolar concentric ring electrode Laplacian

estimates., Annual International Conference of the

IEEE Engineering in Medicine and Biology Society, 3,

pp. 2255-2258.

Besio, W., Aakula, R., Koka, K. and Dai, W. 2006.,

Development of a tri-polar concentric ring electrode

for acquiring accurate Laplacian body surface

potentials.», Annals of biomedical engineering, 34(3),

pp. 426-435.

BIODEVICES 2017 - 10th International Conference on Biomedical Electronics and Devices

Boudria Y., Feltane A., Besio W.. 2014., Significant

improvement in one-dimensional cursor control using

Laplacian electroencephalography over

electroencephalography.», J Neural Eng., 11(3)

:035014 7pp.

Bradshaw, L. A., Richards, W. O. and Wikswo, J. P.

2001., Volume conductor effects on the spatial

resolution of magnetic fields and electric potentials

from gastrointestinal electrical activity.», Medical &

biological engineering & computing, 39(1), pp. 35-43.

Chang, F.-Y., Lu, C.-L., Chen, C.-Y., Luo, J.-C., Lee, S.-

D., Wu, H.-C. and Chen, J. Z. 2007., Fasting and

postprandial small intestinal slow waves non-

invasively measured in subjects with total

gastrectomy., Journal of gastroenterology and

hepatology, 22(2), pp. 247-252.

Chen, J. D., Schirmer, B. D. and McCallum, R. W. 1993.,

Measurement of electrical activity of the human small

intestine using surface electrodes., IEEE transactions

on bio-medical engineering, 40(6), pp. 598-602.

Fleckenstein, P. and Oigaard, A. 1978., Electrical spike

activity in the human small intestine. A multiple

electrode study of fasting diurnal variations.», The

American journal of digestive diseases, 23(9), pp. 776-

780.

Garcia-Casado, J., Zena-Gimenez, V., Prats-Boluda, G.

and Ye-Lin, Y. 2014., Enhancement of non-invasive

recording of electroenterogram by means of a flexible

array of concentric ring electrodes», Annals of

Biomedical Engineering, 42(3), pp. 651-660.

Huizinga J.D., Parsons S.P., Chen J.H., Pawelka A.,

Pistilli M., Li C., Yu Y., Ye P., Liu Q., Tong M., Zhu

Y.F., Wei D.. 2015., Motor patterns of the small

intestine explained by phase-amplitude coupling of

two pacemaker activities: the critical importance of

propagation velocity.», Am J Physiol Cell Physiol.,

309 (6), pp. C403-414.

Lu, C. C. y Tarjan, P. P. 1999., Slow wave dysrhythmias

in the diabetic small intestine, Biomedical

instrumentation & technology / Association for the

Advancement of Medical Instrumentation, 33(1), pp.

76-83.

Ouyang X., Li S., Foreman R., Farber J., Lin L., Yin J.,

Chen J.D.. 2015, Hyperglycemia-induced small

intestinal dysrhythmias attributed to sympathovagal

imbalance in normal and diabetic rats,

Neurogastroenterol Motil., 27(3), pp. 406-415.

Prats-Boluda, G., Garcia-Casado, J., Martinez-de-Juan, J.

L. and Ye-Lin, Y. 2011., Active concentric ring

electrode for non-invasive detection of intestinal

myoelectric signals., Medical engineering & physics.

Institute of Physics and Engineering in Medicine,

33(4), pp. 446-55.

Quigley, E. M. 1996., Gastric and small intestinal motility

in health and disease., Gastroenterology clinics of

North America, 25(1), pp. 113-45.

Somarajan, S., Muszynski, N. D., Cheng, L. K., Bradshaw,

L. A., Naslund, T. C. and Richards, W. O. 2015.,

Noninvasive biomagnetic detection of intestinal slow

wave dysrhythmias in chronic mesenteric ischemia.»,

American journal of physiology. Gastrointestinal and

liver physiology, 309(1), pp. 52-58.

Vantrappen, G. 1997., Small intestinal motility and

bacteria., in Peter J. Heidt, Volker Rusch, K. V. D. W.

(ed.) Gastrointestinal motility. Old Herborn

University, pp. 53-67.

Effects of Conﬁguration and Dimension of Concentric Ring Electrodes in EEnG Recording Applications