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.
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
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
2017 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
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.
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
– MC
Where, MC
, 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):
: defined as the ratio of analysed
windows whose DF is inside the typical
frequency range of intestinal SW (8-12 cpm).
: defined as the ratio between the
power within the SW frequency range and the
power in the respiratory bandwidth, calculated
as follows:
=10· log
8 cpm
12 cp
-1 cp
+1 cpm
: defined as the ratio between the
power within the SW frequency range and the
power in the low frequency bandwidth,
calculated as follows:
=10· log
8 cpm
12 cp
6 cp
8 cpm
: 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.
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
was 57.5% (MC1), 61.4% (BC2)
and 50% (BIP). Also, the power ratio of
signal/interference of respiration (PR
) 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
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).
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
(dB) PR
(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).
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
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.
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Effects of Configuration and Dimension of Concentric Ring Electrodes in EEnG Recording Applications