Vol.3, No.8, 482-486 (2011)
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
Electrical impedance tomography based image
reconstruction and feto-maternal monitoring in
Sharvan Kumar Pahuja1*, Sneh Anand1, Amit Sengupt a1,2
1Centre for Biomedical Engineering, Indian Institute of Technology Delhi; Hauz Khas, New Delhi, India; *pahujas@gmail.com;
2OBGYN, Mumbai, India; senguptaamit@hotmail.com
Received 20 January 2011; revised 5 April 2011; accepted 15 June 2011.
Standard methods of monitoring the fetus and
maternal health during labor are cardioto-
cogram, tocography, ultrasound and magneto-
cardiograpghy. These methods have some limi-
tations in real time continuous monitoring and
cause some degree of inconvenience to the pa-
tient and demand special attendance of the ob-
stetrician also these methods cannot be used
for continuous monitoring of the fetal well being.
To overcome the limitations of above techniques ,
a non-invasive bioimped ance measuring method
is proposed. This technique helps in monitoring
and recording of the electrical field distribution
of a closed object. The output variation on the
outer surface is likely to provide information
because of fetal movements and related physio-
logical parameters. It will also help in the de-
velopment of Electrical Impedance Tomography
based imaging technique for a closed body
system with special reference to fetal monitor-
ing in-utero during pregnancy and labor. Also
we have developed the data acquisition system
of 16 electrodes with software for image recon-
Keywords: Impedance Plethysmography; Electrical
Impedance Tomography; Phantom
Feto-maternal monitoring has become a very importa nt
tool to control a fetal health throughout the pregnancy and
during labor. The vital parameters like fetal ECG, uterine
contraction, fetal movements, and growth of the fetus,
amniotic fl uid vol um e and position of placenta ha ve to be
in good conditio n for the fetus health. Fetus in situ initi-
ates compensatory protective mechanism which enables
it to survive from any altered state/ abnormalities (such as
cerebral palsy, placenta previa, asphyxia, respiratory and
the growth) [12, 13] t hat m ay occur both during norm al as
well as abnormal pregnancy. These abnormalities could
be avoided by the timely diagnosis by continuously
monitoring the fetus and mother by the use of the in-
struments. It is imperative to monitor vital parameters at a
regular interval throughout pregnancy and during labor
for feto-maternal well being and for better outcome [14].
Techniques and Instrumentations have been developed to
monitor various parameters and for feto-maternal well-
Cardiotocogram (CTG) is a standard method for
monitoring of fetal heart rate (FHR) and the uterine con-
tractions (UC) in the later stage of the pregnancy. By
analysis and appropriate interpretation of changes in the
CTG obstetrician are able to prevent still birth or as-
phyxia. Other available techniques such as external and
internal tocography (TOCO) [17], Ultrasound [16] and
Magnetocardiograpghy [17] have also been in used for
monitoring of vital parameters of the fetus and mother
[18]. The growth of the fetus and in understanding of the
anatomy and functions of an organ or a physiological
process, various invasive and non-invasive imagining
techniques are available. All medical modalities rely on
ionizing radiation to produce images of structure and
function through a variety of mechanism but the main
biological risk is cancer when imaging in utero. Ultra-
sound is widely used for imaging of the fetus which has
some limitations like long term monitoring is not possible
and demands well trained experience ultrasonographer
for data acquisi t i on .
Despite their scientific perfection all these methods
cause some degree of inconvenience to the patient and
demand special attendance of the obstetrician. Also these
methods cannot be used for continuously monitoring of
S. K. Pahuja et al. / Health 3 (2011) 482- 486
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
the feto-maternal parameters because they are bulky,
expensive, time consuming and n e ed skilled personnel.
To overcome the limitations, here electrical impe dance
monitoring based instrument is proposed. This technique
helps in continuously recording and monitoring non-
invasively of inside electrical field distribution in term of
voltage for a given current. The output voltage on the
abdomen surface of a pregnant lady is likely to provide
information regarding fetal movement and its growth.
The method has already been used in measurement of
bioimpedance. An electrical impedance plethysmograph
based instrum ents have been using in moni toring of bl ood
flow in t he heart [Nyboer]. Nicander et al. a nd Skour ou et
al. have s hown that a ti ssue’ s im pedance signature may be
more sensitive to presence of tumor tissues than co nven-
tional imaging technique of computed tomography and
ultrasound. Also the technique has already been used for
monitoring respiration [Bake], measurement of cardiac
output [Kubicek]. Further the concept of Electrical Re-
sistive Tomography was proposed independently by
Henderson and Webster for medical imaging. Kim has
applied impedance technique for measurem ent of various
physiological e vents. Eac h organ is an aggre gate of many
different cells held together by intracellular supporting
structures. The conductivity of human tissues varies from
cerebrospinal fluid to bone in very large difference. The
range is 15 mS/cm to 0.067 mS/cm [4]. The Table 1
shows the conductivities of various tissues assumed for
50 Hz [Cech]. As shown in table the distribution of con-
ductivity inside the body shows good contrast hence good
electrical conductivity images can be produced of these
Figure 1 shows p ictorial representation of current dis-
tribution and equi-potential lines on the surface of the
Table 1. show s the conductivities of various tissues assumed
for 50 Hz.
Tissue Conductivity (S m-1)
Bone 0.0201
Fat 0.0196
Heart 0.0827
Muscle 0.233
Skeleton of fetus 0.0201
Soft tissue of fetus 0.216
Spinal cord 0.0227
Uterus 0.229
cell contains homogenous electrolyte solution. The high
frequency low AC current is applied between electrodes
I1, I2 which gets uniformly distributed and the resulting
voltage is measured between electrodes V1 and V2. Fig-
ure 2 shows the complete experimental setup. The exci-
tation current is applied into the subjects between Q-S
electrodes in the range of (0.8 mA - 1 mA AC) at 20 -
100 KHz. The voltage produced between P-R electrodes
is amplified and fed to PC using data acqu isition system.
This set up is act as a bridge configuration as shown
Figure 3. Any variation inside (because of fetal move-
ment) will affect the abdomen surface of the pregnant
woman. This can be measured non-invasively in term
voltage. The current and voltage electrodes are switched
through different combinations so that the transfer im-
pedance is measured for different position of applied
The same principle is used in Electrical Impedance
Tomography (EIT) in which an image of the conductiv-
ity distribution within a cross-section of the body is ob-
tained. The technique exploits the electrical characteris-
tics of the tissues by measuring voltages induced on the
electrodes attached to the surface when the currents are
passed between them. The instrument is makes imped-
ance measurement using 16 electrodes on the surface of
the body. A current is passed between pairs of electrodes
(QS). The voltage developed between remaining pairs of
electrodes is than measured sequentially by an array of
instrument amplifiers and fed to data acquisition system
for recording and further analysis. The general schematic
diagram of the data acquisition is shown in Figure 4.
Presently some preliminary work is being carried out
Figure 1. Four-e lec t rode measurement system.
S. K. Pahuja et al. / Health 3 (2011) 482- 486
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
Figure 2. Block Diagram of impedance measuring system.
Figure 3. Equivalent bridge diagram in case of fetal move-
Figure 4. Block diagram of the real-time EIT configuration.
by conducting experiments on a phantom uterus and
fetus. Vital parameters have been recorded using exter-
nal tocography and impedance measurement system.
And images have been reconstructed by image recon-
struction algorithm.
Advanced experimental studies will be carried out to
develop and standardized the instrumentation. The actual
clinical applicability shall be checked at later stages
during clinical trials (on human and animals). The ex-
periments will be conducted on both pregnant women
(with gestation age 25 - 36 week s) and pregnant animals
for the clinical trials to establish the relationship between
fetal movement and immature fetal autonomic nervous
system from the recorded data.
Presently some preliminary work is being carried out by
conducting experiments on a phantom uterus and fetus.
The work is validated by conducting some experiments
by taking papaya and plastic box as phantom. First ex-
periment is performed on phantom papaya. Papaya is
chosen as it imitates the properties of human’s uterus.
Second experiment is conducted on plastic box.
4.1. Case Study 1
Figure 5 shows papaya, watermelon, melon and co-
conut as phantom where we could observe the variation
when the ac curr ent was supplied through two electro des.
The electrode configuration is different in each case.
4.2. Case Study II
Second experiment was conducted on plastic container.
The set up is as shown in Figure 6. The input here is 4
volts at frequency of 40 KHz. The output was measured
between other pairs of electrode by opposite method of
data acquisition.
4.3. Case study II
The electrical conductivity distribution was measured
for a closed object using data acquisition methods. Data
was collected by applying ac current pattern in the range
of 1 - 5 mA at a frequency of 40 KHz to the phantom
papaya through the two conducting electrodes and then
inside conductivity is measured on the papaya surface in
term of voltage between remaining pairs of the elec-
trodes using op posi t e method.
The current-voltage distribution relationship of the
applied current and measured voltage is determined by
Poisson’s or Laplace’s equation with given boundary
conditions measured at the surface. An image of conduc-
tivity distribution was obtained for the closed object
using appropriate image reconstruction algorithm. Soft-
ware is also developed for creating meshes, nodes and
for solving the independent equations for finding the
pixel intensity of an image using iterative methods. Fig-
ure 7 shows the complete experiment set up and the im-
ages reproduced by using image reconstruction algo-
S. K. Pahuja et al. / Health 3 (2011) 482- 486
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
Figure 5. Experimental Setup with different phantom.
Figure 6. Complete experimental setup with plastic
container as model.
Empty Papaya
Object 1
Object 2
Object 3
Figure 7 (a) Experiment setup (b) The 2-D image of an
empty papaya (c ) The 2-D image of the phantom papaya
with objects inside.
S. K. Pahuja et al. / Health 3 (2011) 482- 486
Copyright © 2011 SciRes. http://www.scirp.org/journal/HEALTH/
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The new technique being proposed in this work is non-
invasive, user friendly, economical and for mass health
care which can be used by the poor community and the
basic health work er. Also the nov el ap pro ach will h elp in
defining the morphological and physiological changes
occurring inside the body using EIT as a functional non
invasive imaging tool.
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