The Microwave Imaging Method for Express

2017 IEEE First Ukraine Conference on Electrical and Computer Engineering (UKRCON)
The Microwave Imaging Method for Express
Diagnostic of Cancer
Dmytro O. Shtoda, Yurii V. Arkusha, Mykola P. Mustetsov
Department of physical and biomedical electronics and integrated information technology
V. N. Karazin Kharkiv National University
Kharkiv, Ukraine
[email protected]
permittivity of biological tissues and fluids. Moreover, these
changes can occur in the early pre-clinical stages of the
disease. Primarily, it refers to cancer diseases.
Abstract — The rapid growth in the number of cancer
patients in the last decade has become a real challenge for
modern medicine. At first, it is due to the fact that in most
instances the effective treatment is possible only in the early
stages of the disease. Modern medical diagnostic methods which
allow to carry out earlier and pre-clinical diagnostic is usually
invasive, costly, not always safe for the patient, and cannot be
widely used for screening. Therefore, currently, the creation of
new inexpensive and safe methods of early non-invasive diagnosis
of cancer is an important task. The report describes the main
issues and challenges related to development of microwave
imaging systems of biological objects.
A lot of medical studies have shown that in most cases the
water content in the cells of malignant tumors is higher than
that of normal cells. This leads to the fact that the contrast of
the permittivity of the tumor relative to healthy tissue can
achieve a ratio of 10:1 for breast tissue and 1.44:1 for the grey
matter of the brain [3-5, 12, 14-15].
For example, in the case of a study of breast tissue (in vivo
or ex vivo), there is a significant contrast between the
dielectric constant and the conductivity of tissues. The
averaged results of numerous measurements of electrophysical
properties of breast tissue are presented in Table 1 [18-19].
The original hardware-software system for the study of
biological objects is created. The system has frequency range
from 137.5 to 4400 MHz and the sensitivity of 55 dB. The
visualization of the object under study is performed according to
the scattering measurements in the near field region.
TABLE I.
Keywords— microwaves, scattering, measurements, microwave
imaging (MWI), permittivity, conductivity.
I.
MEASURED DIELECTRIC PROPERTIES OF EX VIVO FEMALE
BREAST IN THE FRECUENCY RANGE 2 – 3.2 GHZ.
Tissue
Fat
Normal Tissue
Tumor (Malignant)
Tumor (Benign)
INTRODUCTION
New promising directions of visualization are methods
based on the registration of the electrophysical properties of
living matter. The essence of the methods is as follows:
registration of natural electromagnetic radiation fields of
living matter with a view to measuring the depth of
temperatures; study of the reaction of living matter (of organs
or body systems) to external electromagnetic fields;
measurement of the electrical parameters of the deep layers of
the body for the purpose of visualizing the internal structures
of biological objects.
ε′
4-4.5
10-25
45-60
10-50
σ (S/m)
0.11-0.14
0.35-1.05
3.0-4.0
1.0-4.0
In practice, the measurements in vivo, the contrast slightly
reduced, but in most cases the contrast ratio is at least 2:1
[6, 13, 17-18] that allows to use the permittivity for the
diagnosis of cancer.
Microwave imaging (MWI) is a method of visualization
the internal structure of the test object according to the
scattering of electromagnetic radiation in the microwave
range. For medical research, the diagnostic value represents
the visualization of the distribution of the permittivity and
conductivity of biological tissues.
One of the first fundamental studies of the electrical
properties of living matter in a wide range of frequencies were
carried out in 1941-1959 years by German biologist Schwann
and his colleagues.
Initially, attempts were made to obtain the microwave
imaging techniques using simple models and to demonstrate
how linearization algorithms, similar to the methods of
computer tomography - microwave diffraction tomography
[7-8]. However, for medical diagnostics these methods are not
applicable. Primarily, this is due to the fact that most of the
models are valid only in the case study of objects with lowloss and weak scattering [16].
In his works Schwan detail studied the electrical properties
of living matter, the mechanisms of dispersion of the
permittivity and conductivity of biological tissues was
considered [1-2].
Numerous studies of electrical properties of biological
tissues which carried out both in vivo as in vitro, have shown
that the occurrence of pathological processes in the body, in
most cases accompanied by changes in the conductivity and
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2017 IEEE First Ukraine Conference on Electrical and Computer Engineering (UKRCON)
In addition, the mechanisms of interaction of highfrequency electromagnetic radiation with living matter are
much more complicated than the model of the rectilinear
propagation of the X-ray beam (computed tomography). As a
consequence, simple back projection algorithms based on
Fourier transform cannot be used in microwave imaging and
visualization systems [8, 16], which leads to considerable
complication of the obtaining and reconstruction of
tomography images.
It consists of a power supply (1), high frequency generator
(2), a transmission (3) and receiving (4) patch antennas, twocoordinate positioning system (5), the logarithmic detector (6),
control unit (7), the object of study (8) and the microstrip
directional coupler (9).
As the transmitting and receiving antennas we used inset
feed microstrip patch antennas which are calculated on an
operating frequency of 3250 MHz.
The used patch antenna is shown in Fig.2.
Also, in contradistinction to the X-ray computed
tomography, to solve the inverse problem of scattering
microwave radiation is non-linear and unstable. Therefore to
obtain of full tomography imaging using microwave radiation
requires multiple direct and inverse scattering problem using
methods of regularization and optimization [7-8, 16].
Apart from complicated and expensive microwave
imaging system and imaging in medicine, of particular interest
are simple systems for screening. For example, the active
development of express-methods for determining the complex
dielectric permeability of the skin to detect tumors at early
stages of cancer disease is observed. For this purpose used
various microwave techniques which allow you to measure the
dielectric constant of objects with one-way access. Usually it
is realized using microstrip resonators [9] or open-ended
coaxial probe method [10].
Choice of method and technical implementation of the
measuring system depends on the aim of the study, geometric
dimensions and electrical parameters of the object
(conductivity, permittivity and dielectric loss), temperature
range and the frequency.
II.
Fig. 2. Inset feed microstrip patch antenna
The support material is Teflon (FAF-4D) of thickness
h = 1.5 mm. Antenna size: patch dimension is 33.7x27.5 mm,
the substrate - 50x50 mm, inset distance - 10 mm,
inset gap - 1 mm, feed width - 4.2 mm, feed length 15.5 mm.
Fig. 3 shows the reflection coefficient of our antenna
according to the frequency range 3 - 3.5 GHz.
SYSTEM DESCRIPTION
In this series of experiments we used the improved
hardware-software system which described in [11]. It is a twodimensional planar system for the study of objects in the
microwave range.
The block diagram of microwave measuring system is
shown in Fig.1
Fig. 1. Block diagram of the microwave measuring system
Fig. 3. S11-parameter of the microstrip patch antenna.
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2017 IEEE First Ukraine Conference on Electrical and Computer Engineering (UKRCON)
For measurements in reflection mode was manufactured
microstrip line directional coupler. The width of the microstrip
is calculated on empirical formulas 1-4 for the wave resistance
of 50 ohms, the link length is λ / 4 .
First calculated the coefficients A and B:
1
0.11 
 εr +1  2 εr −1 
A=
+
 0.23 +



60  2 
εr +1 
εr 
Z0
B=
60π 2
Z0 ε r
(1)
(2)
For А> 1.52
W
=
h
8exp( A)
exp(2 A) − 2
(3)
Fig. 5. Simulated S11, S13 and S23 parameter in frequency range 2–4 GHz
For А< 1.52
W
2 
ε −1 
0.61  
=  B −1− ln ( 2 B −1) + r  ln ( B −1) + 0.39−

π 
h
ε r  
2ε r 
The detector head is made on the basis of the logarithmic
amplifier AD8317 and 16-bit analog-to-digital converter
AD7683ARMZ located on one shielded PCB. Thus, the signal
is transmitted from the detector head in digital form that
allows decrease the influence of noise. This engineering
solution is allows for stable measurements with a dynamic
range of 55 dB.
(4)
These formulas provide a calculation error of not more
than 1% [17]. Further adjustment of the geometric dimensions
and the communication parameters of microstrip line coupler
were carried out using microwave structures simulation
program. The design of the directional coupler is shown in
Fig.4
The dual-channel high-frequency generator is made on the
basis of the frequency synthesizer chip ADF4350 and can
cover a continuous frequency range from 137.5 MHz to 4400
MHz with a maximum output power of 5 dBm. Minimum step
of frequency is equal 1 kHz.
The detector head with the high-frequency generator,
directional coupler and receiving antenna is equipped with
two-coordinate positioning system, which allows measuring
the field distribution with minimum step of movement
of 0.05 mm.
The developed software allows to carry out measurements
both in manual and automatic mode; to control the highfrequency generator (selection of operating mode, operating
frequency, output power, delay time in scan mode frequency);
to process and render received data; save the raw data for
processing by other programs.
Thus, our hardware-software complex allows carrying out
research in a broad frequency range of 137.5 - 4400 MHz and
a dynamic range of 55 dB.
Fig. 4. Microstrip line directional coupler
According to measurement results, the operating
attenuation does not exceed of 0.31 dB in the frequency range
0.2-4.4 GHz and directivity is more than 18 dB. The isolated
port is load to 50 ohm termination resistor.
In Fig.6 shows a two-dimensional geometric model of the
direct problem of microwave scattering.
Simulated S parameters of the directional coupler are
shown in Figure 5.
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2017 IEEE First Ukraine Conference on Electrical and Computer Engineering (UKRCON)
During the first experiment was carried out measurement
of the scattered radiation caused by two closely spaced objects
in free space with dielectric constants of 4.8 and 49.25.
First, measurement was made by «reflection mode». The
result of the processing and visualization of scattered field is
presented in Fig.7. In this experiment, the range of
visualization of the scattered field is -10.41 dBm for the lower
part of the scale (blue) to -7.79 dBm for the upper part of the
scale (red). Castor oil filled capacity denotes the number – 1,
a solution of glycerol – 2.
Fig. 6. Two-dimensional model of the direct problem of microwave
scattering
The object is illuminated by a source of electromagnetic
wave Einc, which satisfies the requirements of the Helmholtz
equation [7– 8].
In the absence of the research object, the incident wave is
governed by the vector wave equation
2
∇ × ∇ × E inc (r) - k 0 E inc (r) = -jωμ J ( r )
(5)
Here k 02 = ω 2 μ0 ε 0 ε r is the square of the of the background
medium wavenumber.
Fig. 7. The contrast between the сastor oil and 85 % solution of glycerol
The presence of the object of research is to scatter
microwave radiation in the near field area. In this case, the
total field is a superposition of incident Einc (r) and scattered
E scat (r) field.
Next, a study was conducted of the same objects by the
«transmission mode». The result of the processing and
visualization of scattered field is presented in Fig.8. In this
experiment, the range of visualization of the scattered field is 4.02 dBm for the lower part of the scale (blue) to -2.79 dBm
for the upper part of the scale (red).
E measure (r) = E inc (r) + E scat (r)
(6)
The scattered field is determined as the difference between
the distribution of the total field and the field in the absence of
the object of study.
E scat (r) = E measure (r) - E inc (r)
(7)
After carrying measurements and processing of collected
data we obtain a two-dimensional map of the distribution of
the scattered field by the object of study.
Before the measurement, is necessary to calibrate the
system in the absence of the object of study.
III.
EXPERIMENTAL RESULTS
For evaluation of the measuring system and to find ways
for its optimization, we performed a series of experiments
using simple phantoms of biological objects which have a
strong contrast of permittivity.
Fig. 8. The contrast between the сastor oil and 85 % solution of glycerol.
Transmission mode
In finally, we conducted an experiment to study of the
strong contrast object in a homogeneous space filled with
distilled water.
The small plastic tubular containers were used as test
objects. Containers were filled with distilled water, 85%
glycerin solution and hydrogenated castor oil, which
corresponds to the permittivity of the objects - 81, 49.25 and
4.8 respectively.
For this experimentation container filled with castor oil (1)
was placed in a large container with distilled water. In this
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2017 IEEE First Ukraine Conference on Electrical and Computer Engineering (UKRCON)
case, the contrast of the object under study with the
surrounding space was a maximum – 16:1
REFERENCES
[1]
The result of the processing and visualization of scattered
field is presented in Fig.9. In this experiment, the range of
visualization of the scattered field is -12.47 dBm for the lower
part of the scale (blue) to -7.89 dBm for the upper part of the
scale (red).
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
Fig. 9. The contrast between the сastor oil and distilled water space
Reflection mode
[10]
All the measurements presented in this paper were
performed at a constant frequency of 3250 MHz.
[11]
IV.
[12]
CONCLUSIONS
The experimental verification of the microwave sensing
method for the research of biological objects is presented in
this paper.
Series of experiments carried out to study the microwave
scattering by simple model objects, both in free space and
immersed in distilled water.
The comparison of two methods to measure «transmission
mode» and «reflection mode» is made. The measurements
have shown the ability to detect and distinguish two objects
with strong contrast of dielectric permittivity in both
measurement methods.
Series of experiments that are carried out showed the
fundamental detection possibility of contrasting structures in a
uniform medium like an X-ray methods.
However, to obtain an acceptable spatial resolution or the
study of complex biological objects, it is necessary to develop
a more complex visualization algorithm that will allow more
accurately take into account diffraction effects.
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