Investigation of microwave imaging in breast cancer diagnosis

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16 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

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Investigation of
microwave
imaging

in breast cancer

diagnosis
with Dr. Natalia Nikolova


Dr. Natalia Nikolova is a Faculty Member in the Department of Electrical and Computer
Engineering at McMaster University. Dr. Nikolova did her postdoctoral fellowship at McMaster
from 1998 to 1999
and has been a Professor at the university ever since. Dr. Nikolova has also
been appointed
as
Canada Research Chair in High Frequency Electromagn
etics

since 2005
. Her
interest lies in
the areas of
electromagnetic fields and radiation, and her
research
foc
us
es

on
microwaves and radiofrequency fields. Dr. Nikolova is devoted to investigating microwave

imaging techniques to improve the scope for non
-
invasive detection of tumours.
She

is working
in partnership with McMaster’s School of Biomedical Engineering t
o develop objects that will
mimic the human breast. Such objects, called phantoms, will be used to test microwave

imaging
techniques in the detection of tumours associated with breast cancer. Dr. Nikolova’s

goal is to
develop a microwave
imaging technique
that will allow for all women over the age of
50

to
undergo
regular annual
screening for breast cancer
preferably
at their family doctor’s offic
e.
She believes that this will significantly reduce

the
fatal

onset of breast cancer in women.

This
interview fo
cuses on the advancing field of microwave imaging and the implications of this
technology in breast cancer diagnosis.


Q:

Please

share

a little about yourself and your field of research
.

A:
I have been at McMaster since 1998. Initially I was a postdoctoral fellow and then in 1999 I
joined the department as a faculty member. Since then I’ve been around in the Department of
Electrical and Computer Engineering. Currently I am a
P
rofessor, and
,

t
hrough the government
of Canada
,

I have been appointed Canada Research Chair in High Frequency Electromagnetics

since 2005
. As the title of this
C
hair shows, my expertise lies in the general area of
electromagnetic fields and radiation. Within that huge fi
eld my focus as an engineer is on
microwave and radiofrequency fields which have frequencies much lower than optical
frequencies, however much higher than frequencies used in power engineering and radio
broadcasting. This is where my interest lies, and my
PhD work was in the area of computational
electromagnetics. This is an area of research where people are developing computer algorithms
that can simulate electromagnetic fields. However, since 2005 I have started focusing
on

another
area of applied mathema
tics in microwave engineering, and that is microwave imaging. This is a
very
interesting
interdisciplinary
field of study. O
n one side you must understand
electromagnetic fields
,

which is essentially physics
,

and on the other side you must understand
the e
ngineering hardware and the measurement instrumentation involved
,

which is purely
engineering. On the third
,

and very important
, side

you have the mathematical methods which
allow us to interpret the microwave signals that we receive and record in order to

generate
images. These images represent the distribution of the electrical properties of
the tissue. These
properties are

called permittivity and conductivity, but you can think of them as the electrical
properties that determine how a tissue would intera
ct with a microwave field. Because different
tissues have different electrical properties, if we are capable of mapping these electrical
properties, in a way
,

we will be mapping the tissues themselves. In particular, when it comes to
microwave imaging in t
issues we know that the permittivity and conductivity of malignant
tissues are significantly higher than those of healthy tissue
s
.

Every woman above the age of 50 is advised to do an annual exam to test for the
existence of breast cancer, and this exam is
currently
done by X
-
ray mammography. Since
microwaves work with a little higher contrast, the hope is that microwaves can provide b
etter
diagnostic results. Microwaves are also much safer than X
-
rays since they do not ionize
the
tissue. They are referred to as low
-
energy fields, and

the

only known effect of microwaves on
human tissue is heating. However, this heating is estimated to b
e below one
-
thousandth of a
degree, so it is very insignificant.
Unlike X
-
rays
,

microwaves propagate in a very complicated
way through the tissue. We can safely assume that X
-
rays travel along straight paths, but this
cannot be said about microwaves. They
can reflect and
diffract
, and this
significantly
complicates the development of the imaging algorithms that can make sense out of these
measurements. With computed tomography you can obtain very nice images
based on X
-
ray
measurements,
because the computed

tomography assumes that X
-
rays travel in straight paths
,
which is a fair approximation;

X
-
rays

can be blocked by dense tissue such as malignant tissue,

and

they go through transparent tissue such as adipose tissue
. Since this assumption is very close
to
reality, the models come out good. With microwaves we are struggling with the fact that our
models are not good

enough. Currently, this is a major
challenge with microwave imaging, and if
this was not the case then microwave imaging would have been develop
ed a long time ago.
People started looking into microwave tissue imaging in 1970s, and even to this day we do not
have a reliable system that can compete with the other modalities of imaging. While there are
currently microwave systems that are being teste
d on patients, to my knowledge
,

they have not
yet

been put forward for government approval
anywhere in the world
.

That is the general status of microwave imaging right now, and at McMaster we are
one
of the
leaders in this field because we specialize
in real
-
time imaging. That means producing
imaging at the time of the measurements, and this is what really interests the medical
community. There are algorithms out there that require between 15 minutes and several days
of
processing
to produce images,
bu
t all current systems in clinical practice
can produce images in

real

time.
Therefore, if you really want to compete out there with the existing modalities, then
you must be able to produce real
-
time images. Microwave imaging has a lot of advantages

alread
y
, but it also cu
rrently has a lot of drawbacks. One advantage is that

it is a very safe
form
of
radiation and you can undergo the pr
ocedure several times in a day. T
here is

also

no need to
severely compress the breasts as is requi
red in breast X
-
ray mammo
graphy. Finally,

compared to
X
-
ray mammography and
MRI scans,
microwave imaging is significantly cheaper
.

Currently,
you cannot use MRIs and X
-
Ray mammography to scan the whole female population above the
age of
50
on an annual basis because this would be far too costly.
Ideally, if you want to perform
mass screening, you would like cheap technology to be available to family doctors
.
T
his is not
the case
at the moment
with breast cancer screening,
but

microwave imagi
ng could

be the
solution to this issue. At McMaster, we
now
have a prototype scanner that
acquires microwave
signals on tissue phantoms. We do not work with people yet because we have decided that we
need to be absolutely certain that our system will perfo
rm well in breast imaging, and only then
will we start working on people.
Tissue phantoms are artificial substitutes
that we fabricate
ourselves in the lab using chemicals and recipes.
In our case, we
use phantoms to
mimic the
el
ectrical properties of tiss
ues
,

since that is what we are studying.
We are using breast tissue
phantoms to develop and

refine our imaging algorithms, because today

this is the most
challenging part in developing a working system to attain accurate tissue images using
microwaves.


Q:
There is an
improved contrast in using microwave imaging compared to other methods of
imaging, but what are the other advantages that current imaging techniques cannot offer?

A:

The breast cancer research is in dire need of a mass screening tool, but cu
rrently there is no
good mass screening tool. This is the reason why doctors and radiologists are not happy with the
breast cancer situation. Way too often, tumours are discovered late and even today the most
frequently used method to find breast cancer is

palpation.
This is
the
process

of feeling a lump in
the body, and rather than X
-
ray mammography
,

this
is the

way that most women detect the
presence breast cancer
. The reason for this is that, even though X
-
rays can be beneficial, they fail
to find tumour
s in anywhere between 15
-
38% of cases

when a tumour does actually exist
.
This is
due to radiologically dense breasts that do not have much fat. The younger a patient is, the more
likely it is that a patient will have radiologically dense breasts. This is tragic because it means
that X
-
ray mammography is more likely to miss tumo
urs in younger patients. These are typically
people with a long life ahead of them, often with young children who are dependent on them.
For
this reason, X
-
ray mammography does not solve the problem, and MRI

s
cans

are not suitable for
mass
-
s
creening due to

their high
cost
.
Microwave imaging can
improve this
situation

in the
future because it is much
cheaper and more

compact
compared to MRIs and X
-
rays.

Therefore, if
microwave

imaging can be made to
provide the sensitivity that X
-
ray mammography provides,
th
is technology will already be a better option than X
-
ray
mammography
.
This, along with the
significantly increased safety of microwave

imaging due to the lack of tissue ionization,
shows
that microwave imaging could offer a significant a
dvantage over other

imaging tech
niques.


Q:

What are the main challenges that are being faced by researchers in the field of microwave
imaging?

A:
M
icrowave imaging and radars have been around for a long time. However, developing
images for living tissue is very challenging

because living tissue is so heterogeneous. It is one
thing to have a metallic plane in the sky, but it is a completely different thin
g to look for a
tumour that is embedded

and interspersed with healthy tissue which masks
its

presence.
There
are also a nu
mber of challenges on the engineering design and hardware level. We want the best
antennas, because our sensors are essentially antennas.
We also want better receivers, much
better than the receivers in
a

cellphone
and
with a much higher dynamic range.
The hardware
design is not simple; the hardware that is going to be needed
for

microwave imaging is much
more complex than that being used for
commu
nication purposes
.
However, hardware design is
not the major hurdle. More challenging is the hurdle of
findi
ng the best

way to
interpret results,
and

only
after this is done

can we optimally design the antennas and receivers so that they
provide the exact type of results that we will

need
in order
to get a microwave image.
We need to
decide which algorithms are
best for tissue imaging, because there are a number of algorithms
that are used by the radar and microwave imaging community. Adapting these for the challenges
of tissue imaging is what researcher
s in my field are trying to do.


Q
: You are focusing on developing microwave imaging for
breast cancer, but does this
technology help with other similar applications as well, perhaps with other types of cancer?

A
:
The penetration of microwaves
is up to about 8
-
9 centimetres, so the technol
ogy is not
yet
feasible for deep
body tumours.
But the technology
is very useful

for anything that is

as deep as
5
-
6 centimetres.
This is okay for the breast, because the organ is
an exterior organ that is
accessible from all sides
,

and it is compressible.

The imaging

technique

can also be used
on

the
brain
, since
most brain tumours and aneurisms seem to appear close to the surface of the brain
rather than
at

the core.
This is why people are hoping that with microwave imaging we will be
able to image
abnormalitie
s such as tumours and aneurisms in the brain as well.
We

hope that
microwave imaging will eventually have useful applications in

breast and brain i
maging, but to
my knowledge the only other known a
pplication of microwave imaging
is for very sup
erficial
tumours such as melanomas.
The microwaves used for detecting these tumours are very high
frequency
(tera
-
hertz and optical)
waves, and this is already being clinically used
.


Q:

As an engineer, w
hat got you interested in studying breast cancer?

A:

What got me interested is the influence of my colleagues, because our department has a
significa
nt body of biomedical engineers
. None of them are experts on microwave imaging, but
one of our members specializes in medical imaging, and he had a great influ
ence on me. He told
me all about problems with mass screening tools for breast cancer and the problems
in
breast
cancer radiology. I started looking into the world literature for this issue, and I found a
significant body of literature dedicated to
microwa
ves in breast
-
cancer research.
While at this
time I was not studying the area of microwave imaging

or tissue imaging
, I was already in the
broad area of imaging
. All of the people who currently study microwave applications in tissue
imaging are formally
imag
ing experts. You need to have the

knowledge of
how imaging is done
and then you combine it with your expertise as an engineer, because imaging is a very
mathematical subject
. All the reconstr
uction and imaging algorithms are

primarily math, but you
hav
e to combine this knowledge with the proper education in engineering because the signals
that are acquired in microwave imaging are very unique
compared to

signals acquired in other
types of imaging techniques.
Every hardware has specifics, and those speci
fics
dictate th
e
mathematics that is involved.

So my knowledge in the field of imaging, along with the influence
of my colleagues, is what got me interested in the development of micro
wave imaging for breast
cancer.