microwave radar-based differential breast cancer 2003

8/8/2019 Microwave Radar-Based Differential Breast Cancer 2003

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MICROWAVE RADAR-BASED

DIFFERENTIAL BREAST

CANCER IMAGING

Presented By

PRIBIN CHACKO

T7

7941

Guided By

Mrs. Preetha

Basu


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ABSTRACT

An improved antenna is presented for radar-basedbreast cancer imaging. The improvement was achievedby increasing the number of antennas in the array to 31elements, as well as by improving the antenna design

itself. Using an experimental setup, with homogeneouscurved breast phantoms, we have demonstratedsubstantial imaging improvement with the newantenna array. The new system is also able to detect7mm-diameter tumour phantoms in any location withinthe breast, even as close as 4mm from the skin layer.

Additionally, we have shown good imaging results inlow contrast scenarios, where the dielectric contrastbetween tumour and normal tissue was reduced to 2:1.Presented results clearly demonstrate the large impactof antennas characteristics on imaging performance. 2


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CONTENTS

INTRODUCTION

UWB ANTENNA DESIGN

ANTENNA ARRAY DESIGN

3D RADAR IMAGING SETUP

a. Measurement setup

b. 3D breast phantom

c. Differential imaging and focusing algorithm

3D IMAGING RESULTS

a. Comparison with previous antenna arrayb. Location-independent imaging using the new

antenna array

c. Low-contrast imaging using new antenna array

CONCLUSIONS3


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INTRODUCTION

Breast cancer is cancer originating breast fromtissues.

Most commonly found in middle-aged womens.

This paper discusses an application of microwaves for

medical imaging (for cancer detection).

Two main approaches to microwave breast imaging:

1. Microwave tomography and

2. Radar-based imaging

Radar based imaging technique is applied in theproposed method.

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PRINCIPLE

The cancer detection is based on a difference in theelectrical properties of normal and malignant breasttissues

The early work on breast cancer detection was based

on the assumptions of1. High (about 5:1) dielectric contrast, as well as

2. Relatively homogeneous (electrically) internalbreast structure

The most recent studies indicates that that the

contrast might be significantly lower, and also thatthe breast interior is more inhomogeneous thanpreviously assumed.

So breast imaging is much more challenging thanpreviously thought

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PRINCIPLE (CONTD)

Breast phantoms are developed from the MRIscanning images of the breast.

The breast electrical properties differ at the same

level as pixel intensity of MRI images.

The more challenging process is to build a real breast

phantom with the same tissue complexity as in

numerical MRI-based phantoms.

All experimental phantoms reported so far assume

homogeneous breast tissue and only some include the

very important skin layer. In this paper a new antenna array with 31 elements

is presented, designed for microwave radar-based

breast imaging. 6


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PRINCIPLE (CONTD)

System is based on multi-static radar operation Previous prototype used a 16-antenna array, formed

on a section of a hemi-sphere to conform well to the

breast shape.

Here the no. of antenna is increased and antennadesign is improved.

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UWB ANTENNADESIGN

A new improved antenna is selected.

Here we use UWB-Ultra Wide Band antenna.

The main advantages of wide-slot UWB antenna

are

a. low-profile and excellent transientcharacteristics for a wide range of radiation

angles.

The main advantages of the new design are

a. stable radiation pattern across the frequencyband of interest.

b. extremely high fidelity (>95%) of radiated

pulses for radiation angles even up to 600

from bore-sight.

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ANTENNA ARRAY DESIGN

A. Old Array

The old antenna array

design is modified for

improving the

performance The old array contain

only 16 antennas

Arranged on a section of

a hemi-sphere to conformwell to the breast shape.

Old prototype: 16-element array based

on the stacked-patch antenna 9


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ANTENNA ARRAY DESIGN (CONTD)

B. New Array

New antenna array isformed around the lowerpart of a 85mm-radiussphere

3D CAD software is used forthe new array design.

To provide the best radiationcoverage of a breast, allantennas were positioned topoint towards a centre of

curvature. A plastic shell, with

openings for the antennas,has been manufactured toassure the best possibleaccuracy of positioning

antennas

New prototype: 31-element array based

on

the wide-slot antenna.

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ANTENNA ARRAY DESIGN (CONTD)

Schematic of the array modelled using CAD software11


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3D RADAR IMAGING SETUP

A. IMAGING SETUP The array is connected with coaxial cables to a

custom-built network of electromechanical switches

The bank of switches selects all possible pairs of

antennas within the array, and connects them in turn

to a vector network analyser (VNA)

The VNA performs the radar measurement in the

frequency-domain

In a post-reception step, all measured data is

transformed into the time-domain.

With thirty one antenna elements in the array, four

hundred and sixty five independent measurements

(multistatic radar signals) are recorded. 13


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IMAGING SETUP (CONTD)

A computer controls both the VNA and the switch

bank

The measurement takes about 80 seconds to

complete.

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IMAGING SETUP (CONTD)

Experimental setup of our imaging

system.

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3D BREASTPHANTOM

For experimental testing a 3D model of thebreast is developed.

during measurements the antennas are

immersed in a matching liquid, to reduce

reflections from the skin and for a more compactantenna design.

The matching liquid must be able to simulate the

properties of normal breast-fat.

The matching and normal breast tissueequivalent liquid has a relative dielectric

constant of about 10 and an attenuation of 1.2

dB/cm at 6GHz. This material is also dispersive.16


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ALTERNATIVE FOR MATCHING LIQUID

As an alternative to the lossy matching liquid we canuse a ceramic shell to fill the distance between

antennas and a breast skin.

A 1mm thin layer of matching liquid still needs to be used

between antennas and the ceramic shell.

To accommodate breasts of different size, ceramic

insert shells are used.

The ceramic matching shell and inserts are designed,

using low loss material with controlled dielectric

constant (r=10) material Eccostock HiK500F fromEmerson&Cuming.

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DEVELOPMENT OF SKIN PHANTOM

The skin layer is 2mm thick, it is a part of a 67mm-

radius hemi-sphere.

When the skin phantom is fitted into the array it lies

20mm above antenna elements. This distance betweenantennas and breast provides a full coverage of a

breast by an antenna radiation pattern.

The skin layer material is dispersive and, at 6 GHz, it

has a relative dielectric constant of 30 and attenuation

of 16 dB/cm.

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CONSTRUCTION OF TUMOR PHANTOM

Tumour phantom is constructed from a material with

a relative dielectric constant close to 50.

Conductivity of the material is 7 S/m (at 6GHz).

The contrast between dielectric properties of breast

fat and tumour phantom materials is around 1:5.

Recently published data on the electromagnetic (EM)

properties of breast tissues suggest that the contrast

might be significantly lower, and also that the breastinterior is more inhomogeneous than previously thought

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DIFFERENTIALIMAGING

To obtain tumour response from the measured

data we perform two measurements by rotating

the array

This method provides a differential signal, whichis used as an input into focusing algorithm.

Advantage of this differential imaging is that it

does not require a background measurement.

Thus it could be used in realistic scenarios with

breast cancer patients.

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FOCUSING ALGORITHM

A modified delay and sum (DAS) algorithm is

used to form 3D images of scattered energy.

The scattered energy at the given focal point,

within the breast volume, can be expressed as:

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FOCUSINGALGORITHM (CONTD)

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FOCUSINGALGORITHM (CONTD)

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3D IMAGING RESULTS

Comparison with previous antenna array A 10mm (diameter) tumour phantom, located at a

position P(x=20, y=20, z=-20) is considered. In both

cases we have used breast phantom as described

earlier

Phantom used with the 31-elements array had 9mm

bigger radius (skin had r=67mm,for 16 element array

r=58mm only.)

16-element array was slightly smaller due to the fact

that the whole array was formed as a part of spherewith radius 78mm, and the radius of the 31-element

array was 85mm.25


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COMPARISON (CONTD)

To quantitatively assess imaging results, we introduce

a measure of detection quality: ratio of the clutterenergy to the tumour energy, above a certain threshold

t (C/Tt).

The clutter energy is calculated within the entire 3-D

image (hemi-sphere with 67mm radius), and is simply

the sum of focused values exceeding threshold t in all

pixels.

The tumour energy is calculated as the sum of focused

values above the threshold, for pixels located within a

cube of 24x24x24mm3, with the maximum focusedsignal located in the centre of the cube.(volume where wecalculate the clutter is about forty five times larger than that of

the tumour)

Another measure for quantitative assessment of

imaging results is a ratio of peak clutter energy to apeak tumour energy (peakC/T ), calculated within a full

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COMPARISON (CONTD) 3D IMAGES

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COMPARISON (CONTD)

Looking at figures for the

16-element and the 31-elements arrays we cansee that in both casestumour has been detected.

A single artifact is also

visible for the 16-elementarray.

? HOW THE FIGURES

ARE PLOT?

3D images are shown ascontour plots at -1.5dBcut-off (all values smallerthan -1.5dB of a maximumvalue are not shown).


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COMPARISON (CONTD)

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COMPARISON (CONTD) 2D IMAGES

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COMPARISON (CONTD)

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COMPARISON (CONTD)

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COMPARISON (CONTD)

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COMPARISON (CONTD)

Use only sixteen antenna for focusing with new

array with the positions closest to those from theold array

35

Same as old

figure


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COMPARISON (CONTD)

As expected, there is more clutter in the image But these results are still significantly better than

for the old array with the same number of

antennas.

36Old array New array


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COMPARISON (CONTD)

The above results let us finally draw a conclusionthat the superior imaging performance is due to

a. The better antenna design, and

b. The larger number of antennas, which provideslarger array aperture and higher diversity of

the radar data.

This is encouraging and suggest that animprovement could still be achieved by further

working on the better antenna and by adding more

antennas to the array. 37


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LOCATION-INDEPENDENT IMAGING

USING THE NEWANTENNAARRAY

A malignant tissue can be located anywherewithin a breast.

So investigations are done at several locations ofthe breast.

3 locations are picked within +x/+y quadrant (dueto symmetry of the array). They are

1. P1 (x=0,y=50,z=-30),

2. P2 (x=50,y=0,z=-30),

3. P3 (x=40,y=40,z=-30).All three positions represent challenging cases of

tumours in a close proximity of the skin layer.Any other locations further away from a skin areeasier to detect

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RESULTS

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LOCATION-INDEPENDENT IMAGING(CONTD)

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LOW-CONTRAST IMAGING USING NEW

ANTENNAARRAY

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LOW-CONTRAST IMAGING : RESULTS

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LOW-CONTRAST IMAGING (CONTD)

In all the cases the tumor detected without anyproblems.

However, as the dielectric contrast decreases, clutter

increases.

The obtained peak C/T values are

0.36 for a 5:1 contrast,

0.54 for a 2.7:1 contrast, and

0.69 for a 2:1 contrast.

This gives almost 100% increase in peak C/Tvalue,

when dielectric contrast decreases from 5:1 to 2:1.

However, it does not prohibit successful detection.

These results confirm that

The lower dielectric contrast imposes additional

challenges for microwave imaging modalities

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CONCLUSIONS

This paper presents the new improved antenna array forradar-based breast cancer imaging.

Improvement was achieved by increasing the number ofantennas in the array as well as by designing new UWBantenna.

Comparing to the previously used stacked-patch antenna,which have a planar size of 18x23 mm2, the new wide-slotantenna has a size 14x14 mm2.

The main advantages of the new design over the patch are

Stable radiation pattern across a frequency band ofinterest

extremely high fidelity (>95%) of radiated pulses forradiation angles even up to 600 from bore-sight.

significant imaging improvement with the new 31-antennasystem over the previous 16-element array 44


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CONCLUSIONS (CONTD)

With the low threshold level (-7dB) in 3D images,

the 16-element array provided a low quality images

with high clutter. Targets often remain

unrecognized.

For the new array images consisted only of tumour

response with no artifacts. This is achieved by modifying the antenna design.

The new system is able to detect 7mm diameter

tumour phantoms in any location within the

breast, even as close as 4mm from the skin layer. Good imaging results in low-contrast scenarios

(2:1).

To the best of my knowledge, the system presented

in this paper is the most advanced experimental

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REFERENCES

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microwave radar-based differential breast cancer 2003

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