83420232 Advancements in Microwave Breast Imaging Techniques

7/28/2019 83420232 Advancements in Microwave Breast Imaging Techniques

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IJREAS Volume 2, Issue 2 (February 2012) ISSN: 2249-3905

International Journal of Research in Engineering & Applied Sciences 1679

http://www.euroasiapub.org

ADVANCEMENTS IN MICROWAVE BREAST IMAGING

TECHNIQUES

Aman Setia *

S. Kishore Reddy *

ABSTRACT

This paper outlines the applicability of microwave radiations for breast cancer detection.

Due to high contrast in dielectric properties between normal and cancerous tissues this

technique has received a significant attention from the researchers. This paper outlines the

ongoing research going on in the field of microwave breast imaging techniques. The

advantages and disadvantages of various techniques are discussed. The fundamental tradeoff

is indicated between various requirements to be fulfilled in the hardware architecture of an

imaging system for breast cancer detection.

Keywords: Component, Microwave Breast Imaging , Breast Cancer.

*Research Scholar Electronics, JJT University, Rajasthan, India.


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I. INTRODUCTIONMicrowave Imaging Technique is a one of category of medical imaging techniques. It can be

defined as seeing the internal structure of an object by illuminating the object with low power

electromagnetic fields at microwave frequencies that is between 300 MHz 300 GHz. Thebasic fundamental for microwave breast imaging is the high contrast between the permittivity

and conductivity of normal and malignant breast tissue. Several studies in the literature

suggest that a large electrical contrast exists between normal breast tissue and malignant

tumor. The graphs shows conductivity and relative permittivity of normal and malignant

breast tissue over the frequency range of 50 MHz-1 GHz [1].There is a significant increase in

research area of microwavebased systems for detection of breast cancer from the last decade

[2]-[12]. This technique is safer and comfortable because of non-ionization, non invasive, and

breast compression is avoided. Evaluating SAR for specific systems with computer models

ensure and compliance with standards so it poses no health risk. It is expected to be less

expensive, costs a fraction of the equipment needed Gold standard equipment , anticipated to

be very rapid , sensitive (detect most tumors in breast ) and specific (detect only cancerous

tumors)[13]. The recent interest in this technique is caused by the wide availability of low cost

microwave devices, rapid increase in computational power for calculation of complex

electromagnetic problems, improved performance, advancements in human modal and

increased number of reported electromagnetic proper-ties of human tissue. The disadvantages

of this technique includes there is a complex field distribution in the body as breast is

heterogeneous. Many researches have been done towards suppression of cluster due artifacts

from breast skin, chest wall, nipple etc. At microwave frequency normal breast tissue is very

lossy and in case of early breast cancer detection tumor is very small. There is a trade-off

created between penetration depth and spatial resolution due to lossy breast tissue. Employing

higher frequencies to obtain better resolution and to allow the use of small antenna elements

results in lower electromagnetic field penetration inside the lossy biological tissue. Large

computational time is required to reconstruct the image due to higher resolution that enlarges

the size of the corresponding electromagnetic problem.


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Figure 1.Conductivity of human breast tissue

(red curve: malignant tissue; blue curve: normal tissue).

Microwave imaging system for breast cancer diagnosis can be categorized into Active

&Passive Microwave Breast Imaging In active microwave breast imaging technique the

sensing is done by probing the biological object with self generated energy. In passive

microwave breast imaging the energy is generated by the object. Active microwave imaging,

in turn, can be divided into microwave tomography and ultrawideband (UWB) radar

techniques, microwave microscopy and hybrid modalities.

II. PASSIVE IMAGINGA. Microwave Radiometry

The basic principal of operation of Microwave Radiometry refers to measurement through

radiometric ways of breast temperature and compares the thermal images for the two breasts

obtained on microwave frequency. The identification of malignant tissue is made through

spotlight of one high temperature given the normal tissue and the appearance of one

asymmetry between two images.

Where I is the spectral radiance of electromagnetic radiation for a medium with permeability

and permittivity , f is the frequency. T is the temperature of the black body.

h = 6.63 10-34

J.s, k= 1.38-23

J/K and e = 2.71

From above equation it is concluded that the radiation distribution is dependent on

temperature and frequency. Infrared thermography uses wavelength of 10m typical whereas

microwave thermography makes use of much longer wavelength typically 1-20cm In

microwave Radiometry the electromagnetic field spontaneously emitted by warm bodies


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according to planks law is measured. As the detection of malignant tumor is based on

temperature so the microwave radiometry is also called thermography. A microwave receiver

of high precision and low noise to detect electromagnetic radiation from microwave spectrum

is used. Microwave has a greater wave length as compared with the infrared radiation and is

less observed by tissue [10]. There are several contributing factors are there for temperature

increase related to tumor present, malignant cells have more metabolically active and produce

more heat ,they have reduced thermoregulatory capacity, it is also recognized that localized

increase in blood volume can be associated with early tumor growth[15]. In paired organs

such as the breast, thermal symmetry may be useful to improve the sensitivity of temperature

measurements. For example, temperatures in a given quadrant of the left breast would be

compared to temperatures at the corresponding locations on the right breast to determine

temperature differences. The thermal noise power measured by the radiometer is related to

the local temperature distribution in the breast, allowing for its reconstruction from data

collected from various antenna positions. The power radiated in this band is directly

proportional to brightness TB on the absolute scale. Microwave Radiometry can be used to

detect cancer in men that is not possible with mammography. The power radiated by the

tumor is very low that is in the range of (10 -13-10-16) W.A solution to this problem can be

done by using cooling systems to reduce the temperature of microwave detector [14]. The

other difficulty is the estimation of spatial temperature distribution inside the body. The

average temperature of a certain area is measured by the single frequency radiometer. It is

very difficult to differentiate between a hot target located deep in the breast and a cool target

close to skin. Even if the two targets are totally different but the measured brightness

temperature in two cases is same. This technical problem can be solved by using different

frequencies for microwave radiometry [16]. At higher frequencies the intensity of thermal

radiation increases and at the same time the penetration depth into biological tissue decreases,

this is called the dispersive properties of the tissue. The estimation of the depth and size of

heat source can be done by analysis of the measured radiometric data at several frequencies.

III. ACTIVE IMAGINGA. Microwave TomographyThe word tomography comes from the Greek words to slice (tomos) and to write

(graphien). The image of the internal structures of the body is represented slice by slice.

Microwave tomography is also named as X-Ray computer tomography (CT) and magnetic

resonance tomography. In tomographic systems; the object to be imaged is immersed in


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water, weak saline solution or an intralipid solution, depending on the liquid availability and

suitability of electrical properties for minimizing contrast with the body.Antennas are

scanned over planer or cylindrical surfaces and waves transmitted through the object and

received by numerous antennas are used to construct the object function. Today the

application of active microwave imaging methods to visualize the internal structure of the

body is a lso referred to as microwave tomography in spite of their ability to d irectly acquire

three dimensional (3D) images. The basic principal of tomographic frequency domain

systems is the inverse scattering techniques in that technique microwave transmitter

illuminates the breast area and scattered fields at various locations are obtained from

measurements by subtracting the incident field. Based on this information electromagnetic

properties of the body are reconstructed. In bistatic configuration two transmitters and two

receivers are used for doing measurement, mechanical scanning[8], [17],[18] and array of

antennas are scanned electronically [2], [3], [19], [18]. Scattered signal data is obtained from

a given location, data processor is used to store the results and antenna is moved to new

position. The same measurement procedure is repeated for number of locations. In bistatic

configuration, the mechanical scanning system has data acquisition time upto several hours,

to reduce this long acquisition time very accurate positioning of antenna and stability of

system is required. The patients respiration cycle should be equal or less than the optimal

acquisition time an imaging system. By electronically scanning the antenna array optimal

acquisition time with in the limits can be achieved. In electronic scanning configuration each

antenna operates either in transmit or receive mode in order to maximize the amount of

measurement data that can be recorded. Comparison to mechanical scanning system

electronic scanning system has reduced measurement time, have minimal discomfort, so the

procedure is acceptable to the patient.

For the measurement of the scattered field component a highly sensitive receiving system is

required. Superhetrodyne receiver architecture with careful filtering of detected signal can be

used to achieve the high sensitivity. The dynamic range of the reported imaging systems is

more than 120dB [2]. As it in many other microwave tomographs in order to avoid strong

reflections between the air/skin interface a coupling medium is introduced between the

antennas and the body.

The electrical properties of the medium are chosen close to the properties of the body in order

to enhance the coupling of electromagnetic energy into the breast. The electrical properties

are of the medium depends on the temperature so unpredictable local temperature gradients

and any temperature drifts affects the measurement accuracy of the system. One of the


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microwaves imaging system consists of 32 measurement channel. Each channel can operate

in receive and transmit mode, working one antenna in transmitting mode at a time and all the

other antennas are used to measure the scatter fields as receivers. The transmitter and receiver

antennas are dipped in a glycerin and water coupling liquid tank to mimics the electrical

parameters of the breast. Modulated scatter ing is alternative technique to measure the

scattered field from breast area. Two large horn antennas are used in which area under

investigation is illuminated by transmitting antenna[21]-[23]. The probe array of imaging

system, which is placed in front of collected aperture, is used to measure the scattered field.

The dipole array is used as probe array[21]. Each array element is loaded with a diode.

Modulation of the diodes results in a signal at the output of the collector aperture. The

measured signal is proportional to the field at the position of the selected dipole. The ultra

wide band radar technique is also called time domain techniques. In this technique radiated

low power pulses are received at various locations with a probe antenna or by array of

antennas. The information about the scattered signal is obtained by measuring the time delay

between radiated and received pulses. Similar to the case of frequency domain systems

monostatic , bistatic and multistate are three major system in time domain system. The

transmitter is also used as receiver and is mechanically moved across the breast to form a

synthetic aperture in monostatic configuration. In bistatic configuration, a pair of one

receiving and one transmitting antennas are used and moved across the breast to form a

synthetic aperture. Data collection in multistate configuration is obtained by using array of

antennas. There are various advantages of using ultra wide band radar techniques that

includes a simple approach is used to locate strong scattering in the breast area thus avoiding

the full wave electromagnetic analysis. There is a formidable change in this technique [10]

due to the presence of dispersion and therefore for simplicity the frequency dependence of all

breast tissue or frequencydependent radiation patterns of the antennas are usually ignored

[24]-[25]. Strong scattering from breast skin is compensated by aligning signals with respect

to the skin reflection and subsequently subtracting the averaged calibration signal from each

measured signal. The confocal microwave imaging, space-time beamforming or time reverse

wave focusing signal enhancement techniques can be used in order to enhance the detection

process. The key requirements for achieving a good quality of image are a high dynamic

range and measurement accuracy to achieve that all USB radar imaging systems relies on

frequency domain measurements using continuous wave systems. An inverse Fourier

transform is used to achieve the time domain representation [26]-[32]. The reconstruction of

high resolution images with a low computational cost can be achieved with the combination


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of the two previously described frequency and time domain techniques. The combined

approach has emerged with the purpose of overcoming the specific disadvantages of both

included techniques and was proposed recently without reference to measurement

procedure[33].The overall power radiated for such system is much less than that from a

typical cell-phone transmitter aiming to reduce exposure to electromagnetic radiation as

much as possible. The spatial resolution of microwave tomography cannot compete with

spatial resolution of CT because of large difference in wavelength. The high dielectric

contrast at microwave frequencies microwave frequency makes these instruments very

sensitive to the presence of malignant tissue. To solve the full wave 3D inverse scattering

problem in an exact manner results in high computational cost.

B. Microwave Microscopy

The microwave microscopy is based on the basic principal that in a open-ended microwave

cavity resonator the change in the resonant frequency results from the interaction of objects

poisoned under the skin such as breast tumors and the e lectromagnetic field of the resonator

[34]. This technique is based on the near field wave tissue interaction which is not limited

by the diffraction limit so it provides a high spatial resolution. Surface characterization o f

biological tissues with reported spatial resolution has been successfully used for in the range

of /50 to /1000with the help of near field microwave microscopy recently, this technique

was proposed for breast cancer diagnosis [35]. The maximum reported effective detection

depth is few centimeters. For deeply situated tumors the system unfortunately looses its sub-

wavelength focusing ability. There are various advantages of Microwave Microscopy for

breast cancer detection that are there is no need of complex inverse scattering algorithms and

special processing of skin tissues, this technique operates in a very narrow frequency range,

thus there is no need of complex dispersive dielectric models of the breast tissue, the

detection of breast tumor is critically not based on the dielectric properties of tumor, For

detection of breast tumor in this method can also used.

C Hybrid Methods

Microwave Induced Thermal Acoustic Imaging: The basic principal of microwave induced

thermal acoustic imaging combines the advantages of high contrast in the conductivity of

malignant tissue at microwave frequencies and the high spatial resolution of ultrasound

imaging. The breast is irradiated by a microwave pulse generator [36]. The microwave power

Pv absorbed per unit absorbed per unit volume of tissue is proportional to its electric

conductivity . This absorption stimulates thermoelastic expansion of tissue and induces

thermo-acoustic waves, which can be directed by an acoustic sensor array poisoned outside


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the breast. The measured excess pressure is a function of the microwave pulse width and

fractional energy absorption per unit volume of tissue at certain position. The acoustic waves

generated in this manner carry the information about the microwave energy absorption

properties of the tissues under irradiation. The microwave energy absorbed by tumor and

normal breast tissue will be significantly different and a stronger acoustic wave will be

produced by the tumor. Increased level of electromagnetic radiation is the main concern

about the clinical implementation of this technique. The microwave power of pulse required

for the modality is from one to several tens of kilo watts which even in an average is much

higher than used by other microwave imaging systems discussed above[36]-[38].

Homogeneity of the breast tissue is major challenge faced by microwave induced thermal

acoustic imaging system. This lead to a strong interference from skin and chest wall, non

uniform microwave energy distribution and consequently to complicated image

reconstruction algorithms. In a uniform manner the biological tissue should be heated by

microwave otherwise images will be difficult to interpret if thermal acoustic signals will be

induced by a non uniform microwave energy distribution. A non uniform energy distribution

in the breast tissue results from the excitation of undesirable high order electromagnetic field

modes. Tumor absorb the microwave energy because of the breast skin, breast tissue, chest

wall and convert the energy to heat , all of them produce thermal acoustic signals. Responses

from the tumor as well as from other healthy breast tissue are obtained from measured

thermal acoustic waveform. The thermal acoustic signals generated by the skin are much

stronger than those of small tumor because of high conductivity of the skin and the acoustic

sensors being very close to the skin. The arrival time of the acoustic pulse generated at a

location cannot be determined accurately because of non uniform sound speed in biological

tissues. All these factors make it difficult to approximate the back propagation properties of

thermal acoustic signals inside the breast. The skin response is usually compensated by

averaging in a similar to radar technique. The clutter can also be reduced using dispersive

properties the tissue and multi frequency operation, like is the in radiometry for example the

information collected from multi-frequency stimulation can help to mitigate the challenge

mentioned above.

Ultrasound Guided Microwave Imaging: Microwave image reconstruction is guided by

ultrasonography in ultrasound guided microwave imaging is such a combination of two

modalities, where. The ultrasound imaging is used to collect a priority information about

breast structure and geometry of embedded objects[39]. This helps to generate a optimal

mesh with well refined target region for effective numerical analysis of the electromagnetic


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problem. Consequently the spatial resolution of microwave imaging can be enhanced

resulting in more accurate electromagnetic problem consequently; the spatial resolution of

microwave imaging can be enhanced resulting in more accurate imaging of tumors.

IV CONCLUSIONSIn microwave Breast Imaging due to high contrast in tissue dielectr ic properties at microwave

frequencies has a high potential. A number of promising strategies foe microwave imagining

have appeared recently trying to exploit this potential. Some of microwave imaging systems

has actually reached clinical trails.

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83420232 Advancements in Microwave Breast Imaging Techniques

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