UWB Microwave Breast Cancer Detection Using SAR

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1 UWB Microwave Breast Cancer Detection Using SAR M. A. Shahira Banu, S.Vanaja & S. Poonguzhali Center for Medical Electronics, Department of ECE, College of Engineering Guindy, Anna University, Chennai Abstract Breast cancer is one of the leading causes of cancer-related deaths worldwide. Early detection increases the chances of successful treatment and a patients long term health. Ultra-Wideband (UWB) Microwave imaging is a technique that uses wide bandwidth electromagnetic signals to see through the internal structure of the breast. It detects and localizes cancer tumors based on the high dielectric properties contrast with normal tissue. This paper presents a novel method for locating a tumor by illuminating the breast with an ultra-wideband signal of 4 to 9 GHz and identifying the coordinates of maximum value of specific absorption rate (SAR). Results show that at 7 GHz these coordinates could detect a 5 mm tumor and the same was obtained on increasing the size of the breast. On increasing both the size of the tumor as well as the breast, it was found that larger tumors have a better chance of detection compared to smaller tumors at the same location. Also, as the mass of the normal breast increases the absorbed power values increase. Keywords Specific absorption rate (SAR), ultra wide band (UWB), microwave detection, breast cancer. I. INTRODUCTION Breast cancer is the most common cancer in women. In 2012, an estimated 22,900 cases of breast cancer were diagnosed in the United States and Canada with as many as 5,200 cases leading to death. For women, breast cancer mortality rates are higher than for any other cancer [1], [2]. From these statistics, it is clear that it is of immediate and indisputable importance to find new methods for the early detection of breast cancer in order to provide treatment to patients as early as possible. This will not only reduce mortality and incidence rates, but also significantly ease the requirements on treatment and surgery, and the involved cost to the health care system. Current breast cancer screening methods include mammography, ultrasound techniques, and magnetic resonance imaging (MRI). Mammography is the most common method currently being clinically employed and promoted as a regular screening method; however it suffers from a number of drawbacks: the patient's breast is required to undergo heavy compression in order to allow for the measurement, in addition it employs ionizing radiation and suffers from high false-positive and false-negative rates, which is not only very unpleasant for patients mentally and physically, but also represents a significant additional financial burden to health care systems, as it necessitates costly follow-up biopsies. Regarding alternate methods, ultrasound exams struggle with the distinction between malign and benign tumors, and MRI scans are highly expensive and complex. Recent research suggests the use of microwaves for breast tumor detection, in particular the ultra-wideband (UWB) frequency region, offering a promising trade-off between imaging resolution and tissue penetration depth. The technique is based on the significant dielectric contrast between normal and cancerous breast tissues at microwave frequencies. Specific absorption rate (SAR) is the rate at which energy is absorbed in a body tissue and has the unit W/Kg [3]. Keerthi priya et al. obtained the detection of 5mm tumor in a homogeneous breast model at 4 GHz using SAR [4]. Here we have used the heterogeneous breast model in which the 2mm skin layer is used. In the following section, we demonstrate the feasibility of using the coordinates of the maximum value of SAR for detecting different locations of tumor inside the breast. On varying the size of the breast as well as the tumor, the possibility of detection is analyzed. The absorbed power between a normal breast and tumor infected breast for different breast masses is determined and compared. The absorbed power for different tumor locations at different frequencies is also analyzed. A. Breast Model II. MODELS The female breast is composed of four structures: fibro glands, milk ducts, fat and connective tissue. The glands group together into larger units called lobes, which are connected with the nipple via the milk ducts. 87

2 The breast tissues are joined to the skin by fibrous strands. In order to test the validation of any imaging method, a model that represents the main tissues of the breast is needed. Different models have been used by researchers to represent breast [5]-[12]. An isometric view of the three-dimensional model that is utilized in this work is depicted in Fig. 1. To emulate the realistic size of early tumors, three values (1 mm, 3 mm, and 5 mm) are assumed for the tumor radius. In the utilized breast phantom, the frequency dependence of the dielectric constant, is modeled using the first order Debye dispersion function : (1) : dielectric's relaxation time, s and w : the low- and high- frequency dielectric constants. The Debye model parameters shown in Table I are selected here according to the published data for breast tissues. TABLE I DIELECTRIC PROPERTIES OF BREAST TISSUES printed antenna structure, which has compact dimensions of 56*57 mm², is printed on one side of the FR4 substrate with thickness of 0.82 mm and having dielectric constant of 3.38 with the ground on the other side. On the other side, a 50 Ohms micro strip feed line with a fork-shaped tuning stub is placed symmetrically with respect to the center line of the wide slot. This fork feed increases the operational bandwidth [13]. The antenna is excited with a Gaussian pulse and the simulated return loss of the wide slot antenna is below - 10 db between 3.2 GHz and 10.6 GHz as shown in figure 3. The input power to the antenna is 1Watt rms. The dimensions of the antenna structure are shown in Table II. TABLE II DIMENSIONS OF ANTENNA STRUCTURE B. Antenna Model Fig. 1 : Heterogeneous Breast Model. The configuration of the proposed UWB antenna is illustrated in Figure 1. The antenna consists of an u shaped patch, a single slot and a ground plane. The Fig. 2 : Wide slot antenna geometry 88

3 Fig. 3: Simulated S11 characteristics of the wide slot antenna. C. Specific Absorption Rate The Specific Absorption Rate (SAR) is defined as the time derivative of the incremental energy (dw) absorbed by an incremental mass (dm) contained in a volume element (dv) of a given mass density (ρ). It is expressed as [14] (1) SAR can be related to the electric field at a point by (2) Where σ is the conductivity of the tissue (S/m), ρ is the mass density of the tissue (kg/m 3 ) and E is the rms electric field strength (V/m). SAR is a parameter that is the basis for the maximum permissible exposure (MPE) in biological tissues under electromagnetic fields. Table III shows the limits for the peak local SAR values that is averaged over the whole-body (WB), 1 g of tissue (1G), or 10 g of tissue (10G) under different environments [15]. TABLE III SAR EXPOSURE LIMITS IN DIFFERENT ENVIRONMENTS:( WB = WHOLE BODY AVERAGING, 1G= AVERAGING OVER 1 GRAM OF TISSUE, 10G= AVERAGING OVER 10 GRAMS OF TISSUE) As specified by IEEE C95.3 standard the peak spatial-average specific absorption rate is the maximum local SAR averaged over a specified volume or mass, e.g., any 1 g or 10 g of tissue in the shape of a cube [13]. Here the SAR value is averaged in 1 g tissue mass. The absorption loss is derived from Specific Absorption Rate. Both the absorbed power and SAR are in rms values. The normal breast model of radius 50 mm has a tissue mass of kg and the same breast model with a 5 mm tumor has a tissue mass of kg. For a 70 mm radius the normal breast model has a tissue mass of kg and the abnormal breast has a tissue mass of kg. The total absorbed power in these models is calculated using the following equation III. RESULTS AND DISCUSSIONS (3) A. Comparison of normal breast with abnormal breast The heterogeneous breast is illuminated with an ultra wideband signal from the wide slot antenna and the total SAR, 1-g averaged SAR and coordinates of maximum value of SAR are obtained for frequencies ranging from 4 to 9 GHz. Tables IV and V summarizes the values and coordinates of total SAR and maximum SAR obtained using (1) in a normal and abnormal breast respectively. It is observed that both the total and maximum SAR values are higher in the tumor affected breast compared to the normal breast for all the frequencies. At 6 GHz the total and maximum SAR value for a normal breast is W/Kg and W/Kg respectively whereas for a tumor affected breast it is W/Kg and W/Kg respectively. TABLE IV VALUES AND COORDINATES OF 1-G AVERAGED LOCAL SAR IN NORMAL BREAST MODEL 89

4 TABLE V VALUES AND COORDINATES OF 1-G AVERAGED LOCAL SAR IN BREAST MODEL WITH TUMOR TABLE VI ABSORBED POWER FOR DIFFERENT NORMAL BREAST MASSES AT DIFFERENT FREQUENCIES In the abnormal breast the tumor is located at the center (0, -45, 0). At 6 GHz the coordinates of maximum value of SAR is (-0.46, -45.7, 2.25) and at 7 GHz it is (-0.46, -45.7, 0.81). This indicates that the coordinates of maximum value of SAR actually points to the position of the tumor within the tumor affected breast for most of the frequency. If we consider the normal breast the coordinates of maximum value of SAR at 5 GHz and 8 GHz is (-0.46,-49,7.66) and (6.14,- 49,6.32) respectively which points to locations close to the breast surface. This indicates that the maximum local SAR distributions occur in the breast layer close to the antenna in a normal breast and in an abnormal breast they occur in the tumor. Table VII shows the absorbed power for different sizes of the abnormal breast ranging from 50 mm to 70 mm at different frequencies. The tumor is placed at the center of the breast for all the varying sizes. It is observed that when the mass of the breast increases the absorbed power also increases for different frequencies. For example, the absorption loss value for a 50 mm breast at 7 and 8 GHz is W and W respectively. At the same frequencies however the absorbed power values are W and W in a 55 mm breast. TABLE VII ABSORBED POWER FOR DIFFERENT BREAST MASSES WITH TUMOR AT DIFFERENT FREQUENCIES B. Varying the size of the breast Table VI shows the absorbed power for different sizes of the normal breast ranging from 50 mm to 70 mm at different frequencies. It is observed that when the mass of the breast increases the absorbed power also increases for different frequencies. For example, when the breast size is 60 mm the absorbed power at 7 GHz is W and when the breast size is 65 mm the absorbed power at the same frequency is W. When we consider the next frequency 8 GHz the absorbed power value is W for the 60 mm breast and W for the 65 mm breast. This shows that a different range of values is to be established for different breast masses. 90

5 C. Varying the size of the tumor Tables VIII summarizes the coordinates of the maximum value of SAR at 7 GHz, when tumors of different radii ranging from 4 mm to 7 mm are placed inside a 70 mm breast at five different locations. Most of the tumors are better located at 7 GHz however a 5 mm tumor located at the center of the breast is detected better at 7. GHz. For a tumor actually located at (-15,- 35,20) when the size of the tumor is 5 mm the difference between the actual tumor position and the detected position tumor is (-0.62,0.62,0.625). If the size of the tumor increases to 6 mm the difference is (- 0.75,0.75,0.75) and at 7 mm it is (-0.7,0.7,-0.7).This shows that as the size of the tumor increases the difference between the detected position of the tumor and the actual position increases. TABLE VIII DETECTION OF DIFFERENT SIZES OF TUMOR LOCATED IN A 70 MM BREAST MODEL AT 7 GHZ IV. CONCLUSION The above simulated data clearly shows that the SAR and the absorption loss values are higher in a tumor infected breast and these values increase as the mass of the breast increases. At 7 GHz, the penetration depth was the maximum and its absorbed power was location dependent. The coordinates for maximum value of SAR can be used as an indication for locating a tumor. The same was found on increasing the breast diameter. All these indicate a possibility of using EM absorption loss for detecting breast tumors. Future work is needed change the location of the tumor and to develop realistic breast models and expand this method by determining an acceptable range of absorption loss values for normal breast tissues. V. REFERENCES [1] Canadian Cancer Society, Canadian Cancer Statistics 2011 Online publications. Available: [2] Breastcancer.org, U.S Breast Cancer Statistics 2011 Online publications. Available: breastcancer.org/ [3] International Commission on Non-Ionizing Protection (ICNIRP) 1998 Guidelines for limited exposure to time varying electric, magnetic and electromagnetic fields (up to 300 GHz), Health Physics, vol. 74, no. 4, pp , Apr [4] Ponnuraj Kirthi Priya and S. Poonguzhali, Detection of breast cancer using microwave absorption loss, in International Conference on Electronics and Communication Engineering (ICECE), pp , May [5] M. Klemm, I. Craddock, J. Leendertz, A. Preece, and R. Benjamin, Radar-based breast cancer detection using a hemi-spherical antenna array experimental results, IEEE Trans. Antennas Propag., vol. 57, no. 6, pp , [6] A. Abbosh, and S. Crozier, Strain imaging of the breast by compression microwave imaging, IEEE Antennas and Wireless Propagation Letters, vol.9, pp , [7] S. Davis, B. Van Veen, S. Hagness, F. Kelcz, Breast tumor characterization based on ultrawideband microwave backscatter, IEEE Trans. Biomed. Engineering, vol. 55, no. 1, pp , [8] A. Abbosh, Early breast cancer detection using hybrid imaging modality, IEEE International Symposium on Antennas and Propagation, pp.1-4, [9] P. Meaney, et al, Initial clinical experience with microwave breast imaging in women with normal mammography, Academic Radiol., vol. 14, no. 2, pp , [10] W. Khor, M. Bialkowski, A. Abbosh, N. Seman, and S. Crozier, An ultra wideband microwave imaging system for breast cancer detection, IEICE Trans. Comm., vol. E-90B, no. 9, pp , [11] D. Kurrant, and E. Fear, An improved technique to predict the time-of-arrival of a tumor response in radarbased breast imaging, IEEE Trans. Biomed. Engineering, vol. 56, no. 4, pp , [12] A. Abbosh, Early breast cancer detection using Doppler frequency shift," Asia-Pacific Microwave Conference Proceedings (APMC), pp , Dec [13] Begaud Xavier, Ultra wideband wide slot antenna with band-rejection characteristics, in European Conference on Antennas and Propagation (EUCAP), pp. 1-6,

6 [14] Recommended Practice for Measurements and Computations of Radio Frequency Electromagnetic Fields With Respect to Human Exposure to Such Fields, 100 khz-300 GHz, IEEE Standard C95.3, [15] International Commission on Non-Ionizing Protection (ICNIRP) 1998 Guidelines for limited exposure to time varying electric, magnetic and electromagnetic fields (up to 300 GHz), Health Physics, vol. 74, no. 4, pp , Apr