Measurement Techniques for the Relative Power Absorption Ratio of Biological Tissues

Measurement Techniques for the Relative Power Absorption Ratio of Biological Tissues

P. S. N. Bharani1

PG Student [BME], Dept. of ECE, Andhra University College of Engineering (A), Andhra Pradesh, India1

Ch. Rajani Chandra1

PG Student [BME], Dept. of ECE, Andhra University College of Engineering (A), Andhra Pradesh, India1

1. Ratna Kumar2

   Assistant professor (c), Dept. of ECE, Andhra University College of Engineering (A),Andhra Pradesh, India2

   Abstract-Electromagnetic energy is represented by electric and magnetic fields of electromagnetic waves. Its absorption in biological tissues is illustrated by the use of electromagnetic field adjacent tissues; it is possible to estimate relative absorption of electromagnetic energy from the knowledge of fundamental parameters of the tissues and of the wave. It is also dependent on the polarization of the wave. The direction of propagation can be either parallel or perpendicular to the common interface.

   It has been possible to find relative power absorption as a function of frequency. They are consolidated using the Debye equation. It is also well known that they vary with frequency and they are not scalar constants. The results on the relative absorption as the function of frequency for different tissue pairs are presented in this work.

   Keywords- Electromagnetic waves; Electric and Magnetic fields; Relative power absorption; propagation; Debye equation; Frequency; polarization; scalar constants.

   1. INTRODUCTION

      The electromagnetic fields exist in the entire space and they are all around us. The radio waves and television signals, mobile phones, power lines, radar, radio broadcast transmission, electrical appliances etc. are basic sources of electromagnetic waves. They are also present in human bodies in the form of endogenous fields. These fields keep our hearts beating, brains thinking, eyes functioning and

      The electric fields concepts are explained by Coulomb in terms of electric charges and by Gauss in terms of electric flux. The electric field is expressed in terms of the coulomb force per unit test charge. It is represented by the units of Newton/coulombs or volts/meters[3].

      Such an electric field is static in nature when the charge is stationary. When the field is expressed in terms of minus of potential gradient, these do not vary time with and voltage is DC and these fields are measured using antenna devices. Electrocardiogram measures potentials on the surface of the body produced by the beating heart. The electric fields picked up by the straight antennas are oriented parallel to antenna axis. It is difficult to measure the field near the body as the antenna made up of metallic material can perturb the fields. In such cases small dipole antennas are specially designed to receive the localized fields[4]. The fields of arbitrary polarization are measured independently to obtain the total electric field.

   2. FORMULATION

      For an electromagnetic wave propagating within a biological system, two adjacent tissues will absorb power per unit volume in the ratio[6].

      Ap 2 = 2 E2 2 (1)

      muscle moving[1]. Electromagnetic fields are also useful to visualize inner side of the body to diagnose illness in form

      Ap 1

      1 E1

      of medical imaging, electrocardiography, electroencephalography, electromyography, EOG, ERG and electro physiological evaluations. They also have wide applications in treatment of cancer, pain control, bone growth, soft tissue repair and electro physiological stimulations. On the other hand, they have negative effects for example; they injure or even kill living beings through lightning strikes, and shock.

      Electromagnetic fields have used in a number of medical devices. The other promising applications of electromagnetic fields are in the repair of damaged nerve paths to help the blind to get vision, the deaf to hear and the paralyzed to walk[2]. The main importance of electromagnetic fields is to explain how they interact with the body, how to measure them, how to create them, how to evaluate, and how to control them.

      Here is the tissue electrical conductivity,

      E, is the electric field intensity within the tissue, and the subscripts denote each tissue. At frequencies within the 100-500MHz range and below, the irradiated tissue will be within the near field of an applicator is not a uniform plane-wave. For noninvasive applicators, this approximation is expected to have a negligible effect upon the results obtained.

   3. MEASUREMENT OF RELATIVE POWER ABSORPTION RATIO OF TWO ADJACENT TISSUES WITH BOUNDARY CONDITIONS

      The relative absorption of electromagnetic energy is found out by considering the below cases[5].

      CASE 1: The electric field vector of EM energy parallel to the interface between tissues1 and 2.

      The boundary condition is E1=E2

      Relative absorption power ratio in equation (1) becomes,

   4. RESULTS

      For different tissues, the relative abortion is computed and they are presented in the figures. The variables of conductivity and permittivity as a function of frequency are

      Ap 2 = 2

      (2)

      also presented.

      Ap 1 1

      2

      CASE 2: The electric field vector of EM energy perpendicular to the interface between tissues. The conduction and displacement currents must be continuous across the interface as [7].

      Conductivity in (mho/m)

      1.5

      = 1 1

      E2 2+22

      E1 2+22

      (3)

      2 2 1

      oesophagus trachea

      Where is the electrical permittivity of the respective tissue and is the radian frequency. Now,

      Ap2 = 2 ( 1 )2 1+(1/1)2

      (4)

      0.5

      Ap1

      1 2

      1+(2/2)2

      0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

      Frequency (GHz)

      CASE 3: EM energy incident upon tissue 2 from tissue 1, the tissue2 is a sphere and its radius , small compared to the wavelength in tissue 1 [8] is,

      Fig. 1: The fundamental properties of Conductivity () of adjacent tissues Oesophagus and Trachea variation with Frequency.

      Here,

      E2 =

      E1

      3

      *

      *

      2+ 2

      1

      80

      (5)

      75

      70

      Ap2 = 2

      9 1+ 1/1 2

      65

      Relative Permitivity

      (6)

      Ap1

      1 2+ 2 2 21+ 2 60

      1 1 1

      55

      oesophagus trachea

      CASE 4: EM energy incident upon tissue 2 from tissue 1, 50

      the tissue2 is a long Cylinder of radius.

      45

      E2 = 2

      (7)

      E

      *

      *

      1 1+ 2

      1

      40

      0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

      Frequency (GHz)

      and,

      Ap2 = 2

      4[1+( 1 2

      ) ]

      1

      (8)

      Fig. 2: The fundamental properties of Relative Permittivity (r) of adjacent tissues Oesophagus and Trachea variation with Frequency.

      Ap1 1

      2 2 1 2 2

      (1+1) +(1+1)

      The frequency dependence of energy absorption directly related to the polarization of molecules and structural interfaces as a result of the applied electric field with in the biological tissue.

      								1 2 3 4

      12

      10

      Power Abs ratio

      8

      6

      4

      2

      0

      0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

      100

      95

      90

      Relative Permitivity

      85

      80

      75

      70

      65

      60

      55

      small intestine

      stomach

      0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

      Frequency (GHz)

      Frequency (GHz)

      Fig. 3: plot of Power absorption ratio Pa2/Pa1 vs. Frequency with Oesophagus and Trachea for the irradiation conditions:

      Fig. 5: The fundamental properties of Relative Permittivity (r) of adjacent tissues Oesophagus and Trachea variation with Frequency.

      								1 2 3 4

      12

      1. E parallel to interface

      2. E Perpendicular to interface 10

      3. Trachea sphere within Oesophagus, and4) Trachea

      Power Abs ratio

      cylinder within Oesophagus 8

      6

      4

      3

      2

      2.5

      0

      0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

      Frequency (GHz)

      Conductivity in (mho/m)

      2 Fig. 6: plot of Power absorption ratio Pa2/Pa1 vs. Frequency with Small intestine and Stomach for the irradiation

      conditions:

      1.5 1) E parallel to interface 2) E Perpendicular to interface 3) Stomach sphere within Small intestine and 4) Stomach cylinder within Small intestine

      1

      0.5

      small intestine stomach

      0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

      Frequency (GHz)

   5. CONCLUSIONS

      Thus the fundamental properties such as conductivity and

      Fig. 4: The fundamental properties of Conductivity () of adjacent tissues Small intestine and Stomach variation with Frequency

      permittivity of the tissues like the Trachea, Oesophagus, small Intestine, Stomach were obtained. From these properties the power absorption ratio of adjacent tissues such as Trachea, Oesophagus and Small intestine, Stomach were obtained. Here we observed the higest Power absorption ratio in the case of Trachea sphere within Oesophagus when compared to the case of Trachea cylinder within Oesophagus. Similarly the power absorption ratio of the tissues is high in the case of Stomach sphere within Small intestine when compared to the case of Stomach cylinder within Small intestine.

   6. REFERENCES

1. John W Strotech, Hyperthermia and cancer therapy, IEEE, BME- 31, No. 12, December 1984.

2. H.C. Nants, Pyrogen therapy of cancer, Proc. Int Symp. Cancer therapy by hyperthermia and radiation, 1976, pp 239-250.

3. G.M. Hahn, Hyperthermia and cancer, New York, Planum, 1982.

4. N.B. Hornbeck, Hyperthermia and cancer: Human Clinical trail experience, Vol. I and II, FLCRC Press, 1984.

5. G.S.N. Raju, Electromagnetic Field Theory and Transmission Lines,Pearson Education

   (Singapore)Pte.Ltd.,New Delhi,2005.

6. William T.joines,Frequency dependent absorption of electromagnetic energy in biological

   Tissue,IEEE Trans.On biomedical engineering,Vol.BME- 31 No.1,January 1984.

7. S.A.Schelkunoff, Electromagnetic Fields. New York:Blasdell,1963.

8. W.T.Joines,C.F.Blackman,and M.A.Hollis,Broadening of the RF power-density window

For calcium-ion efflux from brain tissue,IEEE Trans.Biomed.Eng.,vol.BME-28,pp.568-573,August 1981

New Delhi, 2005.

AUTHORS DATA

P. Siva Naga Bharani did her B.TECH in Vignans Institute of Information Technology affiliated by JNTU Kakinada. At present she is pursuing her M.TECH in Biomedical Engineering in the Centre for BioMedical Engineering, Dept. of

Electronics and Communication Engineering, AU College of Engineering (A), Visakhapatnam.

CH. Rajani Chandra did her B.TECH in Visakha Institute of Engineering & Technology affliliated by JNTU Kakinada. At present she is pursuing her M.TECH in Biomedical Engineering at the Centre for

BioMedical Engineering, Dept. of Electronics and Communication Engineering, AU College of Engineering (A), Visakhapatnam.

Y. Ratna Kumar did his B.Pharmacy in JNTUH and M.Tech (Biomedical Engg.) in Andhra University. At present, he is Assistant Professor (c) in the Centre for BioMedical Engineering, Dept. of Electronics and Communication Engineering, AU

College of Engineering (A), Visakhapatnam, and Ph.D. under the guidance of Prof. G.S.N. Raju. He has published 7 International Journals/ Conferences. He is a life member of PCI, SEMCE (I), BMSI, and ISB