T.C

SÜLEMAN DEMİREL UNIVERSITY

FEN BİLİMLERİ ENSTİTÜSÜ

Mühendislik fakültesi

ELEKTRONİK VE HABERLEŞME

MÜHENDİSLİĞİ

Biological Effect of Electromagnetic Waves

COURSE OFFERED

Dr. Selçuk Comlekçi

The dielectric properties of human blood

Submitted by

MSc. Student

Khalid Saeed Lateef Al-Badri

Student No. 1330145002

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Introduction:

The body can be considered as a composite volume conductor which comprises

tissues with differin electrical properties Electric conduction within biolo ical

tissues occurs throu h movement of mobile ions Such conduction is related to

the ionic content and ionic mobility of each particular tissue type Functional

activity, as well as patholo ical conditions, results in structural and histolo ical

chan es in the tissue These chan es are accompanied by characteristic

temporal and spectral electric behavior Knowled e re ardin the spatial

dielectric properties distribution can provide useful information re ardin the

functional and patholo ical condition of the tissues1 Blood is one of the

important of body tissues Blood is a hi hly functional body fluid, it delivers

oxy en to the vital parts, it transports nutrients, vitamins, and metabolites and

it also is a fundamental part of the immune system Therefore the precise

knowled e of its constituents, its physical, biolo ical, and chemical properties

and its dynamics is of reat importance Especially its dielectric parameters are

of relevance for various medical applications like cell separation (e , cancer

cells from normal blood cells), checkin the deterioration of preserved blood,

and dielectric coa ulometry In addition, the precise knowled e of the

dielectric properties of blood is prerequisite for fixin limitin values for

electroma netic pollution (via the conductivity in the specific absorption rate

(SAR)2

What is SAR:

Specific absorption rate (SAR) is a measure of the rate at which ener y is

absorbed by the human body when exposed to a radio frequency (RF)

electroma netic field; althou h, it can also refer to absorption of other forms

of ener y by tissue, includin ultrasound3 It is defined as the power absorbed

per mass of tissue and has units of watts per kilo ram (W/k ) SAR is usually

avera ed either over the whole body, or over a small sample volume (typically

1 or 10 of tissue) The value cited is then the maximum level measured in

the body part studied over the stated volume or mass

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SAR for electroma netic ener y can be calculated from the electric field within

the tissue as:

Dielectric properties

The study of the dielectric properties of tissues belon s to basic as well as

applied science The theoretical aspects and the main findin s in this subject

have been widely reviewed (Schwan 1957, Schwan and Foster 1980, Pethi

1984, Pethi and Kell 1987, Foster and Schwan 1989 and Stuchly and Stuchly

1980) Foster and Schwan reflect on the historical perspective provided by over

100 years of interest in the electrical properties of tissues, and review the basic

concepts of dielectric phenomena in biolo ical materials and their

interpretation in terms of interactions at the cellular level Pethi and Kell cover

similar round and provide an overview of theories formulated to explain the

dielectric properties in terms of the underlyin molecular processes Common

to all papers is a more or less extensive tabulation of dielectric properties of

tissues selected to illustrate the theoretical deliberations provided by the

authors More extensive literature reviews of dielectric properties have been

provided by Geddes and Baker (1967), who summarized the early reports on

the specific resistance of tissues; Stuchly and Stuchly (1980), who tabulated the

dielectric properties of tissues in the frequency ran e 10 kHz to 10 GHz; and

Duck (1990), who extended the survey by includin more recent data

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The dielectric properties of materials are obtained from their measured

complex relative permittivity, 𝜀̂ expressed as

𝜀̂ = 𝜀′ − 𝑗𝜀′′

Where:

𝜀′ The relative permittivity of the material

𝜀′′ The out-of-phase loss factor associated with it such that

𝜀′′ = 𝜎/𝜀° 𝜔

𝜎 is the total conductivity of the material which, dependin on the nature of

the sample, may include a contribution from a frequency-independent ionic

conductivity, 𝜎 i In this expression, 𝜀° is the permittivity of free space and 𝜔

the an ular frequency of the field The SI unit of conductivity is siemens per

meter (S m−1) which presumes that in the above expression 𝜀° is expressed in

farads per meter (F m−1) and 𝜔 in radians per second The dielectric properties

are determined as a function of frequency The dielectric properties of a

biolo ical tissue result from the interaction of electroma netic radiation with

its constituents at the cellular and molecular level 4

In-vivo vs. in-vitro

“ in vivo” are those in which the effects of various biolo ical entities are tested

on whole, livin or anisms usually animals includin humans, and plants as

opposed to a partial or dead or anism, or those done in vitro ("within the

lass"), i e , in a laboratory environment usin test tubes, petri dishes etc

Examples of investi ations in vivo include: the patho enesis of disease by

comparin the effects of bacterial infection with the effects of purified bacterial

toxins; the development of antibiotics, antiviral dru s, and new dru s

enerally; and new sur ical procedures Consequently animal testin and

clinical trials are major elements of in vivo research In vivo testin is often

employed over in vitro because it is better suited for observin the overall

effects of an experiment on a livin subject 5

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Biological Hazards

Since the earliest use of RF ener y for communication and medical applications

it has been known that excessive heatin of the tissue can be hazardous and

cause injury However, there also has been interest in and concern for a

thermal effects Ar uments in support of and a ainst the thesis of a thermal

effects developed durin the early history of the therapeutic application of RF

waves In addition to the claimed frequency-specific effects in shortwave

treatment of tumors, Danilewsky and Worobjew demonstrated that

contractions by fro nerve-muscle preparations increased in amplitude when

hi h-frequency currents were applied alon with minimal faradic stimulation

When the hi h-frequency currents were removed, the excitability of the nerve

rapidly returned to its ori inal value With increasin current (at 0 5-1 0 MHz),

a point was reached at which excitability was depressed This same

phenomenon of altered nerve-muscle excitability was also obtained by

irradiatin the sciatic nerve of a warm-blooded animal

Blood

Blood is a circulatin tissue composed of fluid plasma and cells The plasma

forms the liquid part containin electrolytes and lar e or anic electrically

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polarized molecules Apart from the plasma, the blood consists of several kinds

of corpuscles: about 96% of them are red blood cells (also known as

erythrocytes), 3% are white blood cells (leukocytes) and the reminders are

platelets (thrombocytes) In hemolysis blood, erythrocytes are disrupted and

their intracellular material is dischar ed into the liquid Therefore, the electrical

properties of whole blood and hemolysis blood are naturally very different

Whole blood exhibits β, γ and δ dispersion, but curiously almost no α

dispersion Erythrocytes are poor conductors of electrical current at low

frequency compared with the extracellular medium or plasma which surrounds

them It is difficult to determine the dielectric constant of blood at low

frequencies, since the capacitive part of the current is exceedin ly low On the

other hand, the conductivity of the blood has almost linear dependence on

hematocrit (the volume proportion of red blood cells occupied in the blood), so

the concentration of erythrocytes critically determines the blood’s resistivity

The normal hematocrit ran e for adult males is 40% - 54%, and 37% - 47% for

adult females Blood resistivity is also effected by motion, flowin blood

exhibits a lower resistance than stationary blood An extensive table that

summaries most of the factors that influences impedance can be found in

Hirsch et al study

Figure 1Blood macroscopic composition: plasma 44-61% of whole blood; buffy coat containing leukocytes and platelets about 2% of whole blood; erythrocytes about 37-54% of whole blood

1

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Their two terminal experiment setup included desi n of a horizontal cylinder

measurement cell to avoid sedimentation effects They derived a relation

between red cell count and its conductivity Schwan1 compendium study quote

whole blood measurements taken from rabbit at body temperature over the

frequency ran e of 1kHz - 10MHz Bur er and Van Don en1 took four terminal

measurements of human and bovine blood and bovine plasma over the

frequency ran e of 20Hz - 5kHz usin a horizontal tube as a measurement cell

Heparin was added to all samples and they were measured at 20°C and 40°C

They found blood resistivity to be frequency independent at their low -

frequency ran e, but noted a linear relation to temperature ( 1 13 %/o C – and

1 56 %/o C − for human and bovine respectively) Schwan showed that blood

almost does not exhibit α dispersion; for hematocrit of 40%, β dispersion had

total permittivity increment of 2000, and centre frequency of 3MHz Pfutzner

performed two terminal measurements of sheep, porcine, microcytic (small red

blood cells) and normal human blood, at frequency of 50kHz He was

investi atin the effect of haematocrit concentration on impedance When

blood samples of 90% haematocrit were measured it was found to be 4 times

more resistive than those of 20% haematocrit, while in the normal ran e for

human blood, a hi h level of haematocrit is twice as resistive as a low level of

haematocrit Loidel6, measurements provide dielectric data on human blood of

so far unsurpassed precision for a broad parameter ran e By investi atin an

exceptionally broad frequency ran e and by analyzin the hematocrit (Fi 2)

and temperature dependence (Fi 3), valuable new information on the

dynamic processes in blood were obtained The obtained broadband dielectric

spectra of blood show three major dispersions (fi 2,3) Those are termed β-,

γ-, and δ-dispersion* and are revealed by steps in the frequency dependent

dielectric constant and conductivity The first process, located around 10 MHz,

is due to a Maxwell- Wa ner relaxation caused by the in homo eneities

introduced by the presence of the red blood cells The analysis of this

* This relaxation process is nowadays identified as bein of Maxwell-Wa ner type and termed β -relaxation in biophysical literature A relaxation rate near 18 GHz, which can be assi ned to the reorientation of water molecules and which is named γ -dispersion Furthermore, a third relaxation, termed δ -relaxation and located in the low-frequency re ime,f < 100 kHz was detected in some biolo ical materials

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relaxation-like process allows for the test of model predictions and the

determination of various intrinsic cell properties as, e , the capacitance of the

cell membrane Around 18 GHz, a further relaxation process arises from the

tumblin of the dipolar water molecules in the blood sample Between β- and

γ-relaxations, si nificant dispersion is observed, which, however, can be

explained by a superposition of these relaxation processes and is not due to an

†additional “δ-relaxation” often found in biolo ical matter The hu e dispersion

effect observed at the lowest frequencies (< 10kHz) is due to electrode

polarization arisin from the stron ionic conductivity in blood We find no

** Hematocrit (Hct) Levels This is the ratio of the volume of red cells to the volume of whole blood Normal ran e for hematocrit is different between the sexes and is

approximately 45% to 52% for men and 37% to 48% for women This is usually measured by spinnin down a sample of blood in a test tube, which causes the red blood

cells to pack at the bottom of the tube

Figure 2 Dielectric constant and real part of the conductivity of blood samples with different hematocrit values as function of frequency, measured at body temperature (310 K).

**

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evidence for a low frequency relaxation (“α-relaxation”) caused, e , by

counterion diffusion effects as reported for some types of biolo ical matter

Figure 3

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References:

1 Lior Horesh Some Novel Approaches in Modelling and Image

Reconstruction for Multi-Frequency Electrical Impedance Tomography of

the, Human Brain 2 Broadband dielectric spectroscopy on blood, M. Wolf, R. Gulich, P.

Lunkenheimer, A. Loidl 3 Focusin of therapeutic ultrasound throu h a human skull: a numerical study J Acoust Soc Am 4 The dielectric properties of biolo ical tissues: I Literature survey, C Gabriel, S Gabriely and E Corthout 5 http://en wikipedia or /wiki/In_vivo 6 Broadband dielectric spectroscopy on blood, Loidel