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IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 32, NO. 4, AUGUST 2004

A Novel Waveguide-Based Radio

Frequency/Microwave Exposure System for

Studying Nonthermal Effects on Neurotransmitter

Release--Finite-Difference Time-Domain Modeling

Todd Hagan, Indira Chatterjee, Senior Member, IEEE, Dana McPherson, and Gale L. Craviso

field exposures. To explore potential RF/MW field bioeffects on

Abstract--A research effort is underway to identify specific

radio frequency/microwave parameters in the frequency range

the function of neural-type cells, this research utilizes cultured

0.75­1.12 GHz that can produce nonthermal effects on the re-

bovine adrenal medullary chromaffin cells, a well-characterized

lease of catecholamines from cultured bovine adrenal medullary

in vitro model of nontransformed catecholamine secreting cells.

chromaffin cells, an established in vitro model of neural-type cells.

Initial studies are underway in which we investigate how ap-

A well-characterized exposure system is crucial for interpreting

plied RF EM fields in the frequency range of 0.75­1.12 GHz

the biological outcomes of experiments. This paper describes a

novel waveguide-based exposure system that permits perfusion

affect catecholamine release. For this frequency range, a wave-

of the cells with a temperature-controlled balanced salt solution

guide-based exposure system is being used. A novel aspect of

for online monitoring of catecholamine release from the cells

the experimental approach is the combination of a waveguide

during radio frequency/microwave exposure. The finite-difference

and a cell perfusion apparatus inside the waveguide that allows

time-domain method was used to optimize the exposure condi-

for online monitoring and recording of basal and stimulated cat-

tions, the goal being to achieve the maximum possible homogeneity

in the distribution of the specific absorption rate at the location

echolamine release during RF/MW exposure of the cells.

of the cells in the waveguide. At a frequency of 1 GHz, optimal

In order to interpret the outcomes of biological experiments,

coupling of the radio frequency/microwave field into the region

it is essential that the exposure system being used meet the re-

containing the cells was obtained only when the cells were placed

quirements established for in vitro exposure systems in general

at the location of the electric field maximum of the standing wave

[7], [8]. One of these requirements is a precise knowledge of

pattern, with the electric field parallel to the plane containing the

cells. In this case, the specific absorption rate distribution was

the EM fields and hence the specific absorption rate (SAR) to

found to be the highest as well as homogeneous to within 30%.

which the cells are exposed. Another is to maintain as uniform

Index Terms--Finite-Difference time-domain (FDTD), neuro-

a SAR as possible at the cells during exposure to prevent the

transmitter release, nonthermal bioeffects, radio frequency/mi-

occurrence of both thermal and electrical hot spots [9]. Here,

crowave exposure, specific absorption rate, waveguide.

the goal is to limit the variations in SAR over the region con-

taining the cells to within 30%, which has been suggested as

a reasonable homogeneity to aim for [7]. Because quantifying

I. INTRODUCTION

field at precise loca-

the SAR by measuring the electric

A

LARGE number of studies offers evidence that radio fre-

tions of cells during experiments is not feasible, the finite-differ-

quency/microwave (RF/MW) fields affect the central ner-

ence time-domain (FDTD) numerical method is used to predict

vous system [1]. Although tissue heating appears to be the cause

field conditions in the exposure setup. FDTD is a very powerful

for some of the reported effects [2], other effects have been ob-

tool for computing, in detail, the expected EM field and SAR in

served in the absence of heating and are thus considered non-

humans, animals, tissues, and cell preparations [9]­[12]. Thus,

thermal in nature [3], [4]. Such nonthermal effects have been

it can provide an accurate model of the exposure system. The

attributed to electromagnetic (EM) field interactions with spe-

FDTD model used here takes into account the precise geome-

cific cellular constituents, such as neurotransmitter receptors [5]

tries and dielectric properties of each component of the expo-

and ion channels [6]. Thus, RF/MW fields hold the potential for

sure system. Thus, it can provide a detailed characterization of

targeting neural processes in biological systems.

the EM field and SAR at the location of the cells within the

In vitro systems utilizing cultured cells play an important

waveguide exposure system. The FDTD model of the exposure

role in identifying nonthermal biological effects due to RF/MW

system also allows for optimization of the homogeneity of the

SAR distributions at the locations of the cells. Some of these

Manuscript received October 10, 2003; revised February 3, 2004. This work

results have been presented previously [13].

was supported by the Air Force Office of Scientific Research under Grant

F49620-02-1-0306.

II. METHODOLOGY

T. Hagan, I. Chatterjee, and D. McPherson are with the Department of

Electrical Engineering, University of Nevada, Reno, NV 89557 USA (e-mail:

A. Cell Perfusion Apparatus

indira@engr.unr.edu).

G. L. Craviso is with the Department of Pharmacology, University of Nevada,

Cultured bovine adrenal medullary chromaffin cells, prepared

Reno, NV 89557 USA.

and maintained in suspension culture as described by Waymire

Digital Object Identifier 10.1109/TPS.2004.832699

0093-3813/04$20.00 © 2004 IEEE