Simulation Aids First Online Monitoring of

Simulation Aids First Online Monitoring of

RF Effects on Neuroendocrine Cells

Finite difference

Indira Chatterjee, Dana McPherson, and Gale Craviso have

time domain

overcome this problem by combining a waveguide with a

(FDTD) simulation

cell perfusion apparatus that allows online monitoring [1].

played a key role in

Chromaffin cells are immobilized on a glass fiber filter within

the development

a plastic filter holder to allow continuous superfusion of the

of a unique

cells with a balanced salt solution (BSS). The BSS reaches an

exposure system

electrochemical detector, used in the amperometric mode, for

that provides

detecting catecholamines and thus measuring release online.

online monitoring

of nonthermal

Experimental Procedure

radio frequency

(RF) effects on

For experiments, 4-8 million chromaffin cells are gravity

catecholamine

fed onto the glass fiber filter located in the filter holder

release from

and superfused with temperature controlled BSS at a flow

cultured adrenal

rate of 1.2 ml/min. A fraction of the effluent flows into the

medullary

Figure 1: Geometry of the cell perfusion

electrochemical detector and the remaining effluent flows

chromaffin cells, a

apparatus within the waveguide as created

into a fraction detector for later offline quantification of the

well-characterized

in Solid Works and imported into XFDTD.

amount of catecholamine release by high performance liquid

in vitro model

chromatography.

of neural-type cells. While RF effects on cultured cells have

been studied in the past, the new exposure system is believed

Simulating SAR Exposure

to be the first that provides online monitoring of bioactive

molecules secreted from cells, in this case, catecholamines. This

Performing experiments such as these requires a high and

is accomplished by placing the cells within a cell perfusion

consistent level of RF exposure in the area where the cells

apparatus inside a waveguide. Continuous superfusion of the

are located. In addition, it is important to know the SAR

cells, where the perfusate that exits the cell perfusion chamber

distribution. As a way to obtain this information in their

reaches an electrochemical detector, allows for both basal and

experimental exposure setup, the researchers made the

stimulated catecholamine release to be assessed during RF

decision to simulate the RF fields using a commercially

exposure of the cells. A critical aspect of these experiments is

available FDTD software

the need to ensure maximum and consistent electromagnetic

package called XFDTD from

field exposure and specific absorption rate (SAR) for the

Remcom Inc., State College,

cells within the waveguide. To achieve this goal, FDTD

Pennsylvania. A key advantage

electromagnetic simulation software was used both to optimize

of the FDTD method is that it

the design of the waveguide-based exposure system and to

can provide results for a wide

characterize fully the electromagnetic fields during exposure of

band of frequencies in a single

the cells to RF fields in the 0.75-1 GHz frequency range.

computation.

Biological Effects of RF Exposure 

"The FDTD method is well

Thermal vs. Nonthermal

suited to seeing changes over

time, which is required in

Many of the in vivo and in vitro biological effects of RF

our experiments to quantify

exposure that have been reported in the literature can be

the SAR," Hagan said. The

Photograph of the actual cell

explained by tissue heating. On the other hand, some effects

researchers modeled the entire

perfusion apparatus used for

have been observed in the absence of heating, suggesting that

exposure system including both

the experiments.

RF fields can also cause effects by nonthermal mechanisms.

the cell perfusion apparatus

and waveguide. The main

grid covering the area outside the perfusion apparatus was

Providing Online Measurement

composed of cubical Yee cells of dimension 1.524 mm. The

Studies in which cultured cells are exposed to RF radiation to

smaller features of the cell perfusion apparatus as well as the

examine how a particular biological response is affected by

regions in the areas of the waveguide top and bottom slots

the exposure typically employ off-line measurement of the

were represented by a subgrid of smaller cubical Yee cells of

biological response being examined. This situation makes it

dimension 0.3048 mm, one-fifth the size of the main grid

difficult to determine the point at which changes occur, and

cells, in order to increase accuracy in these critical areas.

in general reduces the amount of information that could be

obtained from each experiment.

In the main grid, the brass probe launch and aluminum

waveguide walls were modeled as perfect conductors. The

In their studies investigating nonthermal effects of RF

probe launch was excited by a discrete sinusoidal RF source.

fields on catecholamine release from cultured chromaffin

The glass fiber filter has a very fine mesh and was hence

cells, University of Nevada, Reno researchers Todd Hagan,

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