Topic

Investigation of the question, if macroscopic dielectric properties of tissues have unlimited validity at both cellular and subcellular levels

Start

01.12.2005

End

31.05.2007

Project Management

University of Augsburg

Objective

The goal of this project was to study, how dielectric parameters of different cell types can be characterized at cellular, subcellular and molecular dimensions. Based on the project’s findings, consequences regarding the distribution of electromagnetic fields, energy absorption and perhaps conversion of energy modes had to be derived and discussed.

Results

As an interim report the contractor delivered a literature survey. The report describes experimental methods of biophysics and theoretical approaches for further work on the project.

The report is available as PDF-file in German (2.254 KB).

In the course of the project dielectric spectroscopy on electrolytic solutions, on synthetic membranes and on a variety of (mainly) human cells was carried out at frequencies from 100 MHz up to 40 GHz. Temperature and concentration were varied systematically. The measurements were analyzed and compared to findings for pure water with respect to additional relaxation processes at RF frequencies as these could be linked to specific dielectric properties and/or effects on a cellular or subcellular level.

With one exception only water-like relaxation phenomena were found. Data for blood and suspensions of red blood cells at different hematocrit levels indicate a weak additional relaxation close to 3 GHz. The increase in characteristic relaxation rates by raising temperature is found unique. No theoretical model is derived which could explain the experimental findings. As no correlation between dielectric relaxation strength and hematocrit level could be established the source of this relaxation remains unclear.

The final report is available as PDF-file in German (2.254 KB).

Conclusions

Except for the findings concerning blood and suspensions of red blood cells no evidence has been found with respect to specific dielectric properties that might be linked to some effects on a subcellular level. Ordinarily, describing a measured dielectric spectrum by means of relaxation terms is not unique. The presumed relaxation strength for blood at temperatures of the human body is rather low, not much above the measurement uncertainty of ± 5 %. Concerning the macroscopic conductivity (in S/m) of blood and its absorption properties the data by Gabriel et al., which is usually used in dosimetry nowadays, is conservative as the values provided by Gabriel et al. are higher than those measured here.