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Frontier Research on the Dielectric Properties of Biological Tissue

Periodic Reporting for period 4 - BIOELECPRO (Frontier Research on the Dielectric Properties of Biological Tissue)

Reporting period: 2020-04-01 to 2020-09-30

The dielectric properties of biological tissue are absolutely fundamental in the understanding of the interaction of electromagnetic (EM) signals with the human body. Tissue dielectric properties are a key element in the assessment of the safety of EM radiation, and the development and refinement of EM imaging and therapeutic medical devices. Highlighting the unquestionable importance of an understanding of biological dielectric measurements, the underlying theoretical principles of dielectric measurements has been investigated for over 100 years and are now well-understood. However, the practical challenges associated with the measurement of the dielectric properties of biological tissue are often greatly underestimated and misconceived. The study of these dielectric properties of human tissue requires a multidisciplinary expertise, spanning physics, clinical biology and engineering, and involves theoretical as well as applied science. These difficult constraints routinely leads to inaccurate dielectric results being reported, or conflicting sets of dielectric measurements being presented to researchers. Since the quality of EM dosimetry studies depend wholly on the accuracy of these dielectric measurements, and the direction of EM medical device development is informed by the same measurements, it leaves European researchers building upon very unsatisfactory and unsteady foundations.

Existing review studies which aimed to provide a solid baseline set of measurements for the dielectric properties of human tissue often simply summarised data from smaller single-tissue studies, involving different measurement methods, varying sample sizes and contrasting measurement environments. Many of these studies also considered sources of errors within these dielectric measurements, but almost always as a secondary concern. In more recent studies, suspected origins of errors in dielectric measurements were listed (both random and systematic) and attempts were made to minimise their effects. However, if this approach were satisfactory, one would reasonably expect there to be relatively good agreement in the results of similar dielectric studies. Unfortunately that has been clearly shown not to be the case in a growing number of recent dielectric studies. These studies have provided a very clear motivation for a thorough and detailed investigation into the often unconsidered factors which influence dielectric measurements, how these factors interact, and how they can be modelled or compensated for to establish the “ground-truth” in terms of dielectric measurement. Moreover, the proposed research programme will seek to bridge the growing disconnect between new dielectric measurements and the underlying theoretical framework. As part of an ambitious high-risk/high-gain proposed research programme, the project will use this new understanding of the dielectric properties of human tissue as a platform for the development of new EM-based medical devices, supporting the economic and societal goals of Horizon 2020.
From a dielectric measurement and reporting perspective, we have:
Identified and characterised an in-vivo/ex-vivo difference in measured dielectric properties, based on a surface dehydration effect within the first 10 minutes post-excision. To avoid introducing large errors (up to 25%) into measured dielectric data, surface dielectric measurements should be avoided.
Characterised the sensing radius and sensing depth of the open-ended co-axial probe (the most widely used probe used for biological dielectric measurement. Both the sensing depth and sensing radius were found to be much smaller than reported in the literature. This difference between assumed and actual sensing volume becomes very important when characterising dielectrically heterogeneous tissue.
To avoid errors in dielectric measurements in the future, a new standard for the measurement and reporting of dielectric properties of biological tissue has been published. This new standard seeks to harmonise report and provide transparency on all meta data related to the dielectric measurement. This new standard and data is now available online:
From a medical device perspective, we have made significant progress:
Created a first-generation bladder imaging device, with healthy volunteer studies beginning in Summer 2018. This device will help those with bladder problems (older people with urinary incontinence; those with intellectual disabilities; post-partum women with bladder problems) to better manage their conditions and improve their quality of life.
Created a first-generation thermal treatment device for soft tissue cancers using microwave ablation, currently undergoing bench-top testing. THis device will have applications in breast cancer treatment and in the treatment of benign tumours on organs such as the adrenal gland.
Concluded a large scale study on the relationship between the electrical properties of human bone and various bone diseases. This data will feed into the design and development of a novel bone imaging technology.

Overall, the project has delivered circa 140 international peer-reviewed scientific publications to date. Similarly, the project team have contributed to a number of medical device patent applications, in an effort to translate the technology and knowledge developed within the project into the clinic where it can have a tangible impact on patient care.
The BioElecPro has developed a completely new standard for the measurement and reporting of dielectric measurements of biological tissue. More accurate dielectric data will allow medical device researchers to develop better medical devices. The published meta data will allow future researchers to assess the accuracy and reliability of historical dielectric data. At the end of the BioElecPro project, it is hoped that the new standard (called “Minder”) will have been widely adopted amongst dielectric and medical device researchers.

Through a large scale study of the dielectric properties of human tissue, at the end of the project we hope to have characterised a large number of human tissues. The results of these dielectric studies will be published on the Minder website and made freely available to researchers.

From a medical device perspective, we hope to have built three new medical devices: A bladder imaging device; a bone imaging device based on microwave imaging; and a thermal treatment device for soft-tissue cancers. For all three devices, we hope to take these devices through to first-in-man studies (subject to process and local ethical approval). If these devices are successful, they will have a real and tangible impact on patients in Europe.