Dielectric properties of muscle and liver from 500 MHz–40 GHz

Abstract

Dielectric properties are the most important parameters determining energy deposition when biological tissues are exposed to radio frequency and microwave fields. Energy absorption is determined by the specific absorption rate (SAR). SAR distributions can be computed accurately only if the complex relative permittivity of the target tissue is known to a sufficiently high accuracy, and currently there is a lack of data on the dielectric properties of biological tissues at high frequencies. In this study, tissue dielectric properties are measured using an open-ended coaxial probe technique from 500 MHz up to 40 GHz. We present dielectric data for ex vivo bovine and porcine muscle and liver tissues at 37 °C. One-pole Cole-Cole model is used to fit the measured data as a function of frequency and the dispersion parameters are presented. This data is supported by an accurate study on reference liquids such as methanol and ethanediol.

Investigation of the effect of dehydration on tissue dielectric properties in ex vivo measurements

“…In one of the most comprehensive studies, Gabriel et al (1996) reported the dielectric properties of a large number of biological tissues including freshly excised bovine and porcine tissue, human autopsy material, and human skin and tongue over a frequency range of 10 Hz-20 GHz. Dielectric data for various human and animal tissues reported in other studies (Foster et al 1979, Surowiec et al 1987, Peyman et al 2001, Schmid et al 2003, Lazebnik et al 2006, Abdilla et al 2013, Sasaki et al 2014 align with the data presented in (Gabriel et al 1996), which is widely used in electromagnetic modeling and assessment of specific absorption rate. Stuchly et al (1982) studied inter-species differences in dielectric properties of skeletal muscle, brain cortex, spleen, and liver tissue between 0.1 and 10 GHz, and reported a very small difference (within system uncertainty) between the same tissues of different species, which led researchers to believe that the data from animal studies can be generalized and used for human tissue modeling.…”

Minimum information for dielectric measurements of biological tissues (MINDER): A framework for repeatable and reusable data

“…These confounders are likely the source of inconsistencies in reported data. The main equipment‐based measurement confounders that have been shown to affect the accuracy of dielectric data include: the calibration procedure; calibration drift; calibration refresh; the validation procedure; the reference liquid used for validation and accuracy of its model properties; and the disconnection, reconnection or movement of cables or probe . Uncertainties in the dielectric data caused by these measurement confounders have been thoroughly investigated over the years and can now be reduced or eliminated by following good measurement practice as identified in the literature …”

“…However, clinical confounders have been relatively uninvestigated to date and may introduce a significant level of additional uncertainty into the dielectric data . While not an exhaustive list, clinical confounders that have been identified in the literature are: the tissue source; animal age and weight; the use of anaesthesia/drugs; physiological parameters (blood flow, blood oxygenation, blood pressure, heart rate, respiration rate); in‐vivo vs ex‐vivo measurements; time since death/excision; the sample temperature and cooling or warming of the sample; sample dehydration and blood loss; contamination or artificial drying of surface; quality of probe‐sample contact; probe‐sample pressure; the sensing depth and sample size; tissue sample heterogeneity; the technique for marking measurement location on the tissue sample; sample or data exclusion criteria; pathologist methodology; and the histological analysis technique . Confounders can also be introduced when the dielectric data is reported in the form of models, due to the choice of model type; the number of poles used in the model; the fitting algorithm used to obtain the model parameters; and the accuracy of the fitting technique …”

Modeling of the dielectric properties of biological tissues within the histology region

“…This probe was selected as its small diameter makes it optimal for measuring small tissue samples, and it is commonly used in the literature for this purpose [11], [12], [19], [20]. The probe was calibrated using the standard three-term calibration procedure.…”