Permittivity of Healthy and Diseased Skeletal Muscle

Abstract

A better understanding of the permittivity of skeletal muscle is essential for the development of new diagnostic tools and approaches for neuromuscular evaluation. However, there remain important knowledge gaps in our understanding of this property in healthy and diseased skeletal muscle, which hinder its translation into clinical application. The aim of this project is to provide a platform for the researchers to contribute and share the dissemination of this property in healthy and diseased muscle. Ultimately, the normative data reported will offer the scientific community the opportunity to improve the accuracy of existing techniques as well as developing new diagnostic tools and therapies.

Background

Electromagnetism constitutes a basic physical principle widely used in the field of biomedical engineering, designed to monitor and treat a broad spectrum of conditions including Parkinson’s disease and brain tumors. Understanding how different biological tissues and fluids interact with electromagnetic fields is essential for improving the accuracy of existing analytical techniques as well as developing new diagnostic tools and therapies.

In electromagnetism, permittivity is one fundamental material parameter affecting the propagation of electromagnetic fields. When exposed to an electromagnetic field, the dipole moment of the material's molecules opposes the external electric field and so the net electric field is reduced within the material. In other words, the permittivity is a measure of the ability to store an electric charge in the polarization of the material.

Basic and applied scientific endeavors have reported the permittivity property for well over 100 years in a collective effort to understand the propagation of electromagnetic fields in the human body. However, a recent meta-analysis revealed that major gaps in the knowledge of the frequency-dependence of the permittivity in many tissues still exist, especially for those tissues such as skeletal muscle, in which this property is directionally dependent. In addition, some previous studies of the permittivity of biological specimens did not specify the state of the tissue examined, even though it is known that the permittivity values change postmortem and with temperature, nor did they specify the extent of disease, if any, present, and some did not include healthy control tissue for comparison.  Other noteworthy factors that have not been exhaustively evaluated include the variation of tissues’ permittivity with age, gender, and disease progression. This missing information highlights critical gaps in our understanding of the factors that affect the permittivity property of biological tissues required to aid in identification of clinically abnormal results in pathological tissue.

Methods

All animal procedures were carried out in strict accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the NIH and approved by the Institutional Animal Care and Use Committee at Beth Israel Deaconess Medical Center (Protocol \#087–2016). Data were measured ex vivo from from 9 to 862 kHz using the four-electrode impedance technique. Following euthanasia via carbon dioxide inhalation, the gastrocnemius muscle was excised at its proximal extent just below the knee and distally by cutting the gastrocnemius tendon at its insertions, after removing the bicep femoris muscle. Each gastrocnemius muscle was trimmed with a scalpel to 5 mm (width) x 5 mm (length) centered at the belly of the muscle in order to fit into the dielectric measuring cell. Briefly, the dielectric cell was made of two flat plate stainless steel electrodes for applying electrical current side to side of the slab of muscle. The voltage electrodes were two monopolar EMG needles in contact the top surface of the muscle (Carefusion #902-DMG50-TP). The geometrical dimensions of the dielectric cell were 5 mm (width) x 5 mm (length), the muscle height measured with a caliper. The distance between the voltage electrodes was 4 mm. The slab of muscle was inserted into the cell first with the muscle fibers oriented parallel (longitudinal) and then perpendicular (transverse) to the current electrodes. The geometric factor was determined from measurements of saline solution with the corresponding height of each tissue sample.

Data Description

The format of the data files is the same for healthy and diseased muscle conditions. The anisotropic permittivity property measured in longitudinal and transverse directions is organized in columns while the frequency dependence is organized in rows. For each time point measured, which also is organized in columns, the permittivity average value and the standard error of the mean are reported.

Usage Notes

The csv data files begin with WT for healthy wild-type, or Disease for diseased. They contain mean and standard error of the mean measurements of conductivity and relative permittivity, for both longitudinal and transverse measurements. The mice may also be grouped by age.

Conflicts of Interest

Dr. Sanchez serves as a consultant to Myolex, Inc., and Impedimed, Inc., a company that develop impedance technology for research and clinical use. Dr. Sanchez is Co-Founder of Haystack Diagnostics, Inc., a company that commercializes needle impedance technology. Haystack Diagnostics, Inc., has the option to license patented needle impedance technology of which Dr. Sanchez is named inventor.