Dielectric Properties Of Bone Research Articles

Tumor treating fields suppress tumor cell growth and neurologic decline in models of spinal metastases.

Spinal metastases can result in severe neurologic compromise and decreased overall survival. Despite treatment advances, local disease progression is frequent, highlighting the need for novel therapies. Tumor treating fields (TTFields) impair tumor cell replication and are influenced by properties of surrounding tissue. We hypothesized that bone's dielectric properties will enhance TTFields-mediated suppression of tumor growth in spinal metastasis models. Computational modeling of TTFields intensity was performed following surgical resection of a spinal metastasis and demonstrated enhanced TTFields intensity within the resected vertebral body. Additionally, luciferase-tagged human KRIB osteosarcoma and A549 lung adenocarcinoma cell lines were cultured in demineralized bone grafts and exposed to TTFields. Following TTFields exposure, the bioluminescence imaging (BLI) signal decreased to 10%-80% of baseline, while control cultures displayed a 4.48- to 9.36-fold increase in signal. Lastly, TTFields were applied in an orthotopic murine model of spinal metastasis. After 21 days of treatment, control mice demonstrated a 5-fold increase in BLI signal compared with TTFields-treated mice. TTFields similarly prevented tumor invasion into the spinal canal and development of neurologic symptoms. Our data suggest that TTFields can be leveraged as a local therapy within minimally conductive bone of spinal metastases. This provides the groundwork for future studies investigating TTFields for patients with treatment-refractory spinal metastases.

Dielectric characterization of diseased human trabecular bones at microwave frequency

The objective of this study is to determine whether in vitro dielectric properties of human trabecular bones, can distinguish between osteoporotic and osteoarthritis patients’ bone samples. Specifically this study enlightens intra-patient variation of trabecular bone microarchitecture and dielectric properties, inter-disease comparison of bone dielectric properties, and finally establishes the correlation to traditional bone histomorphometry parameter (bone volume fraction) for diseased bone tissue. Bone cores were obtained from osteoporotic and osteoarthritis patients (n = 12). These were scanned using microCT to examine bone volume fraction. An open-ended coaxial probe measurement technique was employed to measure dielectric properties over the 0.5 – 8.5 GHz frequency range. The dielectric properties of osteoarthritis patients are significantly higher than osteoporotic patients; with an increase of 41% and 45% for relative permittivity and conductivity respectively. The dielectric properties within each patient vary significantly, variation in relative permittivity and conductivity was found to be greater than 25% and 1.4% respectively. A weak correlation (r = 0.5) is observed between relative permittivity and bone volume fraction. Osteoporotic and osteoarthritis bones can be differentiated based on difference of dielectric properties. Although these do not correlate strongly to bone volume fraction, it should be noted that bone volume fraction is a poor predictor of fracture risk. The dielectric properties of bones are found to be influenced by mineralization levels of bones. Therefore, dielectric properties of bones may have potential as a diagnostic measure of osteoporosis.

Dielectric properties of bones for the monitoring of osteoporosis.

Osteoporosis is one of the most common diseases that leads to bone fractures. Dual-energy X-ray absorptiometry is currently employed to measure the bone mineral density and to diagnose osteoporosis. Alternatively, the dielectric properties of bones are found to be influenced by bone mineral density; hence, dielectric properties of bones may potentially be used to diagnose osteoporosis. Microwave tomographic imaging is currently in development to potentially measure in vivo dielectric properties of bone. Therefore, the foci of this work are to summarize all available dielectric data of bone in the microwave frequency range and to analyze the confounders that may have resulted in variations in reported data. This study also compares the relationship between the dielectric properties and bone quality reported across different studies. The review suggests that variations exist in the dielectric properties of bone and the relationship between bone volume fraction and dielectric properties is in agreement across all studies. Conversely, the evidence of a relationship between bone mineral density and dielectric properties is inconsistent across the studies. This summary of dielectric data of bone along with a comparison of the relationship between the dielectric properties and bone quality will accelerate the development of microwave tomographic imaging devices for the monitoring of osteoporosis. Graphical abstract ᅟ.

An automatic approach for calibrating dielectric bone properties by combining finite-element and optimization software tools

The dielectric properties of human bone are one of the most essential inputs required by electromagnetic stimulation for improved bone regeneration. Measuring the electric properties of bone is a difficult task because of the complexity of the bone structure. Therefore, an automatic approach is presented to calibrate the electric properties of bone. The numerical method consists of three steps: generating input from experimental data, performing the numerical simulation, and calibrating the bone dielectric properties. As an example, the dielectric properties at 20 Hz of a rabbit distal femur were calibrated. The calibration process was considered as an optimization process with the aim of finding the optimum dielectric bone properties that match most of the numerically calculated simulation and experimentally measured data sets. The optimization was carried out automatically by the optimization software tool iSIGHT in combination with the finite-element solver COMSOL Multiphysics. As a result, the optimum conductivity and relative permittivity of the rabbit distal femur at 20 Hz were found to be 0.09615 S/m and 19522 for cortical bone and 0.14913 S/m and 1561507 for cancellous bone, respectively. The proposed method is a potential tool for the identification of realistic dielectric properties of the entire bone volume. The presented approach combining iSIGHT with COMSOL is applicable to, amongst others, designing implantable electro-stimulative devices or the optimization of electrical stimulation parameters for improved bone regeneration.

The Correlation Between Dielectric Properties and Microstructure of Femoral Bone in Rats with Different Bone Qualities

Bone dielectric properties (DP) have been extensively studied. However, little literature has reported DP of bone from identical anatomical site under different status and its correlation with microstructure. Therefore, interrelationship between DP and microstructure of rat femurs with varying bone qualities (normal, osteoporotic and partially osteoporotic) was investigated. Diabetic osteoporosis was induced by streptozotocin (STZ) injection. 8 normal rats as control group together with 16 diabetic rats equally assigned to diabetes mellitus (DM) and DM treated by pulsed electromagnetic fields (PEMF) (DM+PEMF) group were used. DM+PEMF group was daily exposed to PEMF of 15Hz, 1mT for 8weeks. After sacrifice, the femurs were harvested for microCT analysis and dielectric measurements (from 10Hz to 1MHz). It was found that DP (conductivity and permittivity) altered after PEMF stimulation improved femoral microstructures (p<0.01). Significant correlations were found between microstructure indices (MI) and conductivity in the full frequency range (|r|≥0.64, n=24) as well as permittivity in middle and low frequencies (|r|≥0.52, n=24, from 1Hz to 1kHz). The findings demonstrated the good correlation between DP and MI of femoral bone in rats, which makes it possible to distinguish bone under different status and predict MI variation through dielectric measurements.

Modeling of the dielectric properties of trabecular bone samples at microwave frequency

In this paper, the dielectric properties of human trabecular bone are evaluated under physiological condition in the microwave range. Assuming a two components medium, simulation and experimental data are presented and discussed. A special experimental setup is developed in order to deal with inhomogeneous samples. Simulation data are obtained using finite difference time domain from a realistic sample. The bone mineral density of the samples are also measured. The simulation and experimental results of the present study suggest that there is a negative relation between bone volume fraction (BV/TV) and permittivity/conductivity: the higher the BV/TV, the lower the permittivity/conductivity. This is in agreement with the recently published in vivo data.

Electrical conduction in bone in frequency range 0.4-1.3 GHz.

Dielectric permittivity and conductivity of bone in different physiological conditions and collagen, a major component of bone are measured in the frequency range 400-1300 MHz using a Network analyzer. The dielectric dispersion observed in each cases are explained in terms of the relaxation of 'bound water' in this frequency range. The relaxation frequency as well as distribution parameter are computed in each case, under certain simplifying conditions, hydration as well as static dielectric permittivity of bound water attached with bone in different physiological conditions and collagen are also calculated. The effect of ultraviolet light irradiation on the dielectric properties of bone in this frequency range is also examined. The change in dielectric properties due to radiation is attributed to the breakage of hydrogen bonds in the ring structure. A consistent physical model in line with other data is presented.