Variation in the dielectric properties of freshly excised colorectal cancerous tissues at different tumor stages

Global sensitivity study for irreversible electroporation: Towards treatment planning under uncertainty

BACKGROUND

Electroporation-based cancer treatments are minimally invasive, nonthermal interventional techniques that leverage cell permeabilization to ablate the target tumor. However, the amount of permeabilization is susceptible to the numerous uncertainties during treatment, such as patient-specific variations in the tissue, type of the tumor, and the resolution of imaging equipment. These uncertainties can reduce the extent of ablation in the tissue, thereby affecting the effectiveness of the treatment.

PURPOSE

The aim of this work is to understand the effect of these treatment uncertainties on the treatment outcome for irreversible electroporation (IRE) in the case of colorectal liver metastasis (CRLM). Understanding the nature and extent of these effects can help us identify the influential treatment parameters and build better models for predicting the treatment outcome.

METHODS

This is an in silico study using a static computational model with a custom applicator design, spherical tissue, and tumor geometry. A nonlinear electrical conductivity, dependent on the local electric field, is considered. Morris analysis is used to identify the influential treatment parameters on the treatment outcome. Seven treatment parameters pertaining to the relative tumor location with respect to the applicator, the tumor growth pattern, and the electrical conductivity of tissue are analyzed. The treatment outcome is measured in terms of the relative tumor ablation with respect to the target ablation volume and total ablation volume.

RESULTS

The Morris analysis was performed with 800 model evaluations, sampled from the seven dimensional input parameter space. Electrical properties of the tissue, especially the electrical conductivity of the tumor before ablation, were found to be the most influential parameter for relative tumor ablation and total ablation volume. This parameter was found to be about 4-15 times more influential than the least influential parameter, depending on the tumor size. The tumor border configuration was identified as the least important parameter for treatment effectiveness. The most desired treatment outcome is obtained by a combination of high healthy liver conductivity and low tumor conductivity. This information can be used to tackle worst-case scenarios in treatment planning. Finally, when the safety margins used in the clinical applications are accounted for, the effects of uncertainties in the treatment parameters reduce drastically.

CONCLUSIONS

The results of this work can be used to create an efficient surrogate estimator for uncertainty quantification in the treatment outcome, that can be utilized in optimal real-time treatment planning solutions.

Measurement and image-based estimation of dielectric properties of biological tissues —past, present, and future—

The dielectric properties of biological tissues are fundamental pararmeters that are essential for electromagnetic modeling of the human body. The primary database of dielectric properties compiled in 1996 on the basis of dielectric measurements at frequencies from 10 Hz to 20 GHz has attracted considerable attention in the research field of human protection from non-ionizing radiation. This review summarizes findings on the dielectric properties of biological tissues at frequencies up to 1 THz since the database was developed. Although the 1996 database covered general (normal) tissues, this review also covers malignant tissues that are of interest in the research field of medical applications. An intercomparison of dielectric properties based on reported data is presented for several tissue types. Dielectric properties derived from image-based estimation techniques developed as a result of recent advances in dielectric measurement are also included. Finally, research essential for future advances in human body modeling is discussed.

Differences in the dielectric properties of various benign and malignant thyroid nodules

PURPOSE

This experiment was conducted to investigate the dielectric properties of different types of thyroid nodules. Our goal was to find a simple and fast method to detect thyroid diseases at different stages from the dielectric properties of thyroid nodules.

METHODS

We used the open-ended coaxial line method to measure the dielectric permittivities of thyroid tissues from 155 patients at frequencies ranging from 1 to 4000 MHz. Tissues that were investigated included normal thyroid tissue and benign and malignant thyroid nodules (nodular goiter, follicular adenoma, papillary carcinoma, and follicular carcinoma), as determined from pathological reports. Differences in dielectric properties were measured between each nodule and the surrounding 1 cm of tissue.

RESULTS

The analysis results revealed that the dielectric permittivity and conductivity values were positively correlated with the degree of malignancy of the nodule (normal < benign < malignant; all differences P < 0.05). This was more obvious at frequencies within 20~70 MHz, following the order normal tissue < nodular goiter < follicular adenoma < papillary carcinoma < follicular carcinoma. A significant difference (P < 0.05) in dielectric permittivity and conductivity was found when comparing these nodules with the surrounding 1 cm of tissue.

CONCLUSIONS

Normal, benign, and malignant nodules were successfully distinguished from one another, and dielectric permittivity was found to be a more sensitive parameter than conductivity. In particular, different disease types can be distinguished at a stimulation frequency of 20~70 MHz, which shows that dielectric properties have application prospects for the detection and diagnosis of cancer. At the same time, the dielectric parameter differences between the surrounding 1 cm of tissue and the diseased nodule can distinguish the tumor and its surrounding tissues in real time during surgery to determine the tumor boundary.

No Increased DNA Damage Observed in the Brain, Liver, and Lung of Fetal Mice Treated With Ethylnitrosourea and Exposed to UMTS Radiofrequency Electromagnetic Fields

The widespread use of mobile phones and Wi-Fi-based communication devices makes exposure to radiofrequency electromagnetic fields (RF-EMF) unavoidable. Previous experiments have revealed the tumor-promoting effects of non-ionizing RF-EMF in adult carcinogen-treated mice in utero. To extend these investigations, we tested whether these effects are due to the co-carcinogenicity of RF-EMF which would manifest as elevated DNA damage. Similar to previous experiments, pregnant mice were exposed to RF-EMF (Universal Mobile Telecommunication System [UMTS] standard, approximately 1,960 MHz) from day 7 post-conception (p.c.) at 0 (sham), 0.04, and 0.4 W/kg SAR. At day 14 p.c., the mice were injected with the carcinogen ethylnitrosourea (ENU, 40 mg/kg). At three time-points specifically 24, 36, and 72 h later, the pregnant females were sacrificed and the fetuses (n = 24-57) were removed. A dye (cy3) specific for adenyl adducts was used to detect DNA damage by fluorescence microscopy in the brain, liver, and lung of each fetus. Compared to control (0 W/kg SAR), exposure to RF-EMF had no effect on the formation of DNA adducts in the inspected tissues. We conclude that increased adenyl formation of DNA by RF-EMF exposure is not a valid explanation for the previously reported tumor-promoting effects of RF-RMF. Our findings may help to gain a deeper insight into the biological effects of RF-EMF exposure in the context of malignancy. © 2020 The Authors. Bioelectromagnetics published by Wiley Periodicals LLC on behalf of Bioelectromagnetics Society.

Evaluation of electrical properties of ex vivo human hepatic tissue with metastatic colorectal cancer

OBJECTIVE

To probe the distribution of electrical properties in tumor-bearing human hepatic tissues with metastatic colorectal cancer.

APPROACH

Electrochemical impedance spectroscopy (EIS) and a non-contact electromagnetic probe were used for distinguishing spatial heterogeneities in fresh, unfixed human hepatic tissues ex vivo from patients with metastatic colorectal cancer (CRC).

MAIN RESULTS

Point-wise EIS measurements reported over a frequency range of 100 Hz-1 MHz showed that the interface tissue between visible tumor and normal tissue exhibits an electrically different domain (p < 0.05) from both normal tissue (over 100 Hz-100 kHz) and tumor tissue (over 100 Hz-1 MHz). Observations of the microstructure on tumor-bearing hepatic tissue from hematoxylin and eosin stained images and the equivalent circuit modelling were used to validate the impedance measurements and characterize previously unidentified interfacial domain between normal and tumor tissue. Lastly, in a proof of concept study, a new in-house designed non-contact electromagnetic probe, as opposed to the invasive EIS measurements, was demonstrated for distinguishing tumor tissue from the normal tissue in a hepatic tissue specimen from a patient with metastatic CRC.

SIGNIFICANCE

EIS measurements, correlated with histological observations, show potential for mapping electrical properties in tumor-bearing human hepatic tissue.

[Sensing volume of tissue dielectric property measurement with open-ended coaxial probe]

OBJECTIVE

To investigate the sensing volume of open-ended coaxial probe technique for measurement of dielectric characteristics.

METHODS

A measurement model combining macro- measurement device with a layer model of dielectric properties parameters was established for evaluating the sensing volume of open-ended coaxial probe technique. We defined sensing depth and sensing diameter to describe the distance that could be detected in vertical and horizontal direction. Using a variety of materials with different dielectric properties (Teflon, deionized water, ethanol, and gradient concentration sodium chloride solution), a layered model of dielectric properties differentiation was established. The total combined uncertainties (TCU) were calculated for different output power, and the output power was controlled to increase from -50 dBm to 15 dBm to calibrate the error range of the dielectric properties measurement system. The optimal output power range was determined based on the results of TCU test. In sensing volume measurement experiment, we set the control groups based on measurement parameters that potentially affect the sensing volume including output power (-10, -5, 0, 3, 6, and 9 dBm), frequency (1-500 MHz), Teflon, deionized water, and ethanol to form a dielectric constant difference between high and low contrast groups. Different concentrations of sodium chloride solution and Teflon were used to generate a conductivity difference between high and low contrast groups. These groups were tested in the sensing depth and sensing diameter measurement experiments.

RESULTS

The result of TCU test indicated that accurate and stable measurement results could be obtained when the output power was greater or equal to-10 dBm (TCU &lt; 2%). Sensing volume measurement experiment revealed a positive correlation between the sensing depth and output power (P &lt; 0.05). As the measured power increased, the sensing depth gradually increased in deionized water and ethanol, and the difference reached 70 μm. The sensing depth was negatively correlated frequency (P &lt; 0.05). As the concentration of sodium chloride solution increased, the corresponding sensing depth gradually decreased, with a difference reaching 270 μm. The sensing depth of high dielectric materials was greater than that pf low dielectric materials. The results of sensing diameter measurement were not obviously affected by the measurement parameters, and the sensing diameter was stable in a fixed range (1.0 to 1.8 mm) between the diameter of the inner conductor and the diameter of the insulation layer, and was less than the diameter of the probe.

CONCLUSIONS

The sensing volume of open-ended coaxial probe technique is affected by measurement parameters and dielectric properties of materials, which significantly affect the sensing depth.

Numerical Experiments on the Contrast Capability of Magnetic Resonance Electrical Property Tomography

Purpose:

Magnetic resonance electrical property tomography (MR EPT) is a technique for non-invasively obtaining the electric property (EP) distribution of biological tissues, with a promising potential for application in the early detection of tumors. However, the contrast capability (CC) of this technique has not been fully studied. This work aims to theoretically explore the CC for detecting the variation of EP values and the size of the imaging region.

Methods:

A simulation scheme was specifically designed to evaluate the CC of MR EPT. The simulation study has the advantage that the magnetic field can be accurately obtained. EP maps of the designed phantom embedded with target regions of designated various sizes and EPs were reconstructed using the homogeneous Helmholtz equation based on B1+ with different signal-to-noise ratios (SNRs). The CC was estimated by determining the smallest detectable EP contrast when the target region size was as large as the Laplacian kernel and the smallest detectable target region size when the EP contrast was the same as the difference between healthy and malignant tissues in the brain, based on the reconstructed EP maps.

Results:

Using noise free B1+, the smallest detectable contrast_σ and contrast_εr were 1% and 3%, respectively, and the smallest detectable target region size was 1 mesh unit (the base unit size used in the simulation) for conductivity and relative permittivity. The smallest detectable EP contrast and target region size were decreased as the B1+ SNR increased.

Conclusion:

The CC of MR EPT was related with the SNR of the magnetic field. A small EP contrast and size were necessary for detection at a high-SNR magnetic field. Obtaining a high-SNR magnetic field is important for improving the CC of MR EPT.

Dielectric Properties of Normal and Metastatic Lymph Nodes Ex Vivo From Lung Cancer Surgeries

The dielectric properties of normal and tumor human tissues have been widely reported in recent years. However, the dielectric properties of intrathoracic lymph nodes (LNs) have not been reported. In this communication, we measured the dielectric properties (i.e., permittivity and conductivity) of ex vivo intrathoracic LNs obtained from lung cancer surgeries. Results show that the permittivity and conductivity of metastatic LNs are higher than those of normal LNs over the frequency range of 1 MHz-4 GHz. Statistically significant differences are observed at single specific frequencies (64, 128, 298, 433, and 915 MHz and 2.45 GHz). Our study provides the basic data to support future-related research and fills the research gap on the dielectric properties of LNs in the lungs. Bioelectromagnetics. 2020;41:148-155. © 2020 Bioelectromagnetics Society.

Role of Simulations in the Treatment Planning of Radiofrequency Hyperthermia Therapy in Clinics

Hyperthermia therapy is a treatment modality in which tumor temperatures are elevated to higher temperatures to cause damage to cancerous tissues. Numerical simulations are integral in the development of hyperthermia treatment systems and in clinical treatment planning. In this study, simulations in radiofrequency hyperthermia therapy are reviewed in terms of their technical development and clinical aspects for effective clinical use. This review offers an overview of mathematical models and the importance of tissue properties; locoregional mild hyperthermia therapy, including phantom and realistic human anatomy models; phase array systems; tissue damage; thermal dose analysis; and thermoradiotherapy planning. This review details the improvements in numerical approaches in treatment planning and their application for effective clinical use. Furthermore, the modeling of thermoradiotherapy planning, which can be integrated with radiotherapy to provide combined hyperthermia and radiotherapy treatment planning strategies, are also discussed. This review may contribute to the effective development of thermoradiotherapy planning in clinics.

Quantitative Estimation of the Equivalent Radiation Dose Escalation using Radiofrequency Hyperthermia in Mouse Xenograft Models of Human Lung Cancer

Hyperthermia is a potent radiosensitizer, and its effect varies according to the different types of cancer cells. In the present study, the radiosensitizing effect of hyperthermia on lung cancer cell lines A549 and NCI-H1299 was determined based on the equivalent radiation dose escalation. In vitro cell experiments were conducted using lung cancer cell lines A549 and NCI-H1299 to determine thermal radiosensitivity. In vivo experiments were conducted using mouse heterotopic xenograft models to determine the treatment response and increase in the temperature of tumors using a 13.56 MHz radiofrequency (RF) hyperthermia device. Using the α and β values of the linear–quadratic equations of cell survival curves, numerical simulations were performed to calculate the equivalent radiation dose escalations. The dielectric properties of tumors were measured, and their effect on the calculated equivalent radiation dose was analyzed. Hyperthermia increased the equivalent radiation dose of lung cancer xenografts and a higher escalation was found in NCI-H1299 cells compared with that observed in A549 cells. An underestimation of the calculated equivalent radiation dose was observed when the dielectric property of the tumor was varied. This study may contribute to the effective planning of thermoradiotherapy in clinics.

Electrical properties tomography: Available contrast and reconstruction capabilities

MR-based electrical properties tomography converts the MRI transmit/receive RF field measurements to tissue electrical property maps through dedicated reconstruction algorithms. Recent reports showed that despite limitations, electrical properties tomography holds promise for generating additional contrast for tumor detection and patient-specific modeling of tissue-RF field interactions. This review summarizes the available tissue electrical property contrasts and compares them with the capabilities of the most commonly used electrical properties tomography reconstruction method. Future directions and prospects of clinical translation are discussed.