Changes of electrical impedance characteristics with the radiation induced damage on biological tissue constituents

Abstract

This study analyzes the response of increasing radiation dose to the pork tenderloin tissue. Considering its significant cell structure, pork tenderloin tissue samples are selected for the experimental objects to measure their electrical impedance characteristics. This study proposes and investigates an effective approach to characterize the variation of the internal change of the components of pork tenderloin tissues caused by radiation. Changes in the pork tenderloin tissues are that the gap of the myotome is more far apart with increase of radiation dose because of the destroyed Myofibrils under the damage. With the increase of radiation dose, the impedance value of the pork tenderloin tissue decreases. Each of mean differences in the impedance values before and after irradiation dose under 1 Gy, 2 Gy and 4 Gy show 0.55±0.03, 1.09±0.14 and 1.97±0.14, respectively. However, the mean difference substantially increases to 13.08±0.16 at irradiation dose of 10 Gy. Thus, the cell membrane shows the most severe rupture at a radiation dose of 10 Gy. Changes in the microstructure of the irradiated pork tenderloin tissue samples are also checked and validated by a transmission electron microscope.

Keywords

Electrical impedance spectroscopy (EIS)electrical impedance characteristics radiation exposure transmission electron microscope (TEM)

1 Introduction

With electrical phenomena defined as the most basic unit of organism, the cells constantly move ions between inside and outside of cells and also change in the flow of these ions which are fundamental signals that induce not only nerve signal transmission but also muscle contraction. It contains a lot of information related to life phenomenon.

Overall, the electrical impedance spectroscopy (EIS) is one of the most often used parameters for characterizing material properties and good for use in tissue characterization [1]. The usage of impedance spectroscopy electrical characterization is a unique approach to comprehend underlying operative phenomena in several material systems, including biological tissues. It is possible to analyze the internal characteristics of a living body according to the frequency response analysis of the resistance distribution of biological tissues and the characteristic curve of the spectrum. Moreover, it has been widely used in the field of biometrics due to its small system interference, comprehensive process information and reliable result. Especially, the electrical impedance of a tissue is a function associated with biological structure such as cell size, density, spacing, and the constituents of the extracellular and intracellular matrices.

Besides, the electrical properties of biological tissues are related to their physiological, morphological and pathological conditions and the electric field requirement varies from cell to cell [2, 3]. Schwan reported that electrical impedance analysis is a powerful research tool for biological research in the electrical properties of tissue and cell suspension [4].

Biological tissue defines a group of cells having the same direction of differentiation and similar shape and function in an individual. The types of tissues are epithelial tissue, connective tissue, muscle tissue, and nerve tissue. By studying the electrical impedance of various tissues over AC frequency range using EIS, its frequency-dependent electric and dielectric behavior can be determined and used for various applications including pathology, prognosis, diagnosis. In addition, the biological tissue consists of different types of cells, and the liquid between the cells is extracellular fluid, which can be regarded as an electrolyte [5]. In other words, biological cells are composed of cytoplasm and cell membrane.

For this reason, studying about the electrical properties of bio-tissue using impedance, the equivalent circuit theory is widely used and actively researched the changes in characteristics of biological tissue using equivalent circuits [6 –8]. For example, the low-frequency conductivity of cell membrane behaves like capacitance in poor status. So, electrical impedance spectroscopy, revealing the variations in electrical impedance with changes infrequency, is good for obtaining both the resistive and capacitive characteristics of tissues. In order to quantitatively analyze the electrical impedance characteristics of cell in detail, the equivalent circuit fitting is necessary.

Recently, it is increasing to use ionizing radiation for cancer treatment. For example, Gamma knife, cyber knife, Novalis, linear accelerators, etc. are representative machines to treat tumor cancer. Furthermore, ionizing radiation works by damaging the DNA of exposed tissue leading to cellular death [9 –11]. However, the radiation affects not only the malignant cell but also normal tissue. Therefore, evaluation of the damage of normal tissue duration and post-radiation therapy is very important to enhance the therapeutic benefit. The demand for techniques to identify irradiated normal tissue as well as cancer tissue is increasing for the control and the public acceptance of irradiated dose.

In order to deploy electrical impedance spectroscopy as a non-invasive tool for radiation response tracking, one would hope to develop a model which can apply the data well and that demonstrate a parametric variation related to changes associated with the progression of tissue injury. Though, it seems that the research has not been widely reported on the critical characteristic change of irradiated biological tissue.

EIS has a great potential to monitor the tissue status. Most of the previous studies showed that the impedance value was reduced by the radiation after irradiation [8 , 13]. In the process of EIS radiation, it is possible to indirectly predict tissue changes through changes in impedance. For direct observation, they only observed changes in the internal structure of the organization by hematoxylin and eosin stain or haematoxylin and eosin stainis instead of transmission electron microscope (TEM). But, to observe the changes in micro-structures of tissue caused by radiation, it should be observed with TEM.

In this study, the degree of tissue damage was indirectly evaluated through EI, and the degree of tissue damage was directly confirmed in the TEM image. Especially, it was confirmed by TEM image that the degree of destruction of pork tenderloin tissue became more severe as the radiation dose increased. Furthermore, when performing high radiation experiments bring about extreme dangerous exposure, it is prerequisite about safety, but it is insufficient of awareness. To avoid radiation exposure, the measurement of electrical characteristics should be done automatically through the LabVIEW in our experiment.

2 Background

Impedance (Z) is a physical quantity representing the degree of difficulty in flowing current in biological materials and depends on frequency. This refers to the value indicating the degree of interruption of current flow when alternating current flows through the biological tissue. When an alternating current is applied to measure impedance, the impedance of tissue changes according to frequency. High-frequency currents can easily flow, but low-frequency currents are difficult to flow into biological materials [14].

In general, the impedance can write as Z = Z’ + jZ”, where Z’ is the real part of the impedance, and Z”, its imaginary part. The electrical impedance quantity, Z = Z’ + jZ”, distributed in the complex plane where the reactive component of the tissue impedance (Z’ = Im[Z]) is plotted along the imaginary (vertical) axis as a function of the concomitant resistive component (Z’ = Re[Z]) which is represented along the real (horizontal) axis at each frequency.

3 Material and experiment method

3.1 Material

In order to explore the electrical impedance characteristics of pork tissues tenderloin, a skeletal muscle with significant cell structure was selected for the experimental objects to explore their electrical impedance characteristics. For the pork tissues specimen used in this study, pork tenderloin slaughtered on the same day, cut into 60×60×30 mm in size, placed on an ice chest (4) and transported to the laboratory, then refrigerated and used for experiment. For experiment, the tissue specimen was divided into 4 equal parts (sample 1, sample 2, sample 3 and sample 4) into 30×30×30 mm sizes, as shown Fig. 1(a). There was little change in the electrical properties of each of the four samples.

Fig. 1

(a) The tissue specimen was divided into 4 equal parts (sample 1, sample 2, sample 3 and sample 4) into 30×30×30 mm sizes. (b) The acrylic plate was processed into a 100×60×60 mm rectangular parallelepiped, after connecting to 16047A Test Fixture, a thin mono-polar needle electrodes (Teflon-Coated Stainless Steel, 75 mm length, 0.46 mm diameter) were placed in a parallel position 20 mm apart, 30 mm depth and inserted into the pork tenderloin tissue.

Perez-Esteve et al. [15] used the EIS method to detect the freshness of meat products. The results showed that the higher the freshness get the greater the impedance value. For minimizing the error from temperature change, the measurement system is equipped with a thermo-hygrostat to minimize the effect of thermally stable environment and moisture. We conducted an experiment on the pork tenderloin with skeletal muscle among pork tissue. Then, the sample was divided into 4 parts, and each was irradiated with radiation. The measured results are shown as the mean value±standard deviation (mean±SD). The Wilcoxon signed rank test was used to evaluate the difference between the impedance absolute value before and after radiation expose. Statistical analysis was done using the SPSS 26.0 software. All tests were two tailed and P value < 0.05 was taken as statistically significant.

3.2 Experimental device and set up

The raw resistance (units of ohms) depend on the sample thickness of pork tenderloin tissue. The electrode area and measurement geometry have been converted to intrinsic tissue impedance properties (units of ohms-meters) under the standard assumptions of planar current flow perpendicular to the electrode surfaces in the parallel measurement configuration which has been used [1]. A four-electrode system used in this study has been reported to eliminate the effect of electrode polarization. This reduces an influence of electrode polarization and noise on the measurement results [16].

For precise data measurement, the acrylic plate was processed into a 100×60×60 mm rectangular parallelepiped, and a hole and a single electrode guide were prepared by drilling holes according to the electrodes. After connecting to 16047A Test Fixture, a thin mono-polar needle electrodes (Teflon-Coated Stainless Steel, 75 mm length, 0.46 mm diameter) were placed in a parallel position 20 mm apart, 30 mm depth and inserted into the pork tenderloin tissue to be tested, as shown in Fig. 1(b).

Table 1 shows the specification of the 4194A Impedance/gain-phase Analyzer. According to the measured impedance absolute value data of the pork tissues, the impedance phase of the pork tissues, under different radiation times in the frequency range of 1 kHz∼1 MHz are obtained. The zero point was corrected by applying a voltage of 10 mV to 1.28 V_rms in the open and short-circuited states of the unipolar needle tip. Then, after setting the sweep mode to the repeat mode, an alternating frequency and phase difference were measured by applying an alternating frequency from 1 kHz to 1 MHz. [impedance/gain-phase analyzer (Model 4194A, Agilent, USA)]

Table 1
Specification of the 4194A Impedance/gain-phase Analyzer

Model Frequency Resolution Measurement Parameters

4194A 1 kHz∼1 MHz 1 × 10^-3 Hz |Z|: Impedance Absolute Value

θ: Impedance Phase

R: Resonance Resistance

X: Equivalent Series Reactance

The pork tissues were immobilized in container and irradiate by a linear accelerator (Irradiation with 6 MV photons at a dose of 360 MU/min in one fraction to the pork tenderloin tissue (3×3 cm²) using a Varian Clinac 21IX accelerator, USA). The radiation dose (1 Gy, 2 Gy, 4 Gy and 10 Gy) was irradiated in irradiation area 10×10 cm², SAD 100 cm.

3.3 Automatic control system

After connecting the tissue specimen and the unipolar needle electrode to the measuring device such as impedance/gain-phase analyzer, measurement parameters were controlled using LabVIEW. It consists of a computer with a LabVIEW-programmed software. To increase the automatic control of measurement systems and data processing efficiency, Programming of impedance/gain-phase analyzer measurement parameters, measurement range, execution sequence, etc. using LabVIEW was made by National Instrument (NI).

4 Result

4.1 Reproducibility of electrical property measurements

In this study, the electrical impedance works as follows: The electrical properties of tissue are dependent upon the structural organization of cells within the tissue. Electrical charge accumulates at the lipid membranes, restriction current to the extracellular space at low frequencies and allowing current to flow through intracellular space at higher frequencies.

The equation (1) is used to calculate the coefficient of variation (CV). $CV (%) = \frac{σ}{\bar{x}} \times 100$ (1)

Table 2 shows the coefficient of variation result on the data of repetitive Measurement Here, CV is the coefficient of variation, σ is the standard deviation and $\bar{X}$ is the average. Figure 2 shows reproducible results of resonance resistance and equivalent series reactance of pork tenderloin tissue form 1 kHz to 1 MHz. The equivalent series reactance and resonance resistance difference were less than 10%, and the fluctuation pattern was not large and stable, and the measured values were reproducible, as shown in Fig. 2.

Table 2

Coefficient of Variation Result on the Data of Repetitive Measurement

F	R		X
	Mean±SD (95% CI)	CV (%)	Mean±SD (95% CI)	CV (%)
1–100	107.41±1.475 (106.72∼108.10)	1.37	–1.46±0.025 (–1.47∼–1.44)	1.74
101–200	106.99±1.466 (106.23∼107.67)	1.37	–0.90±0.031 (–0.92∼–0.89)	3.44
201–300	106.77±1.463 (106.08∼107.45)	1.37	–0.96±0.047 (–0.99∼–0.94)	4.88
301–400	106.57±1.452 (105.89∼107.25)	1.36	–1.06±0.056 (–1.08∼–1.03)	5.32
401–500	106.39±1.445 (105.71∼107.07)	1.36	–1.13±0.068 (–1.16∼–1.10)	6.02
501–600	106.21±1.440 (105.54∼106.89)	1.36	–1.20±0.077 (–1.23∼–1.16)	6.45
601–700	106.04±1.432 (105.37∼106.71)	1.35	–1.24±0.079 (–1.27∼–1.20)	6.41
701–800	105.87±1.427 (105.21∼106.54)	1.35	–1.28±0.091 (–1.32∼–1.23)	7.13
801–900	105.71±1.421 (105.05∼106.38)	1.34	–1.29±0.095 (–1.34∼–1.25)	7.34
901–1000	105.56±1.418 (104.90∼106.23)	1.34	–1.28±0.100 (–1.33∼–1.23)	7.84

F frequency range(kHz), R resonance resistance, X equivalent series reactance, SD standard deviation, CI confidence interval for mean, CV coefficient of variation.

Fig. 2

The equivalent series reactance and resonance resistance difference. Reproducible results of resonance resistance and equivalent series reactance of pork tenderloin tissue form 1 kHz to 1 MHz (a) equivalent series reactance and (b) resonance resistance.

This frequency range was chosen because measurement errors may occur both below 1 kHz, due to electrode impedance, and above 1000 kHz, due to cable effects [17]. As a result of repeated 20 times measurements at 3 minute intervals, we found that reproducibility of the coefficient variation within±10%.

4.2 EIS analysis of the pork tenderloin tissue

Impedance is a physical quantity that indicates the degree of difficulty in flowing an electric current in a biological material and is frequency dependent. When the impedance is measured by applying alternating current, the impedance of the tissue changes with frequency. That is, in various frequency ranges, the electrical characteristics of pork tenderloin tissue are determined by the impedance value by the cell component and the size, internal structure and arrangement of the constituent cells.

In the case of the reactance of a general biological tissue, the contribution of the inductive component is regarded as almost 0, and it is considered that the equivalent circuit only considered the contribution of the capacitive component, as shown in Fig. 3. The pork tenderloin tissue can be considered as a composite capacitor comprising a number of spatially distributed tissues with differing electrical properties. We considered as a simple RC circuit model of human skin membrane [8, 16]. Figure 3 was assumed that the tissues have no or negligible inductive influence. Since biological cells are extremely complex, a number of combinations of series such as parallel capacitances may be needed. We considered C (the capacitance of the membrane) as the combined value of parallel capacitances. It will be a simple and easy model to understand a biological aspect of cell membrane.

Fig. 3

The simplified RC circuit model of cell membrane. C_m (the capacitance of the membrane) is the combined connection of parallel capacitances.

At very high frequencies, due to the very small time constants, current does not flow but only moves back and forth between membrane surfaces and hence neither the resistive pathways nor the capacitive pathways of the membranes have time to play a role [16]. Thus, the imaginary part of the impedance very becomes small. For this reason, the frequency domain is selected from 1 kHz to 1 MHz using the impedance/gain-phase analyzer for the impedance and phase difference of the pork tenderloin tissue, then we apply the alternating frequency.

Figure 4 shows the impedance and phase value of pork tenderloin tissue. We divided the pork tenderloin into 4 parts and measured the impedance and phase of each. As a result, there was little difference in the electrical characteristics of each specimen. In the frequency of 1 kHz to 30 kHz, the magnitude of the impedance shows a sharp decrease and is not proportional to the frequency, as shown in Fig. 4(a). For this reason, the impedance value at low frequency is the result of reflecting characteristics of tissue surface such as extracellular fluid, which can be regarded as an electrolyte and the conductivity. Moreover, impedance characteristics can be affected by the polarization of the electrode surface [18] and by the phenomenon occurring at low frequencies such as Warburg impedance. On the other hand, electric double layer of between sample and electrode reduces the influence of electrode polarization and noise on the measurement results during measurement [6].

Fig. 4

The impedance and phase value of pork tenderloin tissue. Graph of the impedance (a) and (b) phase of pork tenderloin tissue; the box inside the left graph is enlarged from 1 kHz to 100 kHz at the right graph.

However, in the frequency of 30 kHz to 1 MHz, the impedance value decreased in proportion to the frequency as the frequency increased. If the frequency gradually increases above 30 kHz, and the alternating current passes through the cell membrane, the measurement circuit can be regarded as an RC circuit as shown in Fig. 1. In this case, the cell membrane acts as the capacitor. So, the reactance of the cell membrane decreases as the frequency increases.

Since the electrical properties of the resistance of the intracellular substance are analyzed above 30 kHz, it is not affected by phenomena such as polarization of the electrode surface and Warberg impedance. As a result of analyzing the electrical properties of the material in the cell, the impedance value proportionally decreases as the frequency increases. Figure 4(b) shows a little change in phase difference.

4.3 Changes in the electrical characteristics of the impedance according to the radiation dose

In this study, the impedance spectrum of pork tenderloin tissue was measured under different radiation doses (1 Gy, 2 Gy, 4 Gy and 10 Gy). Figure 5 shows the impedance value of pork tenderloin tissue by frequency change at different radiation doses and comparison of impedance absolute value between pre-irradiation and irradiation.

Fig. 5

(a) Impedance of pork tenderloin tissue according to radiation dose (b) Comparison of impedance absolute value between pre-irradiation and irradiation (c) Phase graph of pork tenderloin tissue according to radiation dose (d) Comparison of phase absolute value between pre-irradiation and irradiation.

A frequency-dependent relationship between impedance (Z), conductivity (σ) and relative permittivity (ɛ _r ) is given by the expression of Equation (2) [8]. As shown in this equation, impedance affects not only frequency but also permittivity and conductivity. $Z = \frac{1}{σ + j ω ω_{0} ɛ_{r}}$ (2)

As a result of the experiment, the impedance value of pork tenderloin tissue decreased as the radiation dose increases, as shown in Fig. 5 (a). The cell membrane of pork tenderloin tissue is gradually ruptured while radiation is applied up to 4 Gy. This causes a decrease in impedance value. In particular, it showed a rapid decrease in Z at 10 Gy. This means that the cell membrane of pork tenderloin tissue gradually loses its effectiveness as the dose of radiation increases [19]. The binding force of the cell membrane becomes loose, which is related to the increase of electrical conduction by mobile ions. In addition, the transient dielectric breakdown by radiation increases in the permittivity due to a large amount of current flows. These two effects seem to lead to a decrease in the impedance value.

Unlike other data values, the impedance value is significantly reduced at 10 Gy, as shown in Fig. 5(a). However, even when the radiation increased, there was a little change in phase difference, as shown in Fig. 5(c). As a result of statistical verification of the impedance change according to radiation dose, when compared to the control group, there was statistically difference (^*p < 0.05) at 1 Gy, 2 Gy, 4 Gy and 10 Gy, as shown in Fig. 5(b). In the case of phase difference change, when compared to the control group, all values were statistically differences (^*p < 0.05) to the pork tenderloin tissue against the radiation dose at 1 Gy, 2 Gy, 4 Gy and 10 Gy, as shown in Fig. 5(d). But it was a statistically significant value within the standard deviation.

Figure 6 shows that the internal composition of the pork tenderloin tissue changes with radiation dose. Figure 6 (a) shows several myofibrils, each with the distinct banding pattern of individual sarcomeres. Image of muscle sarcomeres shows distinct banding pattern: the darker bands are called A bands (the A band includes a lighter central zone, called the H band), and the lighter bands are called I bands. Each I band is bisected by a dark transverse line called the Z-line). Paired mitochondria are on either side of the electron opaque Z-line. The Z-Line marks the longitudinal extent of a sarcomere unit. In the pork tissues collected before irradiation, a certain type of myofibril was repeatedly observed, and the sarcomere was also arranged at regular intervals. Sarcoplasmic reticulum and mitochondria remained undamaged and no tissue changes were observed.

Fig. 6

Pork tenderloin tissue by radiation were observed by a transmission electron microscope (TEM: JEM 1200EX-, JEOL×30,000).

Changes in the pork tenderloin tissue by radiation were observed by a transmission electron microscope (TEM: JEM 1200EX-, JEOL×30,000) after double dye in Uranyl acetate and lead citrate. The pork tenderloin tissues collected after 1 Gy irradiation did not show any special change compared to the tissue collected before irradiation. After 2 Gy irradiation, the myofibril was slightly warped and there was a slight gap between the sarcomere. The pork tenderloin tissues collected after 4 Gy irradiation had a wider space between myofibril, and the mitochondria was slightly larger. The myofibril was severely damaged from the pork tenderloin tissues collected after the 10 Gy irradiation and there was a large gap between the sarcomere and the number of mitochondria increased. When irradiated with 10 Gy, the pork tenderloin tissue was almost destroyed, as shown in Fig. 6(e).

Table 3 shows the difference in impedance values before and after irradiation. There is a significant difference in the impedance information of pork tenderloin tissue represented by 10 Gy due to severe cell membrane rupture, as shown in Table 3. Transmission electron microscopy image may explain the phenomenon that the impedance value rapidly decreases at 10 Gy.

Table 3

Difference in impedance values before and after irradiation

	Impedance Absolute Value
	Baseline	Irradiation	Differences
	Mean±SD	Mean±SD	Mean±SD
Sample 1	87.16±0.57	86.60±0.59	0.55±0.03^*
Sample 2	87.05±0.51	85.96±0.65	1.09±0.14^*
Sample 3	87.01±0.49	85.03±0.63	1.97±0.14^*
Sample 4	87.06±0.57	73.97±0.41	13.08±0.16^*

Sample1: pork tenderloin tissue + 1 Gy, Sample2: pork tenderloin tissue + 2 Gy. Sample3: pork tenderloin tissue+4 Gy, Sample4: pork tenderloin tissue + 10 Gy, ^*p < 0.05.

5 Discussion

The knowledge of electrical properties of biological tissues has been one of the keys to helping our understanding of their structure and function. Electrical impedance of biological tissues is a complex quantity combining resistance and capacitance and it depends on the frequency of the AC current applied due to having components such as conductive and charge storage properties. In this research, the electrical characteristics of pork tenderloin tissue are analyzed by an electrical RC circuit with EIS system and the electrical properties of pork tenderloin tissue irradiated were studied for a various range of frequency. According to RC circuit model, the pork tenderloin tissue consists of R_t (tissue resistance) and C_m (combined membrane capacitance).

Our RC circuit model was reported to be a good representation of the electrical properties of biological materials due to relaxation phenomena throughout the frequency range [16]. The simplified RC circuit model was applied for the interpretation of the electrical properties of biological tissues, with R_t (tissue resistance) and C_m (combined membrane capacitance). R_t is contributed by not only the surface of the tissue, but also the inside of the tissue. C_m is contributed by characteristic in cell membranes. The RC circuit model, as depicted in Fig. 3, is simple and easily understood from a biological viewpoint. However, the specific architecture and complex electrolytic plasma of biological tissue imply that its equivalent circuit should in principle be very complicated. We only qualitatively represented the electrical impedance characteristics of biological tissues.

In alternating current, high-frequency current can easily flow, but low-frequency current is difficult to flow to biological materials. As shown in our experimental results, it shows a sharp decrease in impedance at low frequencies of 1 kHz to 30 kHz. That is, since the cell membrane does not act as a capacitor because the alternating current to which a low frequency is applied does not pass through the cell membrane, the impedance value reflects the characteristic of pork tenderloin tissue surface. In the low frequency region of f < 30 kHz, the decrease of impedance is not proportional to the frequency as the frequency increased due to affecting by the polarization of the electrode interface such as Warburg impedance. As the frequency increases above 30 kHz, the impedance decreases as the reactance (Z^″ = 1/2πfC_m) drops by its predominant capacitive behavior. At high frequencies above 10 MHz, the impedance value is very small, impedance of the membrane approaches zero and the membrane appears as a short circuit. In other words, AC current does not flow but only moves back and forth between membrane surfaces and hence neither the resistive pathways nor the capacitive pathways of the membranes have time to play a role.

With increasing radiation dose, the cell membrane is gradually ruptured, resulting in a destruction of dielectric characteristic, which increases in the dielectric constant of pork tenderloin tissue. In addition, the pork tenderloin tissue gradually ruptures and the production of a large amount free mobile ions such as H+, (OH)^- by radiation energy will occur. This easily moves the membrane due to loose connective by the rupture of pork tenderloin tissue as the amount of radiation increases.

Unlike metallic conductors, electrical conduction within biological tissues is due to ions. For this reason, it causes an increase in the electrical conduction (σ) of pork tenderloin tissue. Bound charges within tissues give rise to complex dielectric properties. The permittivity (ɛ_r) will be increased due to a large amount of current flows by a dielectric breakdown. This caused a decrease in impedance ( $Z = \frac{1}{σ + j ω ω_{0} ɛ_{r}}$ ) by irradiation affects [8].

In this study, we also directly observed changes in the microstructure of pork tenderloin tissue by radiation through TEM. Figure 6 shows relation between radiation amount and rupture of the pork tenderloin tissue. As a result of analyzing the TEM image, the pork tenderloin tissue is severely broken at 10 Gy. When radiation is applied to biological tissues, it reacts with membrane in cells to cause various biological disorders through chain reactions as well as structural changes of molecules. This phenomenon can be explained in connection with the cleavage of chemical bonds. In the future, we plan to do an experiment on live animals such as rat. Evaluating the damage to the irradiated tissue is a very important index to increase the therapeutic effect in the field of radiation therapy. In this study, instead of hematoxylin and eosin stain, the microstructure was observed using TEM of high resolution (×30,000). The degree of tissue damage was directly confirmed in the TEM image

Overall, this study provided the basic data for the study of changes in the electrical properties and TEM images analysis of irradiated cells. We will expect the changes in bio-histological properties in actual radiation therapy. This can increase treatment effectiveness by modifying the treatment plan. And biosensors and Lab-on-Chip technologies based on bio-impedance are of great interest in biological, medical, and industrial fields, mainly due to their low-cost and speed in the measurement, and because they can be used in continuous monitoring processes.

6 Conclusion

In order to further explore the electrical impedance characteristics of cells in the pork tenderloin tissue with significant cell structure were selected for the experimental objects to explore their electrical impedance characteristics. This study posed an effective approach to characterize the variation of the internal change of components of pork tenderloin tissues by radiation. The impedance change caused by irradiation could be ascribed to the alteration in the tissue itself such as permeability of membranes and content of electrolytes in the cell constituents rather than electrochemical reaction.

It is important that an accurate assessment of radiation response should be performed as radiation dose-escalation. In the future, non-invasive physiologically based imaging techniques, such as electrical impedance spectroscopy, may be used to measure radiation damage and radiation recovery, on a patient-by patient basis.

Footnotes

Acknowledgments

This work was supported by a Research Institute for Convergence of Biomedical Science and Technology (30-2017-025), Pusan National University Yang-san Hospital.

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Model	Frequency	Resolution	Measurement Parameters
4194A	1 kHz∼1 MHz	1 × 10^-3 Hz	\|Z\|: Impedance Absolute Value
			θ: Impedance Phase
			R: Resonance Resistance
			X: Equivalent Series Reactance