Description

ABSTRACT

In this work, the thermal properties of the organs are also reported as a function of temperature. The thermal diffusivity, thermal conductivity and volumetric heat capacity of these tissues were measured in the temperature range from 22 to around 97⁰C. Concerning the pancreas, a phase change occurred around 45⁰C; therefore, its thermal properties were investigated only until this temperature. Results indicate that the thermal properties of the liver and heart have a non-linear relationship with temperature in the investigated range. In these tissues, the thermal properties were almost constant until 60 to 70⁰C and then gradually changed until 92⁰C. In particular, the thermal conductivity increased by 100% for the heart and 60% for the liver up to 92⁰C, while thermal diffusivity increased by 90% and 40%, respectively. However, the heat capacity did not significantly change in this temperature range. The thermal conductivity and thermal diffusivity were dramatically increased from 92 to 97⁰C, which seems to be due to water vaporization and state transition in the tissues. Moreover, the measurement uncertainty, determined at each temperature, increased after 92⁰C. For the three organs, the best fit curves are provided with regression analysis based on measured data to predict the tissue thermal behavior. The electrical properties of internal organs including lung, liver and heart were measured using an open-ended coaxial probe and an improved virtual transmission-line model and their result were tabulated.

TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWLEDGEMENT

ABSTRACT

CHAPTER ONE

INTRODUCTION

1.1      BACKGROUND OF THE PROJECT

• PROBLEM STATEMENT
• AIM AND OBJECTIVE OF THE STUDY
• SIGNIFICANCE OF THE STUDY
• SCOPE OF THE STUDY

CHAPTER TWO

LITERATURE REVIEW

• REVIEW OF THE STUDY
• DESCRIPTION OF THERMAL PROPERTIES
• ELECTRICAL PROPERTIES OF THE TISSUES
• BIOLOGICAL MATERIALS IN AN ELECTRIC FIELD
• COMPLICATIONS IN DIELECTRIC MEASUREMENTS OF TISSUES
• PHYSIOLOGICAL FACTORS AND CHANGES OF TISSUE
• DIELECTRIC PROPERTIES OF SOME TISSUES

CHAPTER THREE

3.1      MATERIALS AND METHODS

CHAPTER FOUR

• RESULT AND DISCUSSION

CHAPTER FIVE

• CONCLUSION
• REFERENCES

 

CHAPTER ONE

1.0                                                        INTRODUCTION

1.1                                           BACKGROUND OF THE STUDY

Over the last 30 years, hyper-thermal and ablative procedures have been studied as an alternative to surgery in cancer treatment. Different techniques based on thermal processes, e.g., laser ablation, microwave ablation, radiofrequency ablation and focused ultrasound, have been investigated for the hyperthermal treatment of cancer [1]. These methods rely on the localized increase in the tissue temperature above physiological temperature thresholds to induce thermal damage in the cells and coagulative necrosis. Augmented temperatures produce effects on cells in several modalities.   Indeed, the degree of thermal damage can be classified according to the local tissue temperature and duration of treatment at a given temperature [2]. Hyperthermia starts in the temperature range between 42 and 45 ◦C; at 50 ◦C, the reduction in enzymatic activity begins; at 60 ◦C, the denaturation of proteins, coagulation of collagen and membrane permeabilization rapidly occur, leading to a cytotoxic effect and coagulative necrosis, which is the primary cause of cell death during thermal ablation of tumors; and for temperatures close to 100 ◦C and above, the effects of vaporization and tissue carbonization befall [3,4]. Hence, a temperature range of 42 to 100 ◦C is of interest for implementing the different techniques available for cancer treatment, from hyperthermia to thermal ablation [5].

Despite promising results, the principal limitation to the widespread adoption of thermal techniques in clinical settings is still related to the difficulty to guarantee a complete tumor ablation while sparing healthy tissue. From the technological point of view, mathematical modeling for treatment pre-planning has been developed to simulate the tissue temperature profile and therefore increase the treatment efficacy and safety. In this context, information of the tissue thermal properties as a function of temperature is necessary for the accurate prediction of the thermal outcome. Indeed, the result of hyper- thermic therapies is strictly related to the temperature distribution of the treated biological tissues. This is, in turn, influenced by the delivery modality of the thermal dose and the intrinsic physical properties of the tissue, such as the tissue thermal properties, which vary according to temperature due to thermal-induced structural modifications occurring during treatments [6].

The thermal properties characterize the ability of materials to conduct, transfer, store and release heat [8]. The accuracy of the model in Equation (1) is highly dependent on the accurate definition of the thermophysical properties of the target tissue, as it has already been proved by several studies [9]. Therefore, replacing the thermal parameters that are generally considered constant values—usually at room temperature—with temperature- dependent physical parameters can lead to a more accurate prediction of the treatment outcome [10].

Many scientific studies have been presented to measure the thermal properties of bio- logical tissues. These studies are mainly focused on liver tissue and muscles, and some data are reported for other organs, such as the kidney and brain [11]. How- ever, as mentioned before, most of these studies measured the thermal properties at a constant or low temperature which is not completely appropriate for thermal ablation modeling.  One of the first and more extensive studies on the temperature dependency of tissue thermal properties was performed by Valvano et al. in 1985. The authors used a self-heated thermistor to determine the thermal conductivity and diffusivity of ex vivo kidneys, spleens, livers, brains, hearts, lungs, pancreases, colon cancers and breast cancers

within a temperature range between 3 and 45 ◦C [12]. Within this range, the measured properties were slightly temperature-dependent and showed a weak linear increase with temperature. The authors observed a significant inter-tissue variation in thermal diffusivity and conductivity, as well as a match between tissue thermal diffusivity and water thermal diffusivity.

More recent studies have started to measure the tissue-specific heat capacity, thermal diffusivity and conductivity up to the ablative temperatures. Among all the organs, the liver is the most investigated due to the high demand for ablative therapies for liver disease treatment [13]

For the electrical properties, electromagnetic fields radiated from implanted or ingested sources through the complex human body have been widely analyzed by many research groups for the development of wireless biomedical devices [14]. For the same purpose, dominant propagation path and corresponding phenomenon from intestine ingested source was numerically analyzed in our group [18], [19]. Our next goal is experimental confirmation of the numerically analyzed results. However, direct measurement with human body is impossible due to the safety problem. Therefore, preparation of a precise phantom is important for obtaining accurate experimental results.

Several internal organs of animals are being considered by our group to organize more realistic phantom. The internal organs from pig are especially considered due to the known similarity of electrical properties between human and pig organs [20]. As the first step of preparation, complex permittivities of several pig internal organs are measured to check the similarity between their values. Dielectric properties of the employed pig organs also need to be known for precise control of the overall experimental process.

Our open-ended coaxial probe and the improved virtual transmission-line model are employed during the conversion process [21]. Electrical properties of pig lung, liver, heart, kidney, blood, stomach, and small intestine are obtained.

1.2      PROBLEM STATEMENT

The electrical and thermal properties of biological tissues and cell suspensions have been of interest for over a century for many reasons but there are difficulties due to limited or fewer studies regarding it according to [2]. Electrical and thermal properties determine the pathways of current flow through the body and, thus, are very important in the analysis of a wide range of biomedical applications such as functional electrical stimulation and the diagnosis and treatment of various physiological conditions with weak electric currents, radio-frequency hyperthermia, electrocardiography, and body composition. On a more fundamental level, knowledge of these properties can lead to an understanding of the underlying basic biological processes. Indeed, biological impedance studies have long been important in electrophysiology and biophysics; one of the first demonstrations of the existence of the cell membrane was based on dielectric studies on cell suspensions [1].

1.3      AIM AND OBJECTIVES OF THE STUDY

The main aim of this study is to determine the thermal and electrical properties of internal organs of ruminant animals. The objectives of the study are:

1. To provide a clear-cut margin of safety at all temperatures based on the stability of ruminant animals.
2. To demonstrates the critical need for the thermal and electrical analysis of ruminant organs.

1.4      SIGNIFICANCE OF THE STUDY

Knowledge of the thermal and electrical properties of internal organs of ruminants (such as Pig) is important in that the flow of blood can have a direct quantitative effect on the temperature distribution within living organs.

1.5      SCOPE OF THE STUDY

The scope of this study covers determining the thermal properties of the liver and brain have a non-linear relationship with temperature. In this study, the thermal properties were measured with a commercial analyzer  with an SH-3 dual-needle sensor whilst the electrical properties of internal organs are measured using an open-ended coaxial probe and an improved virtual transmission-line model.

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