In the present work, a heterogeneous breast model comprising of fat, glandular and muscle tissues along with a spherical tumor of 2 cm diameter is modelled. The efficacy of Radio Frequency Ablation (RFA) is mainly judged by the extent to which the tumor cells are damaged and hence the volume fraction of necrotic tissue (VFNT) is a response parameter. Several critical factors affect the volume of necrotic tissue, among which the blood perfusion rate, target tip temperature of electrode and location of tumor from the body core are considered as prime input parameters. This work focuses on the selection and the significance of tolerance of these critical factors using ‘cross-array design of experiment’ (CA-DOE) approach. The loose and tight ranges of tolerances of these factors are selected to form Taguchi’s inner and outer orthogonal array and experimental combination sets are prepared. In this study, the effect of each possible set of tolerance on the output parameter i.e. tumor ablation volume generated is analyzed. The different values of the ablation volume generated for each experiment are obtained from finite element analysis. The entire analysis is carried out using a bioheat transfer module coupled with electric currents module in COMSOL multiphysics software. Additionally, target tip temperature is controlled by the implementation of proportional-integral-derivative control strategy. The simulations results are validated with the available published experimental results. The simulation results are further analyzed using statistical methods, such as signal to noise ratio, analysis of mean, and analysis of variance. The presented analysis will be helpful to achieve robust and targeted values of ablation volume with least effort of maintaining process accuracy. The proposed methodology and results are useful for clinicians in the RFA.

The use of a tourniquet leads to nerve damage, even if applied for short periods of time. This damage can be minimized if the limb is cooled. Because of the low conductivities of human tissue, core limb cooling is slow unless the surface temperature is very cool. Subzero surface temperatures can lead to skin injury (i.e., frostbite). Ideally one would adjust the limb surface temperatures as a function of time to maximize the cooling rate while avoiding permanent tissue damage. One possible approach is to use a thermoelectric cooler (TEC) in conjunction with a programmable power supply. TEC performance varies strongly with heat absorption rate, a function of limb thermal properties, and hot side temperatures that are strongly affected by the surface conditions on the hot side, i.e., overall heat transfer coefficients and ambient conditions. The paper describes the use of finite element simulation to predict the usefulness of using thermoelectric coolers applied to the surface of a limb when compared to the standard approach of using ice packs. Since the TEC performance is strongly influenced by its warm side thermal conditions, experimental results are presented for different ambient temperatures, free and forced convection, and evaporation of water from a wickable covering.

Normalization of the scattering phase function is applied to the transient discrete ordinates method for ultrafast radiative transfer analysis in a turbid medium subject to a normal collimated incidence. Previously, the authors have developed a normalization technique which accurately conserves both scattered energy and phase function asymmetry factor after directional discretization for the Henyey-Greenstein phase function approximation in steady-state diffuse radiative transfer analysis. When collimated irradiation is considered, additional normalization must be applied to ensure that the collimated phase function also satisfies both scattered energy and asymmetry factor conservation. The authors’ technique is applied to both the diffuse and collimated components of scattering using the general Legendre polynomial phase function approximation for accurate and efficient ultrafast radiative transfer analysis. The impact of phase function normalization on both predicted heat fluxes and overall energy deposition in a model tissue cylinder is investigated for various phase functions and optical properties. A comparison is shown between the discrete ordinates method and the finite volume method. It is discovered that a lack of conservation of asymmetry factor for the collimated component of scattering causes over-predictions in both energy deposition and heat flux for highly anisotropic media.

Cryosurgery is also called as cryoablation or cryoleision. The third generation of cryo-machine use argon gas for cooling and helium for rewarming to destroy cancer cells. The probes may be put into the tumor during surgery or through the skin (percutaneously). After cryosurgery, the frozen tissue thaws and is either naturally absorbed by the body (for internal tumors), or it dissolves and forms a scab (for external tumors). The main purpose of this paper is to establish a preliminary computer assisted simulation in prostate tumor cryosurgery. A radiologist and an urologist in a medical center in addition to the engineering specialist from the university participated in this interdisciplinary research program. The first step of this simulation protocol is to trim hundreds of two-dimensional medical imaging photos from a patient through the imaging reconstructive software into building a three-dimensional solid modeling. The image data for each patient can be obtained from the x-ray computed tomography (CT), or magnetic resonance imaging (MRI) in the imaging department of hospital. It has successfully built up the related knowledge to overcome the complicacy between the medical imaging modalities and engineering graphic solid modeling with high resolution. It is worthy to mention here that the present solid modeling of prostate can demonstrate the variable diameters and courses of the prostate urethra in vivo. The second step focuses on thermal calculation. So far, there has been no existing commercial software for the specific purpose of the bioheat transfer problem. Hence, user subroutines must be added to the existing commercial software to simulate the clinical situation of cryosurgery. For example, the occurrence of phase change during some specified temperature range and the latent heat of fusion are also incorporated into bio-heat transfer model. It has successfully incorporated bioheat transfer model into the software program to fit the reality in thermal medicine. The third step supplies the data and knowledge concerned with the position of a tumor and the related mechanism of metabolism of living tissue and vessels. The number of probes, the position of each probe, and the operating time of each probe will be explored to ensure a complete killing of the tumor tissue while saving as much healthy surrounding tissue as possible. In this study, the three-dimensional transient temperature distributions based on cryosurgery for prostate tumors have been performed for several cases to find the optimal operating conditions. Different cryoprobes with different freezing time are considered to find the temperature distribution. The simulation results for cryosurgery of prostate tumors will be supplied for practicing physicians as reference to greatly improve the effectiveness of cryosurgery.

Human eye is one of the most sensitive parts of the body when exposed to radiation effects. Since there is no barrier (such as skin) to protect the eye against the absorption of the external thermal waves, radiation can readily interact with cornea. On the other hand, lack of blood flow in the interior part of the eye makes it more vulnerable compared to other organs even in the case of weak heat interaction. Further, blood flow circulation alone cannot establish thermal equilibrium between the eye and body organs effectively. There are limitations in measuring human eye temperature profile experimentally due to the required invasive procedures in monitoring the inner layers. Therefore, there is a need to develop an accurate model to represent the eye structure and energy transport through it. Thermal modeling of the eye is important to investigate the effect of external heat sources as well as in predicting the abnormalities within the eye. Modeling of heat transport through the human eye has been the subject of interest for years, but the application of porous media models in this field is new and will be one of the themes of this study. In this work, iris/sclear is considered as a porous medium and energy transport is modeled using the tissue local thermal equilibrium equations. The eye is assumed to include six different parts: cornea, anterior chamber, posterior chamber, iris/sclera, lens and vitreous. A two-dimensional finite element simulation will be performed. Results are shown in terms of transient corneal surface temperature, isothermal lines in different regions and local temperature of pupillary axis. Effects of external radiation sources, convection coefficient of the surrounding air, blood temperature, blood convection coefficient and ambient temperature on different regions of the eye are also investigated.

Thermal analysis of a cylindrical tissue subject to a train of ultrashort pulse irradiations was made by developing a combined time-dependent radiation and conduction bio-heat transfer model. Ultrashort pulsed radiation transport in the cylindrical tissue is simulated using the transient discrete ordinate method. Treatment of focused beam is introduced. The model skin tissue is stratified as three layers with different optical, thermal and physiological properties. Comparisons between the collimated irradiation and focused beam are conducted. The effect of pulse train is investigated.

In cryosurgery, it is necessary to control heat transfer precisely and actively in order to necrotize diseased part effectively and to avoid freezing healthy tissues. In order to control heat transfer, the cryoprobe utilizing peltier module was developed. This cryoprobe makes it possible to control cooling and heating rate actively and precisely due to peltier effect. Therefore, it is convenient to control the size of cell-destroyed area. In order to confirm cooling performance of the cryoprobe, gelatin cooling experiment and animal experiment was conducted. From the results, it can be said that this cryoprobe has enough cooling performance to destroy undesirable cell and it can control cooling and heating rate actively. Numerical simulation which considers biological heat production, freezing of tissue and peltier effect at same time was developed in order to evaluate frozen region or necrotized area, which are difficult to be measured.

It has been established that focal cooling to suppress epileptiform activity has become a real and viable option. However, the specific thermal parameters necessary to suppress epileptiform activity have only begun to be quantitatively defined. In 2002 it was reported that a 41 year-old man with medically intractable epilepsy undertook surgery to remove his tumor and resect adjacent epileptogenic tissue. Electrocorticography was performed before resection. Cold saline was impinged on the resulting interictal spike foci resulting in transient, complete cessation of spiking. We present a transient post-operative heat transfer analysis of the cold saline impingement on the surface of brain. An approximate temporal and spatial temperature distribution of the perfused human brain response to surface cooling was developed. The realistic extent of cooling below the brain surface due to impinging saline was quantified. The sensitivity of cooling penetration depth to (a) saline exit velocity from the syringe, and (b) syringe inside diameter, was evaluated. A parametric study was performed to characterize the effects of brain metabolism and blood perfusion on surface cooling. The required thermal parameters necessary to suppress epileptiform activity through focal cooling are here quantitatively approximated, i.e. heat flux removal and maximum and realistic cooling penetration depths. The relatively shallow penetration depth suggests that the spreading depolarization associated with epileptiform activity may be abolished through focal cooling without affecting the deeper neurons responsible for motor activity.

Cryosurgery is a surgical technique using low temperature cryogen to achieve selective tissue destruction by freezing. During cryosurgery, the cryoprobe, which is usually cooled by inner circulation of liquid nitrogen (LN 2 ), is inserted into the targeted tumor tissue. The tissue surrounding the cryoprobe is then cooled down to sub-zero temperature and subsequently frozen. Extensive studies have been conducted to understand the mechanism of tissue injury, and various numerical models have been developed to predict the thermal history of the targeted tissues during cryosurgery. Most of the existing models, however, focused on the tissue freezing and applied simplified thermal boundary conditions at the interface between cryoprobe and surrounding tissue, e.g. a constant temperature or a constant heat flux. This paper presents a conjugate model for cryosurgery. The new model treats with both tissue freezing outside of the cryoprobe and turbulent convective heat transfer of LN2 inside the cryoprobe. The thermal condition along the cryoprobe surface is then part of the solution, instead of a presumption. The turbulent convection of single phase LN 2 inside the cryoprobe is described by a Realizable κ-ε model, while the Pennes equation is used to address the heat transfer within the hepatic tissue. An apparent heat capacity method is used to deal with tissue freezing. As an example, the model is used to simulate the hepatic cryosurgery with a single cryoprobe. The model predicts a dynamic, non-unform surface temperature along the cryoprobe surface, which shows a large effect on the ice ball formation outside the cryoprobe. Results are also presented to illustrate the effect of the flow condition and the cryoprobe design on the interface thermal condition in cryosurgery.

This study investigates the transient temperature response in biological tissue with sinusoidal temperature oscillation on the skin surface. Based on the Laplace transform, an exact solution of the Pennes bioheat transfer equation has been derived which includes the whole time domain from the initial transient oscillation to the final steady periodic oscillation. Furthermore, the exact solutions of special cases under no perfusion rate, constant temperature, and the combination of those two assumptions are demonstrated in this study. The primary application for this type of analysis is to assess the blood perfusion rate in the skin by imposing a periodic temperature load onto the skin surface. Through the noninvasive measurement of the maximum heat flux or minimum heat flux on the skin, equation (15) can be utilized to estimate the blood perfusion rate in living tissues. The results show that both the larger perfusion rate and greater tissue depth decrease the amplitude of the sinusoidal temperature response. A larger perfusion rate can also reduce the unstable duration for the estimation of the blood perfusion rate. Meanwhile, the shift of phase angle related to the sinusoidal temperature variation increases with tissue that is deeper and has lower perfusion rate.

Current state-of-the-art thermoregulatory models do not predict body temperatures with the accuracies that are required for the development of automatic cooling control in liquid cooling garment (LCG) systems. Automatic cooling control would be beneficial in a variety of space, aviation, military, and industrial environments for optimizing cooling efficiency, for making LCGs as portable and practical as possible, for alleviating the individual from manual cooling control, and for improving thermal comfort and cognitive performance. In this paper, we adopt the Fiala thermoregulatory model, which has previously demonstrated state-of-the-art predictive abilities in air environments, for use in LCG environments. We compare the model’s tissue temperature predictions with analytical solutions to the bioheat equation, and with experimental data for a 700 W rectangular type activity schedule. The thermoregulatory model predicts rectal temperature, mean skin temperature, and body heat storage (BHS) with mean absolute errors of 0.13°C, 0.95°C, and 11.9 W·hr, respectively. Even though these accuracies are within state-of-the-art variations, the model does not satisfy the target BHS accuracy of ±6.5 W·hr. We identify model deficiencies, which will be addressed in future studies in order to achieve the strict BHS accuracy that is needed for automatic cooling control development.

In this paper a computational heat transfer model for prediction of the temperature distribution within the human eye during laser surgery is presented. The heat transfer within a tissue is described by the classic Pennes bioheat transfer equation. The intraocular temperature distribution is calculated using finite-difference method. Two types of computational domain have been considered: (i) rectangular parallelepiped and (ii) cylindrical. The eye is modeled as a composite layered structure consisting of four different ocular tissues, namely, cornea, aqueous, lens and vitreous. It is assumed that the eye is symmetrical about the pupillary axis. The absorption probability of ocular tissue is modulated based on the Lambert-Beer’s law to reproduce the exponential attenuation of the laser light with depth within a biomaterial. The heat flow is modeled as transient and three-dimensional for rectangular parallelepiped geometry and two-dimensional (axi-symmetric) for the cylindrical geometry. The results indicate that for the insulation condition imposed on the periphery of the eye the model based on rectangular parallelepiped geometry of the eye at no laser power and at the initial temperature of 25°C predicts temperature closer to in-vitro experimental measurements reported in literature whereas the model based on cylindrical geometry predicts higher temperature. The opposite is true (that is, lower temperature is predicted by the model based on cylindrical geometry) for high laser heat flux (2000 W/m 2 ) and higher initial temperature (37°C). This study also presents changes in eye temperature subjected to intermittent laser source used in laser surgery techniques such as PRK and LASIK. A comparison of the results based on three different boundary conditions such as convection (h b = 10 W/m 2 K), constant temperature (37°C) and insulation on the eye periphery reveals that the model based on insulation condition predicts results closer to that of in-vitro experiment at no laser power and initial temperature of 25°C whereas at a laser power of 200 W/m 2 and at the initial temperature of 37°C insulation boundary condition produces highest temperature followed by that produced by convection and constant temperature conditions. The heat transfer is one-dimensional for the insulated eye periphery whereas multi-dimensional heat flow takes place when the circumferential boundary condition is either convective or isothermal.

Numerical simulation is used to investigate the accuracy of a widely used direct-contact device for measuring skin-surface temperature. The device incorporates a foam pad which functions as a de facto thermal resistance to heat flow from the skin surface to the environment. The temperature at the interface of the measurement device and the skin surface is sensed by a micro thermocouple or thermistor. The multidimensional bioheat equation was solved numerically to obtain the temperature field both in the tissue beneath the device and in the device proper. Parametric variations were made of the thermal conductivity of the foam pad and of the blood perfusion rate. Of these, the former was found to have the greater effect on the results. In the limiting case where the thermal conductivity of the foam pad is zero, an error of 1.5 °C in the measured temperature was identified. For foam pad conductivities of 0.03 and 0.06 W/m-°C, the numerical solutions gave temperature measurement errors of 0.5 and 0.15 °C, respectively.

Analysis of biological tissue ablation by an ultra-short pulse laser and the corresponding mathematical modeling of ablation are of fundamental importance to the understanding of laser-tissue interaction for advancing surgical application of lasers. The objective of this paper is to analyze the thermal ablated damage zones during irradiation of freshly excised mouse skin tissue samples by a novel approach of using a focused laser beam from an ultra-short pulse laser source. Experiments are performed using Raydiance Desktop Laser having a wavelength of 1552 nm and a pulse width of 1.3 ps. Mouse tissue samples are translated in a direction perpendicular to the laser beam using three-axis automated motion-controlled stages. Scanning of the tissue sample ensures a fresh region of the tissue is irradiated each time. The surface temperature distribution is measured using a thermal imaging camera. It is observed that use of focused beam results in minimal radial heat spread to the surrounding tissue regions. The ablation phenomenon is analytically modeled by the use of two-phase transient heat conduction model. After completion of tissue irradiation experiments, histological studies are performed using frozen sectioning technique to observe morphological changes in tissue samples in response to laser irradiation. The ablation depth measurements obtained using histological studies are compared with the modeling results. A parametric study of various laser parameters such as time-average power, pulse repetition rate, and pulse energy, and as well as irradiation time and scanning velocity is performed to determine the necessary ablation threshold. Analytical modeling results are in very good agreement with experimentally measured ablation depth. The goal of this research is to develop a tool for selection of appropriate laser parameters for precise clean tissue ablation.

The increased availability of thermal imaging cameras has led to a growing interest in the application of infrared imaging techniques to the detection and identification of subsurface structures. These imaging techniques are based on the following principle: when a surface is heated or cooled, variations in the thermal properties of a structure located underneath the surface result in identifiable temperature contours on it. These contours are characteristic of the structure’s shape, depth, and its thermal properties. We study the use of the transient thermal response of skin layers to determine to which extent the surface temperature distribution reflects the properties of subsurface structures, such as lesions. A numerical model using the finite element method is described to obtain this response and key results are reported in the paper. A sensitivity study is conducted first to better understand the thermal response of the system and the role of various system and model parameters. We explore the extent to which we are able to draw conclusions regarding the size, depth and nature of subsurface structures and accuracy of these conclusions based on the surface temperature response alone. This work validates the idea of examining the transient thermal response and using thermal imaging as a solution for lesion identification. A sensitivity study of surface temperature distribution to variations of thermophysical properties, blood perfusion rate, and thicknesses of skin layers is performed. It is observed that variations in these parameters have little impact on the surface temperature distribution. The work reported in the paper is a portion of a comprehensive research effort involving experiments on a phantom model as well as measurements on patients. Future work will focus on comparing the results of our 2D numerical modeling efforts with the experimental results using a skin tissue-mimicking phantom. Knowledge gained from the modeling and experimental efforts will be utilized in characterizing lesions in patient studies. The focus of this paper is the computational sensitivity analysis.

Damped wave conduction and relaxation in the human skin layer and thermal fabric layer are modeled with a temperature dependent heat source in the human tissue layer. Steady state temperature profiles are derived from the Fourier heat conduction equation. The general solution for the temperature is assumed to be a sum of the transient temperature and steady state temperature. This makes the boundary conditions in space for the skin and fabric layers homogeneous for the transient temperarature. The hyperbolic PDE is solved for by the method of separation of variables. The use of final condition in time in addition to the initial temperature condition leads to bounded infinite Fourier series solutions. These solutions are bounded and does not violate second law of thermodynamics. The model can be used to interpret experimental observations of maximum heat flux that is a parameter of the warm/cool feeling of human skin in winter. For large relaxation times of human skin tissue, τ rs > ( 1 + U * ) 2 ( b − a ) 2 16 π 2 α s , the transient temperature can be expected to undergo oscillations. These oscillations will be supercritical and grow with time for strong heat sources, U* > 1 and may be subcritical damped oscillatory for weak heat sources, U* < 1. For large thermal relaxation times of thermal fabric material, τ rf > a 2 4 π 2 α s , the transient temperature in the thermal fabric layer may be expected to be subcritical damped oscillatory.

A new methodology to control the freezing front propagation during cryosurgical procedures is studied through the use of numerical techniques. Laser irradiation of a target tissue is explored as a new methodology for localizing heat generation and, thus, confining more accurately the desired cryoinjury region and to protect a thicker superficial layer of tissue. In addition to the irradiation of laser energy, the use of dyes is proposed as a means of localizing heat absorption and increasing the thickness of the protected region. A 2D finite volume numerical code based on the enthalpy method was developed to model the freezing process during cryoprobe cooling of a volume of tissue, while heating was applied to the external boundary protecting the superficial layer of tissue. Laser irradiation was modeled with Beer’s Law, and the energy absorption, which is proportional to the intensity, was taken as a source term in the energy equation. The thermophysical properties of the tissue are modeled as temperature dependent properties of water. Temperature contours resulting from a) constant temperature heating b) and regulated laser irradiation heating of tissue indicate that the latter methodology may be more effective in limiting cryoinjury to a predefined region. Additionally, if dyes are used, the protected area increases in thickness. The most dramatic differences between the two methodologies occur when the cryoprobe is placed near the surface, the effective attenuation coefficient of the material is low, and dyes are injected into the tissue to promote localized absorption of laser irradiated energy.

Noninvasive burn depth measurements would allow clinicians to manage burn injury better and improve treatment outcomes. Additionally, knowledge of the burn depth would allow surgeons to excise thermally damaged tissue without harming the underlying healthy tissue which is the source of epithelial cells important for proper healing response. We propose a photoacoustic method for inducing acoustic waves in burns. We used an Nd:YAG laser coupled to an optical fiber probe to deliver laser light to burn injury. Subsequent acoustic wave analysis results in burn depth profiling. We test ex vivo pig skin and optical diffusion theory to extrapolate these measurements to determine the maximum depth determined by this probe. We found that our probe can determine burn depths up to 2.8 mm. We propose changes to extend this depth to about 5 mm, the full thickness of human skin.

Microwave and ultrasound energy sources are commonly used in minimally invasive thermal therapy for benign prostatic hyperplasia. Successful management of the therapy using either of these methods requires an accurate estimation of the thermal dosage. The purpose of this study is to evaluate, theoretically, the thermal damage caused by typical transurethral microwave and ultrasound applicators for different thermal doses and compare the efficacy of the two methods. Using an Alternating-direction implicit method, the Pennes bio-heat transfer equation is solved for different levels of power and heating times. Internal and external cooling is applied to preserve the urethral and rectal lining and to control the temperatures within the tissue. The extent of thermal coagulation is determined from the resulting temperature histories, using the existing experimental thermal damage data for prostate tumor cells. The temperatures and damage contours calculated are validated using an Arrhenius analysis of the temperature and thermal-lesion data from the available experimental results. Results show that the calculated damage zones are in good agreement with those observed in the experiments. Results from calculations for different combinations of the parameters are presented in terms of the transient temperature histories and radial and axial extent of the lesion shapes. These results suggest that both methods can yield comparable thermal damage, though ultrasound appears to possess an improved control of directional heating.

A new noninvasive measurement method is proposed to simultaneously determine the thermal parameters of cylindrical living tissues. The corresponding two-dimensional mathematic model is established based on the Pennes’ bioheat transfer equation. With respect to the measuring points on the surface of the given living tissue, the effects of thermal parameters on the temperature variations, the sensitivity coefficients of the key thermal parameters to the model temperatures and the relativities of these sensitivity coefficients are analyzed and calculated. The results show that the thermal parameters concerned can be estimated with high measuring precision and can be simultaneously estimated. The experimental system of the dynamic tissue phantom is established to validate the presented method. A number of experiments are carried out under different conditions and the experimental results indicate that the measured parameters are in good agreement with the reference values.