Analytical study on bioheat transfer problems with spatial or transient heating on skin surface or inside biological bodies

Skin Comfort Sensation with Mechanical Stimulus from Electronic Skin

The field of electronic skin has received considerable attention due to its extensive potential applications in areas including tactile sensing and health monitoring. With the development of electronic skin devices, electronic skin can be attached to the surface of human skin for long-term health monitoring, which makes comfort an essential factor that cannot be ignored in the design of electronic skin. Therefore, this paper proposes an assessment method for evaluating the comfort of electronic skin based on neurodynamic analysis. The holistic analysis framework encompasses the mechanical model of the skin, the modified Hodgkin-Huxley model for the transduction of stimuli, and the gate control theory for the modulation and perception of pain sensation. The complete process, from mechanical stimulus to the generation of pain perception, is demonstrated. Furthermore, the influence of different factors on pain perception is investigated. Sensation and comfort diagrams are provided to assess the mechanical comfort of electronic skin. The comfort assessment method proposed in this paper provides a theoretical basis when assessing the comfort of electronic skin.

Special function form solutions of multi-parameter generalized Mittag-Leffler kernel based bio-heat fractional order model subject to thermal memory shocks

The primary objective of this research is to develop a mathematical model, analyze the dynamic occurrence of thermal shock and exploration of how thermal memory with moving line impact of heat transfer within biological tissues. An extended version of the Pennes equation as its foundational framework, a new fractional modelling approach called the Prabhakar fractional operator to investigate and a novel time-fractional interpretation of Fourier's law that incorporates its historical behaviour. This fractional operator has multi parameter generalized Mittag-Leffler kernel. The fractional formulation of heat flow, achieved through a generalized fractional operator with a non-singular type kernel, enables the representation of the finite propagation speed of heat waves. Furthermore, the dynamics of thermal source continually generates a linear thermal shock at predefined locations within the tissue. Introduced the appropriate set of variables to transform the governing equations into dimensionless form. Laplace transform (LT) is operated on the fractional system of equations and results are presented in series form and also expressed the solution in the form of special functions. The article derives analytical solutions for the heat transfer phenomena of both the generalized model, in the Laplace domain, and the ordinary model in the real domain, employing Laplace inverse transformation. The pertinent parameter's influence, such as α, β, γ, a0, b0, to gain insights into the impact of the thermal memory parameter on heat transfer, is brought under consideration to reveal the interesting results with graphical representations of the findings.

Thermal damage analysis in tissue caused by electromagnetic radiation using space-time collocation method

Over the past half-century, the usage of external heat sources in medical applications has increased substantially. Controlling heat damage is essential for ensuring the efficacy of the treatment. Living tissues are highly non-homogeneous; hence, it is important to take into account the effects of local non-equilibrium on their thermal behavior. In the present study, two- and three- space dimensional time-space fractional single-phase-lag (SPL) and dual-phase-lag (DPL) models for bio-heat transfer in tissue are considered to study the thermal damage and temperature in tissue caused by electromagnetic radiation as an external heat source. The considered mathematical models are more general and consider non-Fourier as well as non-local effects. We obtain the numerical solution for the models by combining Gaussian RBFs and shifted Chebyshev polynomials in the space and time directions, respectively. The RBFs depend on Euclidean distance, so they can easily be used in multidimensional space domain, and the use of Chebyshev polynomials gives spectral accuracy in time direction. It is also explored how different parameters, such as blood perfusion rate Wb, phase lags τq, τt, and fractional derivatives α, β, affect the temperature distribution and thermal damage in the tissue.

Computational study on 2D three-phase lag bioheat model during cryosurgery using RBF meshfree method

Biological tissue has a multidimensional and non-homogeneous inner structure by nature. The temperature distribution and freezing front locations in biological tissue are crucial to optimizing the damage to tissue during cryosurgery. There is a need for a good mathematical model and effective simulation techniques to predict the effectiveness of the therapy. The present study concerns the numerical study of phase change phenomena during cryosurgery using the three-phase lag (TPL) bioheat model in arbitrary soft tissue domains, i.e., circular (Γ₁), ameba-like (Γ₂), and multiconnected (Γ₃). We employ the effective heat capacity formulation to solve the nonlinear governing equation. The Gaussian radial basis function and Crank-Nicolson finite difference approximation are applied for spatial and time derivatives, respectively. Using the present algorithm, we study the impact of phase lag (τ_v) due to thermal displacement involved in the TPL model on phase change interface position and thermal distribution in all three domains. The obtained results may be beneficial in the field of oncology.

Transcutaneous Pulsed RF Energy Transfer Mitigates Tissue Heating in High Power Demand Implanted Device Applications: In Vivo and In Silico Models Results

This article presents the development of a power loss emulation (PLE) system device to study and find ways of mitigating skin tissue heating effects in transcutaneous energy transmission systems (TETS) for existing and next generation left ventricular assist devices (LVADs). Skin thermal profile measurements were made using the PLE system prototype and also separately with a TETS in a porcine model. Subsequent data analysis and separate computer modelling studies permit understanding of the contribution of tissue blood perfusion towards cooling of the subcutaneous tissue around the electromagnetic coupling area. A 2-channel PLE system prototype and a 2-channel TETS prototype were implemented for this study. The heating effects resulting from power transmission inefficiency were investigated under varying conditions of power delivery levels for an implanted device. In the part of the study using the PLE setup, the implanted heating element was placed subcutaneously 6-8 mm below the body surface of in vivo porcine model skin. Two operating modes of transmission coupling power losses were emulated: (a) conventional continuous transmission, and (b) using our proposed pulsed transmission waveform protocols. Experimental skin tissue thermal profiles were studied for various levels of LVAD power. The heating coefficient was estimated from the porcine model measurements (an in vivo living model and a euthanised cadaver model without blood circulation at the end of the experiment). An in silico model to support data interpretation provided reliable experimental and numerical methods for effective wireless transdermal LVAD energization advanced solutions. In the separate second part of the study conducted with a separate set of pigs, a two-channel inductively coupled RF driving system implemented wireless power transfer (WPT) to a resistive LVAD model (50 Ω) to explore continuous versus pulsed RF transmission modes. The RF-transmission pulse duration ranged from 30 ms to 480 ms, and the idle time (no-transmission) from 5 s to 120 s. The results revealed that blood perfusion plays an important cooling role in reducing thermal tissue damage from TETS applications. In addition, the results analysis of the in vivo, cadaver (R1Sp2) model, and in silico studies confirmed that the tissue heating effect was significantly lower in the living model versus the cadaver model due to the presence of blood perfusion cooling effects.

An Early Stage Researcher's Primer on Systems Medicine Terminology

Background: Systems Medicine is a novel approach to medicine, that is, an interdisciplinary field that considers the human body as a system, composed of multiple parts and of complex relationships at multiple levels, and further integrated into an environment. Exploring Systems Medicine implies understanding and combining concepts coming from diametral different fields, including medicine, biology, statistics, modeling and simulation, and data science. Such heterogeneity leads to semantic issues, which may slow down implementation and fruitful interaction between these highly diverse fields. Methods: In this review, we collect and explain more than100 terms related to Systems Medicine. These include both modeling and data science terms and basic systems medicine terms, along with some synthetic definitions, examples of applications, and lists of relevant references. Results: This glossary aims at being a first aid kit for the Systems Medicine researcher facing an unfamiliar term, where he/she can get a first understanding of them, and, more importantly, examples and references for digging into the topic.

Numerical simulation of electromagnetic heating process of biological tissue via time-fractional Cattaneo transfer equation

In order to simulate the heat transfer in the process of hyperthermia, one-dimensional time-fractional Cattaneo heat transfer equation (TFHE) is established. Based on TFHE, the heat transfer model is solved by using finite difference method, because a single layer of biological tissue in vitro is irradiated by electromagnetic energy. The effect of power parameters (energy flux density P₀, tissue attenuation coefficient h) and equation parameters (relaxation time τ_q and fractional order β) on the prediction of temperature simulated by TFHE were studied. Furthermore, comparative studies on TFHE, Pennes and CV are performed and evaluated. In the heating process, because of the existence of relaxation time τ_q, the temperature response of TFHE and CV are later than Pennes, leading to the lower temperature prediction of TFHE and CV than that of Pennes. The shorter the time is, the higher the energy is, and the more obvious the difference is.

Analysis of the effect of external heating in the human tissue: A finite element approach

Thermal therapy which involves either raising or lowering tissue temperature to treat malignant cells needs precise acknowledgment of thermal history inside the biological system to ensure effective treatment. For this purpose, this study presents a two-dimensional unsteady finite element model (FEM) of the bioheat transfer problem based on Pennes bio-heat equation to analyze the thermal response of tissue subject to external heating. Crank-Nikolson scheme was used for the unsteady solution. A finite element code was developed using C language to calculate results. The obtained numerical result was compared with the analytical and other numerical results available in the literature. A good agreement was found from the comparison. Temperature distribution inside the human body due to constant and sinusoidal spatial and surface heating were analyzed. Response to point heating was also investigated. Moreover, a sensitivity analysis was carried out to know the effect of various parameters, i.e. blood temperature, thermal conductivity, and blood perfusion rate on tissue temperature. The outcome of this study will be helpful for the researchers and physicians involved in the thermal treatment of human tissue.

Numerical study on thermal therapy of triple layer skin tissue using fractional bioheat model

This paper deals with the study of heat transfer and thermal damage in triple layer skin tissue using fractional bioheat model. Here, we consider three types of heating viz. sinusoidal heat flux, constant temperature and constant heat flux heating on skin surface. An implicit finite difference scheme is obtained by approximating fractional time derivative by quadrature formula and space derivative by central difference formula. The temperature profiles and thermal damage in the skin tissue are obtained to study the effect of fractional parameter [Formula: see text] on diffusion process for constant temperature and heat flux boundary heating on skin surface. A parametric study for sinusoidal heat flux at skin surface has also been made.

Two-dimensional closed-form model for temperature in living tissues for hyperthermia treatments

This research article determines an exact analytical expression for 2-D thermal field in single layer living tissues under a therapeutic condition by means of Fourier and non-Fourier heat transfer approaches. An actual spatially dependent initial condition has been adopted to analyze the heat propagation in tissues. The exact analytical determination for this actual initial condition for temperature may be difficult. However, in this study, an approximate analytical method has newly been established for an appropriate initial condition. With this initial expression, an exact temperature distribution for 2-D heat conduction in plane co-ordinates has been investigated for the predefined therapeutic boundary condition to have knowledge for practical aspects of the thermal therapy. Laplace Transform Method (LTM) in conjunction with the Inversion Theorem is used for the analytical solution treatment. We have utilized both Pennes' bioheat equation (PBHE) and thermal wave model of bioheat equation (TWMBHE) for the analysis. The influence of thermo-biological behavior on 2-D heat conduction in tissues has been studied with the variation of several dependable parameters in relation to the Hyperthermia treatment protocol in a moderate temperature range (42-45°C). The result in the present study has been evidenced for the biological heat transfer for the enforcement of different circumstances and also has been validated with the published value where the maximum temperature deviation of 2.6% has been recorded. We conclude that the temperature curve for TWMBHE model shows a higher waveform nature for low thermal relaxation time and this wavy nature gradually diminishes with an increase in relaxation time. The maximum peak temperature attains 46.3°C for the relaxation time = 2s and with the increase in the relaxation time the peak temperature gradually falls. The impact of blood perfusion rate on the relaxation time has also been established in this paper.

Mathematical and numerical analysis of thermal distribution in cancerous tissues under the local heat therapy

The main purpose of this study is to investigate the thermal behavior of living tissues in the presence of spatial external heat source. An effort has been made to formulate the mathematical model to study the temperature distribution in in vivo tissues of the human body. The mathematical formulation is governed by bio-heat equation together with appropriate initial, boundary and interface conditions. The solution of the model was carried out using variational finite element method and computational simulations. The model describes the exchange of heat between the internal biological tissues and other surrounding media. The effect of external heat source under different conditions of atmospheric temperature and as a local hyperthermic method provides an important information to the temperature regulation in biological tissues under normal and malignant conditions. Thermal fluctuations at the targeted regions were obtained with respect to various time-dependent heating sources and scattering coefficients. The results obtained may be helpful for clinical purposes especially in the treatment of cancerous tumors through radiotherapy and other local hyperthermic approaches.

EXACT ANALYTICAL SOLUTION OF BIOHEAT EQUATION SUBJECTED TO INTENSIVE MOVING HEAT SOURCE

Presented is the analytical solution of Pennes bio-heat equation, under localized moving heat source. The thermal behavior of one-dimensional (1D) nonhomogeneous layer of biological tissue is considered with blood perfusion term and modeled under the effect of concentric moving line heat source. The procedure of the solution is Eigen function expansion. The temperature profiles are calculated for three tissues of liver, kidney, and skin. Behavior of temperature profiles are studied parametrically due to the different moving speeds. The analytical solution can be used as a verification branch for studying the practical operations such as scanning laser treatment and other numerical solutions.

Review of Flexible Temperature Sensing Networks for Wearable Physiological Monitoring

Physiological temperature varies temporally and spatially. Accurate and real-time detection of localized temperature changes in biological tissues regardless of large deformation is crucial to understand thermal principle of homeostasis, to assess sophisticated health conditions, and further to offer possibilities of building a smart healthcare and medical system. Additionally, continuous temperature mapping in flexible and stretchable formats opens up many other potential areas, such as artificially electronic skins and reflection of emotional changes. This review exploits a comprehensive investigation onto recent advances in flexible temperature sensors, stretchable sensor networks, and platforms constructed in soft and compliant formats for wearable physiological monitoring. The most recent examples of flexible temperature sensors are first discussed regarding to their materials, structures, electrical and mechanical properties; temperature sensing network technologies in new materials and structural designs are then presented based on platforms comprised of multiple physical sensors and stretchable electronics. Finally, wearable applications of the sensing network are described, such as detection of human activities, monitoring of health conditions, and emotion-related bodily sensations. Conclusions are made with emphasis on critical issues and new trends in the field of wearable temperature sensor network technologies.

SEMI-ANALYTICAL SOLUTION OF BIO-HEAT CONDUCTION FOR MULTI-LAYERS SKIN SUBJECTED TO LASER HEATING AND FLUID COOLING

A semi-analytical solution of bio-heat conduction on the three-layer skin is presented. The performance of the typical heat treatment (heating by laser and cooling by fluid at skin surface) is studied. The transient temperature field and thermal damage of skin are investigated. Effects of several parameters on temperature variation and thermal damage are discussed. The results of the paper will be useful for heat therapy in clinics. In addition, the presented result is very consistent to that by the finite element method. The semi-analytical method can be easily applied for solving the general problem of heat conduction in any multilayer structure.

DEVELOPING ANALYTICAL MODELS OF PREDICTING SKIN TEMPERATURE AND DAMAGE EXTENT FROM SINGLE-LAYER INTO MULTI-LAYER ONES

As a starting point for developing analytical models of predicting skin temperature and damage extent into multi-layer ones, a double-layer model consisting of two distinguished and attached layers is considered: a tissue layer containing blood vessels and a tissue layer containing no blood vessels. The Pennes model is applied for the tissue containing blood vessels. Applying the Laplace transform, then the inversion theorem for Laplace transforms and the Cauchy residue theorem, the desired skin temperature function is obtained. Applying the temperature function in a damage model, the severity and degree of damage can be determined. Validating this model against previous analytical, numerical and experimental data, the error rate is determined.

Hemodialysis Catheter Heat Transfer for Biofilm Prevention and Treatment

Central line-associated bloodstream infections (CLABSIs) are not easily treated, and many catheters (e.g., hemodialysis catheters) are not easily replaced. Biofilms (the source of infection) on catheter surfaces are notoriously difficult to eradicate. We have recently demonstrated that modest elevations of temperature lead to increased staphylococcal susceptibility to vancomycin and significantly soften the biofilm matrix. In this study, using a combination of microbiological, computational, and experimental studies, we demonstrate the efficacy, feasibility, and safety of using heat as an adjuvant treatment for infected hemodialysis catheters. Specifically, we show that treating with heat in the presence of antibiotics led to additive killing of Staphylococcus epidermidis with similar trends seen for Staphylococcus aureus and Klebsiella pneumoniae. The magnitude of temperature elevation required is relatively modest (45-50°C) and similar to that used as an adjuvant to traditional cancer therapy. Using a custom-designed benchtop model of a hemodialysis catheter, positioned with tip in the human vena cava as well as computational fluid dynamic simulations, we demonstrate that these temperature elevations are likely achievable in situ with minimal increased in overall blood temperature.

A model evaluation study for treatment planning of laser-induced thermal therapy

A cross-validation analysis evaluating computer model prediction accuracy for a priori planning magnetic resonance-guided laser-induced thermal therapy (MRgLITT) procedures in treating focal diseased brain tissue is presented. Two mathematical models are considered. (1) A spectral element discretisation of the transient Pennes bioheat transfer equation is implemented to predict the laser-induced heating in perfused tissue. (2) A closed-form algorithm for predicting the steady-state heat transfer from a linear superposition of analytic point source heating functions is also considered. Prediction accuracy is retrospectively evaluated via leave-one-out cross-validation (LOOCV). Modelling predictions are quantitatively evaluated in terms of a Dice similarity coefficient (DSC) between the simulated thermal dose and thermal dose information contained within N = 22 MR thermometry datasets. During LOOCV analysis, the transient model's DSC mean and median are 0.7323 and 0.8001 respectively, with 15 of 22 DSC values exceeding the success criterion of DSC ≥ 0.7. The steady-state model's DSC mean and median are 0.6431 and 0.6770 respectively, with 10 of 22 passing. A one-sample, one-sided Wilcoxon signed-rank test indicates that the transient finite element method model achieves the prediction success criteria, DSC ≥ 0.7, at a statistically significant level.

Source term prediction in a multilayer tissue during hyperthermia

One of the major challenges in the use of hyperthermia to treat cancer is determining the desired heating power of external source in such a way that the thermal injury is confined to the unhealthy tissue. In this study, an inverse method based on the sequential method is proposed to estimate the desired heating power as a function of time for a successful hyperthermia treatment. In order to simulate the measured temperature, the direct problem is solved for a multilayer skin tissue to obtain the temperature data at the skin surface. These data are employed in the inverse problem to estimate the heating power of external source. Two examples are considered to examine the accuracy of the inverse analysis. In addition, the effect of measurement errors is investigated. Results show that the proposed inverse algorithm is able to determine the desired heating power of external source accurately, even in the presence of measurement errors. However, for noisy data, more temperature measurements are required to achieve reliable results.

Heat treatment modelling using strongly continuous semigroups

In this paper, mathematical simulation of bioheat transfer phenomenon within the living tissue is studied using the thermal wave model. Three different sources that have therapeutic applications in laser surgery, cornea laser heating and cancer hyperthermia are used. Spatial and transient heating source, on the skin surface and inside biological body, are considered by using step heating, sinusoidal and constant heating. Mathematical simulations describe a non-Fourier process. Exact solution for the corresponding non-Fourier bioheat transfer model that has time lag in its heat flux is proposed using strongly continuous semigroup theory in conjunction with variational methods. The abstract differential equation, infinitesimal generator and corresponding strongly continuous semigroup are proposed. It is proved that related semigroup is a contraction semigroup and is exponentially stable. Mathematical simulations are done for skin burning and thermal therapy in 10 different models and the related solutions are depicted. Unlike numerical solutions, which suffer from uncertain physical results, proposed analytical solutions do not have unwanted numerical oscillations.

Lock-in thermal imaging for the early-stage detection of cutaneous melanoma: a feasibility study

This paper theoretically evaluates lock-in thermal imaging for the early-stage detection of cutaneous melanoma. Lock-in thermal imaging is based on the periodic thermal excitation of the specimen under test. Resulting surface temperature oscillations are recorded with an infrared camera and allow the detection of variations of the sample's thermophysical properties under the surface. In this paper, the steady-state and transient skin surface temperatures are numerically derived for a different stage of development of the melanoma lesion using a two-dimensional axisymmetric multilayer heat-transfer model. The transient skin surface temperature signals are demodulated according to the digital lock-in principle to compute both a phase and an amplitude image of the lesions. The phase image can be advantageously used to accurately detect cutaneous melanoma at an early stage of development while the maximal phase shift can give precious information about the lesion invasion depth. The ability of lock-in thermal imaging to suppress disturbing subcutaneous thermal signals is demonstrated. The method is compared with the previously proposed pulse-based approaches, and the influence of the modulation frequency is further discussed.

NEW COMPUTATIONAL APPROACHES FOR BIOPHYSICAL HEAT TRANSFER IN TISSUE UNDER ULTRASONIC WAVES: THE VARIATIONAL ITERATION AND CHEBYSCHEV SPECTRAL SIMULATIONS

A mathematical and numerical study is presented for simulating temperature distribution in a two-dimensional tissue medium using Pennes bioheat transfer equation, when the tissue is subjected to ultrasonic waves. Following nondimensionalization of the governing partial differential equation, a novel variational iteration method (VIM) solution is developed. This excellent technique introduced by He [Variational iteration method — a kind of non-linear analytical technique: Some examples, Int J Non-Linear Mech.34:699–708, 1999] employs Lagrange multipliers which can be identified optimally via variational theory. The space and time distributions of temperature are studied and solutions visualized via Mathematica. The influence of thermal conductivity and relaxation time are also examined. Excellent stability and convergence characteristics of VIM are demonstrated. Validation is achieved with a Chebyschev spectral collocation method (CSCM). The present work demonstrates the excellent potential of this powerful semi-numerical method in nonlinear biological heat transfer and furthermore provides an alternative strategy to conventional finite element and finite difference computational simulations. The model finds applications in minimally-invasive spinal laser treatments, glaucoma therapy in ophthalmology and thermoradiotherapy for malignant tumors.

Control of the temperature rise in magnetic hyperthermia with use of an external static magnetic field

Our purpose in this study was to investigate the usefulness of a method for controlling the temperature rise in magnetic hyperthermia (MH) using an external static magnetic field (SMF), and to derive an empirical equation for describing the energy dissipation of magnetic nanoparticles (MNPs) in the presence of both the alternating magnetic field (AMF) and SMF through phantom experiments. We made a device that allows for MH in the presence of an SMF with a field-free point (FFP) using a Maxwell coil pair. We measured the temperature rise of MNPs under various conditions of AMF and SMF and various distances from the FFP (d), and calculated the specific absorption rate (SAR) from the initial slope of the temperature curve. The SAR values decreased with increasing strength of SMF (Hs) and d. The extent of their decrease with d increased with an increase of the gradient of SMF (Gs). The relationships between SAR and Hs and between SAR and d could be well approximated by Rosensweig's equation in which the amplitude of AMF (Hac) is replaced by √[Hac(2)]/√[Hac(2)+Hs(2)], except for the case when Gs was small. In conclusion, the use of an external SMF with an FFP will be effective for controlling the temperature rise in MH in order to reduce the risk of heating surrounding healthy tissues, and our empirical equation will be useful for estimating SAR in the presence of both the AMF and SMF and for designing an effective local heating system for MH.

Numerical study of the solidification process in biological tissue with blood flow and metabolism effects by the dual phase lag model

The bioheat transfer with phase change in biological tissues during the freezing process is simulated by the dual phase lag conduction heat transfer model. A numerical algorithm based on the enthalpy method is established to solve the solidification of biological tissues. The linearly temperature-dependent enthalpy (non-isothermal phase change) is considered here. The results of the parabolic heat conduction model for a slice of cucumber are compared with the experimental data. A comparison between dual phase lag and hyperbolic solutions with small values of relaxation times is applied in order to verify the corresponding parabolic solutions accuracy of the dual phase lag and hyperbolic solutions. The heating source effect owing to blood perfusion and metabolic heat on the heat transfer in a biological tissue subject to freezing process is studied. The relaxation time has an important influence on the transient temperature and temperature gradient. A major discrepancy among bioheat transfer models is found for zones closer to the cooling boundary. The heat source term, owing to blood flow and metabolism in a phase change problem in the biological tissue, has a significant influence on thermal effects of the subject tissue.

Simulation and experimental studies on magnetic hyperthermia with use of superparamagnetic iron oxide nanoparticles

Our purpose of this study was to present simulation and experimental studies on magnetic hyperthermia (MH) with use of an alternating magnetic field (AMF) and superparamagnetic iron oxide nanoparticles (Resovist®). In the simulation studies, the energy dissipation (P) and temperature rise rate (∆T/∆t) were computed under various conditions by use of the probability density function of the particle size distribution based on a log-normal distribution. P and ∆T/∆t and their dependence on the frequency of the AMF (f) largely depended on the particle size of Resovist®. P and ∆T/∆t reached maximum at a diameter of ~24 nm, and were proportional to the amplitude of the AMF (H (0)) raised to a power of ~2.0. In the experimental studies, we made a device for generating an AMF, and measured the temperature rise under various concentrations of Resovist®, H (0), and f. The temperature rise at 10 min after the start of heating was linearly proportional to the concentration of Resovist®, and proportional to H (0) raised to a power of ~2.4, which was slightly greater than that expected from the simulation studies. There was a tendency for the temperature rise to saturate with increasing f. In conclusion, this study will be useful for investigating the feasibility of MH with Resovist® and optimizing the parameters for it.

Medical thermal imaging of electrically stimulated woman breast: a simulation study

Tissues have different electrical conductivity and metabolic energy consumption values depending on their state of health and species. Since metabolic heat generation values show differences from tissue to tissue, thermal imaging has started to play an important role in medical diagnoses. Temperature differences of healthy and cancerous tissue may be changed by means of frequency dependent current stimulation within medical safety limits, and thus, depth dependent imaging performance can be increased. In this study, a three-dimensional realistic model of a woman breast and malignant tissue is generated and frequency dependent feasibility work for the proposed method is implemented. Temperature distributions are obtained by solving Pennes Bio Heat Equation (using finite element method). Temporal and spatial temperature distribution images are obtained at desired depths for two cases; with and without current application. Different temperature distributions are imaged by altering the frequency of the applied current and the corresponding conductivity value. Improvement in the imaging performance can be provided by current stimulation, and the temperature difference generated by 40 mm(3) tumor at 1.5 cm depth can be detected on breast surface with the state-of-the-art thermal imagers.

Relationships of skin depths and temperatures when varying pulse repetition frequencies from 2.0-microm laser light incident on pig skin

Human perception of 2.0-microm infrared laser irradiation has become significant in such disparate fields as law enforcement, neuroscience, and pain research. Several recent studies have found damage thresholds for single-pulse and continuous wave irradiations at this wavelength. However, the only publication using multiple-pulse irradiations was investigating the cornea rather than skin. Literature has claimed that the 2.0-microm light characteristic thermal diffusion time was as long as 300-ms. Irradiating the skin with 2.0-microm lasers to produce sensation should follow published recommendations to use pulses on the order of 10 to 100 ms, which approach the theoretical thermal diffusion time. Therefore, investigation of the heating of skin for a variety of laser pulse combinations was undertaken. Temperatures of ex vivo pig skin were measured at the surface and at three depths from pulse sequences of six different duty factors. Differences were found in temperature rise per unit exposure that did not follow a linear relation to duty factor. The differences can be explained by significant heat conduction during the pulses. Therefore, the common heat modeling assumption of thermal confinement during a pulse may need to be experimentally verified if the pulse approaches the theoretical thermal confinement time.

Transient solution to the bioheat equation and optimization for magnetic fluid hyperthermia treatment

Two finite concentric spherical regions were considered as the tissue model for magnetic fluid hyperthermia treatment. The inner sphere represents the diseased tissue containing magnetic particles that generate heat when an alternating magnetic field is applied. The outer sphere represents the healthy tissue. Blood perfusion effects are included in both the regions. Analytical and numerical solutions of the one-dimensional bioheat transfer equation were obtained with constant and spatially varying heat generation in the inner sphere. The numerical solution was found to be in good agreement with the analytical solution. In an ideal hyperthermia treatment, all the diseased tissues should be selectively heated without affecting any healthy tissue. The present work optimized the magnetic particle concentration in an attempt to achieve the ideal hyperthermia conditions. It was found that, for a fixed amount of magnetic particles, optimizing the magnetic particle distribution in the diseased tissue can significantly enhance the therapeutic temperature levels in the diseased tissue while maintaining the same level of heating in the healthy tissue.

Analytical analysis of the Pennes bioheat transfer equation with sinusoidal heat flux condition on skin surface

This study focuses on the effect of the temperature response of a semi-infinite biological tissue due to a sinusoidal heat flux at the skin. The Pennes bioheat transfer equation such as rho(t)c(t)( partial differentialT/ partial differentialt)+W(b)c(b)(T-T(a))=k partial differential(2)T/ partial differentialx(2) with the oscillatory heat flux boundary condition such as q(0,t)=q(0)e(iomegat) was investigated. By using the Laplace transform, the analytical solution of the Pennes bioheat transfer equation with surface sinusoidal heating condition is found. This analytical expression is suitable for describing the transient temperature response of tissue for the whole time domain from the starting periodic oscillation to the final steady periodic oscillation. The results show that the temperature oscillation due to the sinusoidal heating on the skin surface is unstable in the initial period. Further, it is unavailable to predict the blood perfusion rate via the phase shifting between the surface heat flux and the surface temperature. Moreover, the lower frequency of sinusoidal heat flux on the skin surface induces a more sensitive phase shift response to the blood perfusion rate change, but extends the beginning time of sampling because of the avoidance of the unavailable first cyclic oscillation.

New Modality for Maximizing Cryosurgical Killing Scope While Minimizing Mechanical Incision Trauma Using Combined Freezing-Heating System

Cryosurgery is a minimally invasive surgical technique using extremely low temperature to destroy undesired tissues. A surgical freezing margin of at least 1 cm is often recommended to avoid local tumor recurrence after surgery. For treating slender or elongated solid tumors in a conventional cryosurgery, simultaneous insertion of multiple cryoprobes is a necessity to guarantee an adequate killing scope. However, the risk of mechanical incision trauma may outweigh the benefits of such therapy. To resolve this difficulty, we proposed a new cryosurgical treatment modality, which can significantly maximize the killing scope while minimize the incision trauma, using the recently developed combined cryosurgical-hyperthermia treatment system (CCHTS). The method, named as one time’s percutaneous insertion while multiple times’ freezing∕heating ablation, is rather flexible in administrating a complex cryosurgical process and avoids certain shortcomings of conventional freezing strategies. Owing to the powerful heating function, the present probe can be easily moved back along its original incision tract to the desired positions immediately after initiating the heating. Then, a new iceball can be formed there while the iceballs generated before still remain unmelted in the following cycles. Consequently, a slender iceball could be generated to embrace the whole elongated tumor. This is, however, rather hard to achieve for a conventional cryosurgery with only one single freezing function or using only one probe. To visually demonstrate the feasibility and potential advantage of the present method, proof of concept in vitro gel experiments were performed. In addition, tests and corresponding theoretical simulations were performed on pork tissues. All the results indicate that the elongated iceball could be easily generated by using only one CCHTS probe owing to its strong freezing∕heating capability. In this way, a large number of incisions with multiple probes, commonly adopted in a conventional cryosurgery, can be avoided and the serious mechanical trauma including potential dangers can thus be significantly reduced. Meanwhile, the cost for the operation and postmedical care will be lowered. The present strategies are expected to be valuable in administrating a highly efficient and minimally invasive cryosurgery in the near future.

Correlation Between Peak Spatial-Average SAR and Temperature Increase Due to Antennas Attached to Human Trunk

This paper discusses the correlation between peak spatial-average specific absorption rate (SAR) and maximum temperature increase for antennas attached to the human trunk. Frequency bands considered are 150, 400, and 900 MHz, which are assigned for occupational communications. This problem is throughly investigated with the aid of Green's function. In particular, the effect of variation of thermal constants on the temperature increase is revealed by using one-dimensional model. Computational results suggests that one of the most dominant factors which affect the correlation between peak SAR and maximum temperature increase is blood flow in tissues. This is confirmed by considering a three-dimensional realistic human body model. Uncertainties caused by the calculation of peak SAR and the difference in the body model shape are also quantified.

A novel modeling and simulation technique of photo–thermal interactions between lasers and living biological tissues undergoing multiple changes in phase

Knowledge of heat transfer in biological bodies has many therapeutic applications involving either raising or lowering of temperature, and often requires precise monitoring of the spatial distribution of thermal histories that are produced during a treatment protocol. Extremes of temperature into the freezing and burning ranges are useful in surgical procedures for selective killing and/or removal of target tissues. For example, the primary objective of hyperthermia is to raise the temperature of the diseased tissue to a therapeutic value, typically 41- 44 degrees C, and then thermally destroy it. The present paper therefore aims to develop a mathematical model for effective simulation of photo--thermal interactions between laser rays and biological tissues. In particular, damage of biological tissues when subjected to single point laser diathermy is numerically investigated using a unique enthalpy-based approach for modeling multiple phase change, (namely, melting of fat and vaporization of water content of the tissues) and the associated release/absorption of latent heat in conjunction with unsteady state heat conduction mechanisms. The governing equations of bio-heat transfer coupled with initial and boundary conditions are solved using a finite volume approach in conjunction with line by a line tri-diagonal matrix algorithm (TDMA) solver. Temperature responses of tissues subject to laser heating are quantitatively investigated in detail using the present model, and the resultant solutions are expected to be immensely useful in a variety of Bio-thermal practices in medicine and surgery.

Transport lattice models of heat transport in skin with spatially heterogeneous, temperature-dependent perfusion

BACKGROUND

Investigation of bioheat transfer problems requires the evaluation of temporal and spatial distributions of temperature. This class of problems has been traditionally addressed using the Pennes bioheat equation. Transport of heat by conduction, and by temperature-dependent, spatially heterogeneous blood perfusion is modeled here using a transport lattice approach.

METHODS

We represent heat transport processes by using a lattice that represents the Pennes bioheat equation in perfused tissues, and diffusion in nonperfused regions. The three layer skin model has a nonperfused viable epidermis, and deeper regions of dermis and subcutaneous tissue with perfusion that is constant or temperature-dependent. Two cases are considered: (1) surface contact heating and (2) spatially distributed heating. The model is relevant to the prediction of the transient and steady state temperature rise for different methods of power deposition within the skin. Accumulated thermal damage is estimated by using an Arrhenius type rate equation at locations where viable tissue temperature exceeds 42 degrees C. Prediction of spatial temperature distributions is also illustrated with a two-dimensional model of skin created from a histological image.

RESULTS

The transport lattice approach was validated by comparison with an analytical solution for a slab with homogeneous thermal properties and spatially distributed uniform sink held at constant temperatures at the ends. For typical transcutaneous blood gas sensing conditions the estimated damage is small, even with prolonged skin contact to a 45 degrees C surface. Spatial heterogeneity in skin thermal properties leads to a non-uniform temperature distribution during a 10 GHz electromagnetic field exposure. A realistic two-dimensional model of the skin shows that tissue heterogeneity does not lead to a significant local temperature increase when heated by a hot wire tip.

CONCLUSIONS

The heat transport system model of the skin was solved by exploiting the mathematical analogy between local thermal models and local electrical (charge transport) models, thereby allowing robust, circuit simulation software to obtain solutions to Kirchhoff's laws for the system model. Transport lattices allow systematic introduction of realistic geometry and spatially heterogeneous heat transport mechanisms. Local representations for both simple, passive functions and more complex local models can be easily and intuitively included into the system model of a tissue.