Spatiotemporal modeling of nano-delivered chemotherapeutics for synergistic microwave ablation cancer therapy.

BACKGROUND AND OBJECTIVE: The effectiveness of current microwave ablation (MWA) therapies is limited. Administration of thermosensitive liposomes (TSLs) which release drugs in response to heat has presented a significant potential for enhancing the efficacy of thermal ablation treatment, and the benefits of targeted drug delivery. However, a complete knowledge of the mechanobiological processes underlying the drug release process, especially the intravascular drug release mechanism and its distribution in response to MWA needs to be improved. Multiscale computational-based modeling frameworks, integrating different biophysical phenomena, have recently emerged as promising tools to decipher the mechanobiological events in combo therapies. The present study aims to develop a novel multiscale computational model of TSLs delivery following MWA implantation. METHODS: Due to the complex interplay between the heating procedure and the drug concentration maps, a computational model is developed to determine the intravascular release of doxorubicin from TSL, its transvascular transport into the interstitium, transport in the interstitium, and cell uptake. Computational models can estimate the interplays among liposome and drug properties, tumor perfusion, and heating regimen to examine the impact of essential parameters and to optimize a targeted drug delivery platform. RESULTS: Results indicated that the synergy of TSLs with MWA allows more localized drug delivery with lower side effects. The drug release rate and tumor permeability play crucial roles in the efficacy of TSLs during MWA treatment. The computational model predicted an unencapsulated drug lime around the ablated zone, which can destroy more cancer cells compared to MWA alone by 40%. Administration of TSLs with a high release rate capacity can improve the percentage of killed cancer cells by 24%. Since the heating duration in MWA is less than 15 min, the presented combination therapy showed better performance for highly permeable tumors. CONCLUSION: This study highlights the potential of the proposed computational framework to address complex and realistic scenarios in cancer treatment, which can serve as the future research foundation, including advancements in nanomedicine and optimizing the pair of TSL and MWA for both preclinical and clinical studies. The present model could be as a valuable tool for patient-specific calibration of essential parameters.

Influence of different heat transfer models on therapeutic temperature prediction and heat-induced damage during magnetic hyperthermia.

Magnetic hyperthermia regulates the therapeutic temperature within a specific range to damage malignant cells after exposing the magnetic nanoparticles inside tumor tissue to an alternating magnetic field. The therapeutic temperature of living tissues can be generally predicted using Pennes' bio-heat equation after ignoring both the inhomogeneity of biological structure and the microstructural responses. Although various of the bio-heat transfer models proposed in literature fix these shortages, there is still a lack of a comprehensive report on investigating the discrepancy for different models when applied in the magnetic hyperthermia context. This study compares four different bio-heat equations in terms of the therapeutic temperature distribution and the heat-induced damage situation for a proposed geometric model, which is established based on computed tomography images of a tumor bearing mouse. The therapeutic temperature is also used as an index to evaluate the effect of two key relaxation times for the phase lag behavior on bio-heat transfer. Moreover, this work evaluates the effects of two blood perfusion rates on both the treatment temperature and the cumulative equivalent heating minutes at 43 °C. Numerical analysis results reveal that relaxation times for phase-lag behavior as well as the porosity for living tissues directly affect the therapeutic temperature variation and ultimately the thermal damage for the malignant tissue during magnetic hyperthermia. The dual-phase-lag equation can be converted into Pennes' equation and simple-phase-lag equation when relaxation times meet specific conditions during the process of heat transfer. In addition, different blood perfusion rates can result in an amplitude discrepancy for treatment temperature, but this parameter does not change the characteristics of thermal propagation during therapy.

A comparative study between conventional chemotherapy and photothermal activated nano-sized targeted drug delivery to solid tumor.

Delivery of chemotherapeutic medicines to solid tumors is critical for optimal therapeutic success and minimal adverse effects. We mathematically developed a delivery method using thermosensitive nanocarriers activated by light irradiation. To assess its efficacy and identify critical events and parameters affecting therapeutic response, we compared this method to bolus and continuous infusions of doxorubicin for both single and multiple administrations. A hybrid sprouting angiogenesis approach generates a semi-realistic microvascular network to evaluate therapeutic drug distribution and microvascular heterogeneity. A pharmacodynamics model evaluates treatment success based on tumor survival cell percentage. The study found that whereas bolus injection boosted extracellular drug concentration levels by 90%, continuous infusion improved therapeutic response due to improved bioavailability. Cancer cell death increases by 6% with several injections compared to single injections due to prolonged chemotherapeutic medication exposure. However, responsive nanocarriers supply more than 2.1 times more drug than traditional chemotherapy in extracellular space, suppressing tumor development longer. Also, controlled drug release decreases systemic side effects substantial through diminishing the concentration of free drug in the circulation. The primary finding of this work highlights the significance of high bioavailability in treatment response. The results indicate that responsive nanocarriers contribute to increased bioavailability, leading to improved therapeutic benefits. By including drug delivery features in a semi-realistic model, this numerical study sought to improve drug-bio interaction comprehension. The model provides a good framework for understanding preclinical and clinical targeted oncology study outcomes.

Numerical Modeling and Simulation of Non-Invasive Acupuncture Therapy Utilizing Near-Infrared Light-Emitting Diode.

Acupuncture is one of the most extensively used complementary and alternative medicine therapies worldwide. In this study, we explore the use of near-infrared light-emitting diodes (LEDs) to provide acupuncture-like physical stimulus to the skin tissue, but in a completely non-invasive way. A computational modeling framework has been developed to investigate the light-tissue interaction within a three-dimensional multi-layer model of skin tissue. Finite element-based analysis has been conducted, to obtain the spatiotemporal temperature distribution within the skin tissue, by solving Pennes' bioheat transfer equation, coupled with the Beer-Lambert law. The irradiation profile of the LED has been experimentally characterized and imposed in the numerical model. The experimental validation of the developed model has been conducted through comparing the numerical model predictions with those obtained experimentally on the agar phantom. The effects of the LED power, treatment duration, LED distance from the skin surface, and usage of multiple LEDs on the temperature distribution attained within the skin tissue have been systematically investigated, highlighting the safe operating power of the selected LEDs. The presented information about the spatiotemporal temperature distribution, and critical factors affecting it, would assist in better optimizing the desired thermal dosage, thereby enabling a safe and effective LED-based photothermal therapy.

A spatiotemporal computational model of focused ultrasound heat-induced nano-sized drug delivery system in solid tumors.

Focused Ultrasound (FUS)-triggered nano-sized drug delivery, as a smart stimuli-responsive system for treating solid tumors, is computationally investigated to enhance localized delivery of drug and treatment efficacy. Integration of thermosensitive liposome (TSL), as a doxorubicin (DOX)-loaded nanocarrier, and FUS, provides a promising drug delivery system. A fully coupled partial differential system of equations, including the Helmholtz equation for FUS propagation, bio-heat transfer, interstitial fluid flow, drug transport in tissue and cellular spaces, and a pharmacodynamic model is first presented for this treatment approach. Equations are then solved by finite element methods to calculate intracellular drug concentration and treatment efficacy. The main objective of this study is to present a multi-physics and multi-scale model to simulate drug release, transport, and delivery to solid tumors, followed by an analysis of how FUS exposure time and drug release rate affect these processes. Our findings not only show the capability of model to replicate this therapeutic approach, but also confirm the benefits of this treatment with an improvement of drug aggregation in tumor and reduction of drug delivery in healthy tissue. For instance, the survival fraction of tumor cells after this treatment dropped to 62.4%, because of a large amount of delivered drugs to cancer cells. Next, a combination of three release rates (ultrafast, fast, and slow) and FUS exposure times (10, 30, and 60 min) was examined. Area under curve (AUC) results show that the combination of 30 min FUS exposure and rapid drug release leads to a practical and effective therapeutic response.

Finite element model of female thermoregulation with geometry based on medical images.

INTRODUCTION: this study describes the development of a female finite element thermoregulatory model (FETM) METHOD: the female body model was developed from medical image datasets of a median U.S. female and was constructed to be anatomically correct. The body model preserves the geometric shapes of 13 organs and tissues, including skin, muscles, fat, bones, heart, lungs, brain, bladder, intestines, stomach, kidneys, liver, and eyes. Heat balance within the body is described by the bio-heat transfer equation. Heat exchange at the skin surface includes conduction, convection, radiation, and sweat evaporation. Vasodilation, vasoconstriction, sweating, and shivering are controlled by afferent and efferent signals to and from the skin and hypothalamus. RESULTS: the model was validated with measured physiological data during exercise and rest in thermoneutral, hot, and cold conditions. Validations show the model predicted the core temperature (rectal and tympanic temperatures) and mean skin temperatures with acceptable accuracy (within 0.5 °C and 1.6 °C, respectively) CONCLUSION: this female FETM predicted high spatial resolution temperature distribution across the female body, which provides quantitative insights into human thermoregulatory responses in females to non-uniform and transient environmental exposure.

Bio-thermal response and thermal damage in biological tissues with non-equilibrium effect and temperature-dependent properties induced by pulse-laser irradiation.

Comprehension of thermal behavior underlying the living biological tissues helps successful applications of current heat therapies. The present work is to explore the heat transport properties of irradiated tissue during tis thermal treatment, in which the local thermal non-equilibrium effect as well as temperature-dependent properties arose from complicated anatomical structure, is considered. Based on the generalized dual-phase lag (GDPL) model, a non-linear governing equation of tissue temperature with variable thermal physical properties is proposed. The effective procedure constructed on an explicit finite difference scheme is then developed to predict numerically the thermal response and thermal damage irradiated by a pulse laser as a therapeutic heat source. The parametric study on variable thermal physical parameters including the phase lag times, heat conductivity, specific heat capacity and blood perfusion rate has been performed to evaluate their influence on temperature distribution in time and space. On this basis, the thermal damage with different laser variables such as laser intensity and exposure time are further analyzed.

In silico evaluation of adverse eddy current effects in preclinical tests of magnetic hyperthermia.

BACKGROUND AND OBJECTIVE: Magnetic hyperthermia is an oncological therapy that employs magnetic nanoparticles activated by alternating current (AC) magnetic fields with frequencies between 50 kHz and 1 MHz, to release heat in a diseased tissue and produce a local temperature increase of about 5 °C. To assess the treatment efficacy, in vivo tests on murine models (mice and rats) are typically performed. However, these are often carried out without satisfying the biophysical constraints on the electromagnetic (EM) field exposure, with consequent generation of hot spots and undesirable heating of healthy tissues. Here, we investigate possible adverse eddy current effects, to estimate AC magnetic field parameters (frequency and amplitude) that can potentially guarantee safe animal tests of magnetic hyperthermia. METHODS: The analysis is performed through in silico modelling by means of finite element simulation tools, specifically developed to study eddy current effects in computational animal models, during magnetic hyperthermia treatments. The numerical tools enable us to locally evaluate the specific absorption rate (SAR) and the produced temperature increase, under different field exposure conditions. RESULTS: The simulation outcomes demonstrate that in mice with weight lower than 30 g the thermal effects induced by AC magnetic fields are very weak, also when slightly overcoming the Hergt-Dutz limit, that is the product of the magnetic field amplitude and frequency should be lower than 5·109 A/(m·s). Conversely, we observe significant temperature increases in 500 g rats, amplified when the field is applied transversally to the body longitudinal axis. A strong mitigation of side-effects can be achieved by introducing water boluses or by applying focused fields. CONCLUSIONS: The developed physics-based modelling approach has proved to be a useful predictive tool for the optimization of preclinical tests of magnetic hyperthermia, allowing the identification of proper EM field conditions and the design of setups that guarantee safe levels of field exposure during animal treatments. In such contest, the obtained results can be considered as valid indicators to assess reference levels for animal testing of biomedical techniques that involve EM fields, like magnetic hyperthermia, thus complying with the Directive 2010/63/EU on the protection of animals used for scientific purposes.

Computational modeling of targeted temperature management in post-cardiac arrest patients.

Our core body temperature is held around [Formula: see text]C by an effective internal thermoregulatory system. However, various clinical scenarios have a more favorable outcome under external temperature regulation. Therapeutic hypothermia, for example, was found beneficial for the outcome of resuscitated cardiac arrest patients due to its protection against cerebral ischemia. Nonetheless, practice shows that outcomes of targeted temperature management vary considerably in dependence on individual tissue damage levels and differences in therapeutic strategies and protocols. Here, we address these differences in detail by means of computational modeling. We develop a multi-segment and multi-node thermoregulatory model that takes into account details related to specific post-cardiac arrest-related conditions, such as thermal imbalances due to sedation and anesthesia, increased metabolic rates induced by inflammatory processes, and various external cooling techniques. In our simulations, we track the evolution of the body temperature in patients subjected to post-resuscitation care, with particular emphasis on temperature regulation via an esophageal heat transfer device, on the examination of the alternative gastric cooling with ice slurry, and on how anesthesia and the level of inflammatory response influence thermal behavior. Our research provides a better understanding of the heat transfer processes and therapies used in post-cardiac arrest patients.

Assessing the local temperature of human cornea exposed to surface ablation by different laser refractive-surgery devices: a numerical comparative study.

To evaluate the local temperature at corneal tissue after applying single laser pulse from six commercial devices; Medilex™, Katana laser-soft, MEL90, Technolas-Teneo317, Alcon EX500, and PulzarTMZ1. The temperature distribution is simulated using finite element solution of the Penne's bio-heat transfer equation on a 3-D model of human cornea using the manufacturer's assigning parameters. The obtained results showed that the heating effect of Katana laser soft is 40% lower than MEL90 and Pulzar™ Z1, while the broad beam Medilex™ showed the minimum temperature rise especially at 248-nm laser radiation. The change in laser parameters selected for ablation has significant effect on the corneal local temperature. The broad beam-based device produces lower local corneal temperature than other flying spot types.

Influence of temperature-dependent acoustic and thermal parameters and nonlinear harmonics on the prediction of thermal lesion under HIFU ablation.

According to the traditional method of high intensity focused ultrasound (HIFU) treatment, the acoustic and thermal characteristic parameters of constant temperature (room temperature or body temperature) are used to predict thermal lesion. Based on the nonlinear spherical beam equation (SBE) and Pennes bio-heat transfer equation, and a new acoustic-thermal coupled model is proposed. The constant and temperature-dependent acoustic and thermal characteristic parameters are used to predict thermal lesion, and the predicted lesion area are compared with each other. Moreover, the relationship between harmonic amplitude ratio (P2/P1) and thermal lesion is studied. Combined with the known experimental data of acoustic and thermal characteristic parameters of biological tissue and data fitting method, the relationship between acoustic and thermal characteristic parameters and temperature is obtained; and the thermal lesion simulation calculation is carried out by using the acoustic and thermal characteristic parameters under constant temperature and temperature- dependent acoustic and thermal characteristic parameters, respectively. The simulation results show that under the same irradiation condition, the thermal lesion predicted by temperature-dependent acoustic and thermal characteristic parameters is larger than that predicted by traditional method, and the thermal lesion increases with the decrease of harmonic amplitude ratio.

Numerical analysis of non-Fourier thermal response of lung tissue based on experimental data with application in laser therapy.

BACKGROUND AND OBJECTIVE: The thermal therapy is a minimally invasive technique used as an alternative approach to conventional cancer treatments. There is an increasing concern about the accuracy of the thermal simulation during the process of tumor ablation. This study is aimed at investigating the effect of finite speed of heat propagation in the biological lung tissue, experimentally and numerically. METHODS: In the experimental study, a boundary heat flux is applied to the lung tissue specimens and the temperature variation is measured during a transient heat transfer procedure. In the numerical study, a code is developed based on the finite volume method to solve the classical bio-heat transfer, the Cattaneo and Vernotte, and the Dual-phase-lag (DPL) equations. The thermal response of tissue during the experiments is compared with the predictions of the three heat transfer models. RESULTS: It is found that the trend of temperature variation by the DPL model resembles the experimental results. The experimental observation in parallel with the numerical results reveals that the accumulated thermal energy diffuses to the surrounding tissue with a slower rate in comparison with the conventional bio-heat transfer model. The DPL model is implemented to study the temperature elevation in the laser irradiation to lung tissue in the presence of gold nanoparticles (GNPs). It is concluded that the extent of the necrotic tumoral region and the area of the damaged healthy tissue are reduced, when the non-Fourier heat transfer is taken into account. CONCLUSIONS: Results show that considering the phase lags is crucial in planning for an effective thermal treatment, in which the cancerous tissue is ablated and the surrounding tissues are preserved from irreversible thermal damage.

hBN Nanoparticle-Assisted Rapid Thermal Cycling for the Detection of Acanthamoeba.

Acanthamoeba are widely distributed in the environment and are known to cause blinding keratitis and brain infections with greater than 90% mortality rate. Currently, polymerase chain reaction (PCR) is a highly sensitive and promising technique in Acanthamoeba detection. Remarkably, the rate of heating-cooling and convective heat transfer of the PCR tube is limited by low thermal conductivity of the reagents mixture. The addition of nanoparticles to the reaction has been an interesting approach that could augment the thermal conductivity of the mixture and subsequently enhance heat transfer through the PCR tube. Here, we have developed hexagonal boron nitride (hBN) nanoparticle-based PCR assay for the rapid detection of Acanthamoeba to amplify DNA from low amoeba cell density. As low as 1 × 10-4 wt % was determined as the optimum concentration of hBN nanoparticles, which increased Acanthamoeba DNA yield up to ~16%. Further, it was able to reduce PCR temperature that led to a ~2.0-fold increase in Acanthamoeba DNA yield at an improved PCR specificity at 46.2 °C low annealing temperature. hBN nanoparticles further reduced standard PCR step time by 10 min and cycles by eight; thus, enhancing Acanthamoeba detection rapidly. Enhancement of Acanthamoeba PCR DNA yield is possibly due to the high adsorption affinity of hBN nanoparticles to purine (Guanine-G) due to the higher thermal conductivity achieved in the PCR mixture due to the addition of hBN. Although further research is needed to demonstrate these findings in clinical application, we propose that the interfacial layers, Brownian motion, and percolation network contribute to the enhanced thermal conductivity effect.

Breast tumor parameter estimation and interactive 3D thermal tomography using discrete thermal sensor data.

This work uses a simple low-cost wearable device embedded with discrete thermal sensors to map the breast skin surface temperature. A methodology has been developed to estimate diameter, blood perfusion, metabolic heat generation and location in X, Y, Z coordinate of tumor from this discrete set of data. An interactive 3D thermal tomography was developed which provides a detailed 3D thermal view of the breast anatomy. Using this system, the user can interactively rotate and slice the 3D thermal image of the breast for a detailed study of the tumor. Finite element method (FEM) and an evolution-based inverse method were used for the parameter estimation. The method was first validated using phantom experiments and the results obtained were within an error of 10% (0.005 W cm-3) for heat generation and 15% (0.3 cm) for heater location. Further validation was carried out through clinical trials on 60 human subjects. Estimated blood perfusion rate and metabolic heat generation rate exhibit distinguishable difference between cancerous and non-cancerous breast. Estimated diameter and location of tumor in cancerous breast shows good agreement with the actual clinical reports. We have obtained a sensitivity of 82.78% and specificity of 87.09%. Proposed breast tumor parameter estimation methodology with interactive 3D thermal tomography is a good screening tool for breast cancer detection and also useful for clinicians to find out location including depth.

Fast computation of soft tissue thermal response under deformation based on fast explicit dynamics finite element algorithm for surgical simulation.

BACKGROUND AND OBJECTIVES: During thermal heating surgical procedures such as electrosurgery, thermal ablative treatment and hyperthermia, soft tissue deformation due to surgical tool-tissue interaction and patient movement can affect the distribution of thermal energy induced. Soft tissue temperature must be obtained from the deformed tissue for precise delivery of thermal energy. However, the classical Pennes bio-heat transfer model can handle only the static non-moving state of tissue. In addition, in order to enable a surgeon to visualise the simulated results immediately, the solution procedure must be suitable for real-time thermal applications. METHODS: This paper presents a formulation of bio-heat transfer under the effect of soft tissue deformation for fast or near real-time tissue temperature prediction, based on fast explicit dynamics finite element algorithm (FED-FEM) for transient heat transfer. The proposed thermal analysis under deformation is achieved by transformation of the unknown deformed tissue state to the known initial static state via a mapping function. The appropriateness and effectiveness of the proposed formulation are evaluated on a realistic virtual human liver model with blood vessels to demonstrate a clinically relevant scenario of thermal ablation of hepatic cancer. RESULTS: For numerical accuracy, the proposed formulation can achieve a typical 10-3 level of normalised relative error at nodes and between 10-4 and 10-5 level of total errors for the simulation, by comparing solutions against the commercial finite element analysis package. For computation time, the proposed formulation under tissue deformation with anisotropic temperature-dependent properties consumes 2.518 × 10-4 ms for one element thermal loads computation, compared to 2.237 × 10-4 ms for the formulation without deformation which is 0.89 times of the former. Comparisons with three other formulations for isotropic and temperature-independent properties are also presented. CONCLUSIONS: Compared to conventional methods focusing on numerical accuracy, convergence and stability, the proposed formulation focuses on computational performance for fast tissue thermal analysis. Compared to the classical Pennes model that handles only the static state of tissue, the proposed formulation can achieve fast thermal analysis on deformed states of tissue and can be applied in addition to tissue deformable models for non-linear heating analysis at even large deformation of soft tissue, leading to great translational potential in dynamic tissue temperature analysis and thermal dosimetry computation for computer-integrated medical education and personalised treatment.

Skin temperature maps as a measure of carotid artery stenosis.

In this study, the effect of carotid artery stenosis on the neck skin temperature maps was investigated. With the presence of stenosis, alterations in the carotid artery hemodynamics bring about changes in the heat transfer to the surrounding tissue. This is expected to be captured in the resulting temperature map over the external neck skin surface; possibly it correlates to the presence of stenosis. A total of twenty carotid artery samples, from ten patients with both sides normal (0% stenosis), stenosis (>50%) on one side, and stenosis (>50%) on both sides, were studied. Duplex Ultrasound and infrared (IR) thermography examinations were performed. A computational study, on an ideal 3-dimensional (3D) carotid artery and jugular vein model encapsulated with a solid neck tissue phantom resembling the human neck, was carried out. Incorporating the patient-specific geometrical (depth of artery and stenosis) and flow (peak systolic and end diastolic inlet velocity) boundary conditions, conjugate bio-heat transfer was studied using a finite volume numerical scheme. Simulation results and in-vivo thermal maps show that the average temperature on the external neck skin surface is significantly higher for normal patients (32.82 ± 0.53 °C versus 32.00 ± 0.37 °C, p < 0.001). Furthermore, the thermal region of interests (TROIs) were extracted from the in-vivo thermal images, which both qualitatively and quantitatively distinguish the normal and diseased cases. This study suggests the potential of thermal feature-based screening of patients with carotid artery stenosis.

Neural network methodology for real-time modelling of bio-heat transfer during thermo-therapeutic applications.

Real-time simulation of bio-heat transfer can improve surgical feedback in thermo-therapeutic treatment, leading to technical innovations to surgical process and improvements to patient outcomes; however, it is challenging to achieve real-time computational performance by conventional methods. This paper presents a cellular neural network (CNN) methodology for fast and real-time modelling of bio-heat transfer with medical applications in thermo-therapeutic treatment. It formulates nonlinear dynamics of the bio-heat transfer process and spatially discretised bio-heat transfer equation as the nonlinear neural dynamics and local neural connectivity of CNN, respectively. The proposed CNN methodology considers three-dimensional (3-D) volumetric bio-heat transfer behaviour in tissue and applies the concept of control volumes for discretisation of the Pennes bio-heat transfer equation on 3-D irregular grids, leading to novel neural network models embedded with bio-heat transfer mechanism for computation of tissue temperature and associated thermal dose. Simulations and comparative analyses demonstrate that the proposed CNN models can achieve good agreement with the commercial finite element analysis package, ABAQUS/CAE, in numerical accuracy and reduce computation time by 304 and 772.86 times compared to those of with and without ABAQUS parallel execution, far exceeding the computational performance of the commercial finite element codes. The medical application is demonstrated using a high-intensity focused ultrasound (HIFU)-based thermal ablation of hepatic cancer for prediction of tissue temperature and estimation of thermal dose.

Skin tissue responses to transient heating with memory-dependent derivative.

In this work, the new concept of "memory dependent derivative" in the Pennes' bio-heat transfer process of skin tissues is employed to investigate the one-dimensional problem of a skin tissue under sinusoidal heat flux conditions. Laplace transform technique is utilized to solve the problem. We investigate, numerically, the bio-heat transfer equation with memory-dependent derivative to find the effect on the tissue temperature of the kernel function and the time-delay parameter which are characteristic of memory dependent derivative heat transfer. Correlations are made with the results obtained in the case of the absence of memory-dependent derivative parameters. The effects of the time-delay on the temperature distribution in skin tissue for different forms of kernel functions are examined.

Numerical study on the effects of blood perfusion and body metabolism on the temperature profile of human forearm in hyperthermia conditions.

The development of mathematical models for describing the thermal behavior of living tissues under normal or hyperthermia conditions is of increasing importance. In this research, a 3D forearm model based on anthropometric measurement of 25 samples in Tehran, Iran was developed. The tissue temperature distribution is obtained via the Finite Volume Method (FVM) by considering the appropriate boundary conditions, blood perfusion, body metabolism, and the application of hyperthermia conditions on the tissue. The Pennes Bioheat Transfer Equation (PBHTE) is considered in this regard. Also, various thermophysical properties are assumed for the model in order to clarify the effects of such parameters on the tissue temperature distribution. The results of this study indicate that it is possible to provide the desired conditions for many therapeutic processes by controlling the parameters such as blood perfusion, body metabolism and the type of external heat source applied on the tissue. Generally, by decreasing the body metabolism, increasing the blood perfusion rate in tissue and applying a fluctuating heat flux, instead of uniform heat flux on the surface of the forearm skin, it is possible to provide the hyperthermia conditions without causing damages such as burn injuries to the other parts of the tissue. By using the results of this study, the appropriate conditions of hyperthermia can be obtained.

A numerical study on thermal ablation of brain tumor with intraoperative focused ultrasound.

Focused ultrasound surgery (FUS) is a non-invasive thermal therapeutic method which has been emerged in the field of brain tumors treatment. During intraoperative brain surgery, application of FUS can significantly increase the accuracy of thermal ablation of tumor while reducing undesirable damage to healthy brain tissue. The main objective of this study is acquiring acoustic transducer specifications to achieve optimum thermal treatment in the tumoral tissue. 2D and 3D models are constructed from patient-specific brain MRI images which consist of a malignant vascular tumor. Acoustic pressure and temperature are obtained by using homogenous Helmholtz and bio-heat transfer equations according to insignificant nonlinear effect. Besides that, thermal lesion induced by FUS is obtained by the thermal dose function. Results show the significance of blood vessels' cooling effect on the temperature profile. Moreover, correlation between temperature profile and transducer's operating parameter including power, frequency and duty cycle is obtained. Artificial neural network analysis is conducted to estimate required transducer parameters for optimum temperature rise.