Tissue Temperature Profile Research Articles

Numerical simulation of non–linear skin model with energy dissipation during hyperthermia and its validation with experimental data

This work deals with a non–linear skin model with energy dissipation exposed to hyperthermia therapy based on a Gaussian–type external heat source and also consider that the blood perfusion rate relies linearly on temperature. Since skin tissue is very sensitive to temperature, it is crucial to predict the temperature response with energy dissipation to ensure hyperthermia efficacy and minimize adverse effects. The present model, which is supported by experimental data, indicates that the temperature profile of skin tissue increases less in comparison to the non–linear Pennes model due to energy dissipation. A hybrid strategy is utilized to get computed outcomes for the present problem and obtained outcome is compared to the analytical outcome in a specific situation and is confirmed with high precision through table and graph. To damage a significant number of cancerous cells width, we have to manage or reduce enough value of the antenna constant accordingly, and the length of the probe region may be changed according to the position of the tumor or cancer cells in skin tissue. The temperature profile at the targeted area reduces when the values of rate of thermal conductivity, rate of blood perfusion per unit volume and blood perfusion constant increase.

Computational study on 2D space-time fractional single-phase-lag bioheat model using RBF and Chebyshev polynomial based space-time collocation method

The present study concerns the numerical simulation of the two-dimensional space-time fractional single-phase-lag bioheat model to study the heat transfer during hyperthermia. A space-time collocation method employing Gaussian radial basis functions (RBF) and Chebyshev polynomials in space and time directions, respectively, is proposed to solve the model numerically. The meshfree nature of Gaussian RBF enables us to apply the proposed method in an irregular domain. Further, using the Chebyshev polynomials, fewer nodes in the time direction are required to solve the model, which reduces the computational cost. The proposed method can simultaneously obtain the solution for the whole time domain in regular and irregular spatial domains. The effects of various parameters like heat source parameters, relaxation time(phase-lag), and blood perfusion on heat transfer in tissue are simulated in both regular and irregular domains. Furthermore, the temperature profiles in tissue are obtained for different fractional orders to exhibit their effects on heat transfer in tissue. The results indicate that fractional-order models could provide a unified approach to analyzing the heat transfer process in hyperthermia treatment.

Bio-thermo-viscoelastic behavior in multilayer skin tissue

A theoretical model for skin thermo-viscoelastic behavior is proposed based on the non-Fourier bioheat transfer theory in this article. Skin tissue is regarded as a multilayer structure composed of epidermis, dermis, and subcutis, the properties of each layer is assumed to be homogeneous and thermoviscoelasticity. Analytical solutions of temperature profile and stress distribution in skin tissue are obtained, and the influence of non-Fourier effect, viscoelastic properties of skin, blood perfusion, and time-dependent thermal boundary conditions at skin surface is considered. Numerical results show that the peak stress occurred at skin surface induced by thermal injury is much larger than mechanical threshold of pain perception. The temperature profile in skin tissue may be overestimated for the long-time hyperthermia treatment when the heat convection of blood perfusion in dermis and subcutis is neglected. The thermal stress calculated based on thermoviscoelastic model is significantly lower than that based on classical thermoelastic model due to the inherent rheological properties of skin tissue. This article may be helpful in improving the fundamental understanding of complicated thermomechanical behavior of human skin and designing of biomedical devices for hyperthermia treatment.

System for delivering microwave ablation to subcutaneous tumors in small-animals under high-field MRI thermometry guidance

Purpose Bio-effects following thermal treatments are a function of the achieved temperature profile in tissue, which can be estimated across tumor volumes with real-time MRI thermometry (MRIT). Here, we report on expansion of a previously developed small-animal microwave hyperthermia system integrated with MRIT for delivering thermal ablation to subcutaneously implanted tumors in mice. Methods Computational models were employed to assess suitability of the 2.45 GHz microwave applicators for delivering ablation to subcutaneous tumor targets in mice. Phantoms and ex-vivo tissues were heated to temperatures in the range 47–67 °C with custom-made microwave applicators for validating MRIT with the proton resonance frequency shift method against fiberoptic thermometry. HAC15 tumors implanted in nude mice (n = 6) were ablated in vivo and monitored with MRIT in multiple planes. One day post ablation, animals were euthanized, and excised tumors were processed for viability assessment. Results Average absolute error between temperatures from fiberoptic sensors and MRIT was 0.6 °C across all ex-vivo ablations. During in-vivo experiments, tumors with volumes ranging between 5.4–35.9 mm3 (mean 14.2 mm3) were ablated (duration: 103–150 s) to achieve 55 °C at the tumor boundary. Thermal doses ≥240 CEM43 were achieved across 90.7–98.0% of tumor volumes for four cases. Ablations were incomplete for remaining cases, attributed to motion-affected thermometry. Thermal dose-based ablative tumor coverage agreed with viability assessment of excised tumors. Conclusions We have developed a system for delivering microwave ablation to subcutaneous tumors in small animals under MRIT guidance and demonstrated its performance in-vivo.

Assessment and Modeling of Plasmonic Photothermal Therapy Delivered via a Fiberoptic Microneedle Device Ex Vivo.

Plasmonic photothermal therapy (PPTT) has potential as a superior treatment method for pancreatic cancer, a disease with high mortality partially attributable to the currently non-selective treatment options. PPTT utilizes gold nanoparticles infused into a targeted tissue volume and exposed to a specific light wavelength to induce selective hyperthermia. The current study focuses on developing this approach within an ex vivo porcine pancreas model via an innovative fiberoptic microneedle device (FMD) for co-delivering light and gold nanoparticles. The effects of laser wavelengths (808 vs. 1064 nm), irradiances (20–50 mW·mm−2), and gold nanorod (GNR) concentrations (0.1–3 nM) on tissue temperature profiles were evaluated to assess and control hyperthermic generation. The GNRs had a peak absorbance at ~800 nm. Results showed that, at 808 nm, photon absorption and subsequent heat generation within tissue without GNRs was 65% less than 1064 nm. The combination of GNRs and 808 nm resulted in a 200% higher temperature rise than the 1064 nm under similar conditions. A computational model was developed to predict the temperature shift and was validated against experimental results with a deviation of <5%. These results show promise for both a predictive model and spatially selective, tunable treatment modality for pancreatic cancer.

Temperature Variation in Breast Tissue Model With and Without Tumor Based on Porous Media

The human body is made by 200 different types of cells, which are separated by voids. Blood supplies the nutrients and minerals to all cells within the tissue through these voids. The breast tissue is treated as a porous media in the study. Tumor includes the vascular (blood) and the extra-vascular (solid) regions. The porosity of a tumor is higher than normal tissue. The present work deals with the temperature variation of normal and tumorous breast tissue based on porous media. The finite element method is used to solve the two-dimensional bio-heat equation. The results show that the temperature profile of normal breast tissue in the porous media model is almost identical with the conventional bio-heat model at correction factor is equal to 0:6. The temperature of tumor region in the porous media model is slightly lower than the conventional bio-heat model. When the porosity is increased, the temperature of normal breast tissue is increased. But in tumorous breast tissue, the temperature is slightly increased in skin surface to anterior part of the tumor and slightly decreased in tumor region. The temperature of normal and tumorous breast tissue is increased when metabolism, blood velocity, and room temperature are increased in the porous media model. The central temperature of the tumor region reaches a steady state faster than anterior and posterior temperature of both normal and tumorous breast tissue in conventional bio-heat model and porous media model.

A comparison study of photothermal effect between moxibustion therapy and laser irradiation on biological tissue

Moxibustion and laser irradiation are perceived to achieve satisfactory therapeutic effects by inducing photothermal effects on biological tissue. Understanding the photon transport and heat transfer process is an effective way to reveal their underlying mechanism. The temperature distribution of in-vitro tissue under gentle moxibustion and 808 nm laser irradiation were measured experimentally. Photon transport was simulated by Monte Carlo models. Heat transfer models on in-vitro tissue with convolved Monte Carlo results as heat sources were developed. During moxibustion, photons emitted from burning moxa stick with long-wavelength deposited in skin layer, which induced a maximum temperature on tissue surface. While for 808 nm laser irradiation, most photons penetrated through skin, which resulted in the highest temperature in fat tissue. Laser irradiation with big beam radius could induce a wide and relatively uniform thermal effect. During moxibustion and laser irradiation, the wavelength and beam radius have a significant influence on photons distribution as well as temperature profile in biological tissue. Laser irradiation with suitable parameters can be proposed as a substitution of moxibustion in terms of photothermal effect. This work would provide valuable guidance for understanding the photothermal mechanism of moxibustion and laser irradiation in the combined view of photon transport and heat transfer.

A study of fractional order dual-phase-lag bioheat transfer model.

In this study, we have established a space-time fractional DPL bioheat transfer model in the presence of temperature-dependent metabolic and space-time dependent electromagnetic heat sources. Applying the Legendre wavelet collocation method, the fractional order partial differential equation is reduced into the system of algebraic equations, which has been solved using the Newton iteration method. The error bound as well as stability analysis and numerical scheme validation are provided. The time to achieve for the position of hyperthermia is discussed in three cases: the DPL model, the time-fractional DPL model, and the space-time-fractional DPL model. The effect of variability of time and space fractional derivative orders (α and β), transmitted power (P) and lagging times on the temperature profile in biological tissue at a different time are discussed in detail. We conclude that a suitable value of α, β, τT, τq, and P provides a desirable temperature at a particular time in thermal therapies. Such knowledge will be very useful in the clinical therapeutic application.

Computer Modeling of Drug Delivery with Thermosensitive Liposomes in a Realistic Three-Dimensional Geometry.

Thermosensitive liposomes (TSL) are nanoparticles that can encapsulate therapeutic drugs, and release those drugs when exposed to hyperthermic temperatures (>40 °C). Combined with localized hyperthermia, TSL enable focused drug delivery. In this study, we created a three-dimensional (3D) computer model for simulating delivery with TSL-encapsulated doxorubicin (TSL-Dox) to mouse tumors. A mouse hind limb was scanned by a 3D scanner and the resulting geometry was imported into finite element modeling software, with a virtual tumor added. Then, heating by a surface probe was simulated. Further, a drug delivery model was coupled to the heat transfer model to simulate drug delivery kinetics. For comparison, experimental studies in gel phantoms and in vivo fluorescence imaging studies in mice carrying lung tumor xenografts were performed. We report the tissue temperature profile, drug concentration profile and compare the experimental studies with the computer model. The thermistor produced very localized heating that resulted in highest drug delivery to regions near the probe. The average tumor temperature was 38.2˚C (range 34.4-43.4˚C), and produced an average tumor drug concentration of 11.8 µg/g (0.3-28.1 µg/g) after 15 min heating, and 25.6 µg/g (0.3-52 µg/g), after 60 min heating. The computer model reproduced the temperature profile compared to phantom experiments (mean error 0.71 °C, range 0.59-1.25 °C), as well as drug delivery profile as compared to in vivo studies. Our results suggest feasibility of using this approach to model drug delivery in preclinical studies with accurate model geometry.

A Temperature-Controlled Laser Hot Needle With Grating Sensor for Liver Tissue Tract Ablation

In this article, we proposed a laser hot needle for liver tissue tract ablation. The proposed laser hot needle is powered by a 4500-nm-diode laser incorporated with a closed-loop control system that comprises of a uniform fiber Bragg grating (FBG) temperature sensor and a computer. Based on the real-time feedback input from the FBG temperature sensor, the laser power is regulated by a proportional–integral–derivative (PID) control system to control the needle temperature. In the characterization test, a chirped grating-based distributed temperature sensor is employed for measuring the tissue temperature profile in the ex vivo bovine liver tissue during the ablation. A histological test is conducted to study the impact of tract ablation to the cellular structures of treated tissue and tissue coagulation. In a tract ablation test, a ~50-mm $\times \sim 6$ -mm (length $\times $ width) thermal denaturation zone has been created on ex vivo bovine liver tissue with the laser hot needle at 150 °C.

COMPUTATIONAL ALGORITHM OF TWO PARALLEL ULTRASOUND BEAMS OF 1D CANCER TISSUE MODEL FOR SAFE AND EFFECTIVE HYPERTHERMIA TREATMENT

The mathematical algorithm of two parallel ultrasound beams on a one-dimensional (1D) cancer tissue model for hyperthermia treatment was created using Matlab software. Physically, the model incorporated two beams; the first beam was permanently placed at the center of the tumor, whereas the other was set between the first beam and the tumor. The computational implementation of this technique relies on the Crank–Nicolson method. This technique is a finite different method that offers an exact heat transfer calculation based on the heat analysis of the heat node structure from a 1D biological tissue model. The Matlab software implementation was composed of two stages: tissue temperature profile calculation and optimization computation. To obtain the tissue temperature profile, the beam heat was varied from 45∘C to 75∘C (seven different levels of heat from the same source), while the second beam was allowed to move between the first beam and the tumor to locations at distances of 1 to 9[Formula: see text]mm (nine positions). The obtained tissue temperature profiles were subsequently analyzed to achieve the optimal time, beam position, and beam heat of the treatment. As a result of the optimization, the best position for the second beam was determined to be 5[Formula: see text]mm from the center of the tumor. Further, all tumor cells were observed to have died, whereas all normal tissues were safe. The optimal time, beam position, and beam heat of the treatment were finally collected to create and fit a mathematical function for further hyperthermia treatment.

Bioheat transfer in a spherical biological tissue: a comparison among various models

The investigation of bioheat transfer is a difficult issue because it entails a mixture of many mechanisms to take into account, such as thermal conduction in tissues, convection and blood perfusion, metabolic heat generation, vascular structure, changing of tissue properties depending on physiological condition and so on. This topic has a key role to predict accurately the temperature distribution in tissues, especially during biomedical applications. In this paper, different bioheat transfer models are resumed and compared. The biological tissue is modelled as a porous sphere and liver tissue properties are used. Governing equations are averaged over a Representative Elementary Volume (REV) of the living tissue. Transient bioheat equations based on models like, for example, Pennes model, Local Thermal Non-Equilibrium equations (LTNE model), are employed. In the employed equations, radiative heat transfer is also considered. Governing equations with the appropriate boundary conditions are solved with the finite-element code COMSOL Multiphysics®. The effects of hyperthermia on the living tissue are included with a source term in the tissue energy equation. Results are presented in terms of temperature profiles in the biological tissue; the aim is to appreciate differences due to the various bioheat models.

A numerical investigation of microwave ablation on porous liver tissue

The understanding of heat transport in biological tissues is important for enhanced insight on the physiological mechanisms and thermoregulatory mechanisms. This article presents a numerical simulation of microwave (MW) ablation using a single-slot MW antenna on two layers of porous liver tissue. The two layers are of tumor and normal tissue. A porous media approach is proposed for mathematical model of MW ablation. Three coupled models which include transient momentum equations and a transient energy equation coupled with an electromagnetic wave propagation (EWP) equation are analyzed. This article focuses on the influences of the tumor diameter, tumor porosity, and input MW power on the specific absorption rate (SAR) profile, temperature profile, and blood velocity profile within the porous liver tissue. The results obtained from the calculation of porous media model are examined and compared with the one of bioheat model along with the experimental results from previous work. The results indicated that all parameters have a significant effect on the SAR profile, temperature profile, and blood velocity profile in the porous liver tissue. The advanced results in this research can be used in applications such as it provides guidance on the practical treatment and can be developed medically for therapeutic.

Ultrasonic thermal dust: A method to monitor deep tissue temperature profiles.

We demonstrate a tetherless, sub-millimeter implantable temperature sensing system employing ultrasonic powering and ultrasonic backscatter modulation assembled using commercially available components. We demonstrate two sizes of sensors based on available components with volumes of 1.45 mm3 and 0.118 mm3. Individual sensors are able to resolve ±0.5°C changes in temperature, suitable for medical diagnostic and monitoring purposes. We verify less than 0.3°C drift in temperature readings over 14 days in physiological conditions. This approach is compatible with more sophisticated temperature sensors such as classic proportional to absolute temperature (PTAT) integrated circuits, as well as digital backscatter approaches. Our goal is to solve a long-standing issue: chronic and tetherlessly monitoring deep tissue temperature with high spatial accuracy.

INFLUENCE OF THERMAL-ELECTRICAL PARAMETER COMBINATIONS ON THERMAL LESIONS OF RADIOFREQUENCY TUMOR ABLATION

Several studies have been conducted on the applicability of hyperthermia radiofrequency in the treatment of liver tumors. Many theoretical studies have reported the relevance of various physical parameters in terms of their efficacy in combating tumors and have analyzed the impact of these physical parameters on the temperature profile in the diseased tissue. Parameters such as thermal and electrical conductivities have been investigated during simulations of thermal ablation. Such parameters play an important role in the process of heat transfer in tissues. The purpose of this study is to predict the lesion volume, considering the inclusion of temperature dependence of thermal-electrical properties. This paper introduces a three-dimensional computational model that includes different comparative combinations of tissue thermal-electrical parameters as a mapping of temperature (such as thermal and electrical conductivities and specific heat). The finite-element method is employed for simulating hepatic radiofrequency ablation through the numerical solutions of the bioheat, Laplace, and Navier–Stokes equations. The results suggest that different combinations of tissue temperature-dependent parameters can significantly affect the computed lesion volume and that the temperature dependence of electrical conductivity has a major impact on the computed lesion volume and temperature distribution.

A Paris System-Based Implant Approach to Hyperthermia Cancer Tumor with Gold Seeds and Ultrasound.

A Paris system-based implant approach has been used to improve the bio-heat distribution from implanted gold rods in insonated tissues. Experiments with single-plane implants using parallel equidistant 1.018±0.015cm height and 0.136±0.001cm diameter 24-K gold rods) arranged in triangular and square shapes were performed in Mus musculus white mice (medial dorsal region). The mice were anesthetized and gold rods were implanted by means of a trocar needle and the implanted region was insonated with a 4-cm diameter transducer oscillating with a nominal frequency of 1MHz and power of about 75W. Intramuscular tissue temperature measurements were recorded using implantable needle type thermocouples affixed to a portable Fluke thermometer. Superficial tissue temperature profile was also measured with a FLIR infrared camera and thermographic analysis was performed using the ImageJ computer software. In both cases, the central implant planes have been assigned to that approximately bisects all the implanted rods. Measured with the needle type thermistor, for the triangular implant, the percentage deviation between the maximum and minimum temperature within the triangular plane was 5%. For a square shape, this percentage deviation was 6%. The thermographic analysis have shown a deviation of 3 and 5% for the triangular and square shapes, respectively. The Paris system-based implant approach for gold rods implanted in tissue and exposed to ultrasound may greatly improve the bio-heat propagation and sustain a constant temperature profile inside triangular and square patterns formed by gold rods implants. Additionally, the Paris system may minimize ablations areas and treatment length in hyperthermia if used in cancer tumor treatment with gold seeds and ultrasound.

SU‐F‐E‐04: A Paris System‐Based Implant Approach to Hyperthermia Cancer Tumor with Gold Seeds and Ultrasound

Purpose:To apply the Paris system‐based implant for an uniform bio‐heat distribution from implanted gold rods in tissue insonated with ultrasound.Methods:Experiments with single‐plane implants using parallel equidistant 1.018 ± 0.015 cm height and 0.136 ± 0.001 cm diameter 24‐K gold rods) arranged in triangular and square shapes were performed in Mus Musculus white mice (medial dorsal region). The mice were anesthetized and gold rods were implanted by means of a trocar needle and the implanted region was insonated with a 4‐cm diameter transducer oscillating with a nominal frequency of 1 MHz and power of about 75 W. Intramuscular tissue temperature measurements were taken using implantable needle type thermocouples affixed to a portable Fluke thermometer. Superficial tissue temperature profile was also measured with a FLIR infrared camera and thermographic analysis were performed using the ImageJ computer software. In both cases, the central implant planes have been assigned to that approximately bisects all the implanted rods.Results:Measured with the needle type thermistor, for the triangular implant, the percentage deviation between the maximum and minimum temperature within the triangular plane was 5%. For a square shape, this percentage deviation was 6%. The thermographic analysis have shown a deviation of 3% and 5% for the triangular and square shapes, respectively.Conclusion:Based on the temperature measurements with needle type thermistor and thermographic analysis, the Paris system‐based implant approach for gold rods implanted in tissue and exposed to ultrasound may greatly improve the bio‐heat propagation and sustain a constant temperature profile inside triangular and square patterns formed by gold rods implants. Additionally, the Paris system may minimize ablations areas and treatment length in hyperthermia if used in cancer tumor treatment.

Real-Time Prediction of Temperature for Electromagnetic Heating Therapy in Deep-Seated Tissue

This paper aims to develop a mathematical model for predicting the temperature response of tissues in electromagnetic heating therapy (EHT), when using a magnetic flux concentrator to improve heating efficiency. EHT has two critical challenges when applied to deep-seated tissue heating, i.e., the temperature might not be accurately measured and the magnetic field intensity decreases with increasing depth. The finite-element method (FEM) is suitable for coupled analysis with electromagnetic fields and heat transfer, which can be used to predict temperature profiles in deep tissue implanted with magnetic materials. To improve the accuracy of the FEM model, an adaptive network fuzzy inference system (ANFIS) model is implemented on the basis of measured data and simulated data, which were generated by the FEM model. The ANFIS model can provide a large number of testing data to optimize the parameters in the FEM model; moreover, it can be used to expedite the optimization process.

Spatial and time-course thermodynamics during pulmonary vein isolation using the second-generation cryoballoon in a canine in vivo model.

Thermodynamics in the left atrium-pulmonary vein (PV) junction, phrenic nerve, and esophagus during PV isolation (PVI) using the second-generation cryoballoon are not known. Twenty dogs underwent PVI using second-generation cryoballoon. Ablations were performed for ≤2 deliveries based on PVI without a bonus freeze. Inner balloon, balloon surface, and tissue temperatures were monitored during cryoablation. The tissue thermocouples were placed on the epicardial surface of the left atrium-PV junction, as well as on the phrenic nerve and within the esophagus. A total of 259 cryoballoon and 229 tissue tissue thermocouples profiles during 53 cryoablations of 40 PVs were analyzed. Acutely, PVI was achieved in 36 of 40 PVs (90%). Conductive tissue cooling spread radially from the balloon-left atrium-PV contact point. The lowest tissue temperatures were dependent on the distance of the tissue thermocouples to the balloon surface (r=0.85; P<0.001). In addition, blood flow leaks around the balloon had a warming effect on the balloon and tissue temperature profiles. Chronic isolation (mean, 48±16 days) was achieved in 27 of 36 PVs (75%). In 8 of 9 acutely isolated but with chronic reconnection PVs, the blood flow leak location was concordant with chronic reconnection gap. Although only 1 esophageal ulcerated lesion was observed, neither phrenic nerve palsy nor severe PV stenosis was seen in any dogs. Variance in tissue thermodynamics during cryothermal ablation depends on the distance from balloon and peri-balloon blood flow leaks. This information may be useful for successful PVI without severe complications.

Analytical and numerical study of tissue cryofreezing via the immersed boundary method

Cryosurgery is accepted as a favorable treatment option for eradicating undesirable cancerous tissue due to its minimally invasive nature. This work presents a finite difference study of a biological liver tissue undergoing cryofreezing using the immersed boundary method (IBM). The liver tissue is treated as a non-ideal material having temperature-dependent thermophysical properties. Numerical results exhibit good agreement with available data from literature with maximum errors of 1.7% and 1.5% for simulations and experiments, respectively. The influence of heating effect due to blood flow (through the vessel surface) has been investigated by applying the boundary condition-enforced IBM. Results have indicated that the heat source term due to the blood flow in the vessel embedded in the bioheat transfer equation significantly impacts the tissue temperature profiles and thermal gradient histories. In addition, the ice fronts, namely, 0°C and −40°C, progression can vary by as much as 35% at 500s when the distance between the cryoprobe and the major blood vessel varies. This work has also demonstrated that applying the IBM to a bioheat model focusing on tissue cryofreezing is highly appropriate as far as the analysis of tissue freezing in the vicinity of major blood vessels is concerned.