Blood Perfusion Rate Research Articles

The Use of Core Warming as a Treatment for Coronavirus Disease 2019 (COVID-19): an Initial Mathematical Model

Background: Increasing data suggest that elevated body temperature may be helpful in resolving a variety of diseases, including sepsis, acute respiratory distress syndrome (ARDS), and viral illnesses. SARS-CoV-2, which causes coronavirus disease 2019 (COVID-19), may be more temperature sensitive than other coronaviruses, particularly with respect to the binding affinity of its viral entry via the ACE2 receptor. A mechanical provision of elevated temperature focused in a body region of high viral activity in patients undergoing mechanical ventilation may offer a therapeutic option that avoids arrhythmias seen with some pharmaceutical treatments. We investigated the potential to actively provide core warming to the lungs of patients with a commercially available heat transfer device via mathematical modeling, and examine the influence of blood perfusion on temperature using this approach. Methods: Using the software Comsol Multiphysics, we modeled and simulated heat transfer in the body from an intraesophageal warming device, taking into account the airflow from patient ventilation. The simulation was focused on heat transfer and warming of the lungs and performed on a simplified geometry of an adult human body and airway from the pharynx to the lungs. Results: The simulations were run over a range of values for blood perfusion rate, which was a parameter expected to have high influence in overall heat transfer, since the heat capacity and density remain almost constant. The simulation results show a temperature distribution which agrees with the expected clinical experience, with the skin surface at a lower temperature than the rest of the body due to convective cooling in a typical hospital environment. The highest temperature in this case is the device warming water temperature, and that heat diffuses by conduction to the nearby tissues, including the air flowing in the airways. At the range of blood perfusion investigated, maximum lung temperature ranged from 37.6°C to 38.6°C. Conclusions: The provision of core warming via commercially available technology currently utilized in the intensive care unit, emergency department, and operating room can increase regional temperature of lung tissue and airway passages. This warming may offer an innovative approach to treating infectious diseases from viral illnesses such as COVID-19, while avoiding the arrhythmogenic complications of currently used pharmaceutical treatments.

Heating Protocol Design Affected by Nanoparticle Redistribution and Thermal Damage Model in Magnetic Nanoparticle Hyperthermia for Cancer Treatment

Abstract Recent micro-CT scans have demonstrated a much larger magnetic nanoparticle distribution volume in tumors after localized heating than those without heating, suggesting possible heating-induced nanoparticle migration. In this study, a theoretical simulation was performed on tumors injected with magnetic nanoparticles to evaluate the extent to which the nanoparticle redistribution affects the temperature elevation and thermal dosage required to cause permanent thermal damage to PC3 tumors. 0.1 cc of a commercially available ferrofluid containing magnetic nanoparticles was injected directly to the center of PC3 tumors. The control group consisted of four PC3 tumors resected after the intratumoral injection, while the experimental group consisted of another four PC3 tumors injected with ferrofluid and resected after 25 min of local heating. The micro-CT scan generated tumor model was attached to a mouse body model. The blood perfusion rates in the mouse body and PC3 tumor were first extracted based on the experimental data of average mouse surface temperatures using an infrared camera. A previously determined relationship between nanoparticle concentration and nanoparticle-induced volumetric heat generation rate was implemented into the theoretical simulation. Simulation results showed that the average steady-state temperature elevation in the tumors of the control group is higher than that in the experimental group where the nanoparticles are more spreading from the tumor center to the tumor periphery (control group: 70.6±4.7 °C versus experimental group: 69.2±2.6 °C). Further, we assessed heating time needed to cause permanent thermal damage to the entire tumor, based on the nanoparticle distribution in each tumor. The more spreading of nanoparticles to tumor periphery in the experimental group resulted in a much longer heating time than that in the control group. The modified thermal damage model by Dr. John Pearce led to almost the same temperature elevation distribution; however, the required heating time was at least 24% shorter than that using the traditional Arrhenius integral, despite the initial time delay. The results from this study suggest that in future simulation, the heating time needed when considering dynamic nanoparticle migration during heating is probably between 19 and 29 min based on the Pearce model. In conclusion, the study demonstrates the importance of including dynamic nanoparticle spreading during heating and accurate thermal damage model into theoretical simulation of temperature elevations in tumors to determine thermal dosage needed in magnetic nanoparticle hyperthermia design.

Macrophage Spheroids with Chronological Phenotype Shifting To Promote Therapeutic Angiogenesis in Critical Limb Ischemia

Therapeutic angiogenesis becomes an essential approach to rescue ischemia and the cell-based therapy facilitates ischemia recovery via stimulation of paracrine signals or replacement of damaged cells. Macrophages participate in multiple processes of tissue repair, and the M1 and M2 phenotypes play distinct roles in the sequential stages of healing initiation, angiogenesis stabilization, and tissue maturation. In this study, macrophage spheroids (MøSs) are proposed to promote therapeutic angiogenesis in critical limb ischemia (CLI) via chronological shifting from M1 to M2 phenotypes. Uniform-sized MøSs are prepared by using electrosprayed microcapsules as the confined growth template, and fiber fragments are inoculated to achieve a local release of chrysin for macrophage phenotype manipulation. The macrophage polarization shifting is confirmed from the decreased CD86 expressions (M1 marker) from 64.7 to 31.7% and the concurrent increase in CD206 expressions (M2 marker) from 39.3 to 72.4%. Meanwhile, the tumor necrosis factor-α secretion from M1 is downregulated by around threefold, whereas the levels of interleukin-10 and transforming growth factor-β1 from M2 increase by around threefold. The incubation with conditioned media from the MøS culture could promote the proliferation and migration of endothelial cells (ECs), showing a high healing rate of EC layers. The local treatment of hind-limb ischemia leads to a full recovery from ischemic to normal limbs with a high blood perfusion rate. Histological analysis shows few muscle degeneration and fibrosis areas and high capillary densities. As far as we know, this is the first attempt to develop uniform-sized MøSs and to undergo dynamic phenotypic shifting from early M1 to later M2 for angiogenesis promotion in the CLI treatment.

Semi-analytical solutions for different non-linear models of dual phase lag equation in living tissues

In this study, the heat transfer in a multilayer heated living tissue is investigated. A non-linear dual phase lag (DPL) heat conduction model is presented assuming temperature-dependent blood perfusion rate, heat conductivity and metabolic heat generation. Semi -analytical solutions for the non-linear model are obtained employing the Galerkin weighted residuals method. The effects of the variable thermophysical properties on the temperature distribution within the tissue are investigated through comparison of the results with the corresponding results for the constant thermophysical properties. The results show that the temperature dependence of the blood perfusion rate has a significant effect on the temperature distribution in the different layers of the tissue. As far as the tumor region is considered, 0.43 °C increase in its temperature is observed in comparison with that obtained assuming the constant blood perfusion rate at t = 1800 s. Moreover, increasing the temperature dependence of the thermal conductivity leads to the reduction in the temperature of the tissue except in the muscle layers. Considering the temperature-dependent metabolic heat generation increases the temperature of all of the layers compared to the corresponding temperatures obtained assuming the constant metabolic heat generation.

Vasomodulation of peripheral blood flow by focused ultrasound potentiates improvement of diabetic neuropathy

ObjectiveEffective treatment methods for diabetic peripheral neuropathy are still lacking. Here, a focused ultrasound (FUS) technique was developed to improve blood flow in diabetic peripheral vessels and potentially treat diabetic...

The serotonin 2A receptor agonist 25CN-NBOH increases murine heart rate and neck-arterial blood flow in a temperature-dependent manner.

Background:Serotonin 2A receptors, the molecular target of psychedelics, are expressed by neuronal and vascular cells, both of which might contribute to brain haemodynamic characteristics for the psychedelic state.Aim:Aiming for a systemic understanding of psychedelic vasoactivity, here we investigated the effect of N-(2-hydroxybenzyl)-2,5-dimethoxy-4-cyanophenylethylamine – a new-generation agonist with superior serotonin 2A receptor selectivity – on brain-supplying neck-arterial blood flow.Methods:We recorded core body temperature and employed non-invasive, collar-sensor based pulse oximetry in anesthetised mice to extract parameters of local blood perfusion, oxygen saturation, heart and respiration rate. Hypothesising an overlap between serotonergic pulse- and thermoregulation, recordings were done under physiological and elevated pad temperatures.Results:N-(2-hydroxybenzyl)-2,5-dimethoxy-4-cyanophenylethylamine (1.5 mg/kg, subcutaneous) significantly increased the frequency of heart beats accompanied by a slight elevation of neck-arterial blood flow. Increasing the animal-supporting heat-pad temperature from 37°C to 41°C enhanced the drug’s effect on blood flow while counteracting tachycardia. Additionally, N-(2-hydroxybenzyl)-2,5-dimethoxy-4-cyanophenylethylamine promoted bradypnea, which, like tachycardia, quickly reversed at the elevated pad temperature. The interrelatedness of N-(2-hydroxybenzyl)-2,5-dimethoxy-4-cyanophenylethylamine’s respiro-cardiovascular effects and thermoregulation was further corroborated by the drug selectively increasing the core body temperature at the elevated pad temperature. Arterial oxygen saturation was not affected by N-(2-hydroxybenzyl)-2,5-dimethoxy-4-cyanophenylethylamine at either temperature.Conclusions:Our findings imply that selective serotonin 2A receptor activation modulates systemic cardiovascular functioning in orchestration with thermoregulation and with immediate relevance to brain-imminent neck (most likely carotid) arteries. As carotid branching is a critical last hub to channel cardiovascular output to or away from the brain, our results might have implications for the brain haemodynamics associated with psychedelia.

Solving inverse bioheat problems of skin tumour identification by dynamic thermography

Dynamic thermography is a promising new non-invasive diagnostic technique for skin cancer, not just to identify the skin tumour in its early stage but also to evaluate some of tumour parameters showing the stage and invasiveness. This paper covers the solution of inverse bioheat problems of simultaneous identification of tumour diameter, thickness, blood perfusion rate and thermoregulation coefficient based on the surface temperature difference between healthy skin and lesion during the rewarming period of dynamic thermography. The problem has been treated using numerically generated measurement data for Clark II and Clark IV tumours by adding noise to mimic real measurement data. The solution is based on a more realistic 3D numerical model, composed of different layers including the thermoregulation response of the skin, tumour and surrounding tissue using a deterministic Levenberg–Marquardt optimisation algorithm that is robust and fast. The paper covers the analysis of the starting point of the solution, randomness and level of added noise, as well as the effect of numerical model error on the inverse solution. Tumour diameter and thermoregulation response can be estimated accurately regardless of noise and stage, while blood perfusion and tumour thickness can only be estimated accurately for low noise level or later tumour stage. The solution sensitivity to metabolic heat generation, thickness, blood perfusion rate and thermoregulation coefficient of skin and fat was low, while heat capacity and thermal conductivity of skin and tumour should be determined precisely in the numerical model to be able to evaluate all four tumour parameters as accurately as possible.

Influence of dynamic tissue properties on temperature elevation and lesions during HIFU scanning therapy: Numerical simulation**Project partially supported by the National Natural Science Foundation of China (Grant Nos. 11774088 and 11474090), the Natural Science Foundation of Hunan Province, China (Grant Nos. 2016JJ3090 and 2018JJ3557), and the Scientific Research Fund of Hunan Provincial Education Department, China (Grant Nos. 16B155 and 17B025).

When large tumors are treated, ablation of the entire volume of tumors requires multiple treatment spots formed by high intensity-focused ultrasound (HIFU) scanning therapy. The heating effect of HIFU on biological tissue is mainly reflected in temperature elevation and tissue lesions. Tissue property parameters vary with temperature and, in turn, the distribution of temperature as well as the heating effects change accordingly. In this study, an HIFU scanning therapy model considering dynamic tissue properties is provided. The acoustic fields and temperature fields are solved combining the Helmholtz wave equation with Pennes bio-heat transfer equation based on the finite element method (FEM) to investigate the effects of various tissue properties (i.e., the attenuation coefficient, acoustic velocity, thermal conductivity, specific heat capacity, density, and blood perfusion rate) on heating performance. Comparisons of the temperature distribution and thermal lesions under static and dynamic properties are made based on the data of tissue property parameters varying with temperature. The results show that the dynamic changes of thermal conductivity, specific heat capacity, and acoustic velocity may account for the decrease of temperature elevation in HIFU treatment, while the dynamic changes of attenuation coefficient, density, and blood perfusion rate aggravate the increase of temperature on treatment spots. Compared with other properties, the dynamic change of attenuation coefficient has a greater impact on tissue temperature elevation. During HIFU scanning therapy, the temperature elevation and tissue lesions of the first treatment spot are smaller than those of the subsequent treatment spots, but the temperature on the last treatment spot drops faster during the cooling period. The ellipsoidal tissue lesion is not symmetrical; specifically, the part facing toward the previous treatment spot tends to be larger. Under the condition of the same doses, the temperature elevation and the size of tissue lesions under dynamic properties present significant growth in comparison to static properties. Besides, the tissue lesion begins to form earlier with a more unsymmetrical shape and is connected to the tissue lesion around the previous treatment spot. As a result, lesions around all the treatment spots are connected with each other to form a closed lesion region. The findings in this study reveal the influence of dynamic tissue properties on temperature elevation and lesions during HIFU scanning therapy, providing useful support for the optimization of treatment programs to guarantee higher efficacy and safety.

Coupled thermo-electro-mechanical models for thermal ablation of biological tissues and heat relaxation time effects

Thermal ablation is a widely applied electrosurgical process in medical treatment of soft biological tissues. Numerical modeling and simulations play an important role in prediction of temperature distribution and damage volume during the treatment planning stage of associated therapies. In this contribution we report a coupled thermo-electro-mechanical model, accounting for heat relaxation time, for more accurate and precise prediction of the temperature distribution, tissue deformation and damage volume during the thermal ablation of biological tissues. Finite element solutions are obtained for most widely used percutaneous thermal ablative techniques, viz., radiofrequency ablation (RFA) and microwave ablation (MWA). Importantly, both tissue expansion and shrinkage have been considered for modeling the tissue deformation in the coupled model of high temperature thermal ablation. The coupled model takes into account the non-Fourier effects, considering both single-phase-lag (SPL) and dual-phase-lag (DPL) models of bio-heat transfer. The temperature-dependent electrical and thermal parameters, damage-dependent blood perfusion rate and phase change effect accounting for tissue vaporization have been accounted for obtaining more clinically relevant model. The proposed model predictions are found to be in good agreement against the temperature distribution and damage volume reported by previous experimental studies. The numerical simulation results revealed that the non-Fourier effects cause a decrease in the predicted temperature distribution, tissue deformation and damage volume during the high temperature thermal ablative procedures. Furthermore, the effects of different magnitudes of phase lags of the heat flux and temperature gradient on the predicted treatment outcomes of the considered thermal ablative modalities are also quantified and discussed in detail.

Physiological mechanisms of the low-intensity laser radiation impact on the highly qualified athletes’ special physical performance

In the context of strengthening the fight against doping and limiting the use of synthetic pharmaceuticals, the effective remedies to increase physical performance and accelerate the recovery of athletes are being sought. One of such remedies is exposure to low-level laser radiation (LLLR, LLLT). The study was aimed to investigate the physiological response of highly qualified female rowers’ functional systems to the LLLR irradiation course. To monitor the body of athletes, we used laser Doppler flowmetry (LDF), mathematical analysis of heart rate, neuroenergy mapping, as well as pedagogical testing using the Concept 2 simulator. After irradiation of the neck in the projection of the carotid arteries with pulsed infrared LLLR, the blood perfusion rate increased by 38% (р < 0.05) and cell oxygen utilization rate increased by 48% (р < 0.05). The decrease in the hemoglobin oxygen saturation by 16% (р < 0.05) was also observed. Due to LLLT, the activity of the autonomous regulation mechanism increased with an increase in the total power of the heart rate variability spectrum (TP) by 41% (р < 0.05), and in high-frequency power (HF) by 73% (р < 0.05). The influence of central mechanism decreased with a decrease in amplitude mode (AMo) by 71% (р < 0.05), and in stress-index (SI) by 175% (р < 0.05). Irradiation by LLLR promoted the efficiency of oxygen delivery to certain cerebral cortex areas with the increase of SPL. Аfter LLLT, the speed of 2000 meters distance "passing" by athletes also increased by 3.32% (p > 0.05). The discovered effects of LLLT allow one to expand the range of physiotherapeutic agents that enhance the special physical performance of athletes and accelerate recovery.

Analytical solutions of thermal damage in living tissues due to laser irradiation

ABSTRACT In this article, the analytical solutions of dual-phase-lag (DPL) bioheat equation with various boundary conditions have been constructed for curative therapy of cancerous cells. The volumetric thermal source components in the model of DPL bioheat transfer, such as the metabolic heat generation and the rate of blood perfusion, are considered. The analytical solutions in the Laplace domain are obtained. The thermal injuries to the tissue are assessed by the denatured protein range, using the formulation of Arrhenius. Numerical outcomes for temperatures are graphically introduced. A parametric analysis is devoted to the identification of an appropriate procedure for selecting important design variables in order to predict more accurate to reach effective heating in hyperthermia treatment.

Numerical analysis of power dissipation requirement in magnetic hyperthermia problems.

Control of the therapeutic temperature is essential in performing magnetic fluid hyperthermia. Thus, reliable predictions of the power dissipation are required to determine the correct dosage of magnetic particles to be injected into the cancerous tissue prior to treatment. To meet this requirement, the present study evaluates the power dissipation requirement for two magnetic hyperthermia problems reported in the literature. There is a significant challenge for solving the bio-heat transfer model for concentric bi-layered solid spheres. Consequently, the present study employs a hybrid technique based on Laplace transformation and a modified discretization scheme to solve the considered hyperthermia problems. Analytical solutions are provided to demonstrate the validity of the proposed approach. The unreliability of the results presented in the literature is then demonstrated using the proposed numerical scheme. In general, the results presented in this study show that the power dissipation required to maintain an effective temperature range in the tumor domain is related to the rate of temperature rise, the tumor size, the blood perfusion rate, and the tissue properties. In particular, the power dissipation should be increased for the cooling effect of blood perfusion or a smaller tumor volume.

Wide-area measurement-based supervision of the cerebral venous hemodynamic in a novel rat model

BackgroundTraumatic brain injury (TBI) includes primary and secondary injuries, while monitoring intracranial pressure (ICP) and cerebral blood flow (CBF) is conducive to improve the prognosis of patients. However, the function of cerebral venous in this process is still unclear. New methodAn acute epidural hematoma (AEDH) model was developed by placing a controllable micro balloon in the right epidural space of a rat. The laser speckle contrast imaging (LSCI) system was used to observe CBF in real time, while ICP was monitored simultaneously. And the stability of this model was examined by magnetic resonance imaging (MRI). ResultsThe blood perfusion rate (BPR) of venous was significantly negatively correlated with ICP. In the 100 μ L group, the ipsilateral cerebral venous and microcirculation blood flow significantly decreased. According to the gross observations and pathological results, ischemic brain injury was the most serious on this condition. Comparison with existing method(s)Modeling method is relatively simple, which effectively reduces the cost. The volume of the micro balloon is adjusted to simulate the volume of different size of hematomas. In addition, LSCI, as an advanced blood flow monitoring technology, has high sensitivity to detect subtle changes in CBF. ConclusionThis study successfully developed a stable and reproducible AEDH rat model. Based on this model, it is preliminarily demonstrated that local intracranial hypertension can cause cerebral venous return restriction, which is an indispensable factor leading to the aggravation of secondary brain injury.

Characteristics of renal cortical perfusion and its association with renal function among elderly patients with renal artery stenosis

Objective: To evaluate the characteristics of renal cortical blood perfusion assessed by contrast-enhanced ultrasound (CEUS) in elderly patients with renal artery stenosis (RAS) and its relationship with renal function. Methods: Ninety-three elderly patients diagnosed with RAS, who were admitted in Beijing Hospital during June 2017 and December 2018, were retrospectively enrolled. According to the degree of RAS, 186 renal arteries were divided into normal renal artery group (n=79), mild RAS group (30% to 49%, n=59), moderate RAS group (50% to 70%, n=33), and severe RAS group (70% to 99%, n=15). Renal cortical blood perfusion and renal glomerular filtration rate (GFR) were measured by CEUS and radionuclide renal dynamic imaging. According to the renal GFR, 186 kidneys were divided into normal renal function group (GFR≥35 ml/min, n=42) and mild renal insufficiency group (35 ml/min>GFR≥25 ml/min, n=51), moderate renal insufficiency group (25 ml/min>GFR≥15 ml/min, n=75) and severe renal insufficiency group (GFR<15 ml/min, n=18). The renal cortical blood perfusion time-intensity curve (TIC) and related parameters were analyzed, including the area under the curve (AUC), the slope of the ascending branch (A), the peak intensity (PI), the peak time (TTP) and the mean transit time (MTT), the kidneys of different RAS groups and patients with different renal function groups were analyzed. Pearson correlation analysis was used to evaluate the correlation between renal cortical blood perfusion parameters and renal GFR. Results: (1) Renal cortical blood perfusion and GFR: CEUS showed that parameter A of TIC was significantly reduced, while TTP was prolonged in the mild renal artery stenosis group compared with the normal renal artery group (both P<0.05), GFP was similar between the two groups. Cortical perfusion parameters, such as AUC, A, PI and GFR were significantly lower, while TTP and MTT were significantly prolonged in the moderate and severe renal artery stenosis group than in the normal and mild stenosis groups (all P<0.05). Compared with the moderate stenosis group, AUC, A, PI and GFR were significantly lower while TTP, MTT were significantly prolonged in the severe renal artery stenosis group (all P<0.05). (2) TIC showed that the renal perfusion parameters, AUC, PI and A were significantly lower, while TTP was significantly longer in the mild renal dysfunction group than in the normal renal function group (all P<0.001). The changes aggravated in proportion with renal dysfunction. (3) Correlation between perfusion parameters and GFR: Pearson correlation analysis showed that the AUC (r=0.774, P<0.05), A (r=0.815, P<0.05) and PI (r=0.772, P<0.05) were positively correlated with GFR; serum creatinine level (r=-0.841, P<0.05), renal function grading (r=-0.731, P<0.05), TTP (r=-0.803, P<0.05) and MTT (r=-0.741, P<0.05) were negative correlated with GFR. The degree of stenosis was negatively correlated with GFR (r=-0.427, P<0.05). Conclusion: Cortical perfusion parameters differ significantly among patients with various degree of RAS and renal dysfunction. The renal cortical blood perfusion parameters are correlated with renal GFR.

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.

Numerical modelling of skin tumour tissue with temperature-dependent properties for dynamic thermography

Dynamic thermography has been clinically proven to be a valuable diagnostic technique for skin tumour detection as well as for other medical applications, and shows many advantages over static thermography. Numerical modelling of heat transfer phenomena in biological tissue during dynamic thermography can aid the technique by improving process parameters or by estimating unknown tissue parameters based on measurement data. This paper presents a new non-linear numerical model of multilayer skin tissue containing a skin tumour together with thermoregulation response of the tissue during the cooling-rewarming process of dynamic thermography. The thermoregulation response is modelled by temperature-dependent blood perfusion rate and metabolic heat generation. The aim is to describe bioheat transfer more realistically. The model is based on the Pennes bioheat equation and solved numerically using a subdomain BEM approach treating the problem as axisymmetrical. The paper includes computational tests for Clark II and Clark IV tumours, comparing the models using constant and temperature-dependent properties which showed noticeable differences and highlighted the importance of using a local thermoregulation model. Results also show the advantage of using dynamic thermography for skin tumour screening and detection at an early stage. One of the contributions of this paper is a complete sensitivity analysis of 56 model parameters based on the gradient of the surface temperature difference between tumour and healthy skin. The analysis shows that size of the tumour, blood perfusion rate, thermoregulation coefficient of the tumour, body core temperature and density and specific heat of the skin layers in which the tumour is embedded are important for modelling the problem, and so have to be determined more accurately to reflect realistic skin response of the investigated tissue, while metabolic heat generation and its thermoregulation are not.

Numerical analysis of an enhanced cooling rate cryopreservation process in a biological tissue

Cryopreservation is the method of preservation of biological tissues for future references without causing significant damages to their physical and functional properties. This can be done by exposing them to very low cryogenic temperature that involves a greater heat removal rate. A two dimensional numerical model is developed to study the temperature distribution, cooling rate attained and movement of the freezing front during the cryopreservation process. The Pennes Bio-heat model is used for current study. The Finite Volume Method is employed for discretization of the governing differential equations while the Tri-Diagonal Matrix Algorithm is used to solve the discretized algebraic equations to find temperature distribution inside the domain. The Enthalpy-Porosity method is used to track the solid-liquid interfaces during the freezing process. The current model is first validated with the result of the existing literature. In the present work, freezing of tissue is done from one and two sides in two separate cases and the resulting temperature distribution inside the tissue and cooling rate in the two cases are compared. It is found that the freezing rate of tissue is enhanced about two times when it is freezed from two sides as compared to freezing from single side. Further, it is observed that a lower value of blood perfusion rate causes a lower value of the final temperature of the tissue after freezing. Thus, it can be concluded that the tissue with high blood perfusion rate is to be freezed in a lower cooling medium temperature. In the present condition, metabolic heat generation plays no significant role in the temperature distribution inside the healthy tissue.

Investigation of transient thermo-mechanical responses on the triple-layered skin tissue with temperature dependent blood perfusion rate

A large number of studies indicate that blood perfusion rate in biological tissue cannot be regarded as a constant in burn and thermal therapy analysis. This provides us a motivation to investigate the transient responses in the context of generalized bio-thermoelastic theories with temperature dependent blood perfusion rate. It is difficult to obtain the analytical solutions of nonlinear governing equations due to the consideration of variable blood perfusion rate. In present work, the finite element control equations of skin tissue based on generalized bio-thermoelasticity are derived and the nonlinear thermoelastic responses of the triple-layered skin tissue are obtained in time-domain directly. The influences of variable blood perfusion rate on the responses are discussed and illustrated graphically.

Inducing therapeutic hypothermia via selective brain cooling: a finite element modeling analysis.

Therapeutic hypothermia is a treatment method to reduce brain injuries after stroke, especially for cerebral ischemia. This study investigates in the temperature distribution of the head within selective brain cooling (SBC). Anatomically accurate geometries based on CT images of head and neck regions are used to develop the 3D geometry and physical model for the finite element modeling. Two cooling methods, the direct head surface cooling strategy and the combination cooling strategy of both head and neck, are evaluated to analyze the inducing hypothermia. The results show that for direct head surface cooling, the scalp and skull temperatures decrease significantly as the blood perfusion rate is constrained, but it is hard to affect the brain core temperature. To achieve a lower cerebral temperature, combination cooling strategy of both head and neck is an effective method in improving deep brain cooling. In normal condition, the cerebral temperature is reduced by about 0.12°C in 60min of hypothermia, while the temperature drop is approximately 0.98°C in ischemic condition. Graphical abstract In this study, the 3D geometry of the head and carotid artery model based on the computed tomography (CT) were derived separately and the corresponding investigations were conducted to validate the reliability of the model. Direct head surface cooling strategy and the combination cooling strategy of both the head and neck were numerically researched.

The use of Design of Experiments for steady-state and transient inverse melanoma detection problems

Melanoma is one of the most fatal skin cancers; for this reason, there is a need for the development of new safe, non-invasive and efficient diagnostic techniques. Dynamic thermography is showing to be a promising technique for the early detection of skin cancers. Therefore, this paper investigates two different inverse bioheat problems using steady-state and transient skin temperature measurements. Both problems are investigated numerically to estimate how accurate blood perfusion rate, metabolic heat generation, diameter and thickness of the tumour can be estimated simultaneously under exact and noisy measurement data, based on a complex numerical model describing multilayer tissue. The inverse problems have been tested using different melanoma size, Clark II and Clark IV. The Design of Experiments (DOE) technique has been used to solve and analyse the inverse problems. A substantial number of numerical model evaluations, totalling 2,306,486 simulations, had to be undertaken as part of the full factorial DOE. The results show that it is always possible to obtain tumour parameters using exact static or dynamic measurement data. However, for noisy temperature data, the use of a dynamic approach showed an advantage over the steady-state one, which failed because of the very small temperature differences between the healthy skin and the tumour. The dynamic thermography can retrieve blood perfusion rate, thickness and diameter of the tumour as well as the metabolic heat generation despite the low sensitivity for low and high levels of measurement error; however, to detect melanoma lesions at an early stage, the measurement and model errors should be kept as low as possible.