Ramjee Repaka

Suitability of frequency modulated thermal wave imaging for skin cancer detection—A theoretical prediction

A theoretical study on the quantification of surface thermal response of cancerous human skin using the frequency modulated thermal wave imaging (FMTWI) technique has been presented in this article. For the first time, the use of the FMTWI technique for the detection and the differentiation of skin cancer has been demonstrated in this article. A three dimensional multilayered skin has been considered with the counter-current blood vessels in individual skin layers along with different stages of cancerous lesions based on geometrical, thermal and physical parameters available in the literature. Transient surface thermal responses of melanoma during FMTWI of skin cancer have been obtained by integrating the heat transfer model for biological tissue along with the flow model for blood vessels. It has been observed from the numerical results that, flow of blood in the subsurface region leads to a substantial alteration on the surface thermal response of the human skin. The alteration due to blood flow further causes a reduction in the performance of the thermal imaging technique during the thermal evaluation of earliest melanoma stages (small volume) compared to relatively large volume. Based on theoretical study, it has been predicted that the method is suitable for detection and differentiation of melanoma with comparatively large volume than the earliest development stages (small volume). The study has also performed phase based image analysis of the raw thermograms to resolve the different stages of melanoma volume. The phase images have been found to be clearly individuate the different development stages of melanoma compared to raw thermograms.

Temperature-controlled radiofrequency ablation of different tissues using two-compartment models.

Abstract Purpose: This study aims to analyse the efficacy of temperature-controlled radiofrequency ablation (RFA) in different tissues. Materials and methods: A three-dimensional, 12 cm cubical model representing the healthy tissue has been studied in which spherical tumour of 2.5 cm has been embedded. Different body sites considered in the study are liver, kidney, lung and breast. The thermo-electric analysis has been performed to estimate the temperature distribution and ablation volume. A programmable temperature-controlled RFA has been employed by incorporating the closed-loop feedback PID controller. The model fidelity and integrity have been evaluated by comparing the numerical results with the experimental in vitro results obtained during RFA of polyacrylamide tissue-mimicking phantom gel. Results: The results revealed that significant variations persist among the input voltage requirements and the temperature distributions within different tissues of interest. The highest ablation volume has been produced in hypovascular lungs whereas least ablation volume has been produced in kidney being a highly perfused tissue. The variation in optimal treatment time for complete necrosis of tumour along with quantification of damage to the surrounding healthy tissue has also been reported. Conclusions: The results show that the surrounding tissue environment significantly affects the ablation volume produced during RFA. The optimal treatment time for complete tumour ablation can play a critical role in minimising the damage to the surrounding healthy tissue and ensuring safe and risk free application of RFA. The obtained results emphasise the need for developing organ-specific clinical protocols and systems during RFA of tumour.

Thermographic evaluation of early melanoma within the vascularized skin using combined non-Newtonian blood flow and bioheat models

A theoretical study on vascularized skin model to predict the thermal evaluation criteria of early melanoma using the dynamic thermal imaging technique is presented in this article. Thermographic evaluation of melanoma has been carried out during the thermal recovery of skin from undercooled condition. During thermal recovery, the skin has been exposed to natural convection, radiation, and evaporation. The thermal responses of melanoma have been evaluated by integrating the bioheat model for multi-layered skin with the momentum as well as energy conservation equations for blood flow. Differential changes in the surface thermal response of various melanoma stages except that of the early stage have been determined. It has been predicted that the thermal response due to subsurface blood flow overpowers the response of early melanoma. Hence, the study suggests that the quantification of early melanoma diagnosis using thermography has not reached a matured stage yet. Therefore, the study presents a systematic analysis of various intermediate melanoma stages to determine the thermal evaluation criteria of early melanoma. The comprehensive modeling effort made in this work supports the prediction of the disease outcome and relates the thermal response with the variation in patho-physiological, thermal and geometrical parameters.

THERMAL ANALYSIS OF THE INCREASING SUBCUTANEOUS FAT THICKNESS WITHIN THE HUMAN SKIN—A NUMERICAL STUDY

This article reports a numerical study on the thermal response of skin with increasing fat thickness. The study considers the Pennes bioheat model for skin to simulate the thermal recovery phase after the removal of undercooled condition. Based on the surface thermal maps of a three-dimensional skin, the change in fat thickness within the skin is characterized. Sensitivity study reveals that the major variation in the thermal pattern at the skin surface is mainly due to the change in fat thickness. Possible random noise associated with background disturbances is also considered to determine the associated signal-to-noise ratio.

Thermal analysis of induced damage to the healthy cell during RFA of breast tumor.

Effective pre-clinical computational modeling strategies have been demonstrated in this article to enable risk free clinical application of radiofrequency ablation (RFA) of breast tumor. The present study (a) determines various optimal regulating parameters required for RFA of tumor and (b) introduces an essential clinical monitoring scheme to minimize the extent of damage to the healthy cell during RFA of tumor. The therapeutic capabilities offered by RFA of breast tumor, viz., the rise in local temperature and induced thermal damage have been predicted by integrating the bioheat transfer model, the electric field distribution model and the thermal damage model. The mathematical model has been validated with the experimental results available in the literature. The results revealed that, the effective damage of tumor volume sparing healthy tissue essentially depends on the voltage, the exposure time, the local heat distribution, the tumor stage and the electrode geometric configuration. It has been confirmed that, the assessment of damage front can accurately determine the extent of damage as compared to the thermal front. The study further evaluates the damaged healthy and tumor volumes due to RFA of different stages of breast cancer. The assessment of cell survival and damage fractions discloses the propensity of reappearance/healing of tumor cells after treatment.

Inverse analysis of conductive-convective wet triangular fin for predicting thermal properties and fin dimensions

The present work deals with the application of Homotopy Analysis Method (HAM) in conjunction with Nelder–Mead simplex search method (SSM) to study a triangular wet fin. At first, analytical expression has been derived using HAM to calculate the local temperature field. Then using SSM, the important parameters, namely, thermal conductivity of the material, surface heat transfer coefficient and dimensions of the fin, have been estimated separately for attaining the prescribed temperature field. The transport phenomena involve simultaneous heat and mass transfers. It is found from the present study that many feasible solutions can satisfy a given thermal condition, which will offer the flexibility in selecting the fin material, adjusting the thermal conditions and regulating the fin dimensions. Further, it is determined that the allowable error in the temperature measurement should be limited within ± 15% and a good reconstruction of the temperature field is possible using the HAM–SSM combination.

Inverse Heat Transfer Analysis of Porous Extended Surface Using Simplex Search Method

This work deals with the application of the Nelder-Mead simplex search method (SSM) to study a porous extended surface. At first, analytical expression for calculating the local temperature field has been derived using an implicit Runge-Kutta method. The heat transfer phenomenon is assumed to be governed by conductive, naturally convective and radiative heat transfer, whereas the diffusion of mass through the porous media is also taken into account. Then, using the SSM, critical parameters such as porosity, permeability, and thermal conductivities of the extended surface have been predicted for satisfying a prescribed temperature field. It is found that many alternative solutions can meet a given thermal requirement, which is proposed to offer the flexibility in selecting the material and regulating the thermal conditions. It is observed that the allowable error in the temperature measurement should be limited within 5%. It is also found that even with few temperature measurement points, very good reconstruction of the thermal field is possible using the SSM.Copyright

Numerical study to establish relationship between coagulation volume and target tip temperature during temperature-controlled radiofrequency ablation

ABSTRACT The present study aims at proposing a relationship between the coagulation volume and the target tip temperature in different tissues (viz., liver, lung, kidney, and breast) during temperature-controlled radiofrequency ablation (RFA). A 20-min RFA has been modelled using commercially available monopolar multi-tine electrode subjected to different target tip temperatures that varied from 70°C to 100°C with an increment of 10°C. A closed-loop feedback proportional-integral-derivative (PID) controller has been employed within the finite element model to perform temperature-controlled RFA. The coagulation necrosis has been attained by solving the coupled electric field distribution, the Pennes bioheat and the first-order Arrhenius rate equations within the three-dimensional finite element model of different tissues. The computational study considers temperature-dependent electrical and thermal conductivities along with the non-linear piecewise model of blood perfusion. The comparison between coagulation volume obtained from the numerical and in vitro experimental studies has been done to evaluate the aptness of the numerical models. In the present study, a total of 20 numerical simulations have been performed along with 12 experiments on tissue-mimicking phantom gel using RFA device. The study revealed a strong dependence of the coagulation volume on the pre-set target tip temperature and ablation time during RFA application. Further, the effect of target tip temperature on the applied input voltage has been studied in different tissues. Based on the results attained from the numerical study, statistical correlations between the coagulation volume and treatment time have been developed at different target tip temperatures for each tissue.

An in Vitro Phantom Study to Quantify the Efficacy of Multi-tine Electrode in Attaining Large Size Coagulation Volume During RFA

The present study aims at evaluating the efficacy of commercially available RITA’s StarBurst® XL multi-tine electrode in attaining large size coagulation volumes (≥3 cm in diameter) during radiofrequency ablation (RFA) application. In vitro studies have been conducted on the cylindrical shaped polyacrylamide based tissue-mimicking phantom gels utilizing different active lengths of the multi-tine electrode, viz., 2 cm, 3 cm, 4 cm and 5 cm. A temperature-controlled RFA has been performed at a target tip temperature of 95 °C for 5 min. The variations in the power supply, the target tip temperature and the size of coagulation volume have been reported for different active lengths of the multi-tine electrode. The study revealed that the increase in active length of the multi-tine electrode results in more energy deposition and consequent rise in the coagulation volume during RFA procedure. Further, a simplified novel statistical correlation between the coagulation volume and active length of the multi-tine electrode has been proposed.

Effect of Viscous Dissipation on Forced Convection Heat Transfer in Parallel Plate Channels With Asymmetric Boundary Conditions

Effect of viscous dissipation on steady two-dimensional laminar forced convection in hydrodynamically developed and thermally developing flow between asymmetrically heated parallel plates (the plates have been kept at unequal temperatures) has been studied. The asymmetric heating is characterized by an asymmetry parameter, A, defined as the ratio of wall temperatures in excess of the fluid inlet temperature. Viscous dissipation is characterized by the Brinkman number, Br. Br 0 when the fluid is being cooled. Heating and cooling have been, defined on the basis of average the wall temperatures.When the walls are subjected to equal wall temperature (i.e., A = 1), it may be recalled that the limiting value for the Nusselt number is 17.5 when viscous dissipation is included (Br ≠ 0), and is independent of the Brinkman number, Br. Similarly, when viscous dissipation is not included, for the case of unequal wall temperatures, (i.e., A ≠ 1), the Nusselt number in the conduction limit is 4, and is independent of the value of A, not equal to one. In the present investigation, it has been shown that the local Nusselt number values in the thermally developing region as well as in the limiting condition, do vary continuously with Brinkman number when the plates are kept at unequal temperatures. The axial location where the Nusselt number displays an unbounded swing depends on the Brinkman number for a given A, and vice versa. The axial position where the Nusselt number displays an unbounded swing depends on the combination of Br and A values and differs from the position for A = 1, Br 0, Br = 0.Copyright