Ricardo Romero-Méndez

Analytical solution of the Pennes equation for burn-depth determination from infrared thermographs

A serious problem in emergency medicine is the correct evaluation of skin burn depth to make the appropriate choice of treatment. In clinical practice, there is no difficulty in classifying first- and third-degree burns correctly. However, differentiation between the IIa (superficial dermal) and IIb (deep dermal) wounds is problematic even for experienced practitioners. In this work, the use of surface skin temperature for the determination of the depth of second-degree burns is explored. An analytical solution of the 3D Pennes steady-state equation is obtained assuming that the ratio between burn depth and the burn size is small. The inverse problem is posed in a search space consisting of geometrical parameters associated with the burned region. This space is searched to minimize the error between the analytical and experimental skin surface temperatures. The technique is greatly improved by using local one-dimensionality to provide the shape of the burned region. The feasibility of using this technique and thermography to determine skin burn depth is discussed.

Procedure to Estimate Thermophysical and Geometrical Parameters of Embedded Cancerous Lesions Using Thermography

Based on the fact that malignant cancerous lesions (neoplasms) develop high metabolism and use more blood supply than normal tissue, infrared thermography (IR) has become a reliable clinical technique used to indicate noninvasively the presence of cancerous diseases, e.g., skin and breast cancer. However, to diagnose cancerous diseases by IR, the technique requires procedures that explore the relationship between the neoplasm characteristics (size, blood perfusion rate and heat generated) and the resulting temperature distribution on the skin surface. In this research work the dual reciprocity boundary element method (DRBEM) has been coupled with the simulated annealing technique (SA) in a new inverse procedure, which coupled to the IR technique, is capable of estimating simultaneously geometrical and thermophysical parameters of the neoplasm. The method is of an evolutionary type, requiring random initial values for the unknown parameters and no calculations of sensitivities or search directions. In addition, the DRBEM does not require any re-meshing at each proposed solution to solve the bioheat model. The inverse procedure has been tested considering input data for simulated neoplasms of different sizes and positions in relation to the skin surface. The successful estimation of unknown neoplasm parameters validates the idea of using the SA technique and the DRBEM in the estimation of parameters. Other estimation techniques, based on genetic algorithms or sensitivity coefficients, have not been capable of obtaining a solution because the skin surface temperature difference is very small.

Electrical-thermal performance of a cooled RF applicator for hepatic ablation with additional distant infusion of hypertonic saline: in vivo study and preliminary computer modeling.

Purpose: The Cool-tip electrode is one of the most widely employed applicators in radiofrequency (RF) hepatic ablation. Previous research demonstrated that it is possible to enlarge coagulation volume when the single cooled electrode is associated with distant infusion of saline (hybrid applicator). The aim of this study was to compare the electrical-thermal behaviour of the Cool-tip electrode with that of the hybrid applicator. Materials and methods: Forty-two RF ablations were performed on a total of 10 pigs: 22 with the Cool-tip electrode and 20 with the hybrid applicator (low infused saline volumetric flow rate of 6 mL/h at 2 mm distance). We compared both electrical performance (delivered power and number of roll-offs, i.e. sudden rises in impedance that interrupt the power delivery) and coagulation zone characteristics. In addition, we built a one-dimensional model to provide a basic physical explanation of the difference in performance between the different applicators. Results: The experimental results showed that the number of roll-offs with the Cool-tip electrode was higher (24.3 ± 3.1 versus 6.7 ± 7.0). The hybrid applicator created larger coagulation volumes (19.7 ± 9.5 cm3 versus 9.5 ± 5.8 cm3) with larger transverse diameters (2.5 ± 0.6 versus 1.9 ± 0.5 cm). The one-dimensional model confirmed the delay in the incidence of the first roll-off, but not the heterogeneity of the hybrid applicators electrical performance in the experiments. Conclusions: The hybrid applicator produces fewer roll-off episodes than the Cool-tip electrode and creates larger coagulation volumes with larger transverse diameters.

The Laminar Horseshoe Vortex Upstream of a Short-Cylinder Confined in a Channel Formed by a Pair of Parallel Plates

A flow visualization experiment was performed in order to characterize the laminar horseshoe vortex system that appears upstream of the junction of a short cylinder and a pair of flat parallel plates. The experiments were performed in a water tunnel and the technique used for flow visualization was laser illumination of seeded particles whose traces were captured using long exposure photography. Geometrical and flow parameters, such as Reynolds number and height-to-diameter ratio of the cylinders, are varied during the experiments and the flow regimes are analyzed as a function of these parameters. The behavior of vortex systems is reported. For low Reynolds number cases, the vortices stay in a fixed position, as the Reynolds number is increased the number of vortices grows and for larger Reynolds numbers the vortex system becomes oscillatory and for further increases it becomes periodic. As for the dimensionless height of the cylinders, the vortex system is weak for short cylinders and increases its strength and number of vortices as the cylinder height-to-diameter ratio is increased. For further increases in height the vortex system do not change, which shows that the flow becomes independent of the height-to-diameter ratio for sufficiently tall cylinders. Information of the frequency of appearance of periodic vortices is also included.

Laser-assisted cryosurgery of prostate: numerical study

A new methodology for preventing freezing damage beyond pre-specified boundaries during prostate cryosurgery is proposed herein. It consists of emitting controlled laser irradiation from the urethra, across the wall and into the prostate while conventional cryoprobes freeze the unwanted prostate tissue. The purpose of this methodology is to protect the urethral wall better and confine the desired cryoinjured region more accurately than the current cryosurgery approach. We also explore the potential use of light-absorbing dyes to further enhance the laser light absorption and corresponding heat generation to increase the thickness of the protected region. A finite difference heat diffusion model in polar coordinates with temperature-dependent thermophysical properties simulates the prostate freezing while laser irradiation across the urethral wall is emitted. This approach maintains the temperature of the urethral wall and the adjacent tissue above a pre-specified threshold temperature of -45 degrees C, independent of application time. Temperature contours resulting from prostate cryoablation with (a) conventional constant temperature heating; (b) laser irradiation heating; and (c) laser irradiation heating with pre-injected light-absorbing dye layers indicate that the thickness of the protected region increases in this order, and that the latter two methodologies may be more effective in limiting cryoinjury to a predefined region compared to constant temperature heating. An analysis of laser power requirements and sensibility of laser-assisted cryosurgery (LAC) of prostate is also presented. It is shown that tissue temperature may vary as much as +/-20 degrees C with variations of +/-10% in laser power relative to the nominal power required to maintain the tissue at 37 degrees C. This demonstrates the sensitivity to laser power and the need of an accurate laser power control algorithm.

Effect of Cell Geometry on the Freezing and Melting Processes inside a Thermal Energy Storage Cell

This paper presents an analysis of the charge and discharge processes in a latent thermal energy storage cell. An individual cell is analyzed to study how its behavior affects the performance of a thermal energy storage system. The analysis considers the exchange of thermal energy between a thermal energy storage cell and a source or sink of thermal energy. Two cases are considered, (i) a process in which the phase change material melts and freezes when a constant and uniform temperature is imposed at the lower surface of the cell, and (ii) a process in which the phase change material melts and freezes when a fluid with a constant inlet temperature flows under the cell. The effect of the aspect ratio of the energy storage cell is analyzed in detail as a possible method to enhance heat transfer and improve performance of the thermal energy storage system. The results include, for different aspect ratios of the storage cell, the evolution of the solid-liquid interface, the rates of melting and solidification, the rate of energy storage and the total amount of energy storage.

Experimental Flow Structure Analysis in Plates With 90° Chevron Geometry by a Particle Visualization Technique

The flow structures in the cavities of parallel cross-corrugated surfaces, also called chevron geometry, are investigated in this work using an experimental visualization method. An angle of 45° between the corrugations and the main flow direction has been considered. Reviews show that a considerable amount of investigations, mainly experimental, of heat transfer and pressure drop for cross-corrugated plates has been performed, whereas for the flow field in the cavities has only been investigated numerically. The flow visualization experiments are performed inside a water tunnel using a wide range of the hydraulic diameter-based Reynolds number.© 2007 ASME

Confinement of Freezing Front by Laser Irradiation During Cryosurgery

A new methodology to control the freezing front propagation during cryosurgical procedures is studied through the use of numerical techniques. Laser irradiation of a target tissue is explored as a new methodology for localizing heat generation and, thus, confining more accurately the desired cryoinjury region and to protect a thicker superficial layer of tissue. In addition to the irradiation of laser energy, the use of dyes is proposed as a means of localizing heat absorption and increasing the thickness of the protected region. A 2D finite volume numerical code based on the enthalpy method was developed to model the freezing process during cryoprobe cooling of a volume of tissue, while heating was applied to the external boundary protecting the superficial layer of tissue. Laser irradiation was modeled with Beer’s Law, and the energy absorption, which is proportional to the intensity, was taken as a source term in the energy equation. The thermophysical properties of the tissue are modeled as temperature dependent properties of water. Temperature contours resulting from a) constant temperature heating b) and regulated laser irradiation heating of tissue indicate that the latter methodology may be more effective in limiting cryoinjury to a predefined region. Additionally, if dyes are used, the protected area increases in thickness. The most dramatic differences between the two methodologies occur when the cryoprobe is placed near the surface, the effective attenuation coefficient of the material is low, and dyes are injected into the tissue to promote localized absorption of laser irradiated energy. NOMENCLATURE Bi Biot number, Bi=hyo/ks C specific heat (J kg -1

Comparison of enthalpy method and water fraction method to mathematically model water vaporization during RF ablation

This work received financial support from the Spanish “Plan Nacional de I+D+I del Ministerio de Ciencia e Innovacion” Grant No. TEC2011-27133-C02-01.

Fluid Forces on a Flexible Circular Cylinder in Vortex-Induced Vibrations

In this work fluid forces acting on a flexible circular cylinder in Vortex-Induced Vibrations (VIV) were studied. An experimental campaing was conducted at low mass-damping ratio (\(\mathrm {m_{cil}^{*}\zeta }\) = 0.126) covering the entire lock-in region. The dynamic response of the cylinder was computed using the Particle Tracking Velocimetry technique on the cylinder free end tip. Drag and lift coefficients (\(C_{D}\) and \(C_{L}\)) were determined using the experimental data from the cylinder response in a spring-mass-damping model. Results show that \(C_{L}\) is one order of magnitude greater than \(C_{D}\). Strong cylinder oscillations are associated with a flow pattern showing two vortex center lines corresponding mainly at the upper end of the initial region.