Effect of variable heat transfer coefficient on tissue temperature next to a large vessel during radiofrequency tumor ablation

<p>Abstract</p> <p>Background</p> <p>One of the current shortcomings of radiofrequency (RF) tumor ablation is its limited performance in regions close to large blood vessels, resulting in high recurrence rates at these locations. Computer models have been used to determine tissue temperatures during tumor ablation procedures. To simulate large vessels, either constant wall temperature or constant convective heat transfer coefficient (<it>h</it>) have been assumed at the vessel surface to simulate convection. However, the actual distribution of the temperature on the vessel wall is non-uniform and time-varying, and this feature makes the convective coefficient variable.</p> <p>Methods</p> <p>This paper presents a realistic time-varying model in which <it>h </it>is a function of the temperature distribution at the vessel wall. The finite-element method (FEM) was employed in order to model RF hepatic ablation. Two geometrical configurations were investigated. The RF electrode was placed at distances of 1 and 5 mm from a large vessel (10 mm diameter).</p> <p>Results</p> <p>When the ablation procedure takes longer than 1–2 min, the attained coagulation zone obtained with both time-varying <it>h </it>and constant <it>h </it>does not differ significantly. However, for short duration ablation (5–10 s) and when the electrode is 1 mm away from the vessel, the use of constant <it>h </it>can lead to errors as high as 20% in the estimation of the coagulation zone.</p> <p>Conclusion</p> <p>For tumor ablation procedures typically lasting at least 5 min, this study shows that modeling the heat sink effect of large vessels by applying constant <it>h </it>as a boundary condition will yield precise results while reducing computational complexity. However, for other thermal therapies with shorter treatment using a time-varying <it>h </it>may be necessary.</p

Computer-aided system for diagnosis of Chagas’ disease based on scalograms and self-organizing neural networks

Introdução: A Doença de Chagas é uma endemia rural, prevalente em grande parte da América Central e América do Sul e, aproximadamente, metade dos pacientes contaminados com o parasita Trypanosoma cruzi não apresentam sinais clínicos, eletrocardiográficos e radiológicos de envolvimento cardíaco. Este trabalho, entretanto, propõe uma técnica de auxílio ao diagnóstico da Doença de Chagas baseada em sinais de eletrocardiografia, que extrai informações relevantes desses sinais. Métodos: Duas abordagens são estudadas e implementadas. Ambas utilizam sinais de variabilidade da frequência cardíaca (VFC) e classificação por meio de rede neural, mais especificamente, o mapa auto-organizável de Kohonen. A VFC, que reflete a modulação neural autonômica simpática e parassimpática do coração, é avaliada com base em séries contínuas de intervalos RR do ECG convencional registradas durante 5 minutos. Na primeira abordagem, indicadores estatístico-temporais obtidos diretamente dos sinais de VFC são utilizados como entrada da rede neural para treinamento e teste do método de classificação. Na segunda proposta, são utilizados escalogramas wavelet com função de base DoG (derivative of Gaussian) para avaliação dos sinais de VFC. Indicadores obtidos dos escalogramas são utilizados como entrada da rede neural no treinamento e no teste do algoritmo. Os mapas topológicos de Kohonen são utilizados para comparar a capacidade dos indicadores calculados dos sinais de VFC em discriminar pacientes chagásicos cardiopatas, chagásicos indeterminados e indivíduos normais. Os indicadores temporais convencionais e os indicadores escalográficos são comparados. Resultados: Os resultados mostram que os indicadores escalográficos têm poder discriminatório estatisticamente superior aos indicadores temporais convencionais. Em particular, a potência média da densidade de potência do escalograma na banda de altas frequências mostrou ser estatisticamente o indicador de maior poder discriminatório (p < 0,05 para os 3 casos). Conclusão: A metodologia proposta mostrou-se capaz de distinguir entre indivíduos normais, chagásicos cardiopatas e chagásicos indeterminados. Os índices escalográficos propostos mostraram maior capacidade classificatória que os índices temporais tradicionais.Introduction: Chagas’ disease is an endemic rural disease prevalent in much of Central America and South America, and approximately half of the patients infected with the parasite Trypanosoma cruzi show no clinical, electrocardiographic and radiological cardiac involvement. This paper, however, proposes a technique for the diagnosis of Chagas’ disease based on ECG signals, which extracts relevant information from these signals. Methods: Two approaches are studied and implemented. Both approaches use heart rate variability (HRV) signals, and classification by a neural network, more specifically, the Kohonen self-organizing map. The HRV, which reflects sympathetic and parasympathetic autonomic neural modulation of the heart, is evaluated based on continuous series of RR intervals, calculated from 5-minute records of conventional ECG. In the first approach, statistical/temporal indexes obtained directly from the HRV signals are used as neural network inputs for training and testing of the classification method. In the second approach, derivative of Gaussian (DoG) wavelet scalograms are used to evaluate the HRV signals. Scalographic indexes are used as neural network inputs for training and testing of the algorithm. Kohonen topological maps are used to compare the ability of these HRV indicators of discriminating between patients with Chagas heart disease, Chagas indeterminate heart disease, and normal subjects. Conventional temporal indicators and indicators obtained from DoG scalograms are compared. Results: Results of the application of the proposed methods to HRV signal databases, and performance comparisons, are presented. The results show that scalographic indicators have superior discriminatory power than conventional time-domain indicators. Based on an analysis of statistical significance, we show that the average power of the high-frequency band of the scalogram power spectral density is the indicator with greatest discriminatory power (p < 0,05 for all 3 cases). Conclusion: The proposed method has the ability to discriminate between normal subjects, subjects with Chagas cardiomyopathy, and subjects with the indeterminate form of Chagas’ disease. It was observed that scalographic neural networks present greater discrimination ability than temporal neural networks

Modeling of the human tibia bone using Bond Graph

Introdução: Procedimentos cirúrgicos ortopédicos como a osteotomia, em que se realiza o corte da tíbia, são muito comuns e devem ser muito bem executados para que sejam obtidos bons resultados. Nesse cenário, o estudo de como o osso reage ao processo de corte é um tópico relevante de estudos. O objetivo deste trabalho é apresentar um modelo matemático do processo de corte na tíbia humana por uma serra automática, usando o método de Bond Graph. Métodos: Com base em um trabalho anterior, foi desenvolvido um modelo para a força de reação ao corte da serra. Além disso, foi desenvolvido um modelo embasado no método Bond Graph para se determinar a resposta das diversas partes do osso à ação da serra. Foram também realizadas análises no domínio da frequência para se analisar a estabilidade do sistema. Resultados: Foram obtidos e apresentados os resultados das simulações descritas. Os resultados mostraram boa concordância com o comportamento esperado para a força de reação à serra e para a resposta do material ósseo ao corte. Além disso, as análises no domínio da frequência mostraram que o método de modelagem proposto tem características promissoras com relação a estabilidade do sistema. Conclusão: Os resultados sugerem que o método tem bom potencial para ser usado, no futuro próximo, para análises do processo de perfuração antes de procedimentos cirúrgicos. Entretanto, estudos adicionais sobre a estabilidade e sobre o projeto adequado de um controlador de velocidade são ainda necessários.Introduction: Orthopedic surgical procedures such as osteotomy, in which cutting of the tibia bone is performed, are very common and should be very well performed in order to yield good results. Under this scenario, the study on how the bone reacts to the cutting process is a relevant topic for studies. The goal of this work is to present a mathematical model of the cutting process in the human tibia bone using the Bond Graph method. Methods: Based on a previous work, a model for the reaction force to the cutting action of the saw has been developed. Moreover, a bond graph based model for determining the bone response to the cutting action of the saw has also been developed. Frequency domain analyses were performed for evaluating the stability of the system. Results: The results of the simulations described were obtained and presented. The results were in good agreement with the expected behavior for the reaction force to the saw, and with respect to the response of the bone material to the cutting process. Moreover, the frequency domain analyses showed that the proposed modelling method has promising characteristics regarding system stability. Conclusion: The results suggest that the method has good potential for use, in the near future, for analyses of the cutting process before the surgical procedures. However, additional studies on stability, as well as a proper project of a velocity controller, are still necessary

Characterization of the cicatrization process in diabetic foot ulcers based on the production of reactive oxygen species

The present study aims at evaluating the correlation between the free radical formation and the healing action of lower limbs’ ulcers in a randomized controlled trial with the use of an adhesive derived from natural latex associated with a light-emitting diode (LED) circuit. The sample consists of 15 participants with lower limb lesions divided into three groups: group 1 case (5 participants) received the proposed dressing system adhesive of the natural latex associated with the LED circuit; group 2 control (5 participants) received the dressings at home performed by nurses according to and established by the clinic of wounds (treated with calcium alginate or silver foam); and group 3 (5 participants) also received the dressing in their homes with the use of the dressing adhesive derived from the natural latex associated with the LED circuit. The collected data were analyzed qualitatively and quantitatively by electron paramagnetic resonance for determination of free radical formation. Kruskal-Wallis statistical test was used to evaluate the effect of treatment on the lower limb’s ulcer cicatrization process and its correlation with free radical. The results obtained corroborated the hypothesis about the reduction of the quantity of these molecules in the end of treatment related to the healing wound

Control system for continuous positive airway pressure

Introduction: Continuous Positive Airway Pressure (CPAP) is a mode of non-invasive mechanical ventilation commonly used in neonatology. The incorporation of new therapeutic and technological advances may impact the survival of very low birth weight preterm infants. However, one of the difficulties faced is the high cost of this device and its numerous add-on functions, such as Apnea Hypopnea Index (AHI), flow limitation, among others. Thus, in this study, we aim to address the design and construction of a CPAP device prototype to be used in a Neonatal Intensive Care Unit (NICU). Methods: In order to design the experimental CPAP device with sensory instrumentation for providing data to a micro-controlled system, electro-pneumatic circuits and signal conditioning boards of sensors have been fitted to achieve optimized CPAP function with low energy consumption. While running this setup, a metrological study was carried out to evaluate the sensors’ performance. The methodology employed for the study was the IDOV (Identify, Design, Optimize, and Validate) method, a variant of six sigma, to minimize the failure rates. It is expected that it works under valve activation to maintain positive pressure in the airways of the patient (neonate). Results: The whole system performs satisfactorily (low noise level) for each assessed module. Additionally, it is emphasized that software development for application control has resulted in a significant improvement of hardware functions. Conclusion: In this work, a system that performs the CPAP function was obtained; the research has shown that, by adopting a specific purpose, it may create a better understanding of Assistive Technology

A system for treatment of diabetic foot ulcers using led irradiation and natural latex

Introduction: We developed and tested a new system for inducing the healing of diabetic foot ulcers. The system relies on the regenerative properties of its two components: an insole with a sheet of natural latex and a device that contains a matrix of light emitting diodes with wavelength of 635 nm. Methods: The electronic and latex based devices were developed, and a four weeks test was performed in one control group (CG) of five ulcers and one experimental group (EG) of eight ulcers. The CG was treated with a standard approach, based on a silver-releasing foam dressing, and the EG was treated with the system under test. For each ulcer, an index for quantifying the percentage ulcer recovery, named CRU(%), has been calculated; a CRU(%) = 0% means no healing, and a CRU(%) = 100% means total healing. Results: There were statistically significant increases of CRU(%) of 51.8% (p = 0.022), for the CG, and of 78.4% (p < 0.001), for the EG. The increase in the EG was higher than the increase in the CG, and the difference was statistically significant (p < 0.001). The results showed that the proposed method had, for these particular sets of ulcers, faster healing rates, than for the standard method. Conclusion: The results hint that the proposed method seems promising as a future treatment method. However, the technique must undergo further testing before it can be considered for extensive clinical applications. Key words: Diabetes; Tissue formation; Inducer system; Diabetic foot; Latex; LED