ABSTRACT
Abstract Introduction Therapeutic ultrasound (TUS) is a widespread modality in physiotherapy, and the water bag technique is a coupling method employed in the presence of anatomical irregularities in the treatment area. The aim of the present study is to evaluate the acoustic attenuation of the water bag and its effectiveness as a TUS coupling agent. Methods The rated output powers (ROPs) of the TUS equipment were evaluated based on IEC 61689. Then, a radiation force balance was used to measure ROP with and without a water bag (latex and nitrile gloves filled with deionized water) between a TUS transducer and the cone-shaped target of the balance. Each experiment was performed five times for each nominal power (0.5, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, and 7.0 W) and in the following configurations: without the water bag (A), with nitrile gloves and with (B) and without (C) a height controller, and latex gloves with (D) and without (E) height controller. ROPs obtained in different media were compared. Results The highest relative error of ROP was 16.72% for 0.5 W. Although the power values of the equipment were within the range recommended by IEC, there was a significant difference between the ROP values measured with A and with B, C and D. Conclusion As intensity differences below 0.5 W/cm2 are considered clinically not relevant, conditions A, B, C, D, or E can be used interchangeably.
ABSTRACT
O presente trabalho descreve o projeto e construção de um calorímetro diferencial com a finalidade de avaliar o aquecimento gerado por feixes ultrassônicos em níveis terapêuticos. O calorímetro consiste em duas câmaras cilíndricas de alumínio idênticas (de medição e de referência), preenchidas com um material mimetizador de tecido biológico (phantom). Cada câmara possui seis termopares tipo E (diâmetro 0,24 mm), posicionados ao longo do eixo central de propagação da onda, entre as profundidades 10-60 mm, distantes 10 mm entre si. Foi levantada a curva de potência e estimado o valor da área de radiação efetiva (ERA) dos dois transdutores utilizados. A partir destes dados, a intensidade efetiva foi determinada. Para avaliar o calorímetro, foi utilizado um equipamento de ultrassom de Fisioterapia, operando nas frequências nominais 1 e 3 MHz, modo contínuo, intensidades nominais 0,5; 1,0; 1,5 e 2,0 W.cm-2 e tempo de irradiação 180 segundos. Uma sequência de oito protocolos de medição foi realizada dez vezes. Para ambas as frequências, houve um declínio do aquecimento ao longo da profundidade e a região do "phantom" que mais aqueceu foi a que corresponde à profundidade de 10 mm, em todas as intensidades. O maior aquecimento ocorreu a 2,0 W.cm-2, com médias de 6,7 ± 1,0 ºC e 12,6 ± 1,2 ºC, a 1 MHz e 3 MHz, respectivamente. O calorímetro proposto mostrou-se útil na caracterização de feixes ultrassônicos aplicados em Fisioterapia, principalmente na identificação de possíveis máximos locais de temperatura (pontos quentes) que ocorrem ao longo do eixo principal do feixe.
The present work describes the project and construction of a differential calorimeter designed to evaluate the heating generated by ultrasound beam in therapeutic levels. The calorimeter consists of two identical aluminum cylindrical chambers (for measurement and reference) filled with biological tissue mimicking material (phantom). Each chamber is fitted with six thermocouples type E (0.24 mm diameter) disposed along the wave propagation central axis, between the depths of 10-60 mm, distant 10 mm from each other. The power curve and the value of the effective radiation area (ERA) of the two transducers were estimated. From these data, the effective intensity was determined. The calorimeter was tested by using an ultrasound equipment of Physiotherapy, operating at the frequencies 1 and 3 MHz, continuous mode, nominal intensities 0.5, 1.0, 1.5 and 2.0 W.cm-2 and irradiation time 180 seconds. A sequence of eight protocols of measurement was repeated 10 times. At both frequencies, there was a decline of heating along the depth and the phantom region that heated the most corresponded to 10 mm of depth, in all intensities employed. The greatest increase in temperature occurred after application of 2.0 W.cm-2, with averages of 6.7 ± 1.0 ºC and 12.6 ± 1.2 ºC, at 1 MHz and 3 MHz, respectively. The proposed calorimeter may be useful for identifying possible local temperature maxima (hot spots) that appear along the central axis beam.