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BackgroundOne goal of therapeutic ultrasound is enabling heat generation in tissue. Ultrasound application protocols typically neglect these processes of absorption and backscatter/reflection at the skin/fat, fat/muscle, and muscle/bone interfaces. The aim of this study was to investigate the heating process at interfaces close to the transducer and the bone with the aid of computer simulation and tissue-mimicking materials (phantoms).MethodsThe experimental setup consists of physiotherapeutic ultrasound equipment for irradiation, two layers of soft tissue-mimicking material, and one with and one without an additional layer of bone-mimicking material. Thermocouple monitoring is used in both cases. A computational model is used with the experimental parameters in a COMSOL® software platform.ResultsThe experimental results show significant temperature rise (42 °C) at 10 mm depth, regardless of bone layer presence, diverging 3 °C from the simulated values. The probable causes are thermocouple and transducer heating and interface reverberations. There was no statistical difference in the experimental results with and without the cortical bone for the central thermocouple of the first interface [t(38) = −1.52; 95% CI = −0.85, 0.12; p = 14]. Temperature rise (>6 °C) close to the bone layer was lower than predicted (>21 °C), possibly because without the bone layer, thermocouples at 30 mm make contact with the water bath and convection intensifies heat loss; this factor was omitted in the simulation model.ConclusionsThis work suggests that more attention should be given to soft tissue layer interfaces in ultrasound therapeutic procedures even in the absence of a close bone layer.

Resumo 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 °C e 12,6 ± 1,2 °C, 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. Palavras-chave Calorímetro diferencial, Ultrassom, Aquecimento, Fisioterapia. Differential calorimeter for studying the heating pattern generated by therapeutic ultrasonic beams

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 (

The present work describes a method for acquiring thermal images generated by physiotherapeutic ultrasonic beams along a phantom of fat tissue made of PVCP. Five tests were performed in three ultrasound equipments, transducers operating at 1 and 3 MHz and nominal intensity 1.0 W.cm -2 , totalizing thirty infrared thermal images that were then evaluated on a PC-like microcomputer. The method seems to be useful for calibration and inspection of ultrasound equipments.Keywords --infrared camera, phantom,therapeutic ultrasound.Therapeutic heating by ultrasound (US) is a common clinical practice. Warming biological tissues with intensity both therapeutic and safe is however a complex task as the irradiation distribution inside the tissue varies and depends on differences between US equipments. It is already known that equipments respond differently according to the effective radiation area (ERA) [cm 2 ] and the output power [W], which are related to the intensity emitted [W.cm -2 ] and therapeutic heating. Depending on each equipment response the final temperature may be lower or higher than the expected, therefore it is important a previous evaluation.The literature describes different methods of studying US heating: Calorimeters with thermocouples [1,2], which only provide the temperature at few points. Thermochromic test objects [3,4] and thermochromic crystal liquid sheets [5], which provide qualitative information. The method here proposed consists of employing an infrared camera to measure the temperature inside a phantom submitted to physiotherapeutic US irradiation.The experimental setup proposed employed cylindrical phantom made of PVCP (plasticized polyvinyl chloride) cut along its axis in two halves further joined with US coupling gel. A therapeutical transducer (models Avatar III, KLD) was statically coupled to the top cylinder basis aligned with its axis. US continuous irradiation was applied with nominal intensity of 1.0 W.cm -2 for 120s, taking care to avoid reverberation by coupling an absorbing plate (APTFLEX) to the opposite basis. After irradiation the phantom was split in two and an infrared camera (InfraCam TM, Flir Systems) with temperature range selected between 25 to 45°C recorded the thermal image exposed.The PVCP phantom was constructed in the Ultrasound Laboratory of Biomedical Engineering Program/UFRJ, with US speed of 1480 m.s -1 and attenuation coefficient of 0.3 dB.cm -1 .MHz -1 (fat tissue), dimensions: 10-cm height and 5.3-cm diameter. The environment illumination was common fluorescent, and room temperature was 25± 2.0°C.