Abstract
BackgroundBioheat models have been proposed to predict heat distribution in multilayered biological tissues after therapeutic ultrasound (TUS) stimulation. However, evidence on its therapeutic benefit is still controversial for many clinical conditions. The aim of this study was to evaluate and to compare the TUS heating distribution on commercially available bone phantoms and in vitro femur and tibia human samples, at 1 MHz and several ultrasonic pulse regimens, by means of a thermographic image processing technique.MethodsAn infrared camera was used to capture an image after each 5-min 1-MHz TUS stimulation on bone phantoms, as well as in vitro femur and tibia samples (N = 10). An intensity-based processing algorithm was applied to estimate temperature distribution. Sections of five femurs in the coronal plane were also used for the evaluation of heat distribution inside the medullar canal.ResultsTemperature increased up to 8.2 and 9.8 °C for the femur and tibia, respectively. Moreover, the temperature increased up to 10.8 °C inside the medullar canal. Although temperature distributions inside the region of interest (ROI) were significantly different (p < 0.001), the average and standard deviation values for bone phantoms were more similar to the femur than to the tibia samples. Pulsed regimens caused lower increments in temperature than continuous sonication, as expected.ConclusionsCommercially available bone phantoms could be used in research focusing on thermal effects of ultrasound. Small differences in mean and standard deviation temperatures were observed between bone samples and phantoms. Temperature can reach more than 10 °C inside the medullar canal on a fixed probe position which may lead to severe cellular damage.
Highlights
Bioheat models have been proposed to predict heat distribution in multilayered biological tissues after therapeutic ultrasound (TUS) stimulation
When comparing continuous and pulsed regimens, the increase in temperature is higher in continuous mode, and it decreases as the number of pulses per time unit increases
Temperature distributions inside the region of interest (ROI) were significantly different between bone phantoms and specimens, one may say that average and standard deviation values for bone phantoms were more similar to the femur than to the tibia samples, maybe due to their similar thickness (4–5 mm)
Summary
Bioheat models have been proposed to predict heat distribution in multilayered biological tissues after therapeutic ultrasound (TUS) stimulation. Therapeutic ultrasound (TUS) units are present in most of physical therapy departments worldwide, mainly for the management of musculoskeletal disorders, providing mechanical stimulation and/or heating (non-thermal and thermal effects, respectively). Several clinical trials have already shown different levels of evidence regarding the therapeutic benefit of TUS. Acoustic transducers are of utmost importance for ultrasonic applications They can be used to generate and receive acoustic waves through a property called piezoelectricity in which certain solid materials become electrically polarized when submitted to mechanical stress and vice versa [6]. One may be concerned that the near field is commonly used for therapeutics, and its inhomogeneous acoustic field may lead to high- and low-intensity regions by wave constructive and destructive interference, respectively [7]. A technical report published by Artho et al [8] has shown that the intensity displayed on TUS units does not always correspond to the actual emitted output, raising questions about safety in physical therapy daily practice
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