Experimental Verification of Modeled Thermal Distribution Produced by a Piston Source in Physiotherapy Ultrasound

Abstract

Objectives. To present a quantitative comparison of thermal patterns produced by the piston-in-a-baffle approach with those generated by a physiotherapy ultrasonic device and to show the dependency among thermal patterns and acoustic intensity distributions. Methods. The finite element (FE) method was used to model an ideal acoustic field and the produced thermal pattern to be compared with the experimental acoustic and temperature distributions produced by a real ultrasonic applicator. A thermal model using the measured acoustic profile as input is also presented for comparison. Temperature measurements were carried out with thermocouples inserted in muscle phantom. The insertion place of thermocouples was monitored with ultrasound imaging. Results. Modeled and measured thermal profiles were compared within the first 10 cm of depth. The ideal acoustic field did not adequately represent the measured field having different temperature profiles (errors 10% to 20%). Experimental field was concentrated near the transducer producing a region with higher temperatures, while the modeled ideal temperature was linearly distributed along the depth. The error was reduced to 7% when introducing the measured acoustic field as the input variable in the FE temperature modeling. Conclusions. Temperature distributions are strongly related to the acoustic field distributions.

The effects of ultrasound and shockwave treatment on muscle regional oxygen saturation using near-infrared spectroscopy

“…It seems that no skin hyperthermic effect being observed is mainly due to the fact that the operating frequency of ultrasound transducer was 0.8 MHz, which causes absorption of the sound wave energy at a depth of approximately 2-3 cm and, as is known, only the absorbed energy can induce the thermal effect and a rise in temperature [40,41]. The above observations are consistent with the assumption that the UST treatment less overheats shallow tissues than the deeper ones, and obtaining the rise in skin temperature would require application of maximum ultrasound intensities of approximately 3 W/cm2 [1,8,18,40]. At the same time, the need for application of a couplant during the treatment and its potential impact on skin surface cooling should be emphasised; nonetheless, lower skin temperature values of the analysed regions continued 30 min after the treatment.…”

“…Some isolated evidence points out to the potential of using pressure waves in the treatment of many dysfunctions [1,8,12,19,36]; in practice, however, conclusive physiological improvement when using ultrasound and shockwave in controlled trials has not been definitively confirmed [1,16,37]. For this reason, the described therapeutic effect of pressure waves is sometimes based on hypotheses [4,2,37], and the obtained therapeutic effects are not fully explainable.…”

“…bone and muscle tissues), the sound absorption is significantly higher than at the border of soft tissues (e.g. adipose and muscle tissues) [1,7,8,13,14,15]. The application of 2 sensor types allowed us to differentiate the measurement in relation to the reading depth to 20 and 12.5 mm.…”

“…Each transducer produces a unique acoustic field pattern due to the particular vibration conditions of the piezoelectric disks related to their manufacturing process. These variations in the radiation pattern influence the temperature distributions and could be the cause of unexpected acoustic radiations [8]. The amount of produced heat depends both on the wave parameters and the properties of the medium through which the wave travels.…”

Nonuniform Bessel-Based Radiation Distributions on A Spherically Curved Boundary for Modeling the Acoustic Field of Focused Ultrasound Transducers

“…Usually, the radiation of a boundary is expressed in terms of particle velocity [20,26,31]. In harmonic conditions [32], the particle acceleration a 0 on the radiator surface can be obtained by time-deriving the constant-amplitude particle velocity v 0 e jωt as…”