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Physics of Ultrasound
Published in Marvin C. Ziskin, Peter A. Lewin, Ultrasonic Exposimetry, 2020
Sonoluminescence is the weak emission of light that may be observed when ultrasound, of sufficiently high intensity, passes through a medium containing dissolved gases. Several hypotheses have been advanced to explain the phenomenon.99 These include the microdischarge theory, in which electric charges are formed on the walls of the cavities; the mechanochemical theory, which depends on the photochemical recombination of free ions; the anion discharge theory, where charges on bubbles arising from neutralization of anions by gas molecules are subsequently discharged producing ionization luminescence; and the hot-spot theory, which depends directly on high temperatures produced during cavity collapse. In any event, sonoluminescence can be enhanced by the addition of luminol (5-amino-2,3-dihydro-l,4-phthal-azinedione) to the aqueous medium.100 The phenomenon is unlikely to occur with stable cavitation, except in standing waves.101 Sonoluminescence certainly can be used to detect acoustic cavitation generated by microsecond pulses of ultrasound at 1 MHz.102 Although it can sometimes be seen with the naked eye, it is usually better to photograph it through an image inten-sifier.103
Antimicrobial sonodynamic and photodynamic therapies against Candida albicans
Published in Biofouling, 2018
Fernanda Alves, Ana Cláudia Pavarina, Ewerton Garcia de Oliveira Mima, Anthony P. McHale, John Francis Callan
It has been demonstrated that certain PS can also be activated by ultrasound (US), and as a result, the PS may also be referred to as a sonosensitizer (SS). This approach is known as sonodynamic therapy (SDT) (Ma et al. 2009; Serpe and Giuntini 2015). The advantage of SDT when compared to aPDT is that US propagates deeper into the tissue than light; therefore, SDT may be used to treat deeper lesions overcoming the limitations of light propagation and delivery presented by aPDT (Ma et al. 2009; Costley et al. 2015; Serpe and Giuntini 2015). It has been suggested that in SDT, singlet oxygen generation may result by the indirect photo-activation of the sensitizer drug via sonoluminescence (Umemura et al. 1999). Once excited the sensitizer generates singlet oxygen in the same way as in the aPDT (Umemura et al. 1999; Hiraoka et al. 2006). An alternative hypothesis suggests that the elevated temperatures resulting from cavitation can result in the generation of radicals directly from the PS, and ROS are subsequently produced in much the same way as a Type I photodynamic reaction.