378 Int. J. Functional Informatics and Personalised Medicine, Vol. 1, No. 4, 2008 Copyright © 2008 Inderscience Enterprises Ltd. Analysis of bubble cavitation in ultrasound therapy by wavelet technique Yufeng Zhou Division of Gastroenterology, Department of Medicine, University of Washington, Seattle, WA, 98195, USA E-mail: yufengz@medicine.washington.edu Abstract: Bubble cavitation is one of the major mechanisms for ultrasound treatment. To understand its characteristics, cavitation signals were picked up using passive cavitation detection and then analysed by wavelet transform. Although the Fast Fourier Transform (FFT) has been used widely in signal analysis, the absence of temporal information is one of its limitations. The inertial cavitation strength detected by wavelet method was ~60 folds higher than that using FFT. Furthermore, the relationship of waveform profile and acoustic pressure with the corresponding bubble cavitation were investigated. All together, wavelet approach could be new tool for studying bubble cavitation. Keywords: bubble cavitation; PCD; passive cavitation detection; wavelet transform. Reference to this paper should be made as follows: Zhou, Y. (2008) ‘Analysis of bubble cavitation in ultrasound therapy by wavelet technique’, Int. J. Functional Informatics and Personalised Medicine, Vol. 1, No. 4, pp.378–389. Biographical notes: Yufeng Zhou is a senior fellow at the University of Washington. He received his PhD Degree in bioacoustics from Duke University (2003). His research interests include bubble dynamics, therapeutic ultrasound technology (shock wave lithotripsy for stone treatment, high-intensity focused ultrasound for solid tumour/cancer ablation, shock wave therapy), non-destructive evaluation, acoustic wave propagation. 1 Introduction High intensity ultrasound exposure has become an effective modality in the clinical treatment, such as breaking kidney and urinary stones in Shock Wave Lithotripsy (SWL) (Chaussy et al., 1980) and producing tissue necrosis in a well-defined volume for solid tumour or cancer therapy (ter Harr, 1995; Vallancien et al., 1996), with advantages of non-invasion, lower inpatient cost, and less complications. In addition, ultrasound was also mediated in gene transfection and drug delivery (Lawrie et al., 2000; Lu et al., 2003). In comparison to biochemical and other physical gene therapies, such as using retrovirus vector, lipofection and electroporation, the ultrasound approach can overcome some existing drawbacks, including insertional mutagenesis, adverse systemic, and lack of site