Background: The observation of ultrasound generated cavitation bubbles deep in\ntissue is very difficult. The development of an imaging method capable of investigating\ncavitation bubbles in tissue would improve the efficiency and application of ultrasound\nin the clinic. Among the previous imaging modalities capable of detecting cavitation\nbubbles in vivo, the acoustic detection technique has the positive aspect of in vivo\napplication. However the size of the initial cavitation bubble and the amplitude of the\nultrasound that produced the cavitation bubbles, affect the timing and amplitude of\nthe cavitation bubbles� emissions.\nMethods: The spatial distribution of cavitation bubbles, driven by 0.8835 MHz therapeutic\nultrasound system at output power of 14 Watt, was studied in water using a synchrotron\nX-ray imaging technique, Analyzer Based Imaging (ABI). The cavitation bubble\ndistribution was investigated by repeated application of the ultrasound and imaging\nthe water tank. The spatial frequency of the cavitation bubble pattern was evaluated\nby Fourier analysis. Acoustic cavitation was imaged at four different locations through\nthe acoustic beam in water at a fixed power level. The pattern of cavitation bubbles in\nwater was detected by synchrotron X-ray ABI.\nResults: The spatial distribution of cavitation bubbles driven by the therapeutic\nultrasound system was observed using ABI X-ray imaging technique. It was observed\nthat the cavitation bubbles appeared in a periodic pattern. The calculated distance\nbetween intervals revealed that the distance of frequent cavitation lines (intervals) is\none-half of the acoustic wave length consistent with standing waves.\nConclusion: This set of experiments demonstrates the utility of synchrotron ABI for\nvisualizing cavitation bubbles formed in water by clinical ultrasound systems working\nat high frequency and output powers as low as a therapeutic system.
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