Analysis of acoustic signal incidental to ultrasonic cavitation

conference paper

English

Cavitation phenomenon constitutes inconsiderable hazard in ultrasound diagnostic and therapy that is the reason why early and effective detection is necessary. Cavitation constitutes high risk especially when we use echocontrast agent based on microbubbles. Departure of biophysics in conjunction with departure of physics are try to develops detection cavitation method based on increasing level of cavitation noise in range of low frequencies (about 1 Hz). This method is now provided only in-vitro by using model of body fluid with echocontrast agent. It was created flow-through system whose principle is cylindrical chest with diameter 30 mm and length 350 mm. On the first side of chest is ultrasound exciter and on the other side is piezoelectric sensor. To make chest airless, airless container is installed. At first, 250 ml of solution is applied to the chest, after that it is excited for 20 s by ultrasound with frequency 800 kHz and intensity 0 – 2.5 W/cm-2. Ultrasound signal in microbubble solution evokes cavitation and also particular level of cavitation acoustic noise. Resulting signal is preamplified, sampled and computed by discrete Fourier transformation. In case of cavitation, level of noise voltage is increasing in region from 0.1 to 2 Hz. By this method it is possible to determinate value of cavitation threshold (intensity of excited ultrasound signal when cavitation appears). As an equivalent of echocontrast agent was used cooled 5% solution lyophilized egg albumine excited by ultrasound disintegrator for 30 minutes. 2 hours after suspension is created, it’s important to apply it even if cavitation kernels are still observable after 24 hours. The purpose is to find how could be position of cavitation threshold influenced by changing of measuring conditions and different physical factors like increasing of temperature, changing of viscosity, concentration of applied solution or flow-through of liquid. It’s possible to change the viscosity by adding relative chemical inert component (in our case surfactant Tween – 20).

cavitation, ultrasound, diagnostic, therapy

Kamil Brabec, Vojtech Morstein, Stepan Hefner, Jan Havranek

2005

1. 1. 2005

Ing. Zdenek Novotny CSc., Brno, Ondráčkova 105

Brno

80-214-2990-9

EDS 05

1

154

159

6