Detection and sizing of micro bubbles in streaming fluids with ultrasound

The detection of micro bubbles in fluids is of great practical interest in many medical and biotechnological applications, particularly with the extracorporeal circulation. A self calibrating system is presented which allows a continuous detection and determination of the micro bubble size distribution of tube flows in a range between 10 and 250 μm in diameter. The measuring system is based on ultrasound Doppler technique and is suited for clinical application to monitor heart lung machines as well as for research and development of filter and oxygenation systems. During the measuring a computer-controlled registration and evaluation of the bubbles as well as a self-calibration of the system is performed The bubble size is evaluated due to the back scattered Doppler signal and is corrected by means of a reference signal according to the measuring conditions. The calibration of the bubble counter is performed with a special developed bubble generator system. The bubbles, injected in the tube system, are outlined with a microscope camera system connected to a PC for the exact sizing of each bubble. The number and size of the detected bubbles can be visualized in form of histograms (number versus size, cross section or volume) and as time course (number or concentration per time interval versus time).