Pulse amplitude modulation for ultrasound imaging of contrast microbubbles

Microbubbles are used as a contrast agent in medical ultrasound imaging. Ultrasound scanners have a ‘contrast’ setting which optimises the process for imaging microbubbles utilising their non-linear scatter. One such method is pulse amplitude modulation. Pulse amplitude modulation uses an initial low amplitude pulse, followed by a larger (2x the low amplitude) pulse, followed by a third pulse which is low amplitude the same as the first pulse. The echoes from the three pulses are combined in a way which removes linear scatter from the large (second) pulse. The remaining information is mainly non-linear scatter from the microbubbles. This process removes the linear echoes from surrounding tissue and allows the path of the microbubbles to be visualised.
We have undertaken a range of single microbubble studies including the response of single bubbles to pulse amplitude modulated signals. In the past we have shown that each time a microbubble is insonated, with the same acoustic pulse, there is a different echo produced as the bubble is affected each time it is exposed to ultrasound. The effect depends on many factors such as bubble size, bubble type and ultrasound settings. We would like now to investigate whether we can assess if the outcome of pulse amplitude modulation is affected by the sequence of the pulses, i.e. if the large amplitude pulse is first or two consecutive low amplitude pulses are first.
The talk will describe data we have collected for single microbubbles using pulse amplitude modulation and describe the work we are hoping to do using different order of pulses.