Compression-only behavior of phospholipid-coated contrast bubbles

Ultrasound contrast agents oscillate approximately linearly up to a certain pressure range where nonlinearity sets in. Nonlinear microbubble oscillations are exploited in ultrasound pulse-echo imaging as this improves the contrast-to-tissue ratio. Here we report the observation of a highly nonlinear response of phospholipid-coated contrast agents at pressures as low as 50 kPa, termed compression-only behavior, where the microbubbles only compress, yet hardly expand. Time-resolved bubble dynamics recorded through ultra high-speed imaging revealed that nearly 40% of the coated bubbles show compression-only behavior.