Optically and acoustically triggerable sub-micron phase-change contrast agents for enhanced photoacoustic and ultrasound imaging

To explore the extravascular space, sub-micron phase-change droplets show widespread interest in medical imaging and therapy with various modalities, such as ultrasound and photoacoustic. Existing studies (Wilson 2012, Wei 2014) on such dual-modality contrast agents have demonstrated the generation of both optical and ultrasound contrast after optical activation. However these studies did not explore the option of acoustic activation. Furthermore, high boiling point perfluorocarbons were used in these studies. A low boiling point may be preferred, to minimise un-wanted bioeffects, especially when activating in deeper tissues. In this study, we demonstrate a versatile phase-change sub-micron contrast agent that can provide three modes of contrast enhancement: 1) photoacoustic imaging contrast, 2) ultrasound contrast with optical activation, and 3) ultrasound contrast with acoustic activation. This would add versatility of vaporisation triggering, offering new possibilities in dual mode imaging, molecular imaging and drug delivery.