Using Low-Boiling Point Phase Change Contrast Agent Activation Signals for Super Resolution Ultrasound Localization Microscopy

Ultrasound (US) contrast agents can be used to generate super resolution (SR) images of the vasculature by accumulating the localizations of separable contrast signatures over tens of thousands of frames. This research presents a SR imaging method that localizes the activation signals of octafluoropropane (OFP, C3F8, -37 deg. C boiling point) phase-change contrast agents (PCCAs, or droplets), rather than microbubble signals. The unique activation signature of low-boiling point PCCAs was separated from the tissue background by frequency filtering alone. Plane-wave imaging was used to both activate droplets and image the activation signals. A low-frequency bandwidth (BW) to receive the activation signals and a high-frequency transmit BW enabled the collection of high contrast-to-tissue ratio (CTR) images which were then processed for SR. We demonstrate the application of this technique by localizing activations within a crossed microtube setup in a tissue- mimicking agar phantom kept at 37 deg. C.