Ultra-High-Frequency-Radio-Frequency-Acoustic Molecular Imaging with Saline Nanodroplets in Living Subjects

Molecular imaging is a crucial technique in clinical diagnostics, but it relies on radioactive tracers or high magnetic fields that are unfavorable for many patients, particularly infants and pregnant women. Ultra-high-frequency-radiofrequency-acoustic (UHF-RF-acoustic) imaging using non-ionizing RF pulses allows deep-tissue imaging with sub-millimeter spatial resolution. However, lack of biocompatible and targetable contrast agents has prevented the successful in vivo application of UHF-RF-acoustic imaging. Here, we report our development of targetable nanodroplets for UHF-RF-acoustic molecular imaging of cancers. We synthesize all-liquid nanodroplets containing hypertonic saline that are stable for at least 2 weeks and can produce high intensity UHF-RF-acoustic signals. Compared with concentration-matched iron-oxide nanoparticles, our nanodroplets produce at least 1600 times higher UHF-RF-acoustic signals at the same imaging depth. We demonstrate in vivo imaging using the targeted nanodroplets in a prostate cancer xenograft mouse model expressing gastrin release protein receptor (GRPR), showing targeting specificity by more than two-fold, compared to untargeted nanodroplets or prostate cancer cells not expressing GRPR.