Nanoparticles as contrast agents for photoacoustic brain imaging

Photoacoustic (PA) imaging has emerged as a promising technique for real-time detection and diagnosis of brain-related pathologies, due to its advantages in deep penetration of ultrasound imaging and high resolution of optical fluorescence imaging. We herein provide an overview on the latest developments of nanoparticles as contrast agents specifically designed for PA imaging of brain tumor, and brain vascular and other brain-related diseases. Five design considerations of high-performance PA contrast agents for brain-related disease diagnosis are discussed, which include (1) strong absorption in NIR or NIR-II window, (2) good biocompatibility, (3) high photothermal conversion efficiency, (4) precise nanostructure control, and (5) specific targeting capability. Challenges and perspectives of developing more robust and universal contrast agents for enhanced PA imaging are discussed at the end.