Photoacoustic Contrast Agents: A Review Focusing on Image-Guided Therapy

Abstract

Photoacoustic (PA) imaging is a burgeoning imaging modality that has a broad range of applications in the early diagnosis of cancer, detection of various diseases, and relevant scientific research. It is a non-invasive imaging modality that relies on the absorption coefficient of the imaging tissue and the injected PA imaging contrast agent. Nevertheless, PA imaging exhibits a weak imaging depth due to its exponentially decaying signal intensity that occurs with the increase of tissue depth. To improve the depth and heighten the contrast of imaging, a series of PA contrast agents have been advanced based on nanomaterials. In this review, we present a comprehensive overview of recent advancements in contrast agents for photoacoustic (PA) imaging, encompassing the emergence of first near-infrared region (NIR-I, 700-950 nm) PA contrast agents, second near-infrared region (NIR-II, 1000-1700 nm) PA contrast agents, and ratiometric PA contrast agents. Subsequently, the latest advances in PA image-guided cancer therapy were introduced, such as photothermal therapy (PTT), photodynamic therapy (PDT), sonodynamic therapy (SDT), and PTT-based synergistic therapy. Finally, the prospects of PA contrast agents and their biomedical applications were also discussed. This review provides a systematical summarize of the cutting-edge photoacoustic agents’ development and utilization, which may inspire some fresh thinking in the image agents’ fabrication and application aspect.