Photoacoustic Imaging and Applications with Reversibly Switchable Contrast Agents

Benefiting from both optical and acoustical imaging advantages, pho-toacoustic imaging (PAI) can noninvasively acquire photochemical features of a live tissue with scalable resolution and imaging depth on demand. Looking over accessible contrast from endogenous chromophores, diverse categories of photoacoustic (PA) contrast agents have been actively excavated to reach a deeper imaging depth. However, conventional PA contrast agents must compete with the endogenous contrast from a background tissue, which might limit the imaging depth to background-equivalent depth and perturb molecular specificity. Here, we introduce novel reversibly switchable PA contrast agents that could effectively mute the background signal and eventually achieve exclusive exogenous contrast. In this chapter, we brief the overall principle and scalable configuration of PAI, summarize conventional PA contrast agents categorized by their compositions, and finally introduce reversibly switchable PA contrast agents. Based on our summary, we further suggest a promising outlook that these novel PA contrasts could lead to new biomedical findings.