Photoacoustic Imaging for Cancer Diagnosis

 Photoacoustic imaging (PAI) is a unique modality that overcomes the resolution and depth limitations of optical imaging of tissues while maintaining relatively high contrast. In this article, we reviewthe biomedical applications of PAI, assisted or unassisted by exogenous photoabsorbers (contrast agents). Representative endogenous contrast agents include melanin and hemoglobin, whereas exogenous contrast agents include dyes, metal nanoparticles, and other constructs that absorb strongly in the near-infrared band of the optical spectrum and generate strong photoacoustic responses. These contrast agents, which can be specifically targeted to molecules or cells, have been coupled with photoacoustic imaging for preclinical and clinical applications including detection of cancer cells, sentinel lymph nodes, micrometastases, and monitoring of angiogenesis. Multi-functional agents have also been developed that can carry medicines or simultaneously provide contrast in multiple imaging modalities. Furthermore, contrast agents are used to guide and monitor therapeutic procedures. Overall, photoacoustic imaging has significant potential to assist in diagnosis, therapeutic planning, and monitoring of treatment outcome for cancers and other pathologies.