Photoacoustic imaging using endogenous chromophores as a contrast has been widely applied in biomedical studies owing to its functional imaging capability at the molecular level. Various exogenous contrast agents have also been investigated for use in contrast-enhanced imaging and functional analyses. This review focuses on contrast agents, particularly in the wavelength range, for use in photoacoustic imaging. The basic principles of photoacoustic imaging regarding light absorption and acoustic release are introduced, and the optical characteristics of tissues are summarized according to the wavelength region. Various types of contrast agents, including organic dyes, semiconducting polymeric nanoparticles, gold nanoparticles, and other inorganic nanoparticles, are explored in terms of their light absorption range in the near-infrared region. An overview of the contrast-enhancing capacity and other functional characteristics of each agent is provided to help researchers gain insights into the development of contrast agents in photoacoustic imaging.

Kyung-Hwa Shin, M.D., In-Suk Kim, M.D., Hyun Ji Lee, M.D., Hyung-Hoi Kim, M.D., Chulhun L. Chang, M.D., Young Mi Hong, M.D., Ki Tae Yoon, M.D., and Mong Cho, M.D.. Ann Lab Med 2017;37:204-12. https://doi.org/10.3343/alm.2017.37.3.204

Biomedical imaging is an essential tool for investigating biological responses in vivo. Among the several imaging techniques, optical imaging systems with multispectral analysis of nanoparticles have been widely investigated due to their ability to distinguish the substances in biological tissues in vivo. This review article focus on multispectral optical imaging techniques that can provide molecular functional information. We summarize the basic principle of the spectral unmixing technique that enables the delineation of optical chromophores. Then, we explore the principle, typical system configuration, and biomedical applications of the representative optical imaging techniques, which are fluorescence imaging, two-photon microscopy, and photoacoustic imaging. The results in the recent studies show the great potential of the multispectral analysis techniques for monitoring responses of biological systems in vivo.

Kim KH, et al. J Korean Med Sci. 2017 Jan;32(1):29-32. https://doi.org/10.3346/jkms.2017.32.1.29

Kim JH, et al. Tuberc Respir Dis. 2013 May;74(5):207-214. http://dx.doi.org/10.4046/trd.2013.74.5.207

Shin KH, et al. Ann Lab Med. 2020 Jan;40(1):40-47. https://doi.org/10.3343/alm.2020.40.1.40