Advances of Fluorescence Molecular Imaging: NIR-II Window, Probes, and Tomography

Fluorescence molecular imaging (FMI), a promising in vivo non-invasive optical molecular imaging technology, has high sensitivity, specificity, and spatio-temporal resolution. Owing to its further advantages of low cost and no radiation, FMI has been extensively employed in the diagnosis and treatment of tumors, imaging of the vascular system, and guided delivery of drugs. Nonetheless, affected by the strong photon absorption and scattering, FMI faces two major challenges: limited tissue penetration depth and complicated tomography reconstruction. This review clarifies both the challenges of FMI for the first time by summarizing the advances in near-infrared region II (NIR-II) imaging and fluorescence molecular tomography (FMT). In detail, NIR-II imaging conditions, representative probes, FMT systems, and reconstruction algorithms are reviewed. The NIR-II imaging can achieve deeper penetration and higher resolution, which facilitate more accurate reconstruction of FMT. And in turn, precise FMT reconstruction will promote the development and application of NIR-II imaging. Additionally, the challenges for the future development of NIR-II imaging and FMT are deeply analyzed, and the potential improvement avenues are discussed. The strengthening of the methodological investigation of NIR-II FMT is proposed to impel the deeper and more accurate FMI, ultimately providing more effective optical imaging tools for the biomedical field.