Optical histopathology based on the nonlabeling analysis with multiphoton excitation imaging

Histopathological diagnosis is the definitive method for the evaluation of disease status; however, some problems need to be solved, such as invasiveness, time consumption, and difficulty in three-dimensional observation. To overcome these problems, a novel observation method, distinct from conventional histology, using tissue sections and glass slides is desirable. Fluorescence imaging of human tissues with multiphoton excitation imaging (MpEI), which was originally used for intravital imaging in biological research, is a promising method. Label-free MpEI, which requires only near-infrared excitation, can construct images with autofluorescent signals from fresh tissues, as well as nonlinear optical phenomena. It is possible to perform real-time three-dimensional imaging of human tissues without any tissue removal, fixation, or staining. This method has been reported to be useful for histopathological classification in multiple organs and tissues. Moreover, it is very compatible with quantitative image analyses, including artificial intelligence. Based on these characteristics, label-free MpEI has sufficient potential for clinical applications such as in endoscopy and intraoperative rapid diagnosis. The clinical application of label-free MpEI will bring changes not only to histopathology examination but also the clinical bedside and will contribute to the further development of histopathology.