Disease diagnosis based on the visual inspection of the pathological presentations or symptoms on the epithelial tissue such as the skin are subjective and highly depend on the experience of the doctors. Vital diagnostic information for the accurate identification of diseases is usually located underneath the surface and its depth distribution is known to be related to disease progression. Although optical spectroscopic measurements are fast and non-invasive, the accurate retrieval of the depth-specific diagnostic information is complicated by the heterogeneous nature of epithelial tissues. The optical signal measured from a tissue is often the result of averaging from a large tissue volume that mixes information from the region of interest and the surrounding tissue region, especially from the overlaying layers. Our group has developed a series of techniques for depth sensitive optical measurements from such layered tissues. We will first review the earlier development of composite fiber-optic probe, in which the source-detector separation and the angles of source and detector fibers are varied to achieve depth sensitive measurements. Then the more recent development of non-contact axicon lens based probes for depth sensitive fluorescence measurements and the corresponding numerical methods for optimization will be introduced. Finally, the most recently developed snapshot axicon lens based probe that can measure Raman spectra from five different depths at the same time will be discussed. Results from tissue phantoms, ex vivo pork samples and in vivo fingernail measurements will be presented, which indicates the great potential of depth sensitive optical spectroscopy for clinical tissue diagnosis.
Wei Liu, Xiaojun Yu, Quan Liu, Linbo Liu, and Yi Hong Ong, "Depth-sensitive optical spectroscopy for layered tissue measurements (Conference Presentation)," Proc. SPIE 10060, Optical Biopsy XV: Toward Real-Time Spectroscopic Imaging and Diagnosis, 100600S (Presented at SPIE BiOS: February 01, 2017; Published: 1 May 2017); https://doi.org/10.1117/12.2250121.5409309566001.
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Study of self-shadowing effect as a simple means to realize nanostructured thin films and layers with special attentions to birefringent obliquely deposited thin films and photo-luminescent porous silicon