Confocal Raman spectroscopy (CRS) has been used for noninvasive biochemical analysis of biological tissue in vivo. Reflectance confocal microscopy (RCM) has been integrated with CRS as visual guidance to facilitate simultaneous square-shaped region or point of interest micro-Raman measurement. However, these methods do not allow the acquisition of representative Raman spectra from and only from the area that covers the target micro-structure that has various morphologies. To solve this problem, we developed a method to acquire Raman spectra from a region of interest that has an arbitrary shape under simultaneous RCM imaging guidance using a single laser source.
Confocal Raman spectroscopy (CRS) is a noninvasive optical method capable of providing endogenous molecule fingerprinting information as well as allowing depth-resolved measurements into biological tissue. For precise data acquisition in highly scattering tissue in vivo, reflectance confocal microscopy (RCM) has been integrated as imaging guidance with confocal Raman spectroscopy system. However, building a CRS system for point of interest (POI) Raman measurement with simultaneous full field of view (FOV) RCM imaging using a single laser is a challenge. In this work, we addressed the challenge using an optical Faraday isolator to separate the returning reflectance confocal signal from the incident laser beam. A single laser source was used for both RCM and CRS measurements by utilizing two polarized beam splitters (PBS): one for splitting the beam into a RCM illumination beam and a CRS excitation beam; the other for merging the two beam together before entering the objective lens. The confocal setting minimizes the Raman signal contribution from the scanning RCM beam to as small as 0.18%. Furthermore, this small portion of Raman signal will not contaminate the CRS Raman spectrum because they are excited by the same laser wavelength. The co-registration of the sectioning plane of the RCM and CRS were confirmed to be within 0.2 micron. This new integrated confocal Raman system allowed us to acquire confocal Raman signals at specific POI under real-time full FOV RCM guidance and monitoring. Application examples for both ex vivo sample and in vivo skin measurements will be presented.
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