Second harmonic generation (SHG) microscopy allows in situ visualization of dermal collagen fibers in human skin due to its selectivity for collagen fiber. It is an attractive tool because it does not require staining, is non-invasiveness, and has high-resolution 3D imaging capability. However, its practical use in the dermatological field is still limited due to the bulky and complicated setup. Incorporation of fiber transmission of the laser light and a compact probe head into the microscope would enhance its compactness, robustness, flexibility, and hence convenience. In this study, we constructed a photonic-crystal-fiber (PCF) -coupled, hand-held SHG microscope for in situ monitoring of collagen fibers in human skin. By transmitting pulse light from a mode-locked Cr:Forsterite laser source via a large mode area PCF, it was possible to deliver pulse light with median wavelength of 1250nm and pulse width of 80 fs to the SHG microscope, without the need for external dispersion compensation. Components of a SHG microscope;galvano mirrors, relay lenses, objective lens, dichroic mirror, optical filters, and photon-counting photomultiplier, were mounted into a hand-held probe head (width=310mm, height=150mm, and depth=50mm), which is only 2% of the size of a conventional SHG microscope. We compared the imaging performance between the conventional SHG microscope and the hand-held SHG microscope, and confirmed comparable performance of the two. Finally, we demonstrated in situ visualization of collagen fibers in human skin using the hand-held SHG microscope with a compact probe head coupled to PCF. The hand-held SHG microscope greatly enhances the operability of in situ measurement of the human skin. The novel system will be a powerful tool for various dermatological applications.
2017 Japanese Society for Medical and Biological Engineering