Biomedical Engineering Reference
In-Depth Information
Fig. 1.15 Schematic configuration of the in vivo confocal Raman spectrometer system for depth-
resolved skin Raman measurement (Adapted from Wang et al. [ 41 ], with permission)
1.3.3.3
Spectrograph and CCD Detection System
The spectrograph is a transmissive imaging spectrograph (HoloSpec-f /2.2-NIR,
Kaiser, Ann Arbor, MI) with a holographic grating (HSG-785-LF, Kaiser, Ann
Arbor, MI). The slit was replaced by the single fiber, the image of which occupied
about 5 pixels. The spectral resolution of the system was around 8 cm 1 .
The spectrometer system is equipped with an NIR-optimized back-illuminated
deep-depletion CCD array (Spec-10:100BR/LN, Princeton Instruments, Trenton,
NJ). The CCD has a 16-bit dynamic range and is liquid nitrogen-cooled to 120 ı C.
Hardware binning was used for the Raman spectra measurement, but there was no
need of special treatment of the input as there was only one fiber.
1.3.3.4
Results
Raman spectra with good signal-to-noise ratio were obtained within 15 s under
27 mW of excitation light exposure to the skin surface. The mean normalized Raman
spectra of normal mouse skin from 24 mice are shown in Fig. 1.16 .Wefindthat
Raman spectra at different depths in mouse skin differ significantly. For example,
strong peaks at 1,061, 1,128, and 1,296 cm 1 coming from ceramide can be found
in the spectra of the epidermis, while 855 and 937 cm 1 are two major peaks
that make up the dermal spectral pattern. Four hundred and ninety-four Raman
spectra at different depths and from normal and tumor-bearing sites of 24 mice
were measured. We found different spectral patterns at different depths. A peak at
899 cm 1 (possibly from proline or fatty acids) and one with higher intensity in
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