Advanced Spectroscopy Technique for Biomedicine - Biomedical Optical Imaging Technologies: Design and Applications - page 21

focusing on real-time in vivo Raman spectroscopy system design. First, we present
the designing aspects of two real-time Raman spectroscopy systems: one for in vivo
skin diagnosis and the other for endoscopic in vivo lung cancer diagnosis. Then
we introduce an in vivo confocal Raman spectroscopy system for skin research,
followed by a summary of other types of probes for different applications.

1.3.1 Real-Time Raman Spectroscopy System for Skin

Diagnosis

Human skin has been the subject of numerous investigations involving noninvasive
optical techniques including infrared (IR) spectroscopy and Raman spectroscopy.
Because the probability of Raman scattering is exceedingly low, it has heretofore
been characterized by weak signals or relatively long acquisition times on the
order of several tens of seconds to minutes. These factors have limited its clinical
application in medicine. It is critical to have an integrated system in the clinical
setting that can provide real-time spectral acquisition and analysis. We demonstrated
the feasibility of real-time in vivo Raman spectroscopy by reducing the integration
timetolessthan5s[ 11 ]. A few other real-time in vivo Raman systems have also
been published [ 28 , 29 ].
The real-time NIR Raman system for skin disease diagnosis and evaluation is
schematically shown in Fig. 1.10 [ 11 , 12 ]. It consists of the typical five components
of a spectroscopy system: the excitation light source, the excitation light delivery
unit, the Raman signal collection unit, the spectrograph, and the detection unit, with
each component specially designed for easy access to the measurement site and for
real-time measurement.

1.3.1.1 Light Source

The light sources used in Raman spectroscopy are usually lasers because of their
higher power output and narrower bandwidth. The choice of wavelength for Raman
measurement depends on the specific application and the spectroscopy properties
of the sample. For biomedical applications, a NIR laser is commonly used. NIR
light has deep penetration depth (700-1,100 nm is regarded as the optical window
of biological tissues) and induces lower level of tissue autofluorescence. The output
of the laser source must be stable in its intensity and wavelength. Solid-state and
external-cavity-stabilized diode lasers are popular choices for their portability. Our
current real-time Raman system is equipped with a wavelength-stabilized diode
laser (785 nm, 350 mW, model BRM-785-0.35-100-0.22-SMA, B&W Tek Inc.,
Newark, DE, USA).