Advanced Spectroscopy Technique for Biomedicine - Biomedical Optical Imaging Technologies: Design and Applications - page 30

sphere (Newport Corporation, Stratford, CT), following the procedure described in
Sect. 1.2.6 .
The system was controlled by a custom-designed program, similar to the one
of the in vivo skin Raman system, but with a number of modifications. In order
to facilitate the physician to determine the spot to be measured, a low-power
focusing mode was incorporated which allowed the laser to be operated at 10%
of its maximum power by fast switching (500 Hz). This enabled the physician to see
the laser spot using the autofluorescence imaging system and thus direct the probe
to the point of interest while not exposing the patient to long-term high laser powers.

1.3.3 In Vivo Confocal Raman Spectroscopy System

In this section, we will describe an in vivo confocal Raman spectroscopic system,
which can perform depth-resolved Raman spectroscopy measurements [ 41 ]. The
system is schematically shown in Fig. 1.15 . Similar to other spectroscopic system,
it consists of five components: an excitation laser light source, a microscopic probe
that combines excitation delivery and Raman signal collection, a spectrograph, and
a detection unit.

1.3.3.1 Light Source

A single-mode diode laser (785 nm, 100 mw, model # I0785SU0100B-TK, Innova-
tive Photonic Solutions, Monmouth Junction, NJ) was used as the excitation source.
The laser beam was directed to a lens pair to select the TEM 00 mode and expand the
beam to 6 mm in diameter to fill the aperture of the objective lens. The beam is then
filtered by a 785-nm BP filter to reject noises at other wavelengths.

1.3.3.2 Confocal Raman Probe

The confocal Raman probe consists of a water immersion objective (model #:
LUMPL40 W/IR, NA 0.8, WD 3.3 mm, Olympus, Markham, Ontario, Canada)
and a special attachment for reducing the effects of involuntary body movements.
The 785-nm laser beam passes through a dichroic beam splitter and a mirror and is
directed to the water immersion objective. The laser intensity after the objective is
27 mW, and irradiance on the skin is well below the ANSI maximum permissible
exposure (MPE) level. The raw signal, composed of the Raman scattering signal
and the tissue autofluorescence background, is collected by the same objective lens
in the probe. The signal passes through the mirror, the dichroic beam splitter, and a
785-nm long-pass filter and is focused into a 100-m core-diameter low-OH fiber.
The fiber acts as a confocal pinhole and transmits the signal to the spectrograph.
The lateral and the axial resolution of the system are 2.2 and 8:6 m respectively.