Advanced Spectroscopy Technique for Biomedicine - Biomedical Optical Imaging Technologies: Design and Applications - page 25

Fig. 1.12 Graphic representation of the curve observed in horizontal displacement rounded to
pixels ( dashed lines ). The solid curve is a linear-regression-fitted parabolic line (Adapted from
Huang et al. [ 11 ], with permission)

number of pixels grouped together. We proposed a simple novel solution for full-
chip hardware binning by eliminating this image aberration.
As shown in Fig. 1.13 , the 58 fibers of the fiber bundle are aligned at the
spectrograph end along a curve (Eq. 1.9 ) formed by the horizontal displacement
but in the reverse orientation. Figure 1.13 a shows the image aberration of a 100-m
slit through the spectrograph in our uncorrected system when it is illuminated by a
mercury-argon lamp. Figure 1.13 b shows a CCD image of the fiber bundle illumi-
nated by a mercury-argon lamp after image aberration correction. The center fiber
(dark spot) is used for wavelength calibration. With this specific fiber arrangement,
the spectral lines are substantially straight, which enables image aberration and full-
chip hardware binning along the entire CCD vertical line (256 pixels) without losing
resolution. The S/N ratio improvement that we achieve with our system is 3.3 times
that of the combined hardware- and software-binning procedure and 16 times that
of the complete software binning.

1.3.1.7 Raman Data Acquisition and Processing

The real-time Raman spectroscopic system is controlled by custom-built software
implemented within Labview (National Instruments, Austin, TX drivers from R
Cubed Software, Lawrenceville, NJ). There are three steps in system controlling:
system initialization, real-time data acquisition, and real-time data processing.
The system initialization step includes CCD dark-noise subtraction, wavelength
calibration, spectral response calibration, and intensity calibration, following the
procedures discussed in Sect. 1.2.6 . The CCD dark noise is first measured before
each measurement and sequentially subtracted immediately after the CCD readout.