Biomedical Engineering Reference
In-Depth Information
[49,50] . Since the multiplexing methods presented here collect independent information in
the spectral channels, it is important that the raw pixel intensities are read out from the
sensor and processed separately.
The primary advantages of using an RGB sensor to multiplex phase and fluorescence
information are the simplicity of the optical system designs and the nature of simultaneous
acquisition. A single sensor removes the need for complex detection schemes that can
require synchronization of multiple cameras, shutters, and lasers. Finally, since the
quantitative phase and fluorescence modalities are acquired simultaneously on the RGB
sensor, these systems minimize motion artifacts and theoretically allow frame rates to be
increased to the limit of the camera electronics.
14.5 Nonlinear Phase Dispersion Spectroscopy
We now introduce an interferometric method for profiling the spectral properties of cell
samples. The approach is based on spectral-domain phase microscopy (SDPM), which is an
extension of OCT that provides quantitative OPD information with nano- to picometer
sensitivity [20] . This method is similar to quantitative digital holographic techniques
[51,52] in that SDPM is realized by interfering a sample wave with a reference wave.
However, SDPM retrieves the phase information from spectrally resolved oscillations rather
than spatial fringes. Consequently, spectroscopic information is more readily accessible in
SDPM. In addition, SDPM traditionally uses a focused beam that is swept across the
sample rather than a wide-field imaging approach. Likewise, spectroscopic OCT (SOCT)
[53] is another extension of OCT that takes advantage of the spectral dimension to provide
functional information regarding the wavelength-dependent total attenuation coefficient due
to a sample [54 57] . Similar to SOCT, spectroscopic phase techniques have been
developed to probe the wavelength-dependent real part of the RI, thereby granting access to
the dispersion-inducing biochemical properties of samples [51,58,59] . However, to date,
such methods have required multiple light sources or narrow band-pass filters, thus limiting
the spectral information to a few narrow spectral regions.
In this section, we introduce a spectroscopic phase technique, termed nonlinear phase
dispersion spectroscopy (NLDS), which provides broadband, high-resolution spectral
information of the real part of the RI. In the meantime, complementary information is
obtained from the same sampled data using SDPM and SOCT processing to yield
quantitative topographical maps and spectral profiles of the total attenuation coefficient of
samples, respectively. We present results from proof-of-concept experiments using
fluorescent and nonfluorescent polystyrene beads, and RBCs, and also discuss the
technique's potential applications [60] .
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