Biomedical Engineering Reference
In-Depth Information
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(B)
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Figure 14.7
Microstructure OPD and height maps after quality-map guided phase unwrapping (A and C),
compared to unwrapping performed with two-wavelength unwrapping (B and D). OPD map of
A431 human skin cancer cells unwrapped using two-wavelength unwrapping (E). Source: Adapted
from Ref.
[43]
.
applicability of digital holography and quantitative phase measurements to structures such
as sharp slopes and edges with greater than 2
π
wraps.
14.4.2 Spectral Multiplexing of Quantitative Phase and Fluorescence Biomarkers
Quantitative phase measurements are useful for investigating dynamic morphological
changes in individual cells without the use of exogenous optical labels, and optical phase
measurement has even been used to directly define quantitative parameters for
characterizing cardiomyocyte
[24]
and red blood cell (RBC)
[46]
dynamics. However, while
imaging with endogenous contrast removes the complexity of bioconjugating fluorescent
species and enables to label cell features, there is an overall loss of molecular specificity.
Therefore, the full value of QPM as a cell imaging modality can be realized when paired
with traditional fluorescence techniques.
Previous efforts to combine phase and fluorescence imaging include coregistration of
diffraction phase and fluorescence microscopy to image both the quantitative phase delays
of kidney cells while simultaneously locating their nuclei
[47]
. Molecular labeling was
achieved by introducing DNA-binding Hoescht dye. Coregistered images were acquired in a
single snapshot in this study, which points to the utility of this method for imaging dynamic
systems. A more recent study integrated multiple-wavelength phase unwrapping with wide-
field epi-illumination fluorescence microscopy
[48]
. However, phase maps and fluorescence
images were captured sequentially with shutters used to gate the corresponding illumination
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