Optical imaging modalities such as confocal microscopy and optical coherence tomography (OCT) are emerging as
appealing methods for non-destructive evaluation of engineered tissues. The information offered by such optical
imaging methods depends on the wavelength vis-á-vis the optical scattering properties of the sample. These properties
affect many factors critical to image analysis in a nonlinear and nontrivial manner. Thus, we sought to characterize the
effect wavelength has on the optical properties collagen remodeled by cells at 3 common imaging wavelengths: 488,
633, and 1310 nm. To do this, we seeded smooth muscle cells (SMCs) in soluble collagen gels at a density of 1×106
cells/ml; similar acellular control constructs were also prepared. The constructs were allowed to remodel in the
incubator for 5 days, and were examined at 24 and 120 hours by confocal imaging at 488 and 633 nm, and by OCT
imaging at 1310 nm. From the confocal and OCT data, the attenuation and reflectivity were evaluated by fitting the
data to a theoretical model that relates the tissue optical properties (scattering coefficient and anisotropy factor) and
imaging conditions to the signal. In general, we found that at 1310 nm, the optical properties of the acellular control
constructs had a lower reflectivity (higher anisotropy) than the SMC constructs. The difference in reflectivity between
the SMC construct and acellular controls tended to decrease with wavelength, owing to a relative increase in reflectivity
of acellular controls at lower wavelengths relative to the cellular constructs. Overall, the largest difference in optical
properties occurred at 1310 nm. Taken together, the data show that the shift in optical properties of soluble collagen
gels caused by cellular remodeling is nonlinearly wavelength dependent, and that this information should be considered
when devising how to optimally characterize engineered tissues using optical imaging methods.
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