Significance: A non-destructive technique for accurately characterizing the spatial distribution of optical properties of soft tissue membranes may give improved outcomes in many tissue engineering applications.
Aim: This study aimed to develop a non-destructive macroscopic imaging technique that is sensitive to optical anisotropy, typical of fibrous components in soft tissue membranes, and can address some of the difficulties caused by the complex turbid nature of these tissues.
Approach: A near-infrared Mueller matrix imaging polarimeter employing logarithm decomposition was developed and used to conduct transmission measurements of all the polarization properties across the full thickness of bovine pericardium tissue.
Results: The full Mueller matrix was measured across a 70 mm × 70 mm sample of calf bovine pericardium and revealed significant retardance (linear and circular) and depolarization in this tissue. Regions with a uniform axis of optical anisotropy were identified. Mueller matrix imaging demonstrated that the exhibited circular retardance was sufficient to lead to possible misinterpretation of apparent fiber orientation when using conventional polarization imaging techniques for such tissues.
Conclusions: Mueller matrix imaging can identify regional distributions of optical anisotropy in calf bovine pericardium. This new capability is a promising development in non-destructive imaging for tissue selection.
A non-destructive imaging technique is required for quantifying the anisotropic and heterogeneous structural arrangement of collagen in soft tissue membranes, such as bovine pericardium, which are used in the construction of bioprosthetic heart valves. Previously, our group developed a Stokes imaging polarimeter that measures the linear birefringence of samples in a transmission arrangement. With this device, linear retardance and optic axis orientation; can be estimated over a sample using simple vector algebra on Stokes vectors in the Poincaré sphere. However, this method is limited to a single path retardation of a half-wave, limiting the thickness of samples that can be imaged. The polarimeter has been extended to allow illumination of narrow bandwidth light of controllable wavelength through achromatic lenses and polarization optics. We can now take advantage of the wavelength dependence of relative retardation to remove ambiguities that arise when samples have a single path retardation of a half-wave to full-wave. This effectively doubles the imaging depth of this method. The method has been validated using films of cellulose of varied thickness, and applied to samples of bovine pericardium.
Needle-free jet injection is a transdermal drug delivery technique wherein a liquid drug is pressurized, and ejected through a ~200 μm orifice at high speed (~200 m/s). The resulting fluid jet can rapidly penetrate through the skin, and disperse in the underlying tissue at a speed-related depth. Our electronically controllable injection systems uniquely offer the possibility of depth-control during injection. To this end, we have developed a spatially-resolved diffuse imaging technique to provide an estimate of the injection depth. An injection system was constructed to couple a collimated laser beam into the fluid jet as it was ejected through the orifice. During an injection, the penetration of the jet into a tissue-mimicking phantom eroded an unobstructed optical path for the laser beam before it impinged on the scattering medium at the bottom of the hole. This resulted in a pattern of backscattered light around the injection site that varied as a function of injection depth. We performed laser-coupled injections into a light-scattering polyacrylamide gel, while recording high-speed videos of the diffuse light exiting from the side and surface of the phantom. The centroid of the light distribution exiting from the side of the phantom was used as the estimate for the injection depth. A strong correlation was found between the depth of the centroid and the surface light profile, showing that it is possible to infer the injection depth from the spatial distribution of light around the injection site alone.
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