Liquid crystal-based Mueller matrix spectral imaging polarimetry for parameterizing mineral structural organization.

Herein, we discuss the remote assessment of the subwavelength organizational structure of a medium. Specifically, we use spectral imaging polarimetry, as the vector nature of polarized light enables it to interact with optical anisotropies within a medium, while the spectral aspect of polarization is sensitive to small-scale structure. The ability to image these effects allows for inference of spatial structural organization parameters. This work describes a methodology for revealing structural organization by exploiting the Stokes/Mueller formalism and by utilizing measurements from a spectral imaging polarimeter constructed from liquid crystal variable retarders and a liquid crystal tunable filter. We provide results to validate the system and then show results from measurements on a mineral sample.

Alignment and temperature effects in liquid-crystal-based active polarimetry.

It is well known that in liquid crystal (LC)-based active polarimetry, alignment and temperature effects impact polarimeter performance. Practically speaking, when constructing a polarimetric measurement system from LC variable retarders (LCVRs), unavoidable alignment and temperature uncertainties will occur, leading to systematic error that propagates to the Mueller matrix. Typical calibration methods use only a single metric to assess polarimeter performance (the condition number) and often ignore the relationship between systematic error and specific Mueller matrix elements. Here we explore alignment and temperature effects in a Stokes generator and polarimeter, each consisting of two LCVRs, through a series of simulations to calibrate the polarimeter and measure the Mueller matrix of air. We achieve this by modifying an existing LCVR model to incorporate alignment and temperature effects. This new approach offers insight into employing LCVRs individually and associating particular Mueller matrix element error with specific LCVR effects.

In vivo measurement of epidermal thickness changes associated with tumor promotion in murine models.

The characterization of tissue morphology in murine models of pathogenesis has traditionally been carried out by excision of affected tissues with subsequent immunohistological examination. Excision-based histology provides a limited two-dimensional presentation of tissue morphology at the cost of halting disease progression at a single time point and sacrifice of the animal. We investigate the use of noninvasive reflectance mode confocal scanning laser microscopy (rCSLM) as an alternative tool to biopsy in documenting epidermal hyperplasia in murine models exposed to the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). An automated technique utilizing average axial rCSLM reflectance profiles is used to extract epidermal thickness values from rCSLM data cubes. In comparisons to epidermal thicknesses determined from hematoxylin and eosin (H&E) stained tissue sections, we find no significant correlation to rCSLM-derived thickness values. This results from method-specific artifacts: physical alterations of tissue during H&E preparation in standard histology and specimen-induced abberations in rCSLM imaging. Despite their disagreement, both histology and rCSLM methods reliably measure statistically significant thickness changes in response to TPA exposure. Our results demonstrate that in vivo rCSLM imaging provides epithelial biologists an accurate noninvasive means to monitor cutaneous pathogenesis.

Optical transillumination tomography for imaging of tissue-engineered blood vessels.

Recent progress in tissue engineering led to the development of completely biological human vessels grown from the patient's own cells. Those tissue-engineered blood vessels (TEBV) are grown on an individual basis at high costs per item, and therefore require close growth monitoring and quality control. We designed and tested an optical transillumination tomography system using red laser light to image weakly scattering specimens, such as TEBV. Fixated TEBV were imaged and the results compared to optical coherence tomography. This preliminary scanner prototype had an in-plane resolution of 50 microm and allowedto see small inhomogeneities and defects in the samples. Tissue attenuation was found to be 70 cm(-1). Main advantages of the transillumination tomography scanner over optical coherence tomography were the inexpensive instrumentation and the potential to rapidly acquire complete 3D sections with a CCD camera. The prototype presented in this study provides a basis to further improve image quality and acquisition speed.