Form-biattenuance ( chi) in biological tissue arises from anisotropic light scattering by regularly oriented cylindrical fibers and results in a differential attenuation (diattenuation) of light amplitudes polarized parallel and perpendicular to the fiber axis (eigenpolarizations). Form-biattenuance is complimentary to form-birefringence (n) which results in a differential delay (phase retardation) between eigenpolarizations. We justify the terminology and motivate the theoretical basis for form-biattenuance in depth-resolved polarimetry. A technique to noninvasively and accurately quantify form-biattenuance which employs a polarization-sensitive optical coherence tomography (PS-OCT) instrument in combination with an enhanced sensitivity algorithm is demonstrated on ex vivo rat tail tendon (mean chi = 5.3.10-4, N = 111), rat Achilles tendon ( chi = 1.3.10-4, N = 45), chicken drumstick tendon ( chi = 2.1.10-4, N = 57), and in vivo primate retinal nerve fiber layer ( chi = 0.18.10-4, N = 6). A physical model is formulated to calculate the contributions of chi and n to polarimetric transformations in anisotropic media.

Polarization-sensitive optical coherence tomography provides high-resolution cross-sectional characterization of birefringence in turbid media. Weakly birefringent biological tissues such as the retinal nerve fiber layer (RNFL) require advanced speckle noise reduction for high-sensitivity measurement of form birefringence. We present a novel method for high-sensitivity birefringence quantification by using enhanced polarization-sensitive optical coherence tomography (EPS-OCT) and introduce the polarimetric signal-to-noise ratio, a mathematical tool for analyzing speckle noise in polarimetry. Multiple incident polarization states and non-linear fitting of normalized Stokes vectors allow determination of retardation with +/-1 degrees uncertainty with invariance to unknown unitary polarization transformations. Results from a weakly birefringent turbid film and in vivo primate RNFL are presented. In addition, we discuss the potential of EPS-OCT for noninvasive quantification of intracellular filamentous nanostructures, such as neurotubules in the RNFL that are lost during the progression of glaucoma.

These findings suggest that OCT holds promise for the identification of features defining vulnerable plaque including fibrous cap thickness, lipid core size, and the percentage of lipid content.

This paper considers an approach to teaching ethics in bioengineering based on the How People Learn (HPL) framework. Curricula based on this framework have been effective in mathematics and science instruction from the kindergarten to the college levels. This framework is well suited to teaching bioengineering ethics because it helps learners develop "adaptive expertise". Adaptive expertise refers to the ability to use knowledge and experience in a domain to learn in unanticipated situations. It differs from routine expertise, which requires using knowledge appropriately to solve routine problems. Adaptive expertise is an important educational objective for bioengineers because the regulations and knowledge base in the discipline are likely to change significantly over the course of their careers. This study compares the performance of undergraduate bioengineering students who learned about ethics for stem cell research using the HPL method of instruction to the performance of students who learned following a standard lecture sequence. Both groups learned the factual material equally well, but the HPL group was more prepared to act adaptively when presented with a novel situation.

This paper is an investigation of the How People Learn (HPL)Legacy Cycle's ability to expand adaptive expertise across the developmental span of high school and college. Participants included high school and college students. Pre-test data indicated younger students (high school and first-year college students) were less knowledgeable about the science of stem cells than older students (second-, third-, and fourth year college students), and all students were low in adaptiveness. Post-test data showed that younger students achieved parity with the more advanced students in basic scientific knowledge. The younger students also became highly adaptive by the post-test, but the older students did not advance beyond their pre-curriculum levels. We hypothesize that the older students began the intervention with more preconceived notions about stem cells, and thus were less able to think and analyze flexibly within that framework.