Depts. of Biomedical Engineering & Dermatology, Oregon Health & Science University
“Optically probing the nanoarchitecture of cells and tissues.”
Optical measurements are sensitive to structures on the size scale of a wavelength of light. Hence, cellular and extra-cellular structures with sizes in the range of 200-2000 um dominate optical measurements of biological tissues. The contribution from very small structures (<200 um) is still detectable, however, as apparent “Rayleigh scattering” which is significant in tissues with collagen. Two measurements are able to discern the size distribution:
(1) Confocal reflectance measurements as the depth position (z) of the focus is scanned down into the tissue, R(z) = rho exp(-mu z). In this case, the factor rho is especially sensitive to the size distribution of the scattering structure within a tissue. Using rho, we have detected a single gene mutation (osteogenesis imperfecta) in mouse skin. We have detected the degradation of collagen fibers into fibrils by metal-metalloproteinases. We have detected the effects of “optical clearing” of dermis when dermis is soaked in glycerol.
(2) Wavelength dependence of diffuse light reflectance. In this case, the size distribution of structures in a tissue is described by A (d/1nm)^-B, a fractal distribution of sizes (d = diameter of structure). Such a distribution yields a wavelength (lambda [nm]) dependent reduced scattering coefficient, mus'(lambda) = a (lambda/1nm)^-b. The relationship of b versus B will be shown, along with values of b and apparent B for soft tissues and skin from the literature. Hence a diffuse light spectrum can characterize the sub-micron size distribution of the tissue structures.
Such measurements offer an opportunity to assess and monitor the nanoarchitecture and microarchitecture of skin and other tissues. Detecting the effects of pathology, actinic damage, and pharmaceuticals on the skin are potential applications of these non-invasive optical methods.
Steven L. Jacques, Ph.D., received a B.S. degree in Biology at M.I.T., and an M.S. degree in Electrical Engineering and Computer Science and a Ph.D. degree in Biophysics and Medical Physics from the University of California-Berkeley (1984), where he used dielectric microwave measurements to explore the in vivo distribution of water in the stratum corneum of human skin.
His postdoctoral work was at the Wellman Center for Photomedicine at Massachusetts General Hospital, rising to the position of Lecturer in Dermatology/Bioengineering, Harvard Medical School. His team developed the use of Monte Carlo computer simulations to study optical transport in biological tissues, which is now widely used in the field of biophotonics.
In 1988, he joined the University of Texas M. D. Anderson Cancer as an Assistant Professor of Urology/Biophysics and established a laboratory developing novel laser and optical methods for medicine, later achieving a tenured position as Associate Professor. He developed a hand-held spectrometer and the analysis software to noninvasively measure hyperbilirubinemia in newborns. This device was patented, licensed, and FDA approved to replace painful heel stick tests, and is now in practice in neonatal care. As of 2009, over 20 million newborns had been tested with the device.
In 1996, he joined the Oregon Health & Science University in Portland, Oregon, where he now serves as Professor of Dermatology and Biomedical Engineering. His work continues on developing novel uses of optical technologies for both therapy and diagnosis. He developed a hand-held polarized light camera to visualize skin cancer margins and guide surgical excision, tested in clinical trials and licensed to a company. He developed in vivo sub-nm measurements of vibration of the cochlear membrane of the inner ear in animal models.
He currently works on bridging between the possibilities afforded by optical technologies and the needs of molecular and cellular biology. In particular, he is developing novel microscopes that are sensitive to the ultrastructure of cells and tissues. A current project is imaging the interaction of extracellular matrix and cancer cells (breast, head and neck).
When: Wednesday, May 1, 2013 4:10 PM
Where: 1005 GBSF