Polarization-resolved second-harmonic-generation optical coherence tomography in collagen

We describe a novel imaging technique, second-harmonic-generation optical coherence tomography (SHOCT). This technique combines the spatial resolution and depth penetration of optical coherence tomography (OCT) with the molecular sensitivity of second-harmonic-generation spectroscopy. As a consequence of the coherent detection required for OCT, polarization-resolved images arise naturally. We demonstrate this new technique on a skin sample from the belly of Icelandic salmon, acquiring polarization-resolved SHOCT and OCT images simultaneously

Pump-probe scheme for optical coherence tomography using indocyanine green mixed with albumin or human plasma

Use of indocyanine green (ICG) in a pump-probe scheme for OCT is proposed. The study illustrates that ICG in protein solution shows unusual pump-probe imaging potential, indicating its usefulness as a contrast agent for OCT

Spectral triangulation molecular contrast optical coherence tomography with indocyanine green as the contrast agent

We report a new molecular contrast optical coherence tomography (MCOCT) implementation that profiles the contrast agent distribution in a sample by measuring the agent's spectral differential absorption. The method, spectra triangulation MCOCT, can effectively suppress contributions from spectrally dependent scatterings from the sample without a priori knowledge of the scattering properties. We demonstrate molecular imaging with this new MCOCT modality by mapping the distribution of indocyanine green, a FDA-approved infrared red dye, within a stage 54 Xenopus laevis

Molecular contrast optical coherence tomography: SNR comparison of techniques and introduction of ground state recovery pump-probe OCT

Molecular contrast OCT (MCOCT) is an extension of OCT in which specific molecular species are imaged based on their spectroscopic characteristics. In order to improve the sensitivity and specificity of MCOCT, several techniques have recently been introduced which depend upon coherent detection of inelastically scattered light from molecules of interest in a sample. These techniques include harmonic generation, coherent anti-Stokes Raman scattering, and several different forms of pump-probe spectroscopy. We have developed a theoretical framework to facilitate the comparison of different inelastic scattering-based contrast mechanisms for molecular contrast OCT. This framework is based upon the observation that since the noise floor is defined by the reference arm power in a shot-noise limited heterodyne detection system, the relevant comparison among the techniques is isolated to the available molecular-specific signal power. We have derived the value of the molecular contrast signal power for second harmonic generation OCT (SHOCT) and three different pump-probe OCT (PPOCT) techniques. Motivated by this analysis, we have constructed a preliminary ground state recovery pump-probe OCT system, and demonstrated its performance using rhodamine 6G as the MCOCT contrast agent

Distance-Based Habitat Associations of Northern Bobwhites in a Fescue-Dominated Landscape in Kansas

Northern bobwhites (Colinus virginianus) have a wide distribution across North America which influences its’ associations with habitats in a variety of landscapes. We used radio-marked bobwhites and Euclidean distance to characterize land cover associations of bobwhites at generalized level 1 and specific level 2 land cover classifications during the reproductive (15 Apr-14 Oct) and covey (15 Oct-14 Apr) periods in southeastern Kansas from 2003 to 2005. Habitat associations occurred during the reproductive (Wilkes’ k 1⁄4 0.04, F6,36 1⁄4 143.682, P , 0.001) and covey (Wilkes’ k 1⁄4 0.056, F6, 29 1⁄4 81.99, P , 0.001) periods. Ranking of the reproductive period habitats indicated bobwhites preferred locations in close proximity to fescue (Festuca spp.) over all other habitats. Coveys preferred locations in close proximity to woody cover. Bobwhites were found to associate with specific habitats at the level 2 land cover classification during the reproductive (Wilkes’ k 1⁄4 0.006, F16, 26 1⁄4 284.483, P , 0.001) and covey (Wilkes’ k 1⁄4 0.004, F16, 19 1⁄4 276.037, P , 0.001) periods. Bobwhites preferred locations in close proximity to fescue pastures and roads equally over all other habitats during the reproductive period. Coveys preferred locations in close proximity to roads and Conservation Reserve Program lands during the covey period. Fescue pastures may be avoided by bobwhites during the covey period, provided adequate cover is not provided, but bobwhites are strongly associated with them during the reproductive period because they meet nesting and brooding needs not met by other habitats

Spectral domain phase microscopy for local measurements of cytoskeletal rheology in single cells

We present spectral domain phase microscopy (SDPM) as a new tool for measurements at the cellular scale. SDPM is a functional extension of spectral domain optical coherence tomography that allows for the detection of cellular motions and dynamics with nanometer-scale sensitivity in real time. Our goal was to use SDPM to investigate the mechanical properties of the cytoskeleton of MCF-7 cells. Magnetic tweezers were designed to apply a vertical force to ligand-coated magnetic beads attached to integrin receptors on the cell surfaces. SDPM was used to resolve cell surface motions induced by the applied stresses. The cytoskeletal response to an applied force is shown for both normal cells and those with compromised actin networks due to treatment with Cytochalasin D. The cell response data were fit to several models for cytoskeletal rheology, including one- and two-exponential mechanical models, as well as a power law. Finally, we correlated displacement measurements to physical characteristics of individual cells to better compare properties across many cells, reducing the coefficient of variation of extracted model parameters by up to 50%

In vivo vibrometry inside the apex of the mouse cochlea using spectral domain optical coherence tomography

Sound transduction within the auditory portion of the inner ear, the cochlea, is a complex nonlinear process. The study of cochlear mechanics in large rodents has provided important insights into cochlear function. However, technological and experimental limitations have restricted studies in mice due to their smaller cochlea. These challenges are important to overcome because of the wide variety of transgenic mouse strains with hearing loss mutations that are available for study. To accomplish this goal, we used spectral domain optical coherence tomography to visualize and measure sound-induced vibrations of intracochlear tissues. We present, to our knowledge, the first vibration measurements from the apex of an unopened mouse cochlea

Molecular contrast optical coherence tomography: SNR comparison of techniques and introduction of ground state recovery pump-probe OCT

Molecular contrast OCT (MCOCT) is an extension of OCT in which specific molecular species are imaged based on their spectroscopic characteristics. In order to improve the sensitivity and specificity of MCOCT, several techniques have recently been introduced which depend upon coherent detection of inelastically scattered light from molecules of interest in a sample. These techniques include harmonic generation, coherent anti-Stokes Raman scattering, and several different forms of pump-probe spectroscopy. We have developed a theoretical framework to facilitate the comparison of different inelastic scattering-based contrast mechanisms for molecular contrast OCT. This framework is based upon the observation that since the noise floor is defined by the reference arm power in a shot-noise limited heterodyne detection system, the relevant comparison among the techniques is isolated to the available molecular-specific signal power. We have derived the value of the molecular contrast signal power for second harmonic generation OCT (SHOCT) and three different pump-probe OCT (PPOCT) techniques. Motivated by this analysis, we have constructed a preliminary ground state recovery pump-probe OCT system, and demonstrated its performance using rhodamine 6G as the MCOCT contrast agent

Spectral domain phase microscopy for local measurements of cytoskeletal rheology in single cells

We present spectral domain phase microscopy (SDPM) as a new tool for measurements at the cellular scale. SDPM is a functional extension of spectral domain optical coherence tomography that allows for the detection of cellular motions and dynamics with nanometer-scale sensitivity in real time. Our goal was to use SDPM to investigate the mechanical properties of the cytoskeleton of MCF-7 cells. Magnetic tweezers were designed to apply a vertical force to ligand-coated magnetic beads attached to integrin receptors on the cell surfaces. SDPM was used to resolve cell surface motions induced by the applied stresses. The cytoskeletal response to an applied force is shown for both normal cells and those with compromised actin networks due to treatment with Cytochalasin D. The cell response data were fit to several models for cytoskeletal rheology, including one- and two-exponential mechanical models, as well as a power law. Finally, we correlated displacement measurements to physical characteristics of individual cells to better compare properties across many cells, reducing the coefficient of variation of extracted model parameters by up to 50%

Enhanced Optical Coupling and Raman Scattering via Microscopic Interface Engineering

Spontaneous Raman scattering is an extremely powerful tool for the remote detection and identification of various chemical materials. However, when those materials are contained within strongly scattering or turbid media, as is the case in many biological and security related systems, the sensitivity and range of Raman signal generation and detection is severely limited. Here, we demonstrate that through microscopic engineering of the optical interface, the optical coupling of light into a turbid material can be substantially enhanced. This improved coupling facilitates the enhancement of the Raman scattering signal generated by molecules within the medium. In particular, we detect at least two-orders of magnitude more spontaneous Raman scattering from a sample when the pump laser light is focused into a microscopic hole in the surface of the sample. Because this approach enhances both the interaction time and interaction region of the laser light within the material, its use will greatly improve the range and sensitivity of many spectroscopic techniques, including Raman scattering and fluorescence emission detection, inside highly scattering environments