Using the method of images, we examine the three boundary conditions commonly applied to the surface of a semi-infinite turbid medium. We find that the image-charge configurations of the partial-current and extrapolated-boundary conditions have the same dipole and quadrupole moments and that the two corresponding solutions to the diffusion equation are approximately equal. In the application of diffusion theory to frequency-domain photon-migration (FDPM) data, these two approaches yield values for the scattering and absorption coefficients that are equal to within 3%. Moreover, the two boundary conditions can be combined to yield a remarkably simple, accurate, and computationally fast method for extracting values for optical parameters from FDPM data. FDPM data were taken both at the surface and deep inside tissue phantoms, and the difference in data between the two geometries is striking. If one analyzes the surface data without accounting for the boundary, values deduced for the optical coefficients are in error by 50% or more. As expected, when aluminum foil was placed on the surface of a tissue phantom, phase and modulation data were closer to the results for an infinite-medium geometry. Raising the reflectivity of a tissue surface can, in principle, eliminate the effect of the boundary. However, we find that phase and modulation data are highly sensitive to the reflectivity in the range of 80-100%, and a minimum value of 98% is needed to mimic an infinite-medium geometry reliably. We conclude that noninvasive measurements of optically thick tissue require a rigorous treatment of the tissue boundary, boundary approach.

Amplitude-modulated light launched into multiple-scattering media, e.g., tissue, results in the propagation of density waves of diffuse photons. Photon density wave characteristics in turn depend on modulation frequency () and media optical properties. The damped spherical wave solutions to the homogeneous form of the diffusion equation suggest two distinct regimes of behavior: (1) a highfrequency dispersion regime where density wave phase velocity V has a /; dependence and (2) a low-frequency domain where V, is frequency independent. Optical properties are determined for various tissue phantoms by fitting the recorded phase () and modulation (m) response to simple relations for the appropriate regime. Our results indicate that reliable estimates of tissuelike optical properties can be obtained, particularly when multiple modulation frequencies are employed.

An optical coherence microscope (OCM) has been designed and constructed to acquire 3-dimensional images of highly scattering biological tissue. Volume-rendering software is used to enhance 3-D visualization of the data sets. Lateral resolution of the OCM is 5 µm (FWHM), and the depth resolution is 10 µm (FWHM) in tissue. The design trade-offs for a 3-D OCM are discussed, and the fundamental photon noise limitation is measured and compared with theory. A rotating 3-D image of a frog embryo is presented to illustrate the capabilities of the instrument.

We describe the development and utilization of a new imaging technology for plant biology, optical coherence microscopy (OCM), which allows true in vivo visualization of plants and plant cells. This novel technology allows the direct, in situ (e.g. plants in soil), three-dimensional visualization of cells and events in shoot tissues without causing damage. With OCM we can image cells or groups of cells that are up to 1 mm deep in living tissues, resolving structures less than 5 m in size, with a typical collection time of 5 to 6 min. OCM measures the inherent light-scattering properties of biological tissues and cells. These optical properties vary and provide endogenous developmental markers. Singly scattered photons from small (e.g. 5 ϫ 5 ϫ 10 m) volume elements (voxels) are collected, assembled, and quantitatively false-colored to form a threedimensional image. These images can be cropped or sliced in any plane. Adjusting the colors and opacities assigned to voxels allows us to enhance different features within the tissues and cells. We show that light-scattering properties are the greatest in regions of the Arabidopsis shoot undergoing developmental processes. In large cells, high light scattering is produced from nuclei, intermediate light scatter is produced from cytoplasm, and little if any light scattering originates from the vacuole and cell wall. OCM allows the rapid, repetitive, non-destructive collection of quantitative data about inherent properties of cells, so it provides a means of continuously monitoring plants and plant cells during development and in response to exogenous stimuli.Studies in plant physiology and development characteristically follow changes in space and time that occur as part of normal plant activity or in response to exogenous stimuli. Typical studies require the destruction and analysis of a plant or a tissue sample, followed by the collection and analysis of a second distinct plant or sample. Thus, biological responses or changes are inferred by comparing different plants or samples. Such approaches have been used for centuries and have produced a great deal of knowledge. However, when scientists are able to nondestructively follow biological changes, important concepts and insights have emerged. For example, critical genes involved in programmed cell death were found in Caenorhabditis elegans partially because the developing nematode is nearly transparent, allowing the fate of each cell to be followed in vivo by light microscopy (Gilbert, 1998). Similarly, an elegant fate map for Arabidopsis roots was constructed because the relatively transparent roots allow changes in individual plants to be followed continuously (Dolan et al., 1993). This study led to new discoveries such as the presence of downward communication between mature root cells and the root apical meristem and short-range control of differentiation signals (van den Berg et al., 1997a(van den Berg et al., , 1997b.Except for the relatively transparent Arabidopsis root, plants provide a challenge for in vivo an...

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Abstract. Optical coherence tomography ͑OCT͒ is an evolving noninvasive imaging modality and has been used to image the larynx during surgical endoscopy. The design of an OCT sampling device capable of capturing images of the human larynx during a typical office based laryngoscopy examination is discussed. Both patient's and physician's movements were addressed. In vivo OCT imaging of the human larynx is demonstrated. Though the long focal length limits the lateral resolution of the image, the basement membrane can still be readily distinguished. Office-based OCT has the potential to guide surgical biopsies, direct therapy, and monitor disease. This is a promising imaging modality to study the larynx. © 2006 Society of Photo-Optical Instrumentation Engineers.

We investigate the sensitivity of measurements of muscle birefringence to cross-bridge dynamics in the resting, active, and rigor states. The theory of form birefringence is reviewed, and an optical model is constructed for the form birefringence of muscle. Values for the parameters in the model are selected or deduced from the literature. As an illustration of the use of the model, plausible distributions for the orientations of cross-bridges in the resting, active, and rigor states are constructed using a model for cross-bridge dynamics suggested by Huxley and Kress (1985). The general magnitude of the predictions of our model is comparable with that of published measurements of muscle birefringence. However, the precise values of the predicted birefringence for the resting, active, and rigor states are sensitive to the assumed orientations of cross-bridges. We also investigate the dependence of muscle birefringence on sarcomere length and on disorder in the orientation of the myofilament array. We conclude that measurements of muscle birefringence can play a useful role in distinguishing between proposed models of cross-bridge dynamics.