A novel phase resolved optical coherence tomographic (OCT) and optical Doppler tomographic (ODT) system is developed for simultaneous imaging of tissue structure and physiology with high imaging speed and high spatial resolution.

The emergence of time-resolved fluorescence techniques has been very important to the study of biochemical, biophysical and biomedical research areas. Many of the advances in these fields have been technology driven. The Laboratory for Fluorescence Dynamics (LFD) has been actively involved in development of frequency domain technology for a variety of applications. Our recent work on microwave super heterodyning detectors, fluorescence lifetime resolved spectroscopy, frequency domain fluorescence imaging microscopy, fluorescence lifetime resolved stopped-flow kinetics and global methods of data analysis is summarized in this report. We provide examples of how these new technologies are applied.

We present an all-fiber, compact device for optical frequency-domain reflectometry (OFDR). The device combines a Michelson interferometer with a fiber Fabry-Perot tunable filter for rapid wavelength scanning. The free spectral range of the filter is 32 nm and scans may be completed in less than 2.5 ms. Images of the surface geometry of the material under study can be reconstructed at scan rates up to 400 Hz with an axial resolution of 20 μm.

Frequency domain spectroscopy provides a quantitative measure of the optical properties, namely µa and µs' coefficient spectra, of multiply scattering, macroscopically homogeneous media or tissue. The diffusion model for photon transport provides the theoretical framework for the analytical expressions of the optical properties. Experimentally, we intensity modulated (60 MHz) a light emitting diode, which emits between 620-700 nm. From data sets of relative phase shifts and average intensity at different source-detector separations, we calculated on the basis of the analytical expressions a wavelength resolved absorption µa (?) and scattering µs' (?) coefficient spectrum. The test material was methylene blue, whose absorption spectrum (maximum 656 nm) closely matches the wavelength profile of the diode source. The multiply scattering, macroscopically homogeneous medium for dissolving the methylene blue was provided by a diluted fat emulsion, Liposyn III. The concentrations ofboth the absorbing and scattering materials were adjusted to correspond to ranges typical of µa and µs tissues. We obtained quantitative agreement between the measured µa (?) the scattering medium and a control solution measured in a spectrophotometer under non-scattering conditions.

In this paper we discuss temporal and spatial patterns of brain hemodynamics under rest and motor stimulation conditions obtained by functional magnetic resonance imaging and simultaneous fast multi-channel near-infrared spectro-imaging in the human motor cortex. Our data indicate that the main difference between the brain hemodynamics under the repetitive stimulation and the rest conditions is not in the appearance of hemoglobin concentration changes during the stimulations (since fluctuations occur at rest as well), but in their more regular, Le. phase-synchronous with the stimulation behavior.

Polarization sensitive optical coherence tomography (PS-OCT) was used to determine the depth resolved Stokes parameters of light backscattered from highly scattering biological samples. Through simultaneous detection of the amplitude and relative phase of signal fringes in orthogonal polarization states formed by interference of light backscattered from turbid media and a mirror in the reference arm of a Michelson interferometer, changes in the Stokes parameters due to the optical phase delay between light propagating along the fast and slow axes of birefringent media were measured. Inasmuch as fibrous structures in many biological tissues influence the polarization state of light backscattered. PS-OCT is a potentially useful technique to image the structural properties of turbid biological materials. The method can also be applied to the investigation of birefringent properties in highly scattering materials such as ceramics and crystals.

We demonstrate a high-speed and wide-tuning-range swept laser for optical coherence tomography (OCT) imaging. The repetition rate of the laser is twice the speed of the polygon filter and is achieved by using two delay fibers in a Fox-Smith cavity. The performance of the laser is the following: a scanning range of 110nm centered at 1310nm, and the output power of 10mw at a 102.2 kHz sweeping rate. © 2011 Copyright SPIE - The International Society for Optical Engineering.

Cerebral vasomotion was studied on the human brain in vivo by use of multi-optode frequency domain near-infrared spectroscopy (NIRS). Vasomotion is a spontaneous oscillation with a frequency of 0. 1Hz in the arterial flow. We investigated (1) the fluctuations of cerebral hemodynamics on the dynamical characteristics of cerebral vasomotion and (2) the dynamical coupling between vasomotion in the skin and brain. We found that (1) vasomotion is temporal coherent at least for about 3min; (2) vasomotion observed from NIRS is low-dimensional chaotic with its fractal dimension of about 4.5; (3) vasomotion is spatially coherent with coherence length of about 1-2cm but cerebral vasomotion is dynamically independent from vasomotion in the skin.

In this paper, we analyzed the retinal and choroidal blood vasculature in the posterior segment of the human eye with optimized color Doppler and Doppler variance optical coherence tomography. Depth-resolved structure, color Doppler and Doppler variance images were compared. Blood vessels down to capillary level were able to be obtained with the optimized optical coherence color Doppler and Doppler variance method. For in-vivo imaging of human eyes, bulkmotion induced bulk phase must be identified and removed before using color Doppler method. It was found that the Doppler variance method is not sensitive to bulk motion and the method can be used without removing the bulk phase. A novel, simple and fast segmentation algorithm to indentify retinal pigment epithelium (RPE) was proposed and used to segment the retinal and choroidal layer. The algorithm was based on the detected OCT signal intensity difference between different layers. A spectrometer-based Fourier domain OCT system with a central wavelength of 890 nm and bandwidth of 150nm was used in this study. The 3-dimensional imaging volume contained 120 sequential two dimensional images with 2048 A-lines per image. The total imaging time was 12 seconds and the imaging area was 5x5 mm2. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).