Noise statistics of phase-resolved optical coherence tomography imaging: single-and dual-beam-scan Doppler optical coherence tomography.

Noise statistics of phase-resolved optical coherence tomography (OCT) imaging are complicated and involve noises of OCT, correlation of signals, and speckles. In this paper, the statistical properties of phase shift between two OCT signals that contain additive random noises and speckle noises are presented. Experimental results obtained with a scattering tissue phantom are in good agreement with theoretical predictions.

High-penetration swept source Doppler optical coherence angiography by fully numerical phase stabilization.

A high-penetration swept-source optical coherence tomography (HP-SS-OCT) system based on a 1-μm short cavity laser is developed. Doppler OCT processing is applied, along with a custom-made numerical phase stabilization algorithm; this process does not require additional calibration hardware. Thus, our phase stabilization method is simple and can be employed in a variety of SS-OCT systems.

Dual-beam-scan Doppler optical coherence angiography for birefringence-artifact-free vasculature imaging.

Dual-beam-scan Doppler optical coherence angiography (DB-OCA) enables high-speed, high-sensitivity blood flow imaging. However, birefringence of biological tissues is an obstacle to vasculature imaging. Here, the influence of polarization and birefringence on DB-OCA imaging was analyzed.

Variable velocity range imaging of the choroid with dual-beam optical coherence angiography.

In this study, we present dual-beam Doppler optical coherence angiography with variable beam separation. Altering beam distance, independently of the scanning protocol, provides a flexible way to select the velocity range of detectable blood flow. This system utilized a one-micrometer wavelength light source to visualize deep into the posterior eye, i.

Enhanced imaging of choroidal vasculature by high-penetration and dual-velocity optical coherence angiography.

Dual-beam-scan Doppler optical coherence angiography (DB-OCA) with a 1-μm-wavelength probe is demonstrated for improved in vivo choroidal angiograms of the human eye. This method utilizes two scanning beams with spatial and temporal separation on the retina, and provides two measurable velocity ranges. The method achieves higher sensitivity to very low velocity flows than conventional Doppler optical coherence tomography.

Comprehensive in vivo micro-vascular imaging of the human eye by dual-beam-scan Doppler optical coherence angiography.

Comprehensive angiography provides insight into the diagnosis of vascular-related diseases. However, complex microvascular networks of unstable in vivo organs such as the eye require micron-scale resolution in three dimensions and a high sampling rate to access a wide area as maintaining the high resolution. Here, we introduce dual-beam-scan Doppler optical coherence angiography (OCA) as a label-free comprehensive ophthalmic angiography that satisfies theses requirements.

Parabolic BM-scan technique for full range Doppler spectral domain optical coherence tomography.

A full range spectral domain optical coherence tomography (SD-OCT) technique that relies on the linear phase modulation of one of the interferometer arms has been widely utilized. Although this method is useful, the mirror image elimination is not perfect for samples in which regions with high axial motion exist. In this paper, we introduce a new modulation pattern to overcome this mirror image elimination failure.

Analysis of simulated and experimental backscattered images of turbid media in linearly polarized light: estimation of the anisotropy factor.

Optical characterization of biological tissues is of real interest to improve medical diagnosis, in particular in the detection of precancerous tissues. We propose a new, noninvasive method allowing the estimation of the anisotropy factor. This method is based on the image analysis of the Q element of the Stokes vector backscattered from the turbid medium.

Half-ball lens couples a beveled fiber probe for depth-resolved spectroscopy: Monte Carlo simulations.

In this study, we propose a beveled fiber-optic probe coupled with a half-ball lens for improving the depth-resolved fluorescence measurements of epithelial tissue. The Monte Carlo (MC) simulation results show that for a given excitation-collection fiber separation, the probe design with a bevel-angled collection fiber is more sensitive to detect fluorescence photons emitted from the shallow layer of tissue, whereas the flat-tip collection fiber is in favor of probing fluorescence photons originating from deeper tissue areas. This compact half-ball lens-beveled fiber probe design has the potential to facilitate the depth-resolved fluorescence detection of epithelial tissue.

Estimation of optical properties of turbid media: experimental comparison of spatially and temporally resolved reflectance methods.

We compare two methods for the optical characterization of turbid media. The estimates of the absorption and reduced scattering coefficients (mu(a) and mu(')(s)) by a spatially resolved method and a time-resolved method are performed on tissue-like phantoms. Aqueous suspension of microspheres and Intralipid are used as scattering media with the addition of ink as an absorber.

Beveled fiber-optic probe couples a ball lens for improving depth-resolved fluorescence measurements of layered tissue: Monte Carlo simulations.

In this study, we evaluate the feasibility of designing a beveled fiber-optic probe coupled with a ball lens for improving depth-resolved fluorescence measurements of epithelial tissue using Monte Carlo (MC) simulations. The results show that by using the probe configuration with a beveled tip collection fiber and a flat tip excitation fiber associated with a ball lens, discrimination of fluorescence signals generated in different tissue depths is achievable. In comparison with a flat-tip collection fiber, the use of a large bevel angled collection fiber enables a better differentiation between the shallow and deep tissue layers by changing the excitation-collection fiber separations.

Backscattered stokes vectors of turbid media: anisotropy factor and reduced scattering coefficient estimation.

Optical characterization of biological tissues is of real interest to improve medical diagnosis and in particular in the detection of precancerous tissues. The reduced scattering coefficient micro's and the absorption coefficient microa are the most commonly retrieved coefficients. Some methods also allow to obtain the anisotropy factor g, but only few of them are non-invasive.

Activity of the human visual cortex measured non-invasively by diffusing-wave spectroscopy.

Activity of the human visual cortex, elicited by steady-state flickering at 8Hz, is non-invasively probed by multi-speckle diffusingwave spectroscopy (DWS). Parallel detection of the intensity fluctuations of statistically equivalent, but independent speckles allows to resolve stimulation-induced changes in the field autocorrelation of multiply scattered light of less than 2%. In a group of 9 healthy subjects we find a faster decay of the field autocorrelation function during the stimulation periods for data measured with a long-distance probe (30mm source-receiver distance) at 2 positions over the occipital cortex (t-test: t(8) = -2.

Diffusing-wave spectroscopy from head-like tissue phantoms: influence of a non-scattering layer.

We investigate the influence of a non-scattering layer on the temporal field autocorrelation function of multiple scattered light from a multilayer turbid medium such as the human head. Data from Monte Carlo simulations show very good agreement with the predictions of the correlation-diffusion equation with boundary conditions taking into account non-diffusive light transport within the non-scattering layer. Field autocorrelation functions measured at the surface of a multilayer phantom including a non-scattering layer agree well with theory and simulations when the source-receiver distance is significantly larger than the depth and the thickness of the non-scattering layer.

Small-animal MRI: signal-to-noise ratio comparison at 7 and 1.5 T with multiple-animal acquisition strategies.

Objective: The purpose of this study was to compare the signal-to-noise ratio (SNR) of phantom and rat brain images performed at 1.5 T on a clinical MR system and at 7 T on a small-animal experimental system. Comparison was carried out by taking into account SNR values based on a single sample acquisition at 1.

Pulsation-resolved deep tissue dynamics measured with diffusing-wave spectroscopy.

We present a technique for measuring transient microscopic dynamics within deep tissue with sub-second temporal resolution, using diffusing-wave spectroscopy with gated single-photon avalanche photodiodes (APDs) combined with standard ungated multi-tau correlators. Using the temporal autocorrelation function of a reference signal allows to correct the temporal intensity autocorrelation function of the sample signal for the distortions induced by the non-constant average photon count rate. We apply this technique to pulsation-synchronized measurements of tissue dynamics in humans.

Scattering coefficient determination in turbid media with backscattered polarized light.

A simple empirical method is presented to determine the scattering coefficient mu' s from backscattered polarized images of turbid media. It uses the ratio, pixel by pixel, of two images that are the second and the first backscattered Stokes parameter images Q and I, respectively. Taking this image ratio, then integrating it over the azimuth angle, we get a function depending on the distance from the light entrance point.

Geometric depolarization in patterns formed by backscattered light.

We formulate a framework to extend the idea of Berry's topological phase to multiple light scattering, and in particular to backscattering of linearly polarized light. We show that the randomization of the geometric Berry's phases in the medium leads to a loss of the polarization degree of the light, i.e.

Description and time reduction of a Monte Carlo code to simulate propagation of polarized light through scattering media.

Propagation of polarized light through a scattering medium has been studied with a Monte Carlo code to obtain polarized backscattered images. Studies of these backscattered patterns obtained with polarized illumination can be used as a technique to characterize the medium anisotropy factor g. First we present the different steps of the Monte Carlo simulation that describe polarized light propagation in a turbid medium.