Directional blood flow imaging in volumetric optical microangiography achieved by digital frequency modulation.

An effective digital frequency modulation approach to achieve directional blood flow imaging within microcirculations in tissue beds in vivo for optical microangiography is presented. The method only requires the system to capture one three-dimensional data set within which the interferograms are modulated by a constant frequency modulation that gives one directional flow information. The result is that the imaging speed is doubled and the computational load is halved.

In vivo volumetric imaging of vascular perfusion within human retina and choroids with optical micro-angiography.

Optical micro-angiography (OMAG), based on Fourier domain optical coherence tomography (OCT), is a recently developed imaging modality that provides dynamic blood flow imaging within microcirculation tissue beds in vivo. This paper presents its first application in imaging the blood circulations in posterior chamber of human eye. To eliminate/minimize the motion artifacts in OMAG flow image caused by the inevitable subject movement, we describe a method to compensate the bulk tissue motion by use of phase changes in sequential OCT A scan signals.

Penetration kinetics of dimethyl sulphoxide and glycerol in dynamic optical clearing of porcine skin tissue in vitro studied by Fourier transform infrared spectroscopic imaging.

By use of a Fourier transform infrared (FTIR) spectroscopic imaging technique, we examine the dynamic optical clearing processes occurring in hyperosmotically biocompatible agents penetrating into skin tissue in vitro. The sequential collection of images in a time series provides an opportunity to assess penetration kinetics of dimethyl sulphoxide (DMSO) and glycerol beneath the surface of skin tissue over time. From 2-D IR spectroscopic images and 3-D false color diagrams, we show that glycerol takes at least 30 min to finally penetrate the layer of epidermis, while DMSO can be detected in epidermis after only 4 min of being topically applied over stratum corneum sides of porcine skin.

Quantitative analysis on tongue inspection in traditional Chinese medicine using optical coherence tomography.

Tongue inspection (TI) is an important and unique diagnostic method in traditional Chinese medicine (TCM), because significant connections between various viscerae diseases and abnormalities in the tongue have been verified. In TCM, TI is simple and non invasive, but in clinical applications, TI is subjectively based on the experience and technique of physicians. To avoid this problem, optical coherence tomography (OCT) imaging is introduced here for TI.

Statistics of local speckle contrast.

In describing the first-order properties of laser speckle under polarized illumination conditions, it is almost an article of faith that the contrast is unity. In many processing schemes, however, the contrast defined as the quotient of the standard deviation and the mean is calculated over a localized spatial region. In such cases, this local contrast displays a distribution of values that can depart substantially from unity.

Use of a scanner to modulate spatial interferograms for in vivo full-range Fourier-domain optical coherence tomography.

We report a new yet simple method to achieve full-range complex Fourier-domain optical coherence tomography (OCT) for in vivo imaging. The method utilizes a scanner that is dedicated for lateral scanning in the system to introduce a constant carrier frequency into the OCT spectral interferograms during the scanning. This is achieved by simply offsetting the sampling beam spot away from the pivot point of the scanning mirror.

Quantitative temporal speckle contrast imaging for tissue mechanics.

We demonstrate through a series of simulations that by parameterizing the temporal speckle contrast statistic from a sequence of translating speckle images on a number of experimental constants, the local temporal contrast can be used to quantitatively assess local motion, provided that the spatial and temporal Nyquist sampling criteria are both met. We develop a simple exponential model for quantifying speckle motion for speckle patterns that display arbitrary intensity statistics and provide suggestions for optimizing both the experimental acquisition of speckle data and the temporal contrast analysis of the data. The confounding effects of uncorrelated noise are also discussed.

Three-dimensional optical micro-angiography maps directional blood perfusion deep within microcirculation tissue beds in vivo.

Optical micro-angiography (OMAG) is a recently developed method of imaging localized blood perfusion at capillary level resolution within microcirculatory beds. This paper reports that the OMAG is capable of directional blood perfusion mapping in vivo. This is achieved simply by translating the mirror located in the reference arm back and forth while 3D imaging is performed.

Optimization of image-forming optics for transmission optical projection tomography.

A new optical system for transmission optical projection tomography (TOPT) is presented to reduce the divergence of the projection data from the true parallel projections. This is performed by introducing an iris at the back focus of the objective lens. The influence of the defocusing on TOPT is demonstrated by computational simulations and experiments.

Fourier domain optical coherence tomography achieves full range complex imaging in vivo by introducing a carrier frequency during scanning.

The author describes a Fourier domain optical coherence tomography (FDOCT) system that is capable of full range complex imaging in vivo. This is achieved by introducing a constant carrier frequency into the OCT spectral interferograms at the time when imaging is performed. The complex functions of the spatial interferograms formed by each single wavelength are constructed before performing the Fourier transformation to localize the scatters within a sample.

Mapping of cerebro-vascular blood perfusion in mice with skin and skull intact by Optical Micro-AngioGraphy at 1.3 mum wavelength.

Optical micro-angiography (OMAG) was developed to achieve volumetric imaging of the microstructures and dynamic cerebrovascular blood perfusion in mice with capillary level resolution and high signal-to-background ratio. In this paper, we present a high-speed and high-sensitivity OMAG imaging system by using an InGaAs line scan camera and broadband light source at 1.3 mum wavelength for enhanced imaging depth in tissue.

Spectral domain polarization sensitive optical coherence tomography achieved by single camera detection.

We present a spectral domain polarization sensitive optical coherence tomography (PSOCT) system that incorporates: 1) a spectrometer configured with a single line-scan camera for spectral interferogram detection, 2) a reference delay line assembly that provides a fixed optical pathlength delay between the lights of two orthogonal polarization states, and 3) a moving reference mirror that introduces a constant modulation frequency in the spatial spectral interferograms while the probe beam is scanned over the sample. The system utilizes the full range of complex Fourier plane for polarization sensitive imaging, where OCT images formed by the vertical and horizontal polarization beam components appear adjacent to each other. It is able to provide imaging of retardation, fast optic axis and backscattered intensity of the interrogated biological tissue.

A novel optical coherence tomography-based micro-indentation technique for mechanical characterization of hydrogels.

Depth-sensing micro-indentation has been well recognized as a powerful tool for characterizing mechanical properties of solid materials due to its non-destructive approach. Based on the depth-sensing principle, we have developed a new indentation method combined with a high-resolution imaging technique, optical coherence tomography, which can accurately measure the deformation of hydrogels under a spherical indenter at constant force. The Hertz contact theory has been applied for quantitatively correlating the indentation force and the deformation with the mechanical properties of the materials.

Three dimensional optical angiography.

With existing optical imaging techniques three-dimensional (3-D) mapping of microvascular perfusion within tissue beds is severely limited by the efficient scattering and absorption of light by tissue. To overcome these limitations we have developed a method of optical angiography (OAG) that can generate 3-D angiograms within millimeter tissue depths by analyzing the endogenous optical scattering signal from an illuminated sample. The technique effectively separates the moving and static scattering elements within tissue to achieve high resolution images of blood flow, mapped into the 3-D optically sectioned tissue beds, at speeds that allow for perfusion assessment in vivo.

Time-resolved simultaneous measurement of group index and physical thickness during photopolymerization of resin-based dental composite.

Light-activated resin-based dental composites are increasingly replacing dental amalgam. However, these materials are limited by inefficient setting reactions as a function of depth that constrain the maximum extent of cure. Insufficient curing can contribute to an overall reduction in biocompatibility of the material.

Random media characterization using the analysis of diffusing light data on the basis of an effective medium model.

The transport properties of dense random media such as rutile powder layers and polyball suspensions are analyzed in visible and near infrared on the basis of experimental data on coherent backscattering, diffuse transmittance, and low-coherence interferometry. The developed technique of retrieval of the transport parameters of examined scattering media allows the evaluation of the transport mean free path l* and the effective refractive index n(ef) of the medium without a priori knowledge of the optical properties of the scattering particles. It is found that with decreasing wavelength lambda(0) the value of localization parameter 2pin(ef)l*/lambda(0) of the studied rutile samples abruptly drops and approaches approximately 2.

[Progress in research and application of time-resolved optoacoustic method in biomedicine].

Based on optoacoustic effect, time-resolved optoacoustic technique effectively combines optical technology with acoustic technology and partly overcomes the biological tissue's scatter characteristics which might influence the results of measurement. Optoacoustic technique has the advantages of high sensitivity and high resolution and has been widely applied in biomedicine field. In this paper, the measuring principles, the key technique, application and future direction of this technique are synthetically reviewed to promote the research in theory and application in the future.

OCT-based elastography for large and small deformations.

We present two approaches to speckle tracking for optical coherence tomography (OCT)-based elastography, one appropriate for small speckle motions and the other for large, rapid speckle motions. Both approaches have certain advantages over traditional cross-correlation based motion algorithms. We apply our algorithms to quantifying the strain response of a mechanically inhomogeneous, bi-layered polyvinyl alcohol tissue phantom that is subjected to either small or large dynamic compressive forces while being imaged with a spectral domain OCT system.

Imaging using parallel integrals in optical projection tomography.

We develop and demonstrate improved image-forming optics for optical projection tomography (OPT), with which the parallel integral throughout an object can be obtained. This method results in an improved resolution for OPT images, especially for the cross sections far from the optical axis of the image-forming optics. We find the optimal configuration used in our OPT system by use of a point spread function and simulation technique.

Imaging the mechanical stiffness of skin lesions by in vivo acousto-optical elastography.

Optical elastography is an imaging modality that relies on variations in the local mechanical properties of biological tissues as the contrast mechanism for image formation. Skin lesions, such as melanomas and other invasive conditions, are known to alter the arrangement of collagen fibers in the skin and thus should lead to alterations in local skin mechanical properties. We report on an acousto-optical elastography (AOE) imaging modality for quantifying the mechanical behavior of skin lesions.

Real-time flow imaging by removing texture pattern artifacts in spectral-domain optical Doppler tomography.

We present a new, simple method to suppress texture pattern artifacts induced by the optical heterogeneity of tissues to improve the performance of flow imaging for real-time phase-resolved optical Doppler tomography. The method performs transverse scanning of the probe beam in the forward and then reverse directions, and it takes average of the spatial phase changes between them to obtain the final velocity image. It relies on the fact that the phase changes between successive axial scans due to the optical heterogeneity of the sample are time independent, while those due to the moving particles are time dependent.

The potential role of optical coherence tomography in the evaluation of vulnerable carotid atheromatous plaques: a pilot study.

Purpose: The decision to intervene surgically in patients with carotid artery disease is based on the presence of symptoms, along with the severity of carotid artery stenosis as assessed by ultrasound or X-ray computed tomography (CT). Optical coherence tomography (OCT) is a relatively new imaging technique that offers potential in the identification of, as well as the distinction between, stable and unstable atherosclerotic plaques. The purpose of our study was to evaluate whether OCT can be used as a noninvasive diagnostic tool to reveal the morphology of carotid stenosis from the adventitial surface of the carotid artery.

Matrix approach to quantitative refractive index analysis by Fourier domain optical coherence tomography.

The rapid development in the field of optical coherence tomography has demanded increasingly sophisticated numerical models to enable the interpretation of image data and extract quantitative results. We use a matrix formulation of Fresnel's equations for multilayered media to extract layer-dependent thickness and refractive index directly from Fourier domain optical coherence tomography spectrograms. An eigenanalysis spectral decomposition approach is used to constrain the least squares fitting algorithm, avoiding the need for initial estimates of the parameter values.

A practical approach to eliminate autocorrelation artefacts for volume-rate spectral domain optical coherence tomography.

A simple method is introduced to eliminate the autocorrelation artefacts in ultrafast spectral domain optical coherence tomography (SOCT) by use of the ensemble average of spectra within an individual B scan as the background signal, and then subtracting this from all the A scans within that B scan before performing the FFTs. This is updated continuously frame by frame. The method is tested on a volume-rate (C-mode) SOCT system to image the human fingertip in vivo with a volume rate at 8 s.