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1.
Biomed Opt Express ; 11(4): 2007-2016, 2020 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-32341863

RESUMO

We have developed a multi-functional laser speckle imaging system, which can be operated in both the surface illumination laser speckle contrast imaging (SI-LSCI) mode and the line scan laser speckle contrast imaging (LS-LSCI) mode. The system has been applied to imaging the chicken embryos to visualize both the blood flow and morphological details of the vasculature. The experimental results demonstrated that LS-LSCI is capable of detecting and quantifying blood flow in blood vessels smaller and deeper than those detectable by conventional SI-LSCI. Furthermore, the line scan mode is also capable of producing depth-resolved absorption-based morphological images of tissue, augmenting flow-based functional images.

2.
Opt Lett ; 44(17): 4147-4150, 2019 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-31465349

RESUMO

In biological tissue, longer near-infrared wavelengths generally experience less scattering and more water absorption. Here we demonstrate an optical coherence tomography (OCT) system centered at 2.1 microns, whose bandwidth falls in the 2.2 micron water absorption optical window, for in vivo imaging of the rodent brain. We show in vivo that at 2.1 microns, the OCT signal is actually attenuated less in cranial bone than at 1.3 microns, and is also less susceptible to multiple scattering tails. We also show that the 2.2 micron window enables direct spectroscopic OCT assessment of tissue water content. We conclude that with further optimization, 2.2 micron OCT will have advantages in low-water-content tissue such as bone, as well as applications where extensive averaging is possible to compensate absorption losses.


Assuntos
Encéfalo/diagnóstico por imagem , Tomografia de Coerência Óptica/métodos , Animais , Encéfalo/metabolismo , Processamento de Imagem Assistida por Computador , Ratos , Tomografia de Coerência Óptica/instrumentação , Água/metabolismo
3.
Optica ; 5(5): 518-527, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30417035

RESUMO

Light-scattering methods are widely used in soft matter physics and biomedical optics to probe dynamics in turbid media, such as diffusion in colloids or blood flow in biological tissue. These methods typically rely on fluctuations of coherent light intensity, and therefore cannot accommodate more than a few modes per detector. This limitation has hindered efforts to measure deep tissue blood flow with high speed, since weak diffuse light fluxes, together with low single-mode fiber throughput, result in low photon count rates. To solve this, we introduce multimode fiber (MMF) interferometry to the field of diffuse optics. In doing so, we transform a standard complementary metal-oxide-semiconductor (CMOS) camera into a sensitive detector array for weak light fluxes that probe deep in biological tissue. Specifically, we build a novel CMOS-based, multimode interferometric diffusing wave spectroscopy (iDWS) system and show that it can measure ∼20 speckles simultaneously near the shot noise limit, acting essentially as ∼20 independent photon-counting channels. We develop a matrix formalism, based on MMF mode field solutions and detector geometry, to predict both coherence and speckle number in iDWS. After validation in liquid phantoms, we demonstrate iDWS pulsatile blood flow measurements at 2.5 cm source-detector separation in the adult human brain in vivo. By achieving highly sensitive and parallel measurements of coherent light fluctuations with a CMOS camera, this work promises to enhance performance and reduce cost of diffuse optical instruments.

4.
Biomed Opt Express ; 9(4): 1477-1491, 2018 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-29675296

RESUMO

Chromatic aberrations are an important design consideration in high resolution, high bandwidth, refractive imaging systems that use visible light. Here, we present a fiber-based spectral/Fourier domain, visible light OCT ophthalmoscope corrected for the average longitudinal chromatic aberration (LCA) of the human eye. Analysis of complex speckles from in vivo retinal images showed that achromatization resulted in a speckle autocorrelation function that was ~20% narrower in the axial direction, but unchanged in the transverse direction. In images from the improved, achromatized system, the separation between Bruch's membrane (BM), the retinal pigment epithelium (RPE), and the outer segment tips clearly emerged across the entire 6.5 mm field-of-view, enabling segmentation and morphometry of BM and the RPE in a human subject. Finally, cross-sectional images depicted distinct inner retinal layers with high resolution. Thus, with chromatic aberration compensation, visible light OCT can achieve volume resolutions and retinal image quality that matches or exceeds ultrahigh resolution near-infrared OCT systems with no monochromatic aberration compensation.

5.
Opt Lett ; 43(2): 198-201, 2018 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-29328237

RESUMO

Most flying-spot optical coherence tomography and optical coherence microscopy (OCM) systems use a symmetric confocal geometry, where the detection path retraces the illumination path starting from and ending with the spatial mode of a single-mode optical fiber. Here we describe a visible light OCM instrument that breaks this symmetry to improve transverse resolution without sacrificing collection efficiency in scattering tissue. This was achieved by overfilling a water immersion objective on the illumination path while maintaining a conventional Gaussian mode detection path (1/e2 intensity diameter ∼0.82 Airy disks), enabling ∼1.1 µm full width at half-maximum (FWHM) transverse resolution. At the same time, a ∼0.9 µm FWHM axial resolution in tissue, achieved by a broadband visible light source, enabled femtoliter volume resolution. We characterized this instrument according to paraxial coherent microscopy theory and, finally, used it to image the meningeal layers, intravascular red blood cell-free layer, and myelinated axons in the mouse neocortex in vivo through the thinned skull.


Assuntos
Encéfalo/diagnóstico por imagem , Aumento da Imagem/métodos , Tomografia de Coerência Óptica/métodos , Animais , Desenho de Equipamento , Luz , Camundongos , Microscopia , Fibras Ópticas
6.
Biomed Opt Express ; 8(1): 323-337, 2017 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-28101421

RESUMO

The design of a multi-functional fiber-based Optical Coherence Tomography (OCT) system for human retinal imaging with < 2 micron axial resolution in tissue is described. A detailed noise characterization of two supercontinuum light sources with different pulse repetition rates is presented. The higher repetition rate and lower noise source is found to enable a sensitivity of 96 dB with 0.15 mW light power at the cornea and a 98 microsecond exposure time. Using a broadband (560 ± 50 nm), 90/10, fused single-mode fiber coupler designed for visible wavelengths, the sample arm is integrated into an ophthalmoscope platform, similar to current clinical OCT systems. To demonstrate the instrument's range of operation, in vivo structural retinal imaging is also shown at 0.15 mW exposure with 10,000 and 70,000 axial scans per second (the latter comparable to commercial OCT systems), and at 0.03 mW exposure and 10,000 axial scans per second (below maximum permissible continuous exposure levels). Lastly, in vivo spectroscopic imaging of anatomy, saturation, and hemoglobin content in the human retina is also demonstrated.

7.
Appl Sci (Basel) ; 7(7)2017 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-30009045

RESUMO

Optical Coherence Tomography Angiography (OCTA) refers to a powerful class of OCT scanning protocols and algorithms that selectively enhance the imaging of blood vessel lumens, based mainly on the motion and scattering of red blood cells (RBCs). Though OCTA is widely used in clinical and basic science applications for visualization of perfused blood vessels, OCTA is still primarily a qualitative tool. However, more quantitative hemodynamic information would better delineate disease mechanisms, and potentially improve the sensitivity for detecting early stages of disease. Here, we take a broader view of OCTA in the context of microvascular hemodynamics and light scattering. Paying particular attention to the unique challenges presented by capillaries versus larger supplying and draining vessels, we critically assess opportunities and challenges in making OCTA a quantitative tool.

8.
Opt Express ; 24(1): 329-54, 2016 Jan 11.
Artigo em Inglês | MEDLINE | ID: mdl-26832264

RESUMO

We introduce and implement interferometric near-infrared spectroscopy (iNIRS), which simultaneously extracts optical and dynamical properties of turbid media through analysis of a spectral interference fringe pattern. The spectral interference fringe pattern is measured using a Mach-Zehnder interferometer with a frequency-swept narrow linewidth laser. Fourier analysis of the detected signal is used to determine time-of-flight (TOF)-resolved intensity, which is then analyzed over time to yield TOF-resolved intensity autocorrelations. This approach enables quantification of optical properties, which is not possible in conventional, continuous-wave near-infrared spectroscopy (NIRS). Furthermore, iNIRS quantifies scatterer motion based on TOF-resolved autocorrelations, which is a feature inaccessible by well-established diffuse correlation spectroscopy (DCS) techniques. We prove this by determining TOF-resolved intensity and temporal autocorrelations for light transmitted through diffusive fluid phantoms with optical thicknesses of up to 55 reduced mean free paths (approximately 120 scattering events). The TOF-resolved intensity is used to determine optical properties with time-resolved diffusion theory, while the TOF-resolved intensity autocorrelations are used to determine dynamics with diffusing wave spectroscopy. iNIRS advances the capabilities of diffuse optical methods and is suitable for in vivo tissue characterization. Moreover, iNIRS combines NIRS and DCS capabilities into a single modality.


Assuntos
Interferometria/instrumentação , Lasers , Nefelometria e Turbidimetria/instrumentação , Espectroscopia de Luz Próxima ao Infravermelho/instrumentação , Desenho de Equipamento , Análise de Falha de Equipamento , Luz , Reprodutibilidade dos Testes , Espalhamento de Radiação , Sensibilidade e Especificidade
9.
Opt Lett ; 40(21): 4911-4, 2015 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-26512481

RESUMO

A spectral/Fourier domain optical coherence tomography (OCT) intravital microscope using a supercontinuum light source at 1.7 µm was developed to study subcortical structures noninvasively in the living mouse brain. The benefits of 1.7 µm for deep tissue brain imaging are demonstrated by quantitatively comparing OCT signal attenuation characteristics of cortical tissue across visible and near-infrared wavelengths. Imaging of hippocampal tissue architecture and white matter microvasculature are demonstrated in vivo through thinned-skull, glass coverslip-reinforced cranial windows in mice. Applications of this novel platform include monitoring disease progression and pathophysiology in rodent models of Alzheimer's disease and subcortical dementias, including vascular dementia.


Assuntos
Hipocampo/citologia , Microscopia Intravital/instrumentação , Iluminação/instrumentação , Microvasos/citologia , Tomografia de Coerência Óptica/instrumentação , Substância Branca/irrigação sanguínea , Animais , Desenho de Equipamento , Análise de Falha de Equipamento , Aumento da Imagem/métodos , Microscopia Intravital/métodos , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Tomografia de Coerência Óptica/métodos , Substância Branca/citologia
10.
Biomed Opt Express ; 6(10): 3941-51, 2015 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-26504644

RESUMO

A method of measuring cortical oxygen metabolism in the mouse brain that uses independent quantitative measurements of three key parameters: cerebral blood flow (CBF), arteriovenous oxygen extraction (OE), and hemoglobin concentration ([HbT]) is presented. Measurements were performed using a single visible light spectral/Fourier domain OCT microscope, with Doppler and spectroscopic capabilities, through a thinned-skull cranial window in the mouse brain. Baseline metabolic measurements in mice are shown to be consistent with literature values. Oxygen consumption, as measured by this method, did not change substantially during minor changes either in the fraction of inspired oxygen (FiO2) or in the fraction of inspired carbon dioxide (FiCO2), in spite of larger variations in oxygen saturations. This set of experiments supports, but does not prove, the validity of the proposed method of measuring brain oxygen metabolism.

11.
Biomed Opt Express ; 6(4): 1429-50, 2015 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-25909026

RESUMO

Quantification of chromophore concentrations in reflectance mode remains a major challenge for biomedical optics. Spectroscopic Optical Coherence Tomography (SOCT) provides depth-resolved spectroscopic information necessary for quantitative analysis of chromophores, like hemoglobin, but conventional SOCT analysis methods are applicable only to well-defined specular reflections, which may be absent in highly scattering biological tissue. Here, by fitting of the dynamic scattering signal spectrum in the OCT angiogram using a forward model of light propagation, we quantitatively determine hemoglobin concentrations directly. Importantly, this methodology enables mapping of both oxygen saturation and total hemoglobin concentration, or alternatively, oxyhemoglobin and deoxyhemoglobin concentration, simultaneously. Quantification was verified by ex vivo blood measurements at various pO2 and hematocrit levels. Imaging results from the rodent brain and retina are presented. Confounds including noise and scattering, as well as potential clinical applications, are discussed.

12.
J Biomed Opt ; 18(11): 115003, 2013 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-24194063

RESUMO

The backward second harmonic generation (SHG) in mouse tissues is studied with a confocal multiphoton microscopy system. The total backward collected SHG (B-SHG) consists of the backward generated SHG and the backward-scattered forward-generated SHG (BS-SHG), which can be modeled by a Gaussian and a uniform distribution, respectively, at the confocal pinhole plane. By varying the pinhole size with a series of collection fibers, the proportion of the BS-SHG to the B-SHG and the proportion of BS-SHG to the forward generated SHG can be obtained. The approach is first validated by Monte Carlo simulation. It is then applied to two types of mouse tissues: mouse tail tendon and Achilles tendon. It is found that the BS-SHG contributes less to the B-SHG for the tail tendon than Achilles tendon with thicknesses of ~300 µm. With the thickness of the Achilles tendon tissue increased to 1000 µm but the focal plane kept at the same depth, as high as ~10% of the total forward SHG is backscattered and collected. The results indicate that BS-SHG may not be the major source of B-SHG in the tail tendon, but it may be the major source in the Achilles tendon. These methods and results provide a noninvasive method and supporting information for investigating the generation mechanism of SHG and help with optimizing backward SHG microscopy and spectroscopy measurements.


Assuntos
Microscopia Confocal/métodos , Microscopia de Fluorescência por Excitação Multifotônica/métodos , Processamento de Sinais Assistido por Computador , Tendão do Calcâneo/química , Acústica , Animais , Masculino , Camundongos , Camundongos Endogâmicos C3H , Método de Monte Carlo , Cauda/química , Tendões/química
13.
Biomed Opt Express ; 4(9): 1584-94, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-24049679

RESUMO

Multi-scale multimodal microscopy is a very useful technique by providing multiple imaging contrasts with adjustable field of views and spatial resolutions. Here, we present a tri-modal microscope combining multiphoton microscopy (MPM), optical coherence microscopy (OCM) and optical coherence tomography (OCT) for subsurface visualization of biological tissues. The advantages of the tri-modal system are demonstrated on various biological samples. It enables the visualization of multiple intrinsic contrasts including scattering, two-photon excitation fluorescence (TPEF), and second harmonic generation (SHG). It also enables a rapid scanning over a large tissue area and a high resolution zoom-in for cellular-level structures on regions of interest. The tri-modal microscope can be important for label-free imaging to obtain a sufficient set of parameters for reliable sample analysis.

14.
J Opt Soc Am A Opt Image Sci Vis ; 28(4): 496-501, 2011 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-21478941

RESUMO

Focal modulation microscopy (FMM) is a simple, yet efficient, method to preserve image quality in terms of signal-to-background ratio by selecting ballistic photons for image formation. The aim of this paper is to investigate the effect of the various aperture configurations of the spatial phase modulator on the modulation depth of the FMM signal. The definition of modulation depth in FMM and its calculation method are introduced. According to two brief principles of choosing aperture configuration, three types of configurations with different numbers of zones ranging from two to six (totaling eight aperture configurations) are selected, and their corresponding modulation depths and attainable spatial resolutions are simulated. The results show that the modulation depth increases significantly when the number of zones varies from two to six, with a slight or no sacrifice in resolution. In summary, the annular configuration is superior to the fan- and stripe-shaped configurations in modulation depth and spatial resolution.


Assuntos
Microscopia/métodos , Lentes , Microscopia/instrumentação , Modelos Teóricos
15.
Opt Lett ; 35(11): 1804-6, 2010 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-20517422

RESUMO

Focal modulation microscopy is an emerging fluorescence microscopy technique for in vivo imaging of thick biological tissues. Here, we present a theoretical study to assess its performance. The scalar diffraction theory is combined with Monte Carlo simulation to evaluate the signal-to-background ratio at various depths. The performance of confocal microscopy with a similar optical setup is also evaluated for comparison.


Assuntos
Algoritmos , Interpretação de Imagem Assistida por Computador/métodos , Imageamento Tridimensional/métodos , Microscopia de Fluorescência/métodos , Aumento da Imagem/métodos , Reprodutibilidade dos Testes , Sensibilidade e Especificidade
16.
Biomed Opt Express ; 1(3): 1026-1037, 2010 Sep 30.
Artigo em Inglês | MEDLINE | ID: mdl-21258527

RESUMO

Focal Modulation Microscopy (FMM) is a single-photon excitation fluorescence microscopy technique which effectively rejects the out-of-focus fluorescence background that arises when imaging deep inside biological tissues. Here, we report on the implementation of FMM in which laser intensity modulation at the focal plane is achieved using acousto-optic modulators (AOM). The modulation speed is greatly enhanced to the MHz range and thus enables real-time image acquisition. The capability of FMM is demonstrated by imaging fluorescence labeled vasculatures in mouse brain as well as self-made tissue phantom.

17.
Appl Opt ; 48(17): 3237-42, 2009 Jun 10.
Artigo em Inglês | MEDLINE | ID: mdl-19516376

RESUMO

Focal modulation microscopy (FMM) is an emerging microscopy technique for fluorescence imaging of thick biological tissue in vivo. A spatial phase modulator is a critical component whose characteristics have a significant impact on the performance of a FMM system. We have designed a simple spatial phase modulator based on a tilting glass plate that provides superb modulation stability. Image quality has been improved remarkably after integrating such a modulator into a FMM system.


Assuntos
Microscopia de Fluorescência/instrumentação , Algoritmos , Animais , Células Cultivadas , Condrócitos , Microscopia de Fluorescência/métodos , Microscopia de Contraste de Fase/instrumentação , Microscopia de Contraste de Fase/métodos
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