22 research outputs found
Ultrasound-modulated optical tomography in soft biological tissues
Optical imaging of soft biological tissues is highly desirable since it is nonionizing
and provides sensitive contrast information which enables detection of physiological
functions and abnormalities, including potentially early cancer detection. However,
due to the diffusion of light, it is dificult to achieve simultaneously both good spatial
resolution and good imaging depth with the pure optical imaging modalities.
This work focuses on the ultrasound-modulated optical tomography - a hybrid
technique which combines advantages of ultrasonic resolution and optical contrast.
In this technique, focused ultrasound and optical radiation of high temporal co-herence are simultaneously applied to soft biological tissue, and the intensity of the
ultrasound-modulated light is measured. This provides information about the optical
properties of the tissue, spatially localized at the interaction region of the ultrasonic
and electromagnetic waves.
In experimental part of this work we present a novel implementation of high-resolution ultrasound-modulated optical tomography that, based on optical contrast,
can image several millimeters deep into soft biological tissues. A long-cavity confocal
Fabry-Perot interferometer was used to detect the ultrasound-modulated coherent
light that traversed the scattering biological tissue. Using 15-MHz ultrasound, we
imaged with high contrast light absorbing structures placed 3 mm below the surface
of chicken breast tissue. The resolution along the axial and the lateral directions with respect to the ultrasound propagation direction was better than 70 and 120ùm, respectively. This technology is complementary to other imaging technologies,
such as confocal microscopy and optical-coherence tomography, and has potential for
broad biomedical applications.
In the theoretical part we present various methods to model interaction be-tween the ultrasonic and electromagnetic waves in optically scattering media. We first extend the existing theoretical model based on the diffusing-wave spectroscopy
approach to account for anisotropic optical scattering, Brownian motion, pulsed ul-trasound, and strong correlations between the ultrasound-induced optical phase in-crements. Based on the Bethe-Salpeter equation, we further develop a more general
correlation transfer equation, and subsequently a correlation diffusion equation, for
ultrasound-modulated multiply scattered light. We expect these equations to be
applicable to a wide spectrum of conditions in the ultrasound-modulated optical tomography of soft biological tissues
Development of a beam propagation method to simulate the point spread function degradation in scattering media
Scattering is one of the main issues that limit the imaging depth in deep tissue optical imaging. To characterize the role of scattering, we have developed a forward model based on the beam propagation method and established the link between the macroscopic optical properties of the media and the statistical parameters of the phase masks applied to the wavefront. Using this model, we have analyzed the degradation of the point-spread function of the illumination beam in the transition regime from ballistic to diffusive light transport. Our method provides a wave-optic simulation toolkit to analyze the effects of scattering on image quality degradation in scanning microscopy. Our open-source implementation is available at https://github.com/BUNPC/Beam-Propagation-Method.Accepted manuscrip
In Vivo Imaging of Cerebral Energy Metabolism with Two-Photon Fluorescence Lifetime Microscopy of NADH
Minimally invasive, specific measurement of cellular energy metabolism is crucial for understanding cerebral pathophysiology. Here, we present high-resolution, in vivo observations of autofluorescence lifetime as a biomarker of cerebral energy metabolism in exposed rat cortices. We describe a customized two-photon imaging system with time correlated single photon counting detection and specialized software for modeling multiple-component fits of fluorescence decay and monitoring their transient behaviors. In vivo cerebral NADH fluorescence suggests the presence of four distinct components, which respond differently to brief periods of anoxia and likely indicate different enzymatic formulations. Individual components show potential as indicators of specific molecular pathways involved in oxidative metabolism
Atherosclerosis is associated with a decrease in cerebral microvascular blood flow and tissue oxygenation
Chronic atherosclerosis may cause cerebral hypoperfusion and inadequate brain oxygenation, contributing to the progression of cognitive decline. In this study, we exploited two-photon phosphorescence lifetime microscopy to measure the absolute partial pressure of oxygen (PO2) in cortical tissue in both young and old LDLR-/-, hApoB100+/+ mice, spontaneously developing atherosclerosis with age. Capillary red-blood-cell (RBC) speed, flux, hematocrit and capillary diameter were also measured by two-photon imaging of FITC-labelled blood plasma. Our results show positive correlations between RBC speed, flux, diameter and capillary-adjacent tissue PO2. When compared to the young mice, we observed lower tissue PO2, lower RBC speed and flux, and smaller capillary diameter in the old atherosclerotic mice. The old mice also exhibited a higher spatial heterogeneity of tissue PO2, and RBC speed and flux, suggesting a less efficient oxygen extraction
Quantifying the Microvascular Origin of BOLD-fMRI from First Principles with Two-Photon Microscopy and an Oxygen-Sensitive Nanoprobe
The blood oxygenation level-dependent (BOLD) contrast is widely used in functional magnetic resonance imaging (fMRI) studies aimed at investigating neuronal activity. However, the BOLD signal reflects changes in blood volume and oxygenation rather than neuronal activity per se. Therefore, understanding the transformation of microscopic vascular behavior into macroscopic BOLD signals is at the foundation of physiologically informed noninvasive neuroimaging. Here, we use oxygen-sensitive two-photon microscopy to measure the BOLD-relevant microvascular physiology occurring within a typical rodent fMRI voxel and predict the BOLD signal from first principles using those measurements. The predictive power of the approach is illustrated by quantifying variations in the BOLD signal induced by the morphological folding of the human cortex. This framework is then used to quantify the contribution of individual vascular compartments and other factors to the BOLD signal for different magnet strengths and pulse sequences.National Institutes of Health (U.S.) (Grant P41RR14075)National Institutes of Health (U.S.) (Grant R01NS067050)National Institutes of Health (U.S.) (Grant R01NS057198)National Institutes of Health (U.S.) (Grant R01EB000790)American Heart Association (Grant 11SDG7600037)Advanced Multimodal NeuroImaging Training Program (R90DA023427
Recommended from our members
CD200 restrains macrophage attack on oligodendrocyte precursors via toll-like receptor 4 downregulation
There are numerous barriers to white matter repair after CNS injury and the underlying mechanisms remain to be
fully understood. In this study, we propose the hypothesis that inflammatory macrophages in damaged white
matter attack oligodendrocyte precursor cells (OPCs) via TLR4 signaling thus interfering with this endogenous
progenitor recovery mechanism. Primary cell culture experiments demonstrate that peritoneal macrophages can
attack and digest OPCs via TLR4 signaling, and this phagocytosis of OPCs can be inhibited by using CD200-Fc to downregulate TLR4. In an in vivo model of white matter ischemia induced by endothelin-1, treatment with D200-Fc suppressed TLR4 expression in peripherally circulating macrophages, thus restraining macrophage phagocytosis of OPCs and leading to improved myelination. Taken together, these findings suggest that deleterious macrophage effects may occur after white matter ischemia, whereby macrophages attack OPCs and interfere with endogenous recovery responses. Targeting this pathway with CD200 may offer a novel therapeutic approach to amplify endogenous OPC-mediated repair of white matter damage in mammalian brain
Intrinsic optical signal imaging of the blood volume changes is sufficient for mapping the resting state functional connectivity in the rodent cortex
Published in final edited form as:
J Neural Eng. 2018 June 01; 15(3): 035003–. doi:10.1088/1741-2552/aaafe4.Objective. Resting state functional connectivity (RSFC) allows the study of functional organization in normal and diseased brain by measuring the spontaneous brain activity generated under resting conditions. Intrinsic optical signal imaging (IOSI) based on multiple illumination wavelengths has been used successfully to compute RSFC maps in animal studies. The IOSI setup complexity would be greatly reduced if only a single wavelength can be used to obtain comparable RSFC maps. Approach. We used anesthetized mice and performed various comparisons between the RSFC maps based on single wavelength as well as oxy-, deoxy- and total hemoglobin concentration changes. Main results. The RSFC maps based on IOSI at a single wavelength selected for sensitivity to the blood volume changes are quantitatively comparable to the RSFC maps based on oxy- and total hemoglobin concentration changes obtained by the more complex IOSI setups. Moreover, RSFC maps do not require CCD cameras with very high frame acquisition rates, since our results demonstrate that they can be computed from the data obtained at frame rates as low as 5 Hz. Significance. Our results will have general utility for guiding future RSFC studies based on IOSI and making decisions about the IOSI system designs.We are grateful to Adam Bauer for his guidance on replicating their experimental setup, and Silvina Ferradal and Erin Buckley for useful discussions. We gratefully acknowledge support from the NIH grants NS091230, NS055104, NS057198, EB021018, EB00790, and EB018464, the Fondation Leducq, the State Scholarship Fund of the China Scholarship Council (Construction of high-level university projects, No. 201406100123), and the Natural Science Foundation of China (NSFC, nos. 81472150). (NS091230 - NIH; NS055104 - NIH; NS057198 - NIH; EB021018 - NIH; EB00790 - NIH; EB018464 - NIH; Fondation Leducq; 201406100123 - China Scholarship Council; 81472150 - Natural Science Foundation of China (NSFC))https://iopscience.iop.org/article/10.1088/1741-2552/aaafe4/metaAccepted manuscrip
Automatic graph-based modeling of brain microvessels captured with two-photon microscopy
Published in final edited form as: IEEE J Biomed Health Inform. 2019 November ; 23(6): 2551–2562.Graph models of cerebral vasculature derived from two-photon microscopy have shown to be relevant to study brain microphysiology. Automatic graphing of these microvessels remain problematic due to the vascular network complexity and two-photon sensitivity limitations with depth. In this paper, we propose a fully automatic processing pipeline to address this issue. The modeling scheme consists of a fully-convolution neural network to segment microvessels, a three-dimensional surface model generator, and a geometry contraction algorithm to produce graphical models with a single connected component. Based on a quantitative assessment using NetMets metrics, at a tolerance of 60 μm, false negative and false positive geometric error 19 rates are 3.8% and 4.2%, respectively, whereas false nega- 20 tive and false positive topological error rates are 6.1% and 4.5%, respectively. Our qualitative evaluation confirms the efficiency of our scheme in generating useful and accurate graphical models.299166 - CIHR; R01 NS108472 - NINDS NIH HHS; R24 NS092986 - NINDS NIH HHS; R01 NS091230 - NINDS NIH HHS; U01 HL133362 - NHLBI NIH HHS; R01 EB021018 - NIBIB NIH HHS; P01 NS055104 - NINDS NIH HHS; R01 MH111359 - NIMH NIH HHShttps://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8555544Published versio