13 results on '"Raghav K. Chhetri"'
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2. Longitudinal study of mammary epithelial and fibroblast co-cultures using optical coherence tomography reveals morphological hallmarks of pre-malignancy.
- Author
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Raghav K Chhetri, Zachary F Phillips, Melissa A Troester, and Amy L Oldenburg
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Medicine ,Science - Abstract
The human mammary gland is a complex and heterogeneous organ, where the interactions between mammary epithelial cells (MEC) and stromal fibroblasts are known to regulate normal biology and tumorigenesis. We aimed to longitudinally evaluate morphology and size of organoids in 3D co-cultures of normal (MCF10A) or pre-malignant (MCF10DCIS.com) MEC and hTERT-immortalized fibroblasts from reduction mammoplasty (RMF). This co-culture model, based on an isogenic panel of cell lines, can yield insights to understand breast cancer progression. However, 3D cultures pose challenges for quantitative assessment and imaging, especially when the goal is to measure the same organoid structures over time. Using optical coherence tomography (OCT) as a non-invasive method to longitudinally quantify morphological changes, we found that OCT provides excellent visualization of MEC-fibroblast co-cultures as they form ductal acini and remodel over time. Different concentrations of fibroblasts and MEC reflecting reported physiological ratios [1] were evaluated, and we found that larger, hollower, and more aspherical acini were formed only by pre-malignant MEC (MCF10DCIS.com) in the presence of fibroblasts, whereas in comparable conditions, normal MEC (MCF10A) acini remained smaller and less aspherical. The ratio of fibroblast to MEC was also influential in determining organoid phenotypes, with higher concentrations of fibroblasts producing more aspherical structures in MCF10DCIS.com. These findings suggest that stromal-epithelial interactions between fibroblasts and MEC can be modeled in vitro, with OCT imaging as a convenient means of assaying time dependent changes, with the potential for yielding important biological insights about the differences between benign and pre-malignant cells.
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- 2012
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3. Examining the Effects of Chromatic Aberration, Object Distance, and Eye Shape on Image-Formation in the Mirror-Based Eyes of the Bay Scallop Argopecten irradians
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Amy L. Oldenburg, Daniel I. Speiser, Yakir L. Gagnon, Raghav K. Chhetri, and Sönke Johnsen
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0106 biological sciences ,0301 basic medicine ,Image formation ,genetic structures ,Argopecten irradians ,Curved mirror ,Color ,Plant Science ,Eye ,010603 evolutionary biology ,01 natural sciences ,03 medical and health sciences ,Optical coherence tomography ,Chromatic aberration ,medicine ,Animals ,Vision, Ocular ,Physics ,Retina ,medicine.diagnostic_test ,biology ,Anatomy ,biology.organism_classification ,eye diseases ,Pectinidae ,030104 developmental biology ,Cardinal point ,medicine.anatomical_structure ,Lens (anatomy) ,Animal Science and Zoology ,Extraocular, Non-Visual, and Simple Photoreceptors ,sense organs - Abstract
The eyes of scallops form images using a concave spherical mirror and contain two separate retinas, one layered on top of the other. Behavioral and electrophysiological studies indicate that the images formed by these eyes have angular resolutions of about 2°. Based on previous ray-tracing models, it has been thought that the more distal of the two retinas lies near the focal point of the mirror and that the proximal retina, positioned closer to the mirror at the back of the eye, receives light that is out-of-focus. Here, we propose three mechanisms through which both retinas may receive focused light: (1) chromatic aberration produced by the lens may cause the focal points for longer and shorter wavelengths to fall near the distal and proximal retinas, respectively; (2) focused light from near and far objects may fall on the distal and proximal retinas, respectively; and (3) the eyes of scallops may be dynamic structures that change shape to determine which retina receives focused light. To test our hypotheses, we used optical coherence tomography (OCT), a method of near-infrared optical depth-ranging, to acquire virtual cross-sections of live, intact eyes from the bay scallop Argopecten irradians . Next, we used a custom-built ray-tracing model to estimate the qualities of the images that fall on an eye’s distal and proximal retinas as functions of the wavelengths of light entering the eye (400–700 nm), object distances (0.01–1 m), and the overall shape of the eye. When we assume 550 nm wavelength light and object distances greater than 0.01 m, our model predicts that the angular resolutions of the distal and proximal retinas are 2° and 7°, respectively. Our model also predicts that neither chromatic aberration nor differences in object distance lead to focused light falling on the distal and proximal retinas simultaneously. However, if scallops can manipulate the shapes of their eyes, perhaps through muscle contractions, we speculate that they may be able to influence the qualities of the images that fall on their proximal retinas and—to a lesser extent—those that fall on their distal retinas as well.
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- 2016
4. Monitoring airway mucus flow and ciliary activity with optical coherence tomography
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Raghav K. Chhetri, Amy L. Oldenburg, Brian Button, and David B. Hill
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Pathology ,medicine.medical_specialty ,01 natural sciences ,Cystic fibrosis ,010309 optics ,03 medical and health sciences ,Optical coherence tomography ,0103 physical sciences ,ocis:(170.4500) Optical coherence tomography ,Medicine ,030304 developmental biology ,0303 health sciences ,ocis:(110.4153) Motion estimation and optical flow ,medicine.diagnostic_test ,business.industry ,Cilium ,ocis:(170.2655) Functional monitoring and imaging ,respiratory system ,medicine.disease ,Mucus ,Atomic and Molecular Physics, and Optics ,3. Good health ,ocis:(110.6150) Speckle imaging ,Respiratory epithelium ,Optical Coherence Tomography ,ocis:(170.3880) Medical and biological imaging ,business ,Airway ,Preclinical imaging ,Ex vivo ,Biotechnology ,ocis:(110.0113) Imaging through turbid media - Abstract
Muco-ciliary transport in the human airway is a crucial defense mechanism for removing inhaled pathogens. Optical coherence tomography (OCT) is well-suited to monitor functional dynamics of cilia and mucus on the airway epithelium. Here we demonstrate several OCT-based methods upon an actively transporting in vitro bronchial epithelial model and ex vivo mouse trachea. We show quantitative flow imaging of optically turbid mucus, semi-quantitative analysis of the ciliary beat frequency, and functional imaging of the periciliary layer. These may translate to clinical methods for endoscopic monitoring of muco-ciliary transport in diseases such as cystic fibrosis and chronic obstructive pulmonary disease (COPD).
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- 2012
5. Magnetic and Contrast Properties of Labeled Platelets for Magnetomotive Optical Coherence Tomography
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Raghav K. Chhetri, Amy L. Oldenburg, Kellie N. Beicker, Caterina M. Gallippi, Aaron Richardson, Timothy C. Nichols, Thomas H. Fischer, Dmitry Spivak, and Frank Tsui
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Blood Platelets ,Iron ,media_common.quotation_subject ,Sus scrofa ,Spectroscopy, Imaging, and Other Techniques ,Biophysics ,Contrast Media ,Nanotechnology ,030204 cardiovascular system & hematology ,01 natural sciences ,010309 optics ,Food and drug administration ,Magnetics ,03 medical and health sciences ,Imaging, Three-Dimensional ,0302 clinical medicine ,Optical coherence tomography ,0103 physical sciences ,medicine ,Animals ,Humans ,Contrast (vision) ,Platelet ,Magnetite Nanoparticles ,media_common ,Hemostasis ,Staining and Labeling ,medicine.diagnostic_test ,Phantoms, Imaging ,Chemistry ,Dextrans ,Arteries ,Freeze Drying ,medicine.anatomical_structure ,Iron content ,Tomography, Optical Coherence ,Ex vivo ,Biomedical engineering ,Artery - Abstract
This article introduces a new functional imaging paradigm that uses optical coherence tomography (OCT) to detect rehydrated, lyophilized platelets (RL platelets) that are in the preclinical trial stage and contain superparamagnetic iron oxides (SPIOs) approved by the U.S. Food and Drug Administration. Platelets are highly functional blood cells that detect and adhere to sites of vascular endothelial damage by forming primary hemostatic plugs. By applying magnetic gradient forces, induced nanoscale displacements (magnetomotion) of the SPIO-RL platelets are detected as optical phase shifts in OCT. In this article, we characterize the iron content and magnetic properties of SPIO-RL platelets, construct a model to predict their magnetomotion in a tissue medium, and demonstrate OCT imaging in tissue phantoms and ex vivo pig arteries. Tissue phantoms containing SPIO-RL platelets exhibited >3 dB contrast/noise ratio at ≥1.5 × 109 platelets/cm3. OCT imaging was performed on ex vivo porcine arteries after infusion of SPIO-RL platelets, and specific contrast was obtained on an artery that was surface-damaged (P < 10−6). This may enable new technologies for in vivo monitoring of the adherence of SPIO-RL platelets to sites of bleeding and vascular damage, which is broadly applicable for assessing trauma and cardiovascular diseases.
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- 2010
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6. Probing biological nanotopology via diffusion of weakly constrained plasmonic nanorods with optical coherence tomography
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David B. Hill, Joseph B. Tracy, Richard L. Blackmon, Raghav K. Chhetri, Brian Button, Patricia Casbas-Hernandez, Amy L. Oldenburg, Melissa A. Troester, and Wei-Chen Wu
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Materials science ,Nanoprobe ,Nanoparticle ,Metal Nanoparticles ,Nanotechnology ,Bronchi ,Polyethylene Glycols ,Diffusion ,Dynamic light scattering ,Optical coherence tomography ,medicine ,Humans ,Surface plasmon resonance ,skin and connective tissue diseases ,Nanoscopic scale ,Plasmon ,Cells, Cultured ,Multidisciplinary ,Nanotubes ,medicine.diagnostic_test ,Epithelial Cells ,Extracellular Matrix ,Solutions ,Mucus ,PNAS Plus ,Nanorod ,sense organs ,Collagen ,Gold ,Stromal Cells ,Tomography, Optical Coherence - Abstract
Biological materials exhibit complex nanotopology, i.e., a composite liquid and solid phase structure that is heterogeneous on the nanoscale. The diffusion of nanoparticles in nanotopological environments can elucidate biophysical changes associated with pathogenesis and disease progression. However, there is a lack of methods that characterize nanoprobe diffusion and translate easily to in vivo studies. Here, we demonstrate a method based on optical coherence tomography (OCT) to depth-resolve diffusion of plasmon-resonant gold nanorods (GNRs) that are weakly constrained by the biological tissue. By using GNRs that are on the size scale of the polymeric mesh, their Brownian motion is minimally hindered by intermittent collisions with local macromolecules. OCT depth-resolves the particle-averaged translational diffusion coefficient (DT) of GNRs within each coherence volume, which is separable from the nonequilibrium motile activities of cells based on the unique polarized light-scattering properties of GNRs. We show how this enables minimally invasive imaging and monitoring of nanotopological changes in a variety of biological models, including extracellular matrix (ECM) remodeling as relevant to carcinogenesis, and dehydration of pulmonary mucus as relevant to cystic fibrosis. In 3D ECM models, DT of GNRs decreases with both increasing collagen concentration and cell density. Similarly, DT of GNRs is sensitive to human bronchial-epithelial mucus concentration over a physiologically relevant range. This novel method comprises a broad-based platform for studying heterogeneous nanotopology, as distinct from bulk viscoelasticity, in biological milieu.
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- 2014
7. Motility-, autocorrelation-, and polarization-sensitive optical coherence tomography discriminates cells and gold nanorods within 3D tissue cultures
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Raghav K. Chhetri, Amy L. Oldenburg, Melissa A. Troester, Jason M. Cooper, Wei-Chen Wu, and Joseph B. Tracy
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Light ,Physics::Medical Physics ,Image processing ,Article ,Tissue Culture Techniques ,Speckle pattern ,Optics ,Dynamic light scattering ,Optical coherence tomography ,Medical imaging ,medicine ,Image Processing, Computer-Assisted ,Humans ,Scattering, Radiation ,Mammary Glands, Human ,Physics ,Nanotubes ,medicine.diagnostic_test ,business.industry ,Autocorrelation ,Polarization (waves) ,Atomic and Molecular Physics, and Optics ,Tomography ,Gold ,sense organs ,business ,Tomography, Optical Coherence - Abstract
We propose a method for differentiating classes of light scatterers based upon their temporal and polarization properties computed from time series of polarization-sensitive optical coherence tomography (PS-OCT) images. The amplitude (motility) and time scale (autocorrelation decay time) of the speckle fluctuations are combined with the cross-polarization pixel-wise to render Motility-, autocorrelation-, and polarization-sensitive (MAPS) OCT contrast images. This combination of metrics provides high specificity for discriminating diffusive gold nano-rods and mammary epithelial cell spheroids within 3D tissue culture, based on their unique MAPS signature. This has implications toward highly specific contrast in molecular (nanoparticle-based) and functional (cellular activity) imaging using standard PS-OCT hardware.
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- 2013
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8. Optical Coherence Microrheology using Spherical and Rod-like Microrheological Probes
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Raghav K. Chhetri and Amy L. Oldenburg
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Microrheology ,Physics ,genetic structures ,medicine.diagnostic_test ,business.industry ,eye diseases ,Light scattering ,Viscoelasticity ,Physics::Fluid Dynamics ,Condensed Matter::Soft Condensed Matter ,Optics ,Dynamic light scattering ,Optical coherence tomography ,medicine ,sense organs ,Speckle imaging ,business ,Coherence (physics) ,Complex fluid - Abstract
Processing of light scattering signals from spherical and rod-like probes in optical coherence tomography provides frequency-dependent viscoelasticity of complex fluids, constituting a novel optical coherence microrheological tool.
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- 2012
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9. Dynamic imaging of in vitro human airway epithelium using optical coherence tomography
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Richard C. Boucher, Brian Button, David B. Hill, Amy L. Oldenburg, and Raghav K. Chhetri
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COPD ,Pathology ,medicine.medical_specialty ,Lung ,genetic structures ,medicine.diagnostic_test ,business.industry ,Dynamic imaging ,respiratory system ,medicine.disease ,Mucus ,Cystic fibrosis ,eye diseases ,Epithelium ,respiratory tract diseases ,medicine.anatomical_structure ,Optical coherence tomography ,medicine ,sense organs ,Airway ,business - Abstract
Ultrahigh-resolution optical coherence tomography (OCT) is employed to depth-resolve mucociliary transport on human bronchiepithelial cell cultures. This has relevance for monitoring airway mucus in lung diseases such as cystic fibrosis and COPD.
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- 2012
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10. Imaging three-dimensional rotational diffusion of plasmon resonant gold nanorods using polarization-sensitive optical coherence tomography
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Krystian A. Kozek, Aaron C. Johnston-Peck, Amy L. Oldenburg, Joseph B. Tracy, and Raghav K. Chhetri
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Materials science ,Physics::Optics ,Molecular physics ,Article ,Light scattering ,Diffusion ,Physics::Fluid Dynamics ,Imaging, Three-Dimensional ,Optics ,Optical coherence tomography ,Nephelometry and Turbidimetry ,medicine ,Anisotropy ,Plasmon ,Nanotubes ,medicine.diagnostic_test ,business.industry ,Rotational diffusion ,Surface Plasmon Resonance ,Refractometry ,Nanorod ,Gold ,business ,Tomography, Optical Coherence ,Coherence (physics) ,Localized surface plasmon - Abstract
We demonstrate depth-resolved viscosity measurements within a single object using polarized optical scattering from ensembles of freely tumbling plasmon resonant gold nanorods (GNRs) monitored with polarization-sensitive optical coherence tomography. The rotational diffusion coefficient of the GNRs is shown to correlate with viscosity in molecular fluids according to the Stokes-Einstein relation. The plasmon resonant and highly anisotropic properties of GNRs are favorable for microrheological studies of nanoscale properties.
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- 2011
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11. Plasmonic Gold Nanorods for Depth-Resolved Viscosity in Polarization-Sensitive OCT
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Joseph B. Tracy, Amy L. Oldenburg, Aaron C. Johnston-Peck, Krystian A. Kozek, and Raghav K. Chhetri
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Microrheology ,Physics::Biological Physics ,Materials science ,medicine.diagnostic_test ,Scattering ,business.industry ,Physics::Medical Physics ,Physics::Optics ,Quantitative Biology::Other ,Quantitative Biology::Cell Behavior ,Viscosity ,Optics ,Dynamic light scattering ,Optical coherence tomography ,medicine ,Optoelectronics ,Nanorod ,business ,Plasmon ,Preclinical imaging - Abstract
We demonstrate depth-resolved viscosity via polarized scattering from ensembles of tumbling plasmon-resonant gold nanorods (GNRs) monitored with polarization-sensitive OCT. This has potential for in vivo microrheology imaging of fluids such as mucus.
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- 2011
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12. Magnetomotive optical coherence elastography for relating lung structure and function in cystic fibrosis
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Richard Superfine, Raghav K. Chhetri, Jerome Carpenter, Amy L. Oldenburg, and Scott H. Randell
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Pathology ,medicine.medical_specialty ,Bronchiectasis ,Lung ,biology ,medicine.diagnostic_test ,medicine.disease ,Cystic fibrosis ,Article ,Cystic fibrosis transmembrane conductance regulator ,Extracellular matrix ,medicine.anatomical_structure ,medicine ,biology.protein ,Elastography ,Preclinical imaging ,Ex vivo - Abstract
Cystic fibrosis (CF) is a genetic defect in the cystic fibrosis transmembrane conductance regulator protein and is the most common life-limiting genetic condition affecting the Caucasian population. It is an autosomal recessive, monogenic inherited disorder characterized by failure of airway host defense against bacterial infection, which results in bronchiectasis, the breakdown of airway wall extracellular matrix (ECM). In this study, we show that the in vitro models consisting of human tracheo-bronchial-epithelial (hBE) cells grown on porous supports with embedded magnetic nanoparticles (MNPs) at an air-liquid interface are suitable for long term, non-invasive assessment of ECM remodeling using magnetomotive optical coherence elastography (MMOCE). The morphology of ex vivo CF and normal lung tissues using OCT and correlative study with histology is also examined. We also demonstrate a quantitative measure of normal and CF airway elasticity using MMOCE. The improved understanding of pathologic changes in CF lung structure and function and the novel method of longitudinal in vitro ECM assessment demonstrated in this study may lead to new in vivo imaging and elastography methods to monitor disease progression and treatment in cystic fibrosis.
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- 2010
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13. Contrast to Labeled Rehydrated, Lyophilized Platelets Using Magnetomotive OCT
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Raghav K. Chhetri, Amy L. Oldenburg, Thomas H. Fischer, Timothy C. Nichols, Frank Tsui, and Caterina M. Gallippi
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chemistry.chemical_compound ,Materials science ,Optical coherence tomography ,medicine.diagnostic_test ,chemistry ,medicine ,Iron oxide ,Platelet ,Magnetic resonance imaging ,Biomedical engineering - Abstract
Rehydrated, lyophilized platelets for hemostatic therapy are incorporated with commercial MRI iron oxide contrast agents. We demonstrate that magnetomotive OCT contrasts the platelets and propose this system for monitoring hemopathic sites targeted by platelets.
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- 2010
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