Rodent brain is studied to understand the basics of brain function. The activity of cell populations and networks is commonly recorded in vivo with wide-field optical imaging techniques such as ...intrinsic optical imaging, fluorescence imaging, or laser speckle imaging. These techniques were recently adapted to unrestrained mice carrying transcranial windows. Furthermore, optogenetics studies would benefit from optical stimulation through the skull without implanting an optical fiber, especially for longitudinal studies. In this context, the knowledge of bone optical properties is requested to improve the quantitation of the depth and volume of imaged or stimulated tissues. Here, we provide experimental measurements of absorption and reduced scattering coefficients of freshly excised mice skull for wavelengths between 455 and 705 nm. Absorption coefficients from 6 to 8 months mice skull samples range between 1.67±0.28 mm−1 at 455 nm and 0.47±0.07 mm−1 at 705 nm, whereas reduced scattering coefficients were in the range of 2.79±0.26 mm−1 at 455 nm up to 2.29±0.12 mm−1 at 705 nm. In comparison, measurements carried out on 4 to 5 weeks mice showed similar spectral profiles but smaller absorption and reduced scattering coefficients by a factor of about 2 and 1.5, respectively.
This article aims at demonstrating that the Old Khmer b/vraḥ originates from a syllabic depletion of the Sanskrit word brāhmaṇa through a monosyllabization process, a widespread diachronic phenomenon ...among the Mon-Khmer languages of Mainland Southeast Asia. The paper will also show that this term must have been originally used as an honorific for deities and, consequently, for royalty. It therefore respectfully disagrees with two other current hypotheses according to which b/vraḥ would be an autochthonous Mon-Khmer word or would originate in the Sanskrit/Pali word vara- “excellent, splendid, noble”. After being borrowed from Sanskrit, the Old Khmer braḥ spread via a contact phenomenon: from Old Khmer to Old Siamese, from Old Siamese to Old Shan through the “Thai Continuum”, and from Old Shan to Old Burmese. The implications of this paper are twofold: firstly, it will sketch out a pattern for the historical relationships between different peoples of Mainland Southeast Asia; then, it will propose a first phase of Indianization in Southeast Asia, namely a local reconnotation of Indo-Aryan terms according to autochthonous socio-political contingencies, and consequently bring a draft answer to the “Woltersian” question: what is the local connotation of Indo-Aryan terms?
Line-field Confocal Optical Coherence Tomography (LC-OCT) is an imaging modality based on a combination of time-domain optical coherence tomography and reflectance confocal microscopy. LC-OCT ...provides three-dimensional images of semi-transparent samples with a spatial resolution of ∼1 μm. The technique is primarily applied to
in vivo
skin imaging. The image contrast in LC-OCT arises from the backscattering of incident light by the sample microstructures, which is determined by the optical scattering properties of the sample, characterized by the scattering coefficient
μ
s
and the scattering anisotropy factor
g
. In biological tissues, the scattering properties are determined by the organization, structure and refractive indexes of the sample. The measurement of these properties using LC-OCT would therefore allow a quantitative characterization of tissues
in vivo
. We present a method for extracting the two scattering properties
μ
s
and
g
of tissue-mimicking phantoms from 3D LC-OCT images. The method provides the mean values of
μ
s
and
g
over a lateral field of view of 1.2 mm × 0.5 mm (
x
×
y
). It can be applied to monolayered and bilayered samples, where it allows extraction of
μ
s
and
g
of each layer. Our approach is based on a calibration using a phantom with known optical scattering properties and on the application of a theoretical model to the intensity depth profiles acquired by LC-OCT. It was experimentally tested against integrating spheres and collimated transmission measurements for a set of monolayered and bilayered scattering phantoms.
Optogenetics is widely used in fundamental neuroscience. Its potential clinical translation for brain neuromodulation requires a careful assessment of the safety and efficacy of repeated, sustained ...optical stimulation of large volumes of brain tissues. This study was performed in rats and not in non-human primates for ethical reasons. We studied the spatial distribution of light, potential damage, and non-physiological effects in vivo, in anesthetized rat brains, on large brain volumes, following repeated high irradiance photo-stimulation. We generated 2D irradiance and temperature increase surface maps based on recordings taken during optical stimulation using irradiance and temporal parameters representative of common optogenetics experiments. Irradiances of 100 to 600 mW/mm
with 5 ms pulses at 20, 40, and 60 Hz were applied during 90 s. In vivo electrophysiological recordings and post-mortem histological analyses showed that high power light stimulation had no obvious phototoxic effects and did not trigger non-physiological functional activation. This study demonstrates the ability to illuminate cortical layers to a depth of several millimeters using pulsed red light without detrimental thermal damages.
Multiple exposure speckle imaging has demonstrated its improved accuracy compared to single exposure speckle imaging for relative quantitation of blood flow in vivo . However, the calculation of ...blood flow maps relies on a pixelwise non-linear fit of a multi-parametric model to the speckle contrasts. This approach has two major drawbacks. First, it is computer-intensive and prevents real time imaging and, second, the mathematical model is not universal and should in principle be adapted to the type of blood vessels. We evaluated a model-free machine learning approach based on a convolutional neural network as an alternative to the non-linear fit approach. A network was designed and trained with annotated speckle contrast data from microfluidic experiments. The neural network performances are then compared to the non-linear fit approach applied to in vitro and in vivo data. The study demonstrates the potential of convolutional networks to provide relative blood flow maps from multiple exposure speckle data in real time.
Application of nanotechnology for biomedicine in cancer therapy allows for direct delivery of anticancer agents to tumors. An example of such therapies is the nanoparticle-mediated near-infrared ...hyperthermia treatment. In order to investigate the influence of nanoparticle properties on the spatial distribution of heat in the tumor and healthy tissues, accurate simulations are required. The Geant4 Application for Emission Tomography (GATE) open-source simulation platform, based on the Geant4 toolkit, is widely used by the research community involved in molecular imaging, radiotherapy and optical imaging. We present an extension of GATE that can model nanoparticle-mediated hyperthermal therapy as well as simple heat diffusion in biological tissues. This new feature of GATE combined with optical imaging allows for the simulation of a theranostic scenario in which the patient is injected with theranostic nanosystems that can simultaneously deliver therapeutic (i.e. hyperthermia therapy) and imaging agents (i.e. fluorescence imaging).
Objective
This study aimed to investigate the effects of a high‐fat diet (HFD) and aging on resting and activity‐dependent cerebral blood flow (CBF).
Methods
To run a comparison between obese and ...age‐matched control animals, 6‐week‐old mice were fed either with regular chow or an HFD for 3 months or 8 months. Glucose tolerance and insulin sensitivity were assessed for metabolic phenotyping. Resting and odor‐evoked CBF at the microvascular scale in the olfactory bulb (OB) was investigated by multiexposure speckle imaging. Immunolabeling‐enabled imaging of solvent‐cleared organs was used to analyze vascular density. The ejection fraction was studied by using cardioechography. Olfactory sensitivity was tested by using a buried‐food test.
Results
Glucose intolerance and compromised odor‐evoked CBF were observed in obese mice in the younger group. Prolonged HFD feeding triggered insulin resistance and stronger impairment in activity‐dependent CBF. Aging had a specific negative impact on resting CBF. There was no decrease in vascular density in the OB of obese mice, although cardiac function was impaired at both ages. In addition, decreased olfactory sensitivity was observed only in the older, middle‐aged obese mice.
Conclusions
OB microvasculature in obese mice showed a specific functional feature characterized by impaired sensory‐evoked CBF and a specific deleterious effect of aging on resting CBF.
The Geant4 Application for Emission Tomography (GATE) is an advanced open-source software dedicated to Monte-Carlo (MC) simulations in medical imaging involving photon transportation (Positron ...emission tomography, single photon emission computed tomography, computed tomography) and in particle therapy. In this work, we extend the GATE to support simulations of optical imaging, such as bioluminescence or fluorescence imaging, and validate it against the MC for multilayered media standard simulation tool for biomedical optics in simple geometries. A full simulation set-up for molecular optical imaging (bioluminescence and fluorescence) is implemented in GATE, and images of the light distribution emitted from a phantom demonstrate the relevance of using GATE for optical imaging simulations.
Several endomicroscope prototypes for nonlinear optical imaging were developed in the last decade for in situ analysis of tissue with cellular resolution by using short infrared light pulses. ...Fourier-transform-limited pulses at the tissue site are necessary for optimal excitation of faint endogenous signals. However, obtaining these transform-limited short pulses remains a challenge, and previously proposed devices did not achieve an optimal pulse delivery. We present a study of fibered endomicroscope architecture with an efficient femtosecond pulse delivery and a high excitation level at the output of commercially available double-clad fibers (DCFs). The endomicroscope incorporates a module based on a grism line to compensate for linear and nonlinear effects inside the system. Simulations and experimental results are presented and compared to the literature. Experimentally, we obtained short pulses down to 24 fs at the fiber output, what represents to the best of our knowledge the shortest pulse duration ever obtained at the output of a nonlinear endoscopic system without postcompression. The choice of the optimal DCF among four possible commercial components is discussed and evaluated in regard to multiphoton excitation and fluorescence emission.
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