226 research outputs found
Path-Length-Resolved Dynamic Light Scattering: Modeling the Transition From Single to Diffusive Scattering
Dynamic light-scattering spectroscopy is used to study Brownian motion within highly scattering samples. The fluctuations of the light field that is backscattered by a suspension of polystyrene microspheres are measured as power spectra by use of low-coherence interferometry to obtain path-length resolution. The data are modeled as the sum of contributions to the detected light weighted by a Poisson probability for the number of events that each component has experienced. By analyzing the broadening of the power spectra as a function of the path length for various sizes of particles, we determine the contribution of multiple scattering to the detected signal as a function of scattering anisotropy
Multiple passages of light through an absorption inhomogeneity in optical imaging of turbid media
The multiple passages of light through an absorption inhomogeneity of finite
size deep within a turbid medium is analyzed for optical imaging using the
``self-energy'' diagram. The nonlinear correction becomes more important for an
inhomogeneity of a larger size and with greater contrast in absorption with
respect to the host background. The nonlinear correction factor agrees well
with that from Monte Carlo simulations for CW light. The correction is about
in near infrared for an absorption inhomogeneity with the typical
optical properties found in tissues and of size of five times the transport
mean free path.Comment: 3 figure
Analytical calculation of the mean time spent by photons inside an absorptive inclusion embedded in a highly scattering medium
The mean time spent by photons inside a nonlocalized optically abnormal embedded inclusion has been derived analytically. The accuracy of the results has been tested against Monte Carlo and experimental data. We show that for quantification of the absorption coefficient of absorptive inclusions, a corrective factor that takes into account the size of the inclusion is needed. This finding suggests that perturbation methods derived for very small inclusions which are used in inverse algorithms require a corrective factor to adequately quantify the differential absorption coefficient of nonlocalized targets embedded in optically turbid media
Skin Lesion Correspondence Localization in Total Body Photography
Longitudinal tracking of skin lesions - finding correspondence, changes in
morphology, and texture - is beneficial to the early detection of melanoma.
However, it has not been well investigated in the context of full-body imaging.
We propose a novel framework combining geometric and texture information to
localize skin lesion correspondence from a source scan to a target scan in
total body photography (TBP). Body landmarks or sparse correspondence are first
created on the source and target 3D textured meshes. Every vertex on each of
the meshes is then mapped to a feature vector characterizing the geodesic
distances to the landmarks on that mesh. Then, for each lesion of interest
(LOI) on the source, its corresponding location on the target is first coarsely
estimated using the geometric information encoded in the feature vectors and
then refined using the texture information. We evaluated the framework
quantitatively on both a public and a private dataset, for which our success
rates (at 10 mm criterion) are comparable to the only reported longitudinal
study. As full-body 3D capture becomes more prevalent and has higher quality,
we expect the proposed method to constitute a valuable step in the longitudinal
tracking of skin lesions.Comment: MICCAI-202
Synchronous vs. asynchronous dynamics of diffusion-controlled reactions
An analytical method based on the classical ruin problem is developed to
compute the mean reaction time between two walkers undergoing a generalized
random walk on a 1d lattice. At each time step, either both walkers diffuse
simultaneously with probability (synchronous event) or one of them diffuses
while the other remains immobile with complementary probability (asynchronous
event). Reaction takes place through same site occupation or position exchange.
We study the influence of the degree of synchronicity of the walkers and
the lattice size on the global reaction's efficiency. For odd , the
purely synchronous case () is always the most effective one, while for
even , the encounter time is minimized by a combination of synchronous and
asynchronous events. This new parity effect is fully confirmed by Monte Carlo
simulations on 1d lattices as well as for 2d and 3d lattices. In contrast, the
1d continuum approximation valid for sufficiently large lattices predicts a
monotonic increase of the efficiency as a function of . The relevance of the
model for several research areas is briefly discussed.Comment: 21 pages (including 12 figures and 4 tables), uses revtex4.cls,
accepted for publication in Physica
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Advances in Optical Spectroscopy and Imaging of Breast Lesions
A review is presented of recent advances in optical imaging and spectroscopy and the use of light for addressing breast cancer issues. Spectroscopic techniques offer the means to characterize tissue components and obtain functional information in real time. Three-dimensional optical imaging of the breast using various illumination and signal collection schemes in combination with image reconstruction algorithms may provide a new tool for cancer detection and monitoring of treatment
A continuous time random walk model for financial distributions
We apply the formalism of the continuous time random walk to the study of
financial data. The entire distribution of prices can be obtained once two
auxiliary densities are known. These are the probability densities for the
pausing time between successive jumps and the corresponding probability density
for the magnitude of a jump. We have applied the formalism to data on the US
dollar/Deutsche Mark future exchange, finding good agreement between theory and
the observed data.Comment: 14 pages, 5 figures, revtex4, submitted for publicatio
The use of functional near-infrared spectroscopy in tracking neurodevelopmental trajectories in infants and children with or without developmental disorders: a systematic review
Understanding the neurodevelopmental trajectories of infants and children is essential for the early identification of neurodevelopmental disorders, elucidating the neural mechanisms underlying the disorders, and predicting developmental outcomes. Functional Near-Infrared Spectroscopy (fNIRS) is an infant-friendly neuroimaging tool that enables the monitoring of cerebral hemodynamic responses from the neonatal period. Due to its advantages, fNIRS is a promising tool for studying neurodevelopmental trajectories. Although many researchers have used fNIRS to study neural development in infants/children and have reported important findings, there is a lack of synthesized evidence for using fNIRS to track neurodevelopmental trajectories in infants and children. The current systematic review summarized 84 original fNIRS studies and showed a general trend of age-related increase in network integration and segregation, interhemispheric connectivity, leftward asymmetry, and differences in phase oscillation during resting-state. Moreover, typically developing infants and children showed a developmental trend of more localized and differentiated activation when processing visual, auditory, and tactile information, suggesting more mature and specialized sensory networks. Later in life, children switched from recruiting bilateral auditory to a left-lateralized language circuit when processing social auditory and language information and showed increased prefrontal activation during executive functioning tasks. The developmental trajectories are different in children with developmental disorders, with infants at risk for autism spectrum disorder showing initial overconnectivity followed by underconnectivity during resting-state; and children with attention-deficit/hyperactivity disorders showing lower prefrontal cortex activation during executive functioning tasks compared to their typically developing peers throughout childhood. The current systematic review supports the use of fNIRS in tracking the neurodevelopmental trajectories in children. More longitudinal studies are needed to validate the neurodevelopmental trajectories and explore the use of these neurobiomarkers for the early identification of developmental disorders and in tracking the effects of interventions
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Evaluation of optical imaging and spectroscopy approaches for cardiac tissue depth assessment
NIR light scattering from ex vivo porcine cardiac tissue was investigated to understand how imaging or point measurement approaches may assist development of methods for tissue depth assessment. Our results indicate an increase of average image intensity as thickness increases up to approximately 2 mm. In a dual fiber spectroscopy configuration, sensitivity up to approximately 3 mm with an increase to 6 mm when spectral ratio between selected wavelengths was obtained. Preliminary Monte Carlo results provided reasonable fit to the experimental data
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