89,699 research outputs found
Depth-enhanced maximum intensity projection
The two most common methods for the visualization of volumetric data are Direct Volume Rendering (DVR) and Maximum Intensity Projection (MIP). Direct Volume Rendering is superior to MIP in providing a larger amount of properly shaded details, because it employs a more complex shading model together with the use of user-defined
transfer functions. However, the generation of adequate transfer functions is a laborious and time costly task, even for expert users. As a consequence, medical doctors often use MIP because it does not require the definition of complex transfer functions and because it gives good results on contrasted images. Unfortunately, MIP does not allow to perceive depth ordering and therefore spatial context is lost. In this paper we present a new approach to MIP rendering that uses depth and simple color blending to disambiguate the ordering of internal structures, while maintaining most of the details visible through MIP. It is usually faster than DVR and only requires the
transfer function used by MIP rendering.Peer ReviewedPostprint (author’s final draft
Inverse Design of Perfectly Transmitting Eigenchannels in Scattering Media
Light-matter interactions inside turbid medium can be controlled by tailoring
the spatial distribution of energy density throughout the system. Wavefront
shaping allows selective coupling of incident light to different transmission
eigenchannels, producing dramatically different spatial intensity profiles. In
contrast to the density of transmission eigenvalues that is dictated by the
universal bimodal distribution, the spatial structures of the eigenchannels are
not universal and depend on the confinement geometry of the system. Here, we
develop and verify a model for the transmission eigenchannel with the
corresponding eigenvalue close to unity. By projecting the original problem of
two-dimensional diffusion in a homogeneous scattering medium onto a
one-dimensional inhomogeneous diffusion, we obtain an analytical expression
relating the intensity profile to the shape of the confining waveguide.
Inverting this relationship enables the inverse design of the waveguide shape
to achieve the desired energy distribution for the perfectly transmitting
eigenchannel. Our approach also allows to predict the intensity profile of such
channel in a disordered slab with open boundaries, pointing to the possibility
of controllable delivery of light to different depths with local illumination.Comment: 9 pages, 6 figure
Quantitative analysis of directional spontaneous emission spectra from light sources in photonic crystals
We have performed angle-resolved measurements of spontaneous-emission spectra
from laser dyes and quantum dots in opal and inverse opal photonic crystals.
Pronounced directional dependencies of the emission spectra are observed:
angular ranges of strongly reduced emission adjoin with angular ranges of
enhanced emission. It appears that emission from embedded light sources is
affected both by the periodicity and by the structural imperfections of the
crystals: the photons are Bragg diffracted by lattice planes and scattered by
unavoidable structural disorder. Using a model comprising diffuse light
transport and photonic band structure, we quantitatively explain the
directional emission spectra. This provides detailed understanding of the
transport of spontaneously emitted light in real photonic crystals, which is
essential in the interpretation of quantum-optics in photonic band-gap crystals
and for applications wherein directional emission and total emission power are
controlled.Comment: 10 pages, 10 figures, corrected pdf, inserted new referenc
Dust Streamers in the Virgo Galaxy M86 from Ram Pressure Stripping of its Companion VCC 882
The giant elliptical galaxy M86 in Virgo has a ~28 kpc long dust trail inside
its optical halo that points toward the nucleated dwarf elliptical galaxy, VCC
882. The trail seems to be stripped material from the dwarf. Extinction
measurements suggest that the ratio of the total gas mass in the trail to the
blue luminosity of the dwarf is about unity, which is comparable to such ratios
in dwarf irregular galaxies. The ram pressure experienced by the dwarf galaxy
in the hot gaseous halo of M86 was comparable to the internal gravitational
binding energy density of the presumed former gas disk in VCC 882. Published
numerical models of this case are consistent with the overall trail-like
morphology observed here. Three concentrations in the trail may be evidence for
the predicted periodicity of the mass loss. The evaporation time of the trail
is comparable to the trail age obtained from the relative speed of the galaxies
and the trail length. Thus the trail could be continuously formed from stripped
replenished gas if the VCC 882 orbit is bound. However, the high gas mass and
the low expected replenishment rate suggest that this is only the first
stripping event. Implications for the origin of nucleated dwarf ellipticals are
briefly discussed.Comment: 22 pages, 7 figures, Astronomical Journal, August 2000, in pres
Molecular Emission Line Formation in Prestellar Cores
We investigate general aspects of molecular line formation under conditions
which are typical of prestellar cores. Focusing on simple linear molecules, we
study formation of their rotational lines by radiative transfer simulations. We
present a thermalization diagram to show the effects of collisions and
radiation on the level excitation. We construct a detailed scheme (contribution
chart) to illustrate the formation of emission line profiles. This chart can be
used as an efficient tool to identify which parts of the cloud contribute to a
specific line profile. We show how molecular line characteristics for uniform
model clouds depend on hydrogen density, molecular column density, and kinetic
temperature. The results are presented in a 2D plane to illustrate cooperative
effects of the physical factors. We also use a core model with a non-uniform
density distribution and chemical stratification to study the effects of cloud
contraction and rotation on spectral line maps. We discuss the main issues that
should be taken into account when dealing with interpretation and simulation of
observed molecular lines.Comment: Accepted for publication in Ap
Phase-Retrieved Tomography enables imaging of a Tumor Spheroid in Mesoscopy Regime
Optical tomographic imaging of biological specimen bases its reliability on
the combination of both accurate experimental measures and advanced
computational techniques. In general, due to high scattering and absorption in
most of the tissues, multi view geometries are required to reduce diffuse halo
and blurring in the reconstructions. Scanning processes are used to acquire the
data but they inevitably introduces perturbation, negating the assumption of
aligned measures. Here we propose an innovative, registration free, imaging
protocol implemented to image a human tumor spheroid at mesoscopic regime. The
technique relies on the calculation of autocorrelation sinogram and object
autocorrelation, finalizing the tomographic reconstruction via a three
dimensional Gerchberg Saxton algorithm that retrieves the missing phase
information. Our method is conceptually simple and focuses on single image
acquisition, regardless of the specimen position in the camera plane. We
demonstrate increased deep resolution abilities, not achievable with the
current approaches, rendering the data alignment process obsolete.Comment: 21 pages, 5 figure
Beyond backscattering: Optical neuroimaging by BRAD
Optical coherence tomography (OCT) is a powerful technology for rapid
volumetric imaging in biomedicine. The bright field imaging approach of
conventional OCT systems is based on the detection of directly backscattered
light, thereby waiving the wealth of information contained in the angular
scattering distribution. Here we demonstrate that the unique features of
few-mode fibers (FMF) enable simultaneous bright and dark field (BRAD) imaging
for OCT. As backscattered light is picked up by the different modes of a FMF
depending upon the angular scattering pattern, we obtain access to the
directional scattering signatures of different tissues by decoupling
illumination and detection paths. We exploit the distinct modal propagation
properties of the FMF in concert with the long coherence lengths provided by
modern wavelength-swept lasers to achieve multiplexing of the different modal
responses into a combined OCT tomogram. We demonstrate BRAD sensing for
distinguishing differently sized microparticles and showcase the performance of
BRAD-OCT imaging with enhanced contrast for ex vivo tumorous tissue in
glioblastoma and neuritic plaques in Alzheimer's disease
- …