72,918 research outputs found
3D/2D Registration of Mapping Catheter Images for Arrhythmia Interventional Assistance
Radiofrequency (RF) catheter ablation has transformed treatment for
tachyarrhythmias and has become first-line therapy for some tachycardias. The
precise localization of the arrhythmogenic site and the positioning of the RF
catheter over that site are problematic: they can impair the efficiency of the
procedure and are time consuming (several hours). Electroanatomic mapping
technologies are available that enable the display of the cardiac chambers and
the relative position of ablation lesions. However, these are expensive and use
custom-made catheters. The proposed methodology makes use of standard catheters
and inexpensive technology in order to create a 3D volume of the heart chamber
affected by the arrhythmia. Further, we propose a novel method that uses a
priori 3D information of the mapping catheter in order to estimate the 3D
locations of multiple electrodes across single view C-arm images. The monoplane
algorithm is tested for feasibility on computer simulations and initial canine
data.Comment: International Journal of Computer Science Issues, IJCSI, Volume 4,
Issue 2, pp10-19, September 200
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
Gas micro-well track imaging detectors for gamma-ray astronomy
We describe our program to develop gas micro-well detectors (MWDs) as three-dimensional charged particle trackers for use in advanced gamma-ray telescope concepts. A micro-well detector consists of an array of individual micro-patterned gas proportional counters opposite a planar drift electrode. The well anodes and cathodes may be connected in X and Y strips, respectively, to provide two-dimensional imaging. When combined with transient digitizer electronics, which record the time signature of the charge collected in the wells of each strip, full three-dimensional reconstruction of charged-particle tracks in large gas volumes is possible. Such detectors hold great promise for advanced Compton telescope (ACT) and advanced pair telescope (APT) concepts due to the very precise measurement of charged particle momenta that is possible (Compton recoil electrons and electron-positron pairs, respectively). We present preliminary lab results, including detector fabrication, prototype electronics, and initial detector testing. We also discuss applications to the ACT and APT mission concepts, based on GEANT3 and GEANT4 simulations
"Interaction-Free" Imaging
Using the complementary wave- and particle-like natures of photons, it is
possible to make ``interaction-free'' measurements where the presence of an
object can be determined with no photons being absorbed. We investigated
several ``interaction-free'' imaging systems, i.e. systems that allow optical
imaging of photosensitive objects with less than the classically expected
amount of light being absorbed or scattered by the object. With the most
promising system, we obtained high-resolution (10 \mu m), one-dimensional
profiles of a variety of objects (human hair, glass and metal wires, cloth
fibers), by raster scanning each object through the system. We discuss possible
applications and the present and future limits for interaction-free imaging.Comment: 10 pages, 6 encapsulated Postscript figure files, accepted for
publication in Physical Review
Survey for Galaxies Associated with z~3 Damped Lyman alpha Systems I: Spectroscopic Calibration of u'BVRI Photometric Selection
We present a survey for z~3 Lyman break galaxies (LBGs) associated with
damped Lyman alpha systems (DLAs) with the primary purpose of determining the
DLA-LBG cross-correlation. This paper describes the acquisition and analysis of
imaging and spectroscopic data of 9 quasar fields having 11 known z~3 DLAs
covering an area of 465 arcmin^2. Using deep u'BVRI images, 796 LBG candidates
to an apparent R_AB magnitude of 25.5 were photometrically selected from 17,343
sources detected in the field. Spectroscopic observations of 529 LBG candidates
using Keck LRIS yielded 339 redshifts. We have conservatively identified 211
z>2 objects with =3.02+/-0.32. We discuss our method of z~3 LBG
identification and present a model of the u'BVRI photometric selection
function. We use the 339 spectra to evaluate our u'BVRI z~3 Lyman break
photometric selection technique.Comment: 26 pages, 6 tables, 11 figures, accepted for publication in Ap
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A holographic system for subsea recording and analysis of plankton and other marine particles
We report here details of the design, development, initial testing and field-deployment of the HOLOMAR system for in-situ subsea holography and analysis of marine plankton and nonliving particles. HOLOMAR comprises a submersible holographic camera ("HoloCam") able to record in-line and off-axis holograms at depths down to 100 m, together with specialised reconstruction hardware ("HoloScan") linked to custom image processing and classification software. The HoloCam consists of a laser and power supply, holographic recording optics and holographic plate holders, a water-tight housing and a support frame. It utilises two basic holographic geometries, in-line and off-axis such that a wide range of species, sizes and concentrations can be recorded. After holograms have been recorded and processed they are reconstructed in full three-dimensional detail in air in a dedicated replay facility. A computer-controlled microscope, using video cameras to record the image at a given depth, is used to digitise the scene. Specially written software extracts a binarised image of an object in its true focal plane and is classified using a neural network. The HoloCam was deployed on two separate cruises in a Scottish sea loch (Loch Etive) to a depth of 100 m and over 300 holograms were recorded
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