Search results for "Image resolution"
showing 10 items of 377 documents
A Monte-Carlo based model of the AX-PET demonstrator and its experimental validation
2013
AX-PET is a novel PET detector based on axially oriented crystals and orthogonal wavelength shifter (WLS) strips, both individually read out by silicon photo-multipliers. Its design decouples sensitivity and spatial resolution, by reducing the parallax error due to the layered arrangement of the crystals. Additionally the granularity of AX-PET enhances the capability to track photons within the detector yielding a large fraction of inter-crystal scatter events. These events, if properly processed, can be included in the reconstruction stage further increasing the sensitivity. Its unique features require dedicated Monte-Carlo simulations, enabling the development of the device, interpreting …
Inclusion of Inter Crystal Scatter data in PET
2012
In PET, as the spatial resolution of the measurement system is increased, multiple interactions of a single photon may be separately measured and such events are often removed from the data used in image reconstruction. While for some PET imaging tasks this effect is unimportant, for primate, brain and high-spatial-resolution imaging where sensitivity is important, such Inter Crystal Scattering (ICS) events may constitute a large fraction of the measured data. On-the-fly list-mode image reconstruction is generally required in order to use all the information provided by ICS. Simulated One-Pass List-mode image reconstruction is used in this investigation to study the inclusion of ICS informa…
Imaging magnetic scalar potentials by laser-induced fluorescence from bright and dark atoms
2014
We present a spectroscopic method for mapping two-dimensional distributions of magnetic field strengths (magnetic scalar potential lines) using charge-coupled device (CCD) recordings of the fluorescence patterns emitted by spin-polarized Cs vapour in a buffer gas exposed to inhomogeneous magnetic fields. The method relies on the position-selective destruction of spin polarization by magnetic resonances induced by multi-component oscillating magnetic fields, such that magnetic potential lines can be directly detected by the CCD camera. We also present a generic algebraic model allowing for the calculation of the fluorescence patterns and find excellent agreement with the experimental observa…
HOLIMO II: a digital holographic instrument for ground-based in situ observations of microphysical properties of mixed-phase clouds
2013
Measurements of the microphysical properties of mixed-phase clouds with high spatial resolution are important to understand the processes inside these clouds. This work describes the design and characterization of the newly developed ground-based field instrument HOLIMO II (HOLographic Imager for Microscopic Objects II). HOLIMO II uses digital in-line holography to in situ image cloud particles in a well-defined sample volume. By an automated algorithm, two-dimensional images of single cloud particles between 6 and 250 μm in diameter are obtained and the size spectrum, the concentration and water content of clouds are calculated. By testing the sizing algorithm with monosized beads a system…
Centre-to-limb variation of photospheric facular radiance and image resolution
2005
Abstract We study the effect of the angular resolution on the determination of the angular properties of the facular radiance. We analyze photospheric intensity in the continuum, around the Ni 676.8 nm line, and longitudinal magnetic field along the line of sight, measured by the MDI instrument aboard SOHO with two spatial resolutions, 4″ and 1.2″ (2″ and 0.6″ pixels, respectively). The effect of the limited photometric sensitivity of the instrument and the limited information on the angular structure of the magnetic field tubes are considered. Our study of the high-resolution data shows that intensity contrast of magnetic features between 80 and 600 Gauss increases from centre to limb up t…
Shock–cloud interactions in the Vela SNR: preliminary results of an XMM-Newton observation
2004
Abstract The study of the clumpy and irregular features in the X-ray emission of middle-aged supernova remnants shells allows us to shed light on the various characteristic of the interstellar medium, like its structure and composition. We have observed with XMM-Newton a small knot in the Vela SNR, which previous ROSAT studies have indicated as one of the best examples of an interaction between the SNR shock and an isolated cloud. We present preliminary results of this study. Thanks to the combination of good spectral and spatial resolution of the EPIC camera, we have realized maps of the X-ray emission in three different bands, pinpointing the contribution from different spatial regions. W…
Wavelength dependence of visual acuity in goldfish.
2003
Visual acuity was measured in a two-choice training experiment with food reward. Four goldfish were trained to select a homogeneously illuminated testfield when a high-contrast grating (transparency) was shown for comparison at the second testfield. Measurements were performed for white and monochromatic testfield illuminations in the light adapted state. Fourteen wavelengths between 404 nm and 683 nm were tested. For each wavelength (and white light) the testfield intensity was determined for which spatial resolution was highest. Between 446 nm and 683 nm maximal values of 2.0 cycles/deg (corresponding to a visual acuity of 15' of arc) were found. At 404 nm and in the ultraviolet resolutio…
DEPFET based Instrumentation for the MIXS focal plane on BepiColombo
2009
BepiColombo, ESA's fifth cornerstone mission, is a planetary exploration mission to Mercury. On board of BepiColombo's Mercury Planetary Orbiter (MPO), the MIXS instrument will perform a complete X-ray fluorescence analysis of Mercury's crust with unprecedented spectral and spatial resolution. This is achieved by using a lightweight X-ray mirror system and by using of DEPFET based Macropixel devices as X-ray detectors. DEPFET based Macropixel detectors combine the advantages of the DEPFETs, like flexible readout modes, Fano-limited energy resolution and low power consumption, with the properties of the drift detectors, like arbitrary scalable pixel size and geometry. In addition, the excell…
The wide field imager for the International X-ray Observatory
2009
The large collecting area of the X-ray optics on the International X-ray Observatory (IXO), their good angular resolution, the wide bandwidth of X-ray energies and the high radiation tolerance required for the X-ray detectors in the focal plane have stimulated a new development of devices which unify all those science driven specifications in one single detector. The concept of a monolithic, back-illuminated silicon active pixel sensor (APS) based on the DEPFET structure is proposed for the IXO mission, being a fully depleted, back-illuminated 450 μm thick detector with a physical size of about 10 × 10 cm 2 corresponding to the 18 arcmin field of view. The backside will be covered with an i…
Linear inverse filtering improves spatial separation of nonlinear brain dynamics: a simulation study.
2000
We examined topographic variations in nonlinear measures based on scalp voltages, which were generated by two simulated current dipoles each placed in a different hemisphere of a spherical volume conductor (three-shell model). Dipole dynamics were that of a three-torus and the x-component of the Lorenz-system and scalp voltage were calculated for a configuration of 29 electrode positions. Although estimates for correlation dimension D2 and Lyapunov exponent L1 were close to the theoretical values for the original time series, the simulated scalp voltage data showed almost no topographic resolution of dipole positions. In order to enhance topographic differentiation, we constructed linear in…