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Multiple Images (multiple + image)
Selected Abstracts7 Tesla MR imaging of the human eye in vivoJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2009Kathryn Richdale OD Abstract Purpose: To develop a protocol which optimizes contrast, resolution and scan time for three-dimensional (3D) imaging of the human eye in vivo using a 7 Tesla (T) scanner and custom radio frequency (RF) coil. Materials and Methods: Initial testing was conducted to reduce motion and susceptibility artifacts. Three-dimensional FFE and IR-TFE images were obtained with variable flip angles and TI times. T1 measurements were made and numerical simulations were performed to determine the ideal contrast of certain ocular structures. Studies were performed to optimize resolution and signal-to-noise ratio (SNR) with scan times from 20 s to 5 min. Results: Motion and susceptibility artifacts were reduced through careful subject preparation. T1 values of the ocular structures are in line with previous work at 1.5T. A voxel size of 0.15 × 0.25 × 1.0 mm3 was obtained with a scan time of approximately 35 s for both 3D FFE and IR-TFE sequences. Multiple images were registered in 3D to produce final SNRs over 40. Conclusion: Optimization of pulse sequences and avoidance of susceptibility and motion artifacts led to high quality images with spatial resolution and SNR exceeding prior work. Ocular imaging at 7T with a dedicated coil improves the ability to make measurements of the fine structures of the eye. J. Magn. Reson. Imaging 2009;30:924,932. © 2009 Wiley-Liss, Inc. [source] Source Camera Identification for Heavily JPEG Compressed Low Resolution Still Images,JOURNAL OF FORENSIC SCIENCES, Issue 3 2009Erwin J. Alles M.Sc. Abstract:, In this research, we examined whether fixed pattern noise or more specifically Photo Response Non-Uniformity (PRNU) can be used to identify the source camera of heavily JPEG compressed digital photographs of resolution 640 × 480 pixels. We extracted PRNU patterns from both reference and questioned images using a two-dimensional Gaussian filter and compared these patterns by calculating the correlation coefficient between them. Both the closed and open-set problems were addressed, leading the problems in the closed set to high accuracies for 83% for single images and 100% for around 20 simultaneously identified questioned images. The correct source camera was chosen from a set of 38 cameras of four different types. For the open-set problem, decision levels were obtained for several numbers of simultaneously identified questioned images. The corresponding false rejection rates were unsatisfactory for single images but improved for simultaneous identification of multiple images. [source] Probing galactic dark matter in dense environments: on the strong lensing efficiency of galaxies in rich clustersMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2007Lindsay J. King ABSTRACT The recent detection by Limousin et al. of five new strong lensing events dominated by galaxy cluster members in Abell 1689, and outside the critical regime of the cluster itself, offers a way to obtain constraints on the cluster mass distribution in a region inaccessible to standard lensing analysis. In addition, modelling such systems will provide another window on the dark matter haloes of galaxies in very dense environments. Here, it is shown that the boost in image separation due to the external shear and convergence from a smooth cluster component means that more numerous, less massive galaxies have the potential to create multiple images with detectable separations, relative to isolated field galaxies. This comes in addition to a potential increase in their lensing (source plane) cross-section. To gain insight into the factors involved and as a precursor to a numerical study using N -body simulations, a simple analytic model of a cluster at z= 0.3 lensing background galaxies at z= 2 is considered here. The fiducial model has cluster members with isothermal density profiles and luminosities L, distributed in a Schechter function (faint-end slope ,=,1.25), related to their velocity dispersions , via the Faber,Jackson scaling L,,4. Just outside the critical regime of the cluster, the scale of galaxy-dominated image separations is significantly increased. Folding in the fact that less massive galaxies present a lower lensing cross-section, and that the cross-section can itself be enhanced in an external field leads to a factor of a few times more detected events relative to field galaxies. These values will be higher closer to the critical curve. Given that the events in Abell 1689 were detected over a very small region of the cluster where ACS data were available, this motivates the search for such events in other clusters. [source] Deconvolution of the interatomic vector set using a convolution tableACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2009Jianglin Feng The deconvolution of the interatomic vector set (the ideal Patterson function) with the superposition technique is not complete because of the vector overlaps: multiple images and false peaks usually exist in the superposition map. Here, a new method for the deconvolution of the interatomic vector set is presented. This method involves constructing a table termed the `convolution table' from vectors in a superposition map and then sorting the table so that vectors belonging to different images are separated, and thus the overlaps are naturally solved. This method does not use the symmetry information. [source] | ||||||||||