Monte Carlo tomographic reconstruction in SPECT impact of bootstrapping and number of generated events

In Single Photon Emission Computed Tomography (SPECT), 3D images usually reconstructed by performing a set of bidimensional (2D) analytical or iterative reconstructions can also be reconstructed using an iterative reconstruction algorithm involving a 3D projector. Accurate Monte Carlo (MC) simulations modeling all the physical effects that affect the imaging process can be used to estimate this projector. However, the accuracy of the projector is affected by the stochastic nature of MC simulations. In this paper, we study the accuracy of the reconstructed images with respect to the number of simulated histories used to estimate the MC projector. Furthermore, we study the impact of applying the bootstrapping technique when estimating the projectorComment: 15 pages, 9 figures, 2 table

Infrared Spectroscopy of GX 1+4/V2116 Oph: Evidence for a Fast Red Giant Wind?

We present infrared spectroscopy of the low-mass X-ray binary GX 1+4/V2116 Oph. This symbiotic binary consists of a 2-min accretion-powered pulsar and an M5 III red giant. A strong He I 1.083 micron emission line with a pronounced P Cygni profile was observed. From the blue edge of this feature, we infer an outflow velocity of 250(50) km/s. This is an order of magnitude faster than a typical red giant wind, and we suggest that radiation from the accretion disk or the neutron star may contribute to the acceleration of the outflow. We infer a wind mass loss rate of around 10^-6 Msun/yr. Accretion from such a strong stellar wind provides a plausible alternative to Roche lobe overflow for supplying the accretion disk which powers the X-ray source. The H I Paschen beta and He I 1.083 micron lines showed no evidence for the dramatic changes previously reported in some optical lines, and no evidence for pulsations at the 2-min pulsar period.Comment: 11 pages including 2 PS figures. To appear in ApJ Letter

"No Good Reason to Remove Features": Expert Users Value Useful Apps over Secure Ones

Application sandboxes are an essential security mechanism to contain malware, but are seldom used on desktops. To understand why this is the case, we interviewed 13 expert users about app appropriation decisions they made on their desktop computers. We collected 201 statements about app appropriation decisions. Our value-sensitive empirical analysis of the interviews revealed that (a) security played a very minor role in app appropriation; (b) users valued plugins that support their productivity; (c) users may abandon apps that remove a feature – especially when a feature was blocked for security reasons. Our expert desktop users valued a stable user experience and flexibility, and are unwilling to sacrifice those for better security. We conclude that sandboxing – as currently implemented – is unlikely to be voluntarily adopted, especially by expert users. For sandboxing to become a desirable security mechanism, they must first accommodate plugins and features widely found in popular desktop apps

Effect of noise and modeling errors on the reliability of fully 3D Monte Carlo reconstruction in SPECT

We recently demonstrated the value of reconstructing SPECT data with fully 3D Monte Carlo reconstruction (F3DMC), in terms of spatial resolution and quantification. This was shown on a small cubic phantom (64 projections 10 x 10) in some idealistic configurations. The goals of the present study were to assess the effect of noise and modeling errors on the reliability of F3DMC, to propose and evaluate strategies for reducing the noise in the projector, and to demonstrate the feasibility of F3DMC for a dataset with realistic dimensions. A small cubic phantom and a realistic Jaszczak phantom dataset were considered. Projections and projectors for both phantoms were calculated using the Monte Carlo simulation code GATE. Projectors with different statistics were considered and two methods for reducing noise in the projector were investigated: one based on principal component analysis (PCA) and the other consisting in setting small probability values to zero. Energy and spatial shifts in projection sampling with respect to projector sampling were also introduced to test F3DMC in realistic conditions. Experiments with the cubic phantom showed the importance of using simulations with high statistics for calculating the projector, and the value of filtering the projector using a PCA approach. F3DMC was shown to be robust with respect to energy shift and small spatial sampling off-set between the projector and the projections. Images of the Jaszczak phantom were successfully reconstructed and also showed promising results in terms of spatial resolution recovery and quantitative accuracy in small structures. It is concluded that the promising results of F3DMC hold on realistic data set

From Paternalistic to User-Centred Security: Putting Users First with Value-Sensitive Design

Usable security research to date has focused on making users more secure, by identifying and addressing usability issues that lead users to making mistakes, or by persuading users to pay attention to security and make secure choices. However, security goals were set by security experts, who were unaware that users often have other priorities and value security differently. In this paper, we present examples of circumventions and non-adoption of secure systems designed under this paternalistic mindset. We argue that security experts need to identify user values and deliver on them. To do that, we need a methodological framework that can conceptualise values and identify those that impact user engagement with security. We show that (a) engagement with, and adherence to security, are mediated by user values, and that (b) it is necessary to model those values to understand the nature of security’s failures and to design viable alternatives

Reconstruction tri-dimensionnelle complete d'images en spect-ct par modelisation Monte-Carlo

présenté par Z. El Bitar, proceedings sous forme de CDEn tomographie d'émission monophotonique (SPECT), les images 3D normalement reconstruites par des algorithmes de reconstruction analytiques ou itératives bidimensionnelles (2D) pourraient aussi bien être reconstruites avec des algorithmes de reconstruction itérative (3D) qui permettent de compenser les effets physiques perturbant le processus de formation de l'image notamment l'atténuation et la diffusion. Nous avons étudié une technique de reconstruction 3D complète (F3DMC) (Lazaro et al. NIM 2004), dans laquelle le projecteur 3D impliqué dans la reconstruction est estimé par des simulations Monte-Carlo effectuées à partir de données tomodensitométriques du patient

Gene deficiency in activating Fcγ receptors influences the macrophage phenotypic balance and reduces atherosclerosis in mice

Immunity contributes to arterial inflammation during atherosclerosis. Oxidized low-density lipoproteins induce an autoimmune response characterized by specific antibodies and immune complexes in atherosclerotic patients. We hypothesize that specific Fcγ receptors for IgG constant region participate in atherogenesis by regulating the inflammatory state of lesional macrophages. In vivo we examined the role of activating Fcγ receptors in atherosclerosis progression using bone marrow transplantation from mice deficient in γ-chain (the common signaling subunit of activating Fcγ receptors) to hyperlipidemic mice. Hematopoietic deficiency of Fcγ receptors significantly reduced atherosclerotic lesion size, which was associated with decreased number of macrophages and T lymphocytes, and increased T regulatory cell function. Lesions of Fcγ receptor deficient mice exhibited increased plaque stability, as evidenced by higher collagen and smooth muscle cell content and decreased apoptosis. These effects were independent of changes in serum lipids and antibody response to oxidized low-density lipoproteins. Activating Fcγ receptor deficiency reduced pro-inflammatory gene expression, nuclear factor-κB activity, and M1 macrophages at the lesion site, while increasing anti-inflammatory genes and M2 macrophages. The decreased inflammation in the lesions was mirrored by a reduced number of classical inflammatory monocytes in blood. In vitro, lack of activating Fcγ receptors attenuated foam cell formation, oxidative stress and pro-inflammatory gene expression, and increased M2-associated genes in murine macrophages. Our study demonstrates that activating Fcγ receptors influence the macrophage phenotypic balance in the artery wall of atherosclerotic mice and suggests that modulation of Fcγ receptor-mediated inflammatory responses could effectively suppress atherosclerosis