Cerebral arterial inflow assessment with F-FDG PET: Methodology and feasibility

Positron emission tomography (PET) with ¹⁸fluorodeoxyglucose (¹⁸F-FDG) is increasingly used in neurology. The measurement of cerebral arterial inflow (QA) using ¹⁸F-FDG complements the information provided by standard brain PET imaging. Here, injections were performed after the beginning of dynamic acquisitions and the time to arrival (t0) of activity in the gantry's field of view was computed. We performed a phantom study using a branched tube (internal diameter: 4 mm) and a ¹⁸F-FDG solution injected at 240 mL/min. Data processing consisted of (i) reconstruction of the first 3 s after t0, (ii) vascular signal enhancement and (iii) clustering. This method was then applied in four subjects. We measured the volumes of the tubes or vascular trees and calculated the corresponding flows. In the phantom, the flow was calculated to be 244.2 mL/min. In each subject, our QA value was compared with that obtained by quantitative cine-phase contrast magnetic resonance imaging; the mean QA value of 581.4 ± 217.5 mL/min calculated with ¹⁸F-FDG PET was consistent with the mean value of 593.3 ± 205.8 mL/min calculated with quantitative cine-phase contrast magnetic resonance imaging. Our ¹⁸F-FDG PET method constitutes a novel, fully automatic means of measuring QA.     

On the electronic nature of silicon and germanium based oxynitrides and their related mechanical,optical and vibrational properties as obtained from DFT and DFPT

Electronic structure, bonding and optical properties of the orthorhombic oxynitrides Si₂N₂O and Ge₂N₂O are studied using the density function theory as implemented in pseudo-potential plane wave and full-potential (linearized) augmented plane wave plus local orbitals methods. Generalized gradient approximation is employed in order to determine the band gap energy. Indeed, the Si₂N₂O exhibits a large direct gap whereas Ge₂N₂O have an indirect one. Bonding is analyzed via the charge densities and Mulliken population, where the role of oxygen is investigated. The analysis of the elastic constants show the mechanical stability of both oxynitrides. Their bulk and shear modulus are slightly smaller than those reported on nitrides semiconductors due to the oxygen presence. The optical properties, namely the dielectric function, optical reflectivity, refractive index and electron energy loss, are reported for radiation up to 30 eV. The phonon dispersion relation, zone-center optical mode frequency, density of phonon states are calculated using the density functional perturbed theory. Thermodynamic properties of Si₂N₂O and Ge₂N₂O, such as heat capacity and Debye temperature, are given for reference. Our study suggests that Si₂N₂O and Ge₂N₂O could be a promising potential materials for applications in the microelectronics and optoelectronics areas of research.     

Full-potential study of structural and electronic properties of MB2-type metal diborides (M = Be,Mg and Ca)

Structural, electronic and bonding properties of BeB₂ and CaB₂ were studied using the full-potential linearized augmented plane-wave (FP-LAPW) method, based on the density functional theory implemented in the WIEN2k code and are compared with those of the isostructural superconductor MgB₂. The exchange and correlation potential energies are treated using the local density approximation (LDA), The results are compared with available theoretical and experimental data. In particular, Our result of density of states at the Fermi level N(E_F) for CaB₂ equal to 0.993 states/(eV-f.u.) are found more close to recent pseudopotential result of Choi et al., which give 0.960 states/(eV-f.u.) and is different from 0.796 states/(eV-f.u.) as previously published result by Ravidran et al. We also evaluate the electronic structure of BeB₂ in order to obtain further insight into its surprising difference from the superconducting MgB₂ and therefore attempt to predict the nature of CaB₂, one of the interesting candidates for the higher T_c.     

Hybrid functional calculations of potential hydrogen storage material: Complex dimagnesium iron hydride

By employing the state of art first principles approaches, comprehensive investigations of a very promising hydrogen storage material, Mg₂FeH₆ hydride, is presented. To expose its hydrogen storage capabilities, detailed structural, elastic, electronic, optical and dielectric aspects have been deeply analysed. The electronic band structure calculations demonstrate that Mg₂FeH₆ is semiconducting material. The obtained results of the optical bandgap (4.19 eV) also indicate that it is a transparent material for ultraviolet light, thus demonstrating its potential for optoelectronics application. The calculated elastic properties reveal that Mg₂FeH₆ is highly stiff and stable hydride. Finally, the calculated hydrogen (H₂) storage capacity (5.47 wt.%) within a reasonable formation energy of −78 kJ mol⁻¹, at room temperature, can be easily achievable, thus making Mg₂FeH₆ as potential material for practical H₂ storage applications.     

Improved attenuation correction via appropriate selection of respiratory-correlated PET data

PURPOSE: We propose a respiratory-correlated PET data processing method (called "BH-CT-based") based on breath-hold CT acquisition to reduce the smearing effect and improve the attenuation correction. The resulting images are compared with the ungated PET images acquired using a standard, free-breathing clinical protocol. METHODS: The BH-CT-based method consisted of a list-mode acquisition with simultaneous respiratory signal recording. An additional breath-hold CT acquisition was also performed in order to define a tissue position from which PET events can be selected. A phantom study featured a 0.5-ml sphere (filled with 18F-fluorodeoxyglucose ((18)F-FDG) solution) pushed onto a rubber balloon (filled with (18)F-FDG solution and iodinated contrast agent). The feasibility of the BH-CT-based method was also assessed in two patients. RESULTS: In the phantom study, the contrast-to-noise ratios (CNRs) were -1.6 for the Ungated volume and 5.1 for the BH-CT-based volume. For patients, CNRs were higher for BH-CT-based volumes than those for Ungated volumes (17.3 vs. 6.3 and 7.3 vs. 3.8, for patients 1 and 2, respectively). Bias-variance measurements were performed and yielded bias reduction of 40% with BH-CT-based. CONCLUSION: The application of a BH-CT-based method decreases motion bias in PET images. This method resolves issues related to both PET-to-CT misregistration and erroneous attenuation correction and increases lesion detectability.     

Al Hamra塔,科威特

Al Hamra塔坐落于科威特市,是一座包含有办公空间、健身俱乐部、剧院、美食广场的高端商业中心的商业综合体。建筑高度达到412m。这座标志性的写字楼将成为科威特市最高的建筑。Al Hamra塔的建设目前已经接近尾声,办公面积达到18.6万m2,其旁边是一座由当地建筑师设计的面积达3.4万m2的商业裙房。该项目的业主是一位当地开发商和一位总承包商,但建造一座超高层建筑却并不是他们的初衷。事实上,在项目之初他们已经开始动工建造一座由当地建筑师设计的50层高的塔楼     

Rb and Cs doping effects in sodium borohydride: Density functional theory for hydrogen (H2) storage purpose

Fuel cell technology based on stationary and mobile applications is needing new hydrogen storage materials equipped with huge gravimetric and volumetric hydrogen densities. Examining the fundamental properties of hydrides is an important part of such process, mainly to understand the structure change's impact on the hydrogen storage. Herein, we applied ab-initio density functional theory using full potential linear augmented plane method to explore the effect of rubidium and cesium doping in sodium borohydride, NaBH₄. The electronic structure calculations exposed the semiconducting nature of NaBH₄ and derived doped structures NaRbBH₄ and NaCsBH₄. The hydrogen (H₂) storage capacity is found 10.66 wt %, 3.27 wt % and 2.36 wt % within a reasonable free energy of ?28.514 kJ/mol, ?29.709 kJ, ?28.51 kJ/mol for NaBH₄, NaRbBH₄ and NaCsBH₄ respectively from quasi-harmonic approximation. Also, we extracted the heat capacity and Debye temperature from vibrational analysis based on phonon calculation. The discovered features show the potential use of presented sodium borohydrides for practical H₂ storage devices.     

Motion correction based on an appropriate system matrix for statistical reconstruction of respiratory-correlated PET acquisitions

Respiratory motion correction in positron emission tomography (PET) seeks to incorporate motion information into an image reconstruction algorithm by using the full counting statistics of an acquisition to generate a single, motion-free volume. Here, we present a motion-incorporated ordered subsets expectation maximization (MOSEM) reconstruction based on a device-dedicated tomographic projector in which each matrix element is calculated directly from the voxels’ Cartesian coordinates alone. The motion is corrected by updating this projector as a function of the respiratory level. The performance of the reconstruction method was investigated with three datasets: two simulations of a transaxially or axially moving lesion on a patient acquisition and a third acquisition of a moving sphere. After the 16th sub-iteration, the normalized mean square error (NMSE, with a motionless acquisition as reference) was 0.20 for the non-corrected (ungated) image and 0.01 for the MOSEM image with transaxial motion simulation. Likewise, NMSE was 0.30 for the ungated image and 0.03 for MOSEM image with axial motion simulation. For the phantom, ungated reconstruction yielded an error of 0.78, whereas MOSEM yielded 0.43. The error reduction resulted from enhancement and reduced spreading of the moving uptake. Our results show that MOSEM reconstruction yields motion-corrected images which are similar to motionless reference images.     

Reliable and energy aware query-driven routing protocol for wireless sensor networks

Wireless sensor networks become very attractive in the research community, due to their applications in diverse fields such as military tracking, civilian applications and medical research, and more generally in systems of systems. Routing is an important issue in wireless sensor networks due to the use of computationally and resource limited sensor nodes. Any routing protocol designed for use in wireless sensor networks should be energy efficient and should increase the network lifetime. In this paper, we propose an efficient and highly reliable query-driven routing protocol for wireless sensor networks. Our protocol provides the best theoretical energy aware routes to reach any node in the network and routes the request and reply packets with a lightweight overhead. We perform an overall evaluation of our protocol through simulations with comparison to other routing protocols. The results demonstrate the efficiency of our protocol in terms of energy consumption, load balancing of routes, and network lifetime.     

Predicted Thermoelectric Properties of the Layered XBi<Subscript>4</Subscript>S<Subscript>7</Subscript> (X = Mn,Fe) Based Materials: First Principles Calculations

We report a theoretical investigation of electronic structures, optical and thermoelectric properties of two ternary-layered chalcogenides, MnBi₄S₇ and FeBi₄S₇ , by combining the first principles density functional calculations and semi-local Boltzmann transport theory. The calculated electronic band structure have demonstrated that both compounds exhibit indirect band gaps. The optical transitions are explored via the dielectric function (real and imaginary parts) along with other related optical constants including refractive index, reflectivity, and energy loss spectrum. These chalcogenides have exhibited interesting thermoelectric properties such as Seebeck’s coefficient, electrical and thermal conductivity, and power factor as function of temperatures.