A new approach for quantitative evaluation of reconstruction algorithms in SPECT

Background: In nuclear medicine, phantoms are mainly used to evaluate the overall performance of the imaging systems, and practically there is no phantom exclusively designed for the evaluation of the software performance. In this study the Hoffman brain phantom was used for quantitative evaluation of reconstruction techniques. The phantom is modified to acquire tomographic and planar image of the same structure. The planar image may be used as the reference image to evaluate the quality of reconstructed slices, using the companion software developed in MATLAB. Materials and Methods: The designed phantom was composed of 4 independent 2D slices that could have been placed juxtapose to the 3D phantom. Each slice was composed of objects of different size and shape (for example: circle, triangle, and rectangle). Each 2D slice was imaged at distances ranging from 0 to 15 cm from the collimator surface. The phantom in 3D configuration was imaged acquiring 128 views of 128×128 matrix size. Reconstruction was performed using different filtering condition and the reconstructed images were compared to the corresponding planar images. The modulation transfer function, scatter fraction and attenuation map were calculated for each reconstructed image. Results: Since all the parameters of the acquisition were identical for the 2D and the 3D imaging, it was assumed that the difference in the quality of the images has exclusively been due to the reconstruction condition. The planar images were assumed to be the most perfect images which could be obtained with the system. The comparison of the reconstructed slices with the corresponding planar images yielded the optimum reconstruction condition. The results clearly showed that Wiener filter yields superior quality image among the entire tested filters. The extent of the improvement has been quantified in terms of universal image quality index. Conclusion: The phantom and the accompanying software were evaluated and found to be quite useful in determining the optimum filtering condition and mathematical evaluation of the scatter and attenuation in tomographic images. A new approach for quantitative evaluation of reconstruction algorithms in SPECT (PDF Download Available). Available from: https://www.researchgate.net/publication/229005593_A_new_approach_for_quantitative_evaluation_of_reconstruction_algorithms_in_SPECT [accessed Nov 07 2017]

Catalyst preparation for fluidized bed reactors by spray drying

Spray dried fluidized bed catalysts belong to the Geldart Group A classification and vary between 22 m to 200 m in diameter (1). Binder is either distributed throughout the particle with the active phase or surrounds the active phase as in a core-shell structure (2, 3). We slurried WO3/TiO2 micronized powder (0.2 m to 2 m) with colloidal silica (LUDOX® HS-40) to form a slurry with a mass fraction of 5 % to 20 % solids. The solution entered the top of GB-22 Yamato fluidized bed spray dryer chamber (0.12 m ID) through a two-fluid nozzle and the drying air entered the bottom counter-currently. We varied the feed slurry concentration, binder concentration, slurry and drying air flow rates, two-phase nozzle pressure drop and inlet temperature. Most conditions only produced a very fine powder (Group C, dpm) (Fig. 1a). (Ideally, the particle size should exceed 80 m for laboratory experimental equipment). The small particles were often fully spherical but we also produced large clusters that reached 150 m (Fig. 1b). The high pressure drop through the nozzle and low slurry concentration produced the fine powder. Particles agglomerated in the fluidized bed when we increased the slurry flow rate to the chamber such that the powder had not yet dried sufficiently. Please click Additional Files below to see the full abstract

Edge-illumination x-ray phase contrast imaging with Pt-based metallic glass masks

Edge-illumination x-ray phase contrast imaging (EI XPCI) is a non-interferometric phase-sensitive method where two absorption masks are employed. These masks are fabricated through a photolithography process followed by electroplating which is challenging in terms of yield as well as time- and cost-effectiveness. We report on the first implementation of EI XPCI with Pt-based metallic glass masks fabricated by an imprinting method. The new tested alloy exhibits good characteristics including high workability beside high x-ray attenuation. The fabrication process is easy and cheap, and can produce large-size masks for high x-ray energies within minutes. Imaging experiments show a good quality phase image, which confirms the potential of these masks to make the EI XPCI technique widely available and affordable

A serial evaluation of electrocardiographic indices and cardiac arrhythmias during pregnancy, lactation and dry periods in Saanen goats

Aim of this study was to investigate the effects of lactation, pregnancy and dry period on electrocar-diographic (ECG) parameters and cardiac arrhythmias in the Saanen goat. A total of twenty female adult clinically healthy Saanen goats 3 years of age with a body condition score of 3.5 and average weight of 30.2±2.20 kg were randomly selected. The whole duration of the study (8 months) was divided into four periods including dry and non-pregnant (P1), 2 months pregnant (P2), 4 months pregnant (P3), and lactating (P4) periods. In late pregnancy and lactation periods, the amplitudes of P, QRS and T waves were significantly higher compared to other periods (P<0.01). P-R, Q-T and R-R intervals in late pregnancy were significantly shorter and heart rate was significantly higher than those in other periods. Sinus arrhythmias were the only irregularity observed on the ECG traces and were diagnosed in 30%, 15%, 20% and 35.25% of the goats in P1, P2, P3 and P4, respectively. There were no significant difference in configuration of ECG waves and cardiac arrhythmias among different periods. Based on the results of the present study, it was concluded that although no cardiac morpho-logical changes have been reported in goats during the lactation, late pregnancy and dry periods, sig-nificant changes in ECG parameters were observed in base-apex lead in Saanen goats during late pregnancy and lactation periods. The physiological cardiac arrhythmias and variations in ECG pa-rameters observed during different periods in the current study can be used as a base to achieve more accurate diagnoses of heart diseases using ECG

Microstructure development and high tensile properties of He/H2 milled oxide dispersion strengthened copper

This study describes the effect of microstructural development on high tensile properties of a newly developed He/H2 milled oxide dispersion strengthened copper in a large centimeter sized spherical morphology. Electron back scattered diffraction showed development of a strong texture of (110) plane in micron sized (1.2 μm) grains on the surface of milled spheres. A combination of microstructural features of inhomogeneous grain size, nanoscale lenticular/rectangular deformation twins, high dislocation density and fine oxide particles distribution induced a very high ultimate tensile strength (688 MPa)-ductility (8.6% elongation)

Microstructure and mechanical properties of mechanically alloyed ODS copper alloy for fusion material application

Advanced oxide dispersion strengthened copper alloys are promising structural materials for application in divertor system of future fusion reactors due to high irradiation resistance, high thermal conductivity, and good mechanical properties. In this study, a new ODS copper including 0.42wt%Y2O3 nanosized oxide particles wasdeveloped successfully by mechanical alloying method using addition of 1 wt% Stearic acid in Ar atmosphere.Mechanical alloying resulted in decrease of crystallite size to 28 nm in concurrent with increment of dislocation density and hardness to the saturated level of × −1.7 10 m15 2 and 226HV0.1 after 48 h milling, respectively.Consolidated ODS copper by SPS and then hot roll-annealing at 900 °C/60 min showed an average grain size of 1.1 μm with a near random texture. Furthermore, TEM observations demonstrated fine semicoherent Y2O3 oxide particles distributed with a misfit parameter (δ) of 0.17 in copper matrix with an average size of 10.8 nm andinterparticle spacing of 152 nm. Finally, tensile test evaluation determined comparable mechanical properties of the annealed ODS copper (Cu-0.42wt%Y2O3) with Glidcop-Al25 including a yield strength of 272 MPa and total elongation of 12%, by two mechanisms of grain boundary strengthening and oxide particle strengthening

Brass-texture induced grain structure evolution in room temperature rolled ODS copper

Currently, advanced ODS copper alloy is under study as a potential fusion material providing good mechanical properties. In this work, in order to develop a high performance ODS copper containing 0.5 wt% Y2O3 oxide particles, the effect of room temperature rolling and subsequent annealing on the grain structure evolution, texture development and tensile properties are studied using EBSD, TEM and tensile tests. Microstructure evolution studies show the grain structure coarsens by enhancing the Brass texture during increase of rolling reduction and a unique single crystal-like brass-texture deformed structure is achieved after 80% rolling reduction. We found the deformation mechanism of partial slip by a/6 ⟨211⟩ by dislocations facilitated by the pinning of a/2 ⟨101⟩ perfect dislocations through fine oxide particles is responsible for formation of Brass texture during room temperature rolling. Furthermore, the recrystallization of ODS copper retards to high temperature of ~700 °C and shows a fine-grained microstructure with different orientations of Goss, Brass, S and Copper. Evaluation of microstructure-mechanical properties of the recrystallized samples expresses that the bimodal grain size distribution at 800 °C for 30 min offers a good tensile strength-ductility (UTS: 491 MPa, elt: 19%) at ambient temperature

Microstructure development in cryogenically rolled oxide dispersion strengthened copper

Recently, advanced oxide dispersion strengthened (ODS) copper alloys have been developed using mechanical alloying process as a fusion material. In this study, to develop a superior ODS copper alloy containing 0.5wt% Y2O3, the effect of cryogenic rolling on microstructure development and tensile properties was studied using high resolution EBSD, TEM and tensile tests. During cryogenic deformation of ODS copper, grain structure remains in submicron size scale as a combinatorial result of geometrically effects, nanotwin bundle deformation, interaction of dislocations with fine oxide particles and some diffusional processes including static recovery and recrystallization. Clear microstructural characterizations confirmed nucleation of fine new oriented recrystallized grains mainly on the HABs of 80%cryogenic rolled ODS copper. Quantitative analyses indicated grain boundary migration at room temperature following cryogenic deformation originated from high driving force induced by grain boundary bulging and high mobility induced by vacancies. The tensile properties of cryogenic deformed samples showed superior tensile strength than room temperature deformation leading to UTS: 624 MPa, elt: 5.5%, while saturation of strength between 60%-80% reduction, approved occurrence of softening by diffusional processes

High potential for weathering and climate effects of non-vascular vegetation in the Late Ordovician

It has been hypothesized that predecessors of today’s bryophytes significantly increased global chemical weathering in the Late Ordovician, thus reducing atmospheric CO2 concentration and contributing to climate cooling and an interval of glaciations. Studies that try to quantify the enhancement of weathering by non-vascular vegetation, however, are usually limited to small areas and low numbers of species, which hampers extrapolating to the global scale and to past climatic conditions. Here we present a spatially explicit modelling approach to simulate global weathering by non-vascular vegetation in the Late Ordovician. We estimate a potential global weathering flux of 2.8 (km3 rock) yr−1, defined here as volume of primary minerals affected by chemical transformation. This is around three times larger than today’s global chemical weathering flux. Moreover, we find that simulated weathering is highly sensitive to atmospheric CO2 concentration. This implies a strong negative feedback between weathering by non-vascular vegetation and Ordovician climate

Is metal artefact reduction mandatory in cardiac PET/CT imaging in the presence of pacemaker and implantable cardioverter defibrillator leads?

Abstract Purpose Cardiac PET/CT imaging is often performed in patients with pacemakers and implantable cardioverter defibrillator (ICD) leads. However, metallic implants usually produce artefacts on CT images which might propagate to CTbased attenuation-corrected (CTAC) PET images. The impact of metal artefact reduction (MAR) for CTAC of cardiac PET/ CT images in the presence of pacemaker, ICD and ECG leads was investigated using both qualitative and quantitative analysis in phantom and clinical studies. Methods The study included 14 patients with various leads undergoing perfusion and viability examinations using dedicated cardiac PET/CT protocols. The PET data were corrected for attenuation using both artefactual CT images and CT images corrected using the MAR algorithm. The severity and magnitude of metallic artefacts arising from these leads were assessed on both linear attenuation coefficient maps (μ-maps) and attenuation-corrected PET images. CT and PET emission data were obtained using an anthropomorphic thorax phantom and a dedicated heart phantom made in-house incorporating pacemaker and ICD leads attached at the right ventricle of the heart. Volume of interest-based analysis and regression plots were performed for regions related to the lead locations. Bull&apos;s eye view analysis was also performed on PET images corrected for attenuation with and without the MAR algorithm. Results In clinical studies, the visual assessment of PET images by experienced physicians and quantitative analysis did not reveal erroneous interpretation of the tracer distribution or significant differences when PET images were corrected for attenuation with and without MAR. In phantom studies, the mean differences between tracer Nucl Med Mol Imaging (2011) 38:252-262 DOI 10.1007/s00259-010-1635 uptake obtained without and with MAR were 10.16±2.1% and 6.86±2.1% in the segments of the heart in the vicinity of metallic ICD or pacemaker leads, and were 4.43±0.5% and 2.98±0.5% in segments far from the leads. Conclusion Although the MAR algorithm was able to effectively improve the quality of μ-maps, its clinical impact on the interpretation of PET images was not significant. Therefore cardiac PET images corrected for attenuation using CTAC in the presence of metallic leads can be interpreted without correction for metal artefacts. It should however be emphasized that in some special cases with multiple ICD leads attached to the myocardium wall, MAR might be useful for accurate attenuation correction. Eur