Relationships between composition, structure and strength of inorganic polymers, part 2: fly ash-derived inorganic polymers

This article is the second in a two-part series and discusses inorganic polymers derived from fly ash. Part 1 [1] concerns inorganic polymers derived from a metakaolin precursor. For this study, 15 fly ash-derived inorganic polymers were produced with various compositions. The effect of the concentration of each of the four component oxides (Na2O, SiO2, Al2O3 and H2O) and two alkali cations (Na and K) on the microstructure and compressive strengths were assessed. Similar to metakaolin-derived inorganic polymers, it was observed that high-strength fly ash inorganic polymers were related to low porosity and a dense, fine-grained microstructure. Such structures were characteristic of formulations with high silica mole fractions (SiO2/Al2O3 ~3.9) and low water contents, as well as those with high alkali and low alumina contents. For the latter, not only was a characteristic slower strength development with increasing alkali content observed, but there was also a limit of alkali concentration (Na2O/Al2O3 ~1) beyond which the strength deteriorated. Furthermore, SEM micrographs disclose that the fly ash precursor dissolves more readily in the sodium-based system compared to the potassium equivalent. The interrelation between microstructures of the respective formulations and their strength development are discussed. It is observed that the charge-balancing role of the alkali cations in the fly ash formulations may be dominant compared to initial alkali dissolution reaction of the aluminosilicate fly ash particles, which is partly responsible for initial strength development

Relationships between composition, structure and strength of inorganic polymers, part I: metakaolin-derived inorganic polymers

"Inorganic polymers", or geopolymers, are novel synthetic binders produced by reactions between alkali silicate solutions and solid aluminosilicates. In Part 1 of this study, 12 metakaolin-derived inorganic polymers were produced with various compositions. The effect of the concentration of each of the four most important oxide components of inorganic polymers (Na2O, SiO2, Al2O3 and H2O) was assessed by electron microscopy and by strength testing. Additionally, the effect of the type of alkali cation was determined. In general, the results followed expected trends and there were clear correlations between composition, microstructure and strength. It was found that high strength was related to low porosity and a dense, fine grained microstructure. Such a structure was found in inorganic polymers with high alkali contents (Na2O/Al2O3 = 1.2) and low water contents (H2O/Al2O3 = 12). High silica and low alumina contents (SiO2/Al2O3 = 3.5-3.8) also produced this structure, however, there was a limit beyond which the strength deteriorated. In relation to the effect of alkali cations, sodium was found to give higher resin strength than potassium. The results of the study further confirm that the selection of precursor raw materials remains a critical factor to initial strength development. The relationship between different resin formulations and resulting microstructures are discussed

Prototype Ultrahigh-Resolution Computed Tomography for Chest Imaging: Initial Human Experience

Item does not contain fulltextOBJECTIVE: The objective of this study was to evaluate a prototype, ultrahigh-resolution computed tomography offering higher reconstruction matrix (1024 x 1024) and spatial resolution (0.15 mm) for chest imaging. METHODS: Higher (1024) matrix reconstruction enabled by ultrahigh-resolution computed tomography scanner (128-detector rows; detector width, 0.25 mm; spatial resolution, 0.15 mm) was compared with conventional (512) reconstruction with image quality grading on a Likert scale (1, excellent; 5, nondiagnostic) for image noise, artifacts, contrast, small detail, lesion conspicuity, image sharpness, and diagnostic confidence. Image noise and signal-to-noise ratio were quantified. RESULTS: Diagnostic image quality was achieved for all scans on 101 patients. The 1024 reconstruction demonstrated increased image noise (20.2 +/- 4.0 vs 17.2 +/- 3.8, P < 0.001) and a worse noise rating (1.98 +/- 0.63 vs 1.75 +/- 0.61, P < 0.001) but performed significantly better than conventional 512 matrix with fewer artifacts (1.37 +/- 0.43 vs 1.50 +/- 0.48, P < 0.001), better contrast (1.50 +/- 0.56 vs 1.62 +/- 0.57, P < 0.001), small detail detection (1.06 +/- 0.19 vs 2.02 +/- 0.22, P < 0.001), lesion conspicuity (1.08 +/- 0.23 vs 2.02 +/- 0.24, P < 0.001), sharpness (1.09 +/- 0.24 vs 2.02 +/- 0.28, P < 0.001), and overall diagnostic confidence (1.09 +/- 0.25 vs 1.18 +/- 0.34, P < 0.001). CONCLUSIONS: Ultrahigh-resolution computed tomography enabled a higher reconstruction matrix and improved image quality compared with conventional matrix reconstruction, with a minor increase in noise

Ischemia and No Obstructive Stenosis (INOCA) at CT Angiography, CT Myocardial Perfusion, Invasive Coronary Angiography, and SPECT: The CORE320 Study

Background: CT allows evaluation of atherosclerosis, coronary stenosis, and myocardial ischemia. Data on the characterization of ischemia and no obstructive stenosis (INOCA) at CT remain limited.Purpose: This was an observational study to describe the prevalence of INOCA defined at coronary CT angiography with CT perfusion imaging and associated clinical and atherosclerotic characteristics. The analysis was also performed for the combination of invasive coronary angiography (ICA) and SPECT as a secondary aim.Materials and Methods: The prospective CORE320 study (ClinicalTrials.gov: NCT00934037) enrolled participants between November 2009 and July 2011 who were symptomatic and referred for clinically indicated ICA. Participants underwent CT angiography, rest-adenosinestress CT perfusion, and rest-stress SPECT prior to ICA. For this ancillary study, the following three phenotypes were considered, using either CT angiography/CT perfusion or ICA/SPECT data: (a) participants with obstructive (>= 50%) stenosis, (b) participants with no obstructive stenosis but ischemia (ie, INOCA) on the basis of abnormal perfusion imaging results, and (c) participants with no obstructive stenosis and normal perfusion imaging results. Clinical characteristics and CT angiography athero-scleroticplaque measures were compared by using the Pearson chi(2) or Wilcoxon rank-sum test.Results: A total of 381 participants (mean age, 62 years [interquartile range, 56-68 years]; 129 [34%] women) were evaluated. A total of 31 (27%) of 115 participants without obstructive (>= 50%) stenosis at CT angiography had abnormal CT perfusion findings. The corresponding value for ICA/SPECT was 45 (30%) of 151. The prevalence of INOCA was 31 (8%) of 381 (95% confidence interval [CI]: 5%, 11%) with CT angiography/CT perfusion and 45 (12%) of 381 (95% CI: 9%, 15%) with ICA/SPECT. Participants with CT-defined INOCA had greater total atheroma volume (118 vs 60 mm(3), P =.008), more positive remodeling (13% vs 1%, P =.006), and greater low-attenuation atheroma volume (20 vs 10 mm(3), P =.007) than participants with no obstructive stenosis and no ischemia. Comparisons for ICA/SPECT showed similar trends.Conclusion: In CORE320, ischemia and no obstructivestenosis (INOCA) prevalence was 8% and 12% at CT angiography/CT perfusion and invasive coronary angiography/SPECT, respectively. Participants with INOCA had greater atherosclerotic burden and more adverse plaque features at CT compared with those with no obstructive stenosis and no ischemia. (C) RSNA, 2019Cardiolog