Automated Quantitative Stress Perfusion Cardiac Magnetic Resonance in Pediatric Patients

Background: Myocardial ischemia occurs in pediatrics, as a result of both congenital and acquired heart diseases, and can lead to further adverse cardiac events if untreated. The aim of this work is to assess the feasibility of fully automated, high resolution, quantitative stress myocardial perfusion cardiac magnetic resonance (CMR) in a cohort of pediatric patients and to evaluate its agreement with the coronary anatomical status of the patients.Methods: Fourteen pediatric patients, with 16 scans, who underwent dual-bolus stress perfusion CMR were retrospectively analyzed. All patients also had anatomical coronary assessment with either CMR, CT, or X-ray angiography. The perfusion CMR images were automatically processed and quantified using an analysis pipeline previously developed in adults.Results: Automated perfusion quantification was successful in 15/16 cases. The coronary perfusion territories supplied by vessels affected by a medium/large aneurysm or stenosis (according to the AHA guidelines), induced by Kawasaki disease, an anomalous origin, or interarterial course had significantly reduced myocardial blood flow (MBF) (median (interquartile range), 1.26 (1.05, 1.67) ml/min/g) as compared to territories supplied by unaffected coronaries [2.57 (2.02, 2.69) ml/min/g, p < 0.001] and territories supplied by vessels with a small aneurysm [2.52 (2.45, 2.83) ml/min/g, p = 0.002].Conclusion: Automatic CMR-derived MBF quantification is feasible in pediatric patients, and the technology could be potentially used for objective non-invasive assessment of ischemia in children with congenital and acquired heart diseases.

Myocardial perfusion after COVID-19 infection: No persisting impaired myocardial blood flow in surviving patients

Funding Acknowledgements Type of funding sources: None. Background Acute myocardial damage is common in hospitalized patients with severe COVID-19, with evidence of myocardial infarction and myocarditis demonstrated on cardiovascular magnetic resonance (CMR). Post-mortem studies have also implicated microvascular thrombosis, which may cause persistent microvascular disease. Purpose To determine the long-term coronary sequelae in recovered COVID-19 using multiparametric CMR including state-of-the-art inline quantitative stress myocardial blood flow (sMBF) mapping to assess global and regional sMBF. Methods Prospective, multicentre observational study of recovered COVID-19 patients scanned at three London CMR units. Results were compared to a propensity-matched, pre-COVID chest pain cohort (104 patients referred for perfusion CMR, with subsequently demonstrated unobstructed coronary arteries) and 27 healthy volunteers (HV). Perfusion image analysis was performed using a novel artificial intelligence approach deriving global and regional stress and rest MBF with a cut-off of >2.25mL/g/min signifying normal sMBF and <1.82mL/g/min abnormal sMBF (Kotecha JCVI 2019). Results 104 recovered, post-COVID patients (median age 62 years, 76% male; 89[87%] hospitalised, 41/89[46%] requiring ICU) underwent adenosine-stress perfusion CMR at a median 131(IQR 43-179) days from COVID-19 diagnosis. Median LVEF was 67% (IQR 60-71%; 12 (11.5%) with impaired LVEF), 51 patients (49%) had late gadolinium enhancement (LGE); 18% infarct-pattern and 33% non-ischaemic LGE. Global stress MBF in post-COVID patients was no different to age-, sex- and co-morbidities-matched controls (2.57 ± 0.77 vs. 2.40 ± 0.75 ml/g/min, p = 0.11, Figure 1), though lower than HV (3.00 ± 0.76 ml/g/min, p = 0.001). Post-COVID, multivariate predictors of low sMBF were male sex (OR 0.57, 95%CI 0.41-0.80, p = 0.001) and hypertension (OR 0.67, 95%CI 0.51-0.88, p = 0.004), but not COVID-19 disease severity (ICU admission) or presence of scar (ischemic/non-ischemic). 21/42 with reduced sMBF (<2.25mL/g/min) had regional perfusion defects consistent with epicardial coronary disease. Conclusions COVID-19 survivors do not demonstrate evidence of reduced global MBF by CMR compared to risk factor matched controls. Stress perfusion CMR identifies etiology of acute myocardial damage (infarction/myocarditis) and presence of occult coronary ischemia.

Comparison and Selection of Data Processing Methods for the Application of Cr3+ Photoluminescence Piezospectroscopy to Thermal Barrier Coatings

Thermal barrier coatings (TBCs) are an indispensable part of the blades used in aeroengines. Under a high-temperature service environment, the thermal oxidation stress at the interface is the main cause of thermal barrier failure. Cr3+ photoluminescence piezospectroscopy has been successfully used to analyze the thermal oxidation stress of TBCs, but systematic and quantitative analysis results for use in data processing are still lacking, especially with respect to the identification of peak positions. The processing methods used to fit spectral data were studied in this work to accurately characterize TBC thermal oxidation stress using Cr3+ photoluminescence spectroscopy. Both physical and numerical experiments were carried out, where Cr3+ photoluminescence spectra were detected from alumina ceramic samples under step-by-step uniaxial loading, and the simulated spectra were numerically deduced from the measured spectral data. Then, the peak shifts were obtained by fitting all spectral data by using Lorentzian, Gaussian and Psd-Voigt functions. By comparing the fitting results and then discussing the generation mechanism, the Lorentzian function—not the Psd-Voigt function that is most widely utilized—was regarded as the most applicable method for the application of Cr3+ photoluminescence piezospectroscopy to TBCs because of its sufficient sensitivity, stability and confidence for quantitative stress analysis.

Measuring stress and strain in rocks by spectroscopy

<p>Microstructures and the different thermoelastic properties of minerals ensure that no rock is ever under perfect hydrostatic stress at the grain level. If deviatoric stresses and strains significantly modify thermodynamic properties of minerals so that the equilibrium assemblage and compositions are different from that predicted from hydrostatic conditions, it is crucial to be able to measure the stress state of minerals in-situ in rocks. Forty years ago it was considered that ‘Analysis of residual stresses at the scale of mineral grains within a polycrystalline aggregate such as a rock is virtually intractable’ [1]. This is no longer true.</p><p>Confocal Raman spectroscopy allows spectra to be collected from small volumes of mineral grains within a section. The positions of Raman peaks depends on the elastic strains in the minerals through the phonon-mode Grüneisen tensors [2]. The development of precise DFT simulations of crystal structures and their Raman spectra now allows the components of the phonon-mode Grüneisen tensors to be calculated [3]. With these tensors it is possible to determine the strains from measured Raman peak positions, to thereby map the strain, and hence the stress state, of individual mineral grains. We have now extended the DFT simulations to show that the Raman shifts of crystals subject to symmetry-breaking stresses (e.g. around inclusions) are, as expected, not solely determined by the phonon-mode Grüneisen tensors of the ideal crystal. We have also recently developed the measurement of the change in peak intensities in cross-polarised Raman spectra to determine the stress [4] in these cases. For minerals such as garnets, this effect is stronger and therefore more sensitive to stress than the shifts in peak positions and offers at the moment the possibility to quickly visualise stress and strain fields in minerals in-situ in rocks. Quantitative stress values from this method await the determination of the piezo-phonon tensors for garnets, but comparison of peak positions and intensities show that the two methods return consistent results.</p><p>This work was supported by ERC-StG TRUE DEPTHS grant (number 714936) to M. Alvaro. N. Campomenosi was also supported by the University of Genova.</p><p> </p><p>[1] Holzhausen & Johnson (1979) Tectonophysics 58, 237.</p><p>[2] Angel et al. (2019) Zeitschrift für Kristallographie, 234, 129.</p><p>[3] Murri et al. (2018) American Mineralogist, 103, 1869.</p><p>[4] Campomenosi et al. (2020) Contributions to Mineralogy and Petrology, accepted.</p>

Detection of stress in polymers: mechanochemical activation of CuAAC click reactions in poly(urethane) networks

We report on copper(i)-bis(N-heterocyclic carbene)s (NHC) for quantitative stress-sensing. This mechanophore is embedded within a polyurethane network, triggering a fluorogenic copper(i) azide alkyne cycloaddition (CuAAC) of 8-azido-2-naphtol and 3-hydroxy phenylacetylene.