Do macromolecular and spline baselines affect the metabolite quantification at 9.4T?

Purpose/Introduction: One of the major goals in order to make MRSpectroscopy relevant for clinical practice is to ensure a robust quantitation of the spectra. Several previous studies investigated the influence of the macromolecular baseline(MMB) on the spectral quantification accuracy and precision1–12. This work extends previous work by investigating the influence of (1) the brain region specificity of the macromolecular baseline model and (2) the parameters of the additional spline-baseline on the quantification accuracy of spectra measured in the human brain at 9.4T. Subjects and Methods: Metabolite-cycled semiLASER (MCsLASER) 13 spectra (TR = 6000 ms/TE = 24 ms) were acquired from 8 volunteers(aged 28 ± 3) at a 9.4T Siemens Magnetom scanner from the occipital lobe(Occ.) with a mixed grey(40) and white matter(56) content, and from the left parietal lobe (lPar.) with a high white matter content(80). MMB models were created from data acquired using a double inversion MCsLASER sequence(-TI1 = 2360 ms/TI2 = 625 ms)14 from both regions (Fig. 1). using either of the two different MMB models to fit spectra from both brain regions; (2) varying parameters of the spline-baseline stiffness. The paired Wilcoxon test was used to find statistically significant differences in metabolite concentrations. Results: Up to 16 metabolites were readily quantified for both regions with Cramer Rao Lower Bounds of less than 20. The changes in concentrations for quantifying the spectra using the MMB from the corresponding region, versus using the MMB from the other region showed no significant difference (Fig. 2). The parameter settings for the spline-baseline did not influence this result. A-B show the fitted metabolite concentrations and their standard deviations for the different subjects, comparing the use of the different MMB for the fitting of the left parietal and the occipital lobe respectively (dkntmn = 1). The lowest measured p-value for a metabolite concentration change upon changing the MMB was 0.093 (not corrected for multiple comparisons). C-D show sample fit results for using the different MMBs for a left parietal spectrum. However, changes in the stiffness of the fitted spline-baseline lead to statistically significant concentration differences for multiple metabolites between stiff and more flexible spline-baselines (Fig. 3). Already moderately flexible spline-baselines (dkntmn\0.5) influence the accuracy and precision of concentration estimates for several metabolites. A–B show the fitted metabolite concentrations and their standard deviations for the different subjects, comparing the use of the different stiffness parameters of the spline baseline for the fitting (the region specific MMB was used). The red stars indicate metabolite concentration pairs for which a significant change in concentrations was observed (p-value\0.05, not corrected for multiple comparisons). C-D show sample fit results for using the different spline baseline stiffness values for an occipital spectrum. Discussion/Conclusion: This work shows for the first time, that using MMBs from different locations (lPar. and Occ.), with different underlying tissue composition does not lead to significant changes in the fitting results of the metabolites at 9.4T human studies. However, it was found, that the stiffness of the additional spline-baseline fit can significantly influence the metabolite concentrations, hence the flexibility of the spline-baseline should be restricted when quantifying spectra

Fitting comparison for 9.4T 1D semi-LASER and 2D-J-resolved semi-LASER data

In this abstract, we present an adapted version of the ProFit-V2 fitting software to fit J-resolved semi-LASER data at 9.4T. Simulated basis sets with ideal pulses show the need to reduce the echo time to account for the spin locking effect of the adiabatic pulses. Further, a comparison of the fitting error estimations using correlation matrices and Cramer-Rao Lower Bounds with a metabolite cycled semi-LASER fitted with LCModel is done

Qualitative Comparison between In Vivo J-Resolved Semi-LASER at 3 T and 9.4 T

J-resolved semi-LASER with maximum-echo sampling is optimized at 9.4T and compared with the same implementation at 3T in terms of SNR and spectral resolution. SODA scheme is appreciated for the sequence rather than the MC scheme. SNR at 9.4T (t1 steps: 85) was approximately 5.8 times greater than at 3T (t1 steps: 100) and strongly coupled peaks are well-resolved. However, the trade-off between SNR and spectral resolution is explained as lactate (1.32 ppm), a weakly-coupled metabolite, is better resolved at 3T. Higher band-width AFP pulses helped in almost vanishing the J-refocused peaks which made the J-resolved peaks clearly distinguishable. A few interesting downfield peaks and the doublet of NAA (7.82ppm) are observed

Civic and political engagement during the multifaceted COVID-19 crisis

Measures to cope with the COVID-19 pandemic have put a sudden halt to street protests and other forms of citizen involvement in Europe. At the same time, the pandemic has increased the need for solidarity, motivating citizens to become involved on behalf of people at risk and the vulnerable more generally. This research note empirically examines the tension between the demobilisation and activation potential of the COVID-19 crisis. Drawing on original survey data from seven Western European countries, we examine the extent, forms, and drivers of citizens’ engagement. Our findings show the remarkable persistence of pre-existing political and civic engagement patterns. Concurrently, we show that threat perceptions triggered by the multifaceted COVID-19 crisis have mobilized Europeans in the early phase of the pandemic. Similarly, the role of extreme ideological orientations in explaining (regular) political engagement indicates that the current situation may create its specific mobilisation potentials.The data were collected in the context of the research project “Policy Crisis and Crisis Politics, Sovereignty, Solidarity and Identity in the EU Post-2008” financed by EU Grant Agreement 810356 – ERC-2018-SyG (SOLID)