Non-alcoholic fatty liver disease and the risk of progression to steatohepatitis, cirrhosis and hepatocellular carcinoma have been identified as major public health concerns. We have demonstrated the ...feasibility and potential value of measuring liver fat content by magnetic resonance imaging (MRI) in a large population in this study of 4,949 participants (aged 45-73 years) in the UK Biobank imaging enhancement. Despite requirements for only a single (≤3min) scan of each subject, liver fat was able to be measured as the MRI proton density fat fraction (PDFF) with an overall success rate of 96.4%. The overall hepatic fat distribution was centred between 1-2%, and was highly skewed towards higher fat content. The mean PDFF was 3.91%, and median 2.11%. Analysis of PDFF in conjunction with other data fields available from the UK Biobank Resource showed associations of increased liver fat with greater age, BMI, weight gain, high blood pressure and Type 2 diabetes. Subjects with BMI less than 25 kg/m2 had a low risk (5%) of high liver fat (PDFF > 5.5%), whereas in the higher BMI population (>30 kg/m2) the prevalence of high liver fat was approximately 1 in 3. These data suggest that population screening to identify people with high PDFF is possible and could be cost effective. MRI based PDFF is an effective method for this. Finally, although cross sectional, this study suggests the utility of the PDFF measurement within UK Biobank, particularly for applications to elucidating risk factors through associations with prospectively acquired data on clinical outcomes of liver diseases, including non-alcoholic fatty liver disease.
Several studies have demonstrated the accuracy, precision, and reproducibility of proton density fat fraction (PDFF) quantification using vendor-specific image acquisition protocols and PDFF ...estimation methods. The purpose of this work is to validate a confounder-corrected, cross-vendor, cross field-strength, in-house variant LMS IDEAL of the IDEAL method licensed from the University of Wisconsin, which has been developed for routine clinical use.
LMS IDEAL is implemented using a combination of patented and/or published acquisition and some novel model fitting methods required to correct confounds which result from the imaging and estimation processes, including: water-fat ambiguity; T2* relaxation; multi-peak fat modelling; main field inhomogeneity; T1 and noise bias; bipolar readout gradients; and eddy currents. LMS IDEAL has been designed to use image acquisition protocols that can be installed on most MRI scanners and cloud-based image processing to provide fast, standardized clinical results. Publicly available phantom data were used to validate LMS IDEAL PDFF calculations against results from originally published IDEAL methodology. LMS PDFF and T2* measurements were also compared with an independent technique in human volunteer data (n = 179) acquired as part of the UK Biobank study.
We demonstrate excellent agreement of LMS IDEAL across vendors, field strengths, and over a wide range of PDFF and T2* values in the phantom study. The performance of LMS IDEAL was then assessed in vivo against widely accepted PDFF and T2* estimation methods (LMS Dixon and LMS T2*, respectively), demonstrating the robustness of LMS IDEAL to potential sources of error.
The development and clinical validation of the LMS IDEAL algorithm as a chemical shift-encoded MRI method for PDFF and T2* estimation contributes towards robust, unbiased applications for quantification of hepatic steatosis and iron overload, which are key features of chronic liver disease.
Many electroencephalographic (EEG) studies on the cortical dynamics induced by unpleasant picture viewing demonstrated the modulation of event-related potentials (ERPs) components as a function of ...valence and the increase of gamma band responses to emotional stimuli; while only a few studies investigated phase synchronization phenomena such as inter-trial or between regions phase locking of gamma responses to emotional stimulation. The aim of this study was to provide a complete description of the cortical dynamics induced by unpleasant and neutral pictures viewing, from the ERP averages to gamma rhythm modulation, and its phase synchronization.
Gamma rhythm modulation was estimated by the event-related synchronization (ERS) approach, and phase synchrony between trials and between cortical regions was studied by extending the phase-locking statistics (PLS) approach.
Consistent with previous literature, an increase in P300 and late positive potential and an increase in gamma activity during viewing of unpleasant pictures as compared to neutral ones were found. No inter-trial synchronization was evoked by the stimuli, whereas widespread phase locking between sites was identified. In particular, differences in gamma synchronization between unpleasant and neutral stimuli were found. Specifically, at early (0–250ms) lags from stimulus onset, in the 38–45Hz gamma interval, stronger inter-site synchronizations for the unpleasant stimuli, even though quite widespread across the scalp, mainly involved the interhemispheric synchronization between temporal and frontal regions. In contrast, in the 30–37Hz gamma interval, stronger synchronizations for the responses to neutral trials were found in the 500–750 time interval, mainly involving the temporo-parietal regions.
These findings suggest that the full elaboration of unpleasant stimuli requires a tight interhemispheric communication between temporal and frontal regions that is realized by means of phase synchronization at about 40Hz. In addition, in contrast with the idea of a broadband modulation of high-frequency activity by cognitive/emotional stimuli, the present findings i.e. stronger BRS responses to either emotional or neutral trials at specific frequency and time range, indicate that specific intervals of gamma activity could be each primarily involved in a specific aspect of stimulus processing.
► We studied the cortical dynamics induced by unpleasant picture viewing. ► We analyzed ERPs, gamma rhythm modulation, its inter-trial and between-areas phase synchrony. ► We found increased gamma activity during viewing of unpleasant pictures. ► Stronger synchronizations for unpleasant stimuli occurred at low gamma frequencies. ► Specific intervals of gamma are involved in specific aspects of emotion processing.
Blood flow assessment is essential to fully understand cardiovascular function in disease pathologies and for identification of individuals at long-term risk of cardiovascular disease development. ...Qualitative and quantitative assessments of blood flow by imaging modalities have been limited, and much of the accurate quantification has relied on invasive measures.
This review discusses how four-dimensional velocity cardiovascular magnetic resonance (4D flow CMR) offers increasing potential for the non-invasive assessment of blood flow in the heart and major blood vessels such as the aorta. 4D flow CMR refers to phase contrast CMR with flow encoding in all three spatial directions that is resolved relative to all three dimensions of space and to the dimension of time throughout the cardiac cycle.
It has been demonstrated that 4D flow CMR can be used to assess parameters such as flow, pressure, velocity, wall shear stress and turbulent kinetic energy throughout the heart and major vessels of the cardiovascular system. It has been possible to gain new insights into cardiovascular pathologies such as, but not limited to, hypertrophic cardiomyopathy, dilated cardiomyopathy, Marfan syndrome and aortic bicuspid valve disease.
Future work to standardize 4D flow CMR scan acquisition parameters is required. Furthermore, the development of automated analysis tools and standardized reporting of quantitative metrics are needed to increase capacity for larger studies and for translation to clinical practice. In doing so, the potential for 4D flow CMR to disentangle complex questions related to cardiovascular function will be maximized.
Non-invasive quantitation of liver disease using multiparametric magnetic resonance imaging (MRI) could refine clinical care pathways, trial design and preclinical drug development. The aim of this ...study was to evaluate the use of multiparametric MRI in experimental models of liver disease. Liver injury was induced in rats using 4 or 12 weeks of carbon tetrachloride (CCl
) intoxication and 4 or 8 weeks on a methionine and choline deficient (MCD) diet. Liver MRI was performed using a 7.0 Tesla small animal scanner at baseline and specified timepoints after liver injury. Multiparametric liver MRI parameters T1 mapping, T2* mapping and proton density fat fraction (PDFF) were correlated with gold standard histopathological measures. Mean hepatic T1 increased significantly in rats treated with CCl
for 12 weeks compared to controls 1122±78 ms versus 959±114 ms; d=162.7, 95% CI (11.92, 313.4),
=0.038 and correlated strongly with histological collagen content (r
=0.717,
=0.037). In MCD diet-treated rats, hepatic PDFF correlated strongly with histological fat content (r
=0.819,
<0.0001), steatosis grade (r
=0.850,
<0.0001) and steatohepatitis score (r
=0.818,
<0.0001). Although there was minimal histological iron, progressive fat accumulation in MCD diet-treated livers significantly shortened T2*. In preclinical models, quantitative MRI markers correlated with histopathological assessments, especially for fatty liver disease. Validation in longitudinal studies is required.This article has an associated First Person interview with the first author of the paper.
Being the main responsible for the huge production of polyolefins, heterogeneous Ziegler-Natta catalysts are among the most important catalysts in the chemical industry and they have been optimized ...over the years since their discovery in 1953 crossing many different generations. Lastly, catalysts of the 5th generation are characterized by the introduction in the pre-catalyst of 1,3-diether compounds as internal electron donors, which are stable in the presence of AlR3 activators and do not require the further addition of external donors during the following steps of the catalytic process to control the activity and selectivity. In this work, we synthetized and systematically investigated by a multi-technique approach three Ziegler-Natta catalysts characterized by the same 1,3-diether donor, but differing in the synthesis route. We found that the synthetic route influences the MgCl2 particle size, as well as the properties of the Ti species. In particular, the reprecipitation method brings the smallest MgCl2 particles and the most positive Ti4+ sites in the pre-catalyst, but also the largest amount of accessible Ti3+ sites after TEAl activation. These structural and spectroscopic data correlate pretty well with the kinetic of gas-phase propylene polymerization in very mild conditions.
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•5th generation Ziegler-Natta catalysts prepared with 1,3-diether electron donor.•MgCl2 particles size affects the electronic properties of the Ti sites.•Two families of Ti sites with different geometry for monomer insertion.•1,3-diether donor and TiCl4 species are co-adsorbed on MgCl2 surface.•The catalysts are active in gas-phase propylene polymerization in mild conditions.
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