To expedite testing, Time-Dependent Dielectric Breakdown (TDDB) analyses are conducted on commercial 4H-SiC MOSFETs at high gate-to-source voltages (<inline-formula><tex-math notation="LaTeX">\bm ...{V_{GS}}</tex-math></inline-formula>), under Fowler-Nordheim conduction only. However, as inferred, such conditions induce impact ionization-generated holes in the dielectric layer (SiO<inline-formula><tex-math notation="LaTeX">\bm {_{2}}</tex-math></inline-formula>), resulting in a state transition in the effective dipolar moment. This accelerates the SiO<inline-formula><tex-math notation="LaTeX">\bm {_{2}}</tex-math></inline-formula> degradation leading to an overestimation of its intrinsic lifetime at typical <inline-formula><tex-math notation="LaTeX">V_{GS}</tex-math></inline-formula> values for gate driving in power converters. To address this, a physics-based approach is proposed to design TDDB tests under such conditions and to correct the intrinsic lifetime prediction at nominal <inline-formula><tex-math notation="LaTeX">\bm {V_{GS}}</tex-math></inline-formula> values, shortening the testing time by up to 2 orders of magnitude. Thus, the proposed method is a well-suited candidate to be considered in SiC power device qualification standards, still under development.
The behavior of the barrier height of the SiC/SiO 2 interface has been investigated over a wide temperature range, from 173 K to 523 K. These data complement the literature, providing a better ...knowledge of this parameter, which was studied only over a more restricted temperature range, and never before for low temperatures. It is highlighted that the measured samples exhibit a barrier height temperature dependence very near to the theoretical one (≈-0.7 meVK -1 ). Beyond 473 K, the barrier height seems to drop faster for some samples, reaching ≈-1.4 meVK -1 . If this faster decreasing rate is maintained for higher temperatures, it could limit 4H-SiC MOSFETs performances or reliability for high-temperature applications. It is expected that the data provided here will allow for more accurate modeling of the gate current and the charge injection in the oxide layer of power MOSFETs, leading to more reliable predictions of the oxide lifetime for 4H-SiC MOSFETs.
Recent advances in high resolution magnetic resonance (MR) imaging of the spine provide a basis for the automated assessment of intervertebral disc (IVD) and vertebral body (VB) anatomy. High ...resolution three-dimensional (3D) morphological information contained in these images may be useful for early detection and monitoring of common spine disorders, such as disc degeneration. This work proposes an automated approach to extract the 3D segmentations of lumbar and thoracic IVDs and VBs from MR images using statistical shape analysis and registration of grey level intensity profiles. The algorithm was validated on a dataset of volumetric scans of the thoracolumbar spine of asymptomatic volunteers obtained on a 3T scanner using the relatively new 3D T2-weighted SPACE pulse sequence. Manual segmentations and expert radiological findings of early signs of disc degeneration were used in the validation. There was good agreement between manual and automated segmentation of the IVD and VB volumes with the mean Dice scores of 0.89 ± 0.04 and 0.91 ± 0.02 and mean absolute surface distances of 0.55 ± 0.18 mm and 0.67 ± 0.17 mm respectively. The method compares favourably to existing 3D MR segmentation techniques for VBs. This is the first time IVDs have been automatically segmented from 3D volumetric scans and shape parameters obtained were used in preliminary analyses to accurately classify (100% sensitivity, 98.3% specificity) disc abnormalities associated with early degenerative changes.
To investigate whether global and regional beta-amyloid (Abeta) burden as measured with 11C Pittsburgh compound B (PIB) PET is associated with hippocampal atrophy characterized using MRI in healthy ...controls and patients with amnestic mild cognitive impairment (aMCI) or Alzheimer disease (AD).
Ninety-two elderly healthy controls, 32 subjects with aMCI, and 35 patients with AD were imaged using 11C-PIB PET and MRI. Hippocampal volume was measured and PIB standardized uptake value ratio was extracted after partial volume correction within 41 regions of interest. Global, regional, and voxel-based correlations between PIB and hippocampal volume were computed for each group.
In healthy control participants with elevated neocortex PIB retention, significant correlation was found between PIB retention in the inferior temporal region and hippocampal volume using both region-based and voxel-based approaches. No correlation was found in any other group.
The strong correlation between hippocampal atrophy and beta-amyloid (Abeta) burden in the Pittsburgh compound B-positive healthy control group suggests that Abeta deposition in the inferior temporal neocortex is related to hippocampal synaptic and neuronal degeneration.
The earliest detectable change in Alzheimer's disease (AD) is the buildup of amyloid plaque in the brain. Early detection of AD, prior to irreversible neurological damage, is important for the ...efficacy of current interventions as well as for the development of new treatments. Although PiB-PET imaging and CSF amyloid are the gold standards for early AD diagnosis, there are practical limitations for population screening. AD-related pathology occurs primarily in the brain, but some of the hallmarks of the disease have also been shown to occur in other tissues, including the retina, which is more accessible for imaging. Retinal vascular changes and degeneration have previously been reported in AD using optical coherence tomography and laser Doppler techniques. This report presents results from analysis of retinal photographs from AD and healthy control participants from the Australian Imaging, Biomarkers and Lifestyle (AIBL) Flagship Study of Ageing. This is the first study to investigate retinal blood vessel changes with respect to amyloid plaque burden in the brain. We demonstrate relationships between retinal vascular parameters, neocortical brain amyloid plaque burden and AD. A number of RVPs were found to be different in AD. Two of these RVPs, venular branching asymmetry factor and arteriolar length-to-diameter ratio, were also higher in healthy individuals with high plaque burden (P = 0.01 and P = 0.02 respectively, after false discovery rate adjustment). Retinal photographic analysis shows potential as an adjunct for early detection of AD or monitoring of AD-progression or response to treatments.
The fluid and white matter suppression sequence (FLAWS) provides two T1-weighted co-registered datasets: a white matter (WM) suppressed contrast (FLAWS1) and a cerebrospinal fluid (CSF) suppressed ...contrast (FLAWS2). FLAWS has the potential to improve the contrast of the subcortical brain regions that are important for Deep Brain Stimulation surgery planning. However, to date FLAWS has not been optimized for 1.5 T.
In this study, the FLAWS sequence was optimized for use at 1.5 T. In addition, the contrast-enhancement properties of FLAWS image combinations were investigated using two voxel-wise FLAWS combined images: the division (FLAWS-div) and the high contrast (FLAWS-hc) image.
FLAWS sequence parameters were optimized for 1.5 T imaging using an approach based on the use of a profit function under constraints for brain tissue signal and contrast maximization. MR experiments were performed on eleven healthy volunteers (age 18–30). Contrast (CN) and contrast to noise ratio (CNR) between brain tissues were measured in each volunteer. Furthermore, a qualitative assessment was performed to ensure that the separation between the internal globus pallidus (GPi) and the external globus pallidus (GPe) is identifiable in FLAWS1.
The optimized set of sequence parameters for FLAWS at 1.5 T provided contrasts similar to those obtained in a previous study at 3 T. The separation between the GPi and the GPe was clearly identified in FLAWS1. The CN of FLAWS-hc was higher than that of FLAWS1 and FLAWS2, but was not different from the CN of FLAWS-div. The CNR of FLAWS-hc was higher than that of FLAWS-div.
Both qualitative and quantitative assessments validated the optimization of the FLAWS sequence at 1.5 T. Quantitative assessments also showed that FLAWS-hc provides an enhanced contrast compared to FLAWS1 and FLAWS2, with a higher CNR than FLAWS-div.
Dementia is a global epidemic with Alzheimer's disease (AD) being the leading cause. Early identification of patients at risk of developing AD is now becoming an international priority. Neocortical ...Aβ (extracellular β-amyloid) burden (NAB), as assessed by positron emission tomography (PET), represents one such marker for early identification. These scans are expensive and are not widely available, thus, there is a need for cheaper and more widely accessible alternatives. Addressing this need, a blood biomarker-based signature having efficacy for the prediction of NAB and which can be easily adapted for population screening is described. Blood data (176 analytes measured in plasma) and Pittsburgh Compound B (PiB)-PET measurements from 273 participants from the Australian Imaging, Biomarkers and Lifestyle (AIBL) study were utilised. Univariate analysis was conducted to assess the difference of plasma measures between high and low NAB groups, and cross-validated machine-learning models were generated for predicting NAB. These models were applied to 817 non-imaged AIBL subjects and 82 subjects from the Alzheimer's Disease Neuroimaging Initiative (ADNI) for validation. Five analytes showed significant difference between subjects with high compared to low NAB. A machine-learning model (based on nine markers) achieved sensitivity and specificity of 80 and 82%, respectively, for predicting NAB. Validation using the ADNI cohort yielded similar results (sensitivity 79% and specificity 76%). These results show that a panel of blood-based biomarkers is able to accurately predict NAB, supporting the hypothesis for a relationship between a blood-based signature and Aβ accumulation, therefore, providing a platform for developing a population-based screen.
We aimed to describe and characterize the gut microbiota composition and diversity in children with obesity according to their metabolic health status.
Anthropometry, Triglycerides, HDL cholesterol, ...HOMA-IR, and systolic and diastolic blood pressure (SBP, DBP) were evaluated (and z-score calculated) and faecal samples were collected from 191 children with obesity aged from 8 to 14. All children were classified depending on their cardiometabolic status in either a “metabolically healthy” (MHO; n = 106) or “metabolically unhealthy” (MUO; n = 85) group. Differences in gut microbiota taxonomies and diversity between groups (MUO vs MHO) were analysed. Alpha diversity index was calculated as Chao1 and Simpson’s index, and β-diversity was calculated as Adonis Bray–Curtis index. Spearman’s correlations and logistic regressions were performed to study the association between cardiometabolic health and the microbiota.
Children in the MUO presented significantly lower alpha diversity and richness than those in the MHO group (Chao1 index p = 0.021, Simpson’s index p = 0.045, respectively), whereas microbiota β-diversity did not differ by the cardiometabolic health status (Adonis Bray–Curtis, R2 = 0.006; p = 0.155). The MUO group was characterized by lower relative abundances of the genera Christensenellaceae R7 group (MHO:1.42% 0.21–2.94; MUO:0.47% 0.02–1.60, p < 0.004), and Akkermansia (MHO:0.26% 0.01–2.19; MUO:0.01% 0.00–0.36, p < 0.001) and higher relative abundances of Bacteroides (MHO:10.6% 4.64–18.5; MUO:17.0% 7.18–27.4, p = 0.012) genus. After the adjustment by sex, age, and BMI, higher Akkermansia (OR: 0.86, CI: 0.75–0.97; p = 0.033), Christensenellaceae R7 group (OR: 0.86, 95% CI: 075–0.98; p = 0.031) and Chao1 index (OR: 0.86, CI: 0.96–1.00; p = 0.023) represented a lower risk of the presence of one or more altered cardiovascular risk factors.
Lower proportions of Christensenellaceae and Akkermansia and lower diversity and richness seem to be indicators of a metabolic unhealthy status in children with obesity.
There is significant interest in whether diffusion-weighted MR imaging indices, such as the minimum apparent diffusion coefficient, may be useful clinically for preoperative tumor grading and ...treatment planning. To help establish the pathologic correlate of minimum ADC, we undertook a study investigating the relationship between minimum ADC and maximum FDOPA PET uptake in patients with newly diagnosed glioblastoma multiforme.
MR imaging and FDOPA PET data were acquired preoperatively from 15 patients who were subsequently diagnosed with high-grade brain tumor (WHO grade III or IV) by histopathologic analysis. ADC and SUVR normalized FDOPA PET maps were registered to the corresponding CE MR imaging. Regions of minimum ADC within the FDOPA-defined tumor volume were anatomically correlated with areas of maximum FDOPA SUVR uptake.
Minimal anatomic overlap was found between regions exhibiting minimum ADC (a putative marker of tumor cellularity) and maximum FDOPA SUVR uptake (a marker of tumor infiltration and proliferation). FDOPA SUVR measures for tumoral regions exhibiting minimum ADC (1.36±0.22) were significantly reduced compared with those with maximum FDOPA uptake (2.45±0.88, P=.0001).
There was a poor correlation between minimum ADC and the most viable/aggressive component of high-grade gliomas. This study suggests that other factors, such as tissue compression and ischemia, may be contributing to restricted diffusion in GBM. Caution should be exercised in the clinical use of minimum ADC as a marker of tumor grade and the use of this index for guiding tumor biopsies preoperatively.
Waist-to-height ratio (WHtR) predicts abdominal fat and cardiometabolic risk. In children with obesity, the most adequate cut-off to predict cardiometabolic risk as well as its ability to predict ...risk changes over time has not been tested. Our aim was to define an appropriate WHtR cut-off to predict cardiometabolic risk in children with obesity, and to analyze its ability to predict changes in cardiometabolic risk over time.
This is an observational prospective study secondary to the OBEMAT2.0 trial. We included data from 218 participants (8-15 years) who attended baseline and final visits (12 months later). The main outcome measure was a cardiometabolic risk score derived from blood pressure, lipoproteins, and HOMA index of insulin resistance.
The optimal cut-off to predict the cardiometabolic risk score was WHtR ≥0.55 with an area under the curve of 0.675 (95% CI: 0.589-0.760) at baseline and 0.682 (95% CI: 0.585-0.779) at the final visit. Multivariate models for repeated measures showed that changes in cardiometabolic risk were significantly associated with changes in WHtR.
This study confirms the clinical utility of WHtR to predict changes in cardiometabolic risk over time in children with obesity. The most accurate cut-off to predict cardiometabolic risk in children with obesity was WHtR ≥0.55.
In children, there is no consensus on a unique WHtR cut-off to predict cardiometabolic risk. The present work provides sufficient evidence to support the use of the 0.55 boundary. We have a large sample of children with obesity, with whom we compared the previously proposed boundaries according to cardiometabolic risk, and we found the optimal WHtR cut-off to predict it. We also analyzed if a reduction in the WHtR was associated with an improvement in their cardiometabolic profile.
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