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In this paper, we observe the dynamic expansion process of positive leader channels under impulses with different rise times in a 1-m air gap using a Mach-Zehnder interferometry and a high-speed video camera. The thermal parameters describing the leader channel under a lightning and switching impulse are obtained through an analysis of interference fringes. The influences of different voltage waveforms on the dynamic expansion of leader channels are obtained. Firstly, the expansion rates of the channel radius are higher for shorter rise times. The average expansion rates are 72.30 ± 9.54, 28.09 ± 5.05, and 14.38 ± 3.02 m/s for the rise times of 1.2, 40, and 100 μs and the crest value of 425 kV for a 0.5-cm-diameter cone electrode; moreover, the temperatures at the centre of the leader channels are 5000–7000 K, 4000–6000 K, and 3000–4500 K, respectively. Secondly, the high-temperature region is larger for the shorter rise times. A numerical model was used to study the expansion of the leader channels, and the simulation results for the leader channel diameters showed good consistency with the experimental measurements. The continuous energy injection results in an over-pressure process in the leader channels and ultimately in their expansion. For a 1.2/50 μs waveform, the vibrational-translational relaxation (QVT) and the thermal dissociation (QD), which dominate the energy flow, are about one order of magnitude greater than that in a 100/2500 μs waveform. The convection loss and the ionization mechanism during the expansion process are also discussed. [ABSTRACT FROM AUTHOR]

Background: One of the widespread manifestations of cerebral small vessel disease (CSVD) of the brain parenchyma is white matter lesion, which appears as white matter hyperintensities (WMHs) on magnetic resonance imaging (MRI). Previous studies have illustrated that large artery atherosclerosis is related to CSVD, but the precise progress of pathogenesis remains unknown. High-resolution MRI (HR-MRI) has the ability to delineate intracranial vascular walls, enabling a thorough exploration of the structure and composition of unstable plaques. This study aimed to apply HR-MRI to characterize the wall changes and plaque characteristics of middle cerebral arteries in patients with WMHs and to investigate the correlation between plaque vulnerability parameters and different degrees of WMHs., Methods: In this study, 138 patients with acute ischemic stroke at Harbin Medical University's First Clinical Hospital (May 2021 to October 2023) were cross-sectionally reviewed and underwent conventional brain and HR-MRI using T1-weighted 3D volumetric isotropic turbo spin echo acquisition (T1W-3D-VISTA) of the unilateral middle cerebral artery (MCA). According to Fazekas grade (0-6), the patients were divided into two groups: Fazekas score 0-2, no-or-mild WMHs; and Fazekas 3-6, moderate-to-severe WMHs. The intraplaque hemorrhage, plaque distribution, plaque enhancement, plaque load, remodeling pattern, and stenosis of the two groups were measured. Binary logistic regression analysis was conducted to evaluate the relationship between vulnerable plaques and WMHs., Results: Of the participants who were initially considered for inclusion, 71 were deemed eligible, among whom 34 were placed in the no-or-mild WMH group and 37 in the moderate-to-severe WMH group. Between the two groups, there were significant differences in intraplaque hemorrhage (P=0.01), a wide distribution (P=0.02), and plaque enhancement (P=0.02). Univariate analysis showed that WMHs were associated with age [odds ratio (OR) =1.080; 95% confidence interval (CI): 1.020-1.144; P=0.008], hypertension (OR =3.500; 95% CI: 1.276-9.597; P=0.01), intraplaque hemorrhage (OR =3.955; 95% CI: 1.247-12.538; P=0.02), a wide distribution (OR =3.067; 95% CI: 1.159-8.115; P=0.02), and significant plaque enhancement (OR =4.372; 95% CI: 1.101-17.358; P=0.03); however, the multivariate results showed that the only independent factors associated with WMHs were age (OR =1.095; 95% CI: 1.019-1.176; P=0.01) and intraplaque hemorrhage (OR =5.88; 95% CI: 1.466-23.592; P=0.01)., Conclusions: Our findings suggest that age and intraplaque hemorrhage may be associated with more severe WMHs in patients with acute ischemic stroke, which may be helpful for further clinical examination and intervention treatment., Competing Interests: Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-23-1856/coif). J.L. is an employee of Philips Healthcare (Beijing, China). The other authors have no conflicts of interest to declare., (2024 Quantitative Imaging in Medicine and Surgery. All rights reserved.)