Transition of intracranial aneurysmal wall enhancement from high to low wall shear stress mediation with size increase: A hemodynamic study based on 7T magnetic resonance imaging.

Background: Wall shear stress (WSS) has been proved to be related to the formation, development and rupture of intracranial aneurysms. Aneurysm wall enhancement (AWE) on magnetic resonance imaging (MRI) can be caused by inflammation and have confirmed its relationship with low WSS. High WSS can also result in inflammation but the research of its correlation with AWE is lack because of the focus on large aneurysms limited by 3T MRI in most previous studies.This study aimed to assess the potential association between high or low WSS and AWE in different aneuryms. Especially the relationship between high WSS and AWE in small aneurysm. Methods: Forty-three unruptured intracranial aneurysms in 42 patients were prospectively included for analysis. 7.0 T MRI was used for imaging. Aneurysm size was measured on three-dimensional time-of-flight (TOF) images. Aneurysm-to-pituitary stalk contrast ratio (CRstalk) was calculated on post-contrast black-blood T1-weighted fast spin echo sequence images. Hemodynamics were assessed by four-dimensional flow MRI. Results: The small aneurysms group had more positive WSS-CRstalk correlation coefficient distribution (dome: 78.6 %, p = 0.009; body: 50.0 %, p = 0.025), and large group had more negative coefficient distribution (dome: 44.8 %, p = 0.001; body: 69.0 %, p = 0.002). Aneurysm size was positively correlated with the significant OSI-CRstalk correlation coefficient at the dome (p = 0.012) and body (p = 0.010) but negatively correlated with the significant WSS-CRstalk correlation coefficient at the dome (p < 0.001) and body (p = 0.017). Conclusion: AWE can be mediated by both high and low WSS, and translate from high WSS- to low WSS-mediated pathways as size increase. Additionally, AWE may serve as an indicator of the stage of aneurysm development via different correlations with hemodynamic factors.

Dynamics of green macroalgal micro-propagules and the influencing factors in the southern Yellow Sea, China.

Micro-propagules (banks of microscopic forms) play important roles in the expansion of green tides, which are spreading on eutrophic coasts worldwide. In particular, large-scale green tides (Yellow Sea Green Tide, YSGTs) have persisted in the Yellow Sea for over 15 years, but the dynamics and functions of micro-propagules in their development remain unclear. In the present study, year-round field surveys were conducted to identify the reservoirs and investigate the persistence mechanisms and associated biotic and abiotic factors driving the temporal and spatial variations of micro-propagules. Micro-propagules in the southern Yellow Sea (SYS) showed evident spatial heterogeneity in terms of seasonal patterns and major influencing factors. Offshore of the SYS, the micro-propagule population underwent ephemeral expansion along with a large-scale bloom of floating Ulva algae in late spring and early summer. The Subei Shoal, particularly the sediments in the central raft region, had the highest micro-propagule abundance (MA) and was a major reservoir. The pronounced seasonal variation of MA in the Subei Shoal was primarily associated with the attached Ulva algae on Neopyropia aquaculture rafts. Vast aquaculture rafts provided essential substrates for micro-propagules to complete their life cycle and replenish the seed bank, thereby sustaining persistent YSGTs. It implied that habitat modification has pronounced ecological impacts on this intertidal muddy flat. The unique environmental conditions (enriched nutrients, esp. nitrate, favourable seawater temperatures in spring, and strong tidal mixing) facilitated the abundance, seasonal variation and recruitment of micro-propagules in the Subei Shoal. Given the current mitigation measures implemented in the raft region, further research is required to monitor and investigate the physiological and ecological responses of micro-propagule populations to the complex hydrobiological, geochemical, and physical matrices.

Variations of arterial compliance and vascular resistance due to plaque or infarct in a single vascular territory of the middle cerebral artery.

Background: Arterial compliance (AC) and vascular resistance (VR) are crucial for the regulation capacity of the vascular system. However, alterations of these features and hemodynamics due to atherosclerosis in a single intracranial artery territory have not been extensively investigated. Thus this study aimed to examine the AC, VR, and hemodynamic variations due to plaque and infarction in the middle cerebral artery (MCA). Methods: Patients with symptomatic MCA atherosclerosis were recruited. Both sides of the MCA were assessed and then classified according to the following scheme: group 0, without plaque; group 1, with plaque but without infarct; group 2, with plaque and infarct in the supplying territories. Data on AC, VR, blood flow, and pulsatility index (PI) were obtained based on 4D flow magnetic resonance imaging (MRI) and the Windkessel model. Results: A total of 63 patients were recruited. After 17 MCAs were excluded (occlusion, n=6; poor image quality, n=11), datasets on 109 MCAs were finally collected and classified into group 0 (n=39), group 1 (n=40), and group 2 (n=30). From groups 0 to 2, there was a decrease in AC (0.0060±0.0031 vs. 0.0052±0.0029 vs. 0.0026±0.0020 mL/mmHg) and an increase in VR [28.65±16.11 vs. 42.59±27.53 vs. 63.21±40.37 mmHg/(mL/s)]. Compared to group 1, group 2 had significantly decreased AC (0.0052±0.0029 vs. 0.0026±0.0020 mL/mmHg; P=0.003) and increased VR [42.59±27.53 vs. 63.21±40.37 mmHg/(mL/s); P=0.021]. From group 0 to group 2, there was a decrease in blood flow (179.29±73.57 vs. 125.11±59.04 vs. 92.05±48.79 mL/min; P<0.001). The PI varied significantly among the 3 groups (0.86±0.20 vs. 1.12±0.50 vs. 0.79±0.16; P<0.001), with group 1 having the highest PI. Conclusions: With the occurrence of plaque and infarct, AC and blood flow progressively decrease while VR increases. The PI was the highest in the group with plaque and without infarct. Assessments of vascular function and hemodynamics in a single artery territory can clarify comprehensive alterations in the cerebral vascular system (CVS).