As a central hub in the interconnected brain network, the precuneus has been reported showing disrupted functional connectivity and hypometabolism in Alzheimer’s disease (AD). However, as a highly heterogeneous cortical structure, little is known whether individual subregion of the precuneus is uniformly or differentially involved in the progression of AD. To this end, using a hybrid PET/fMRI technique, we compared resting-state functional connectivity strength (FCS) and glucose metabolism in dorsal anterior (DA_pcu), dorsal posterior (DP_pcu) and ventral (V_pcu) subregions of the precuneus among 20 AD patients, 23 mild cognitive impairment (MCI) patients, and 27 matched cognitively normal (CN) subjects. The sub-parcellation of precuneus was performed using a K-means clustering algorithm based on its intra-regional functional connectivity. For the whole precuneus, decreased FCS ( p = 0.047) and glucose hypometabolism ( p = 0.006) were observed in AD patients compared to CN subjects. For the subregions of the precuneus, decreased FCS was found in DP_pcu of AD patients compared to MCI patients ( p = 0.011) and in V_pcu for both MCI ( p = 0.006) and AD ( p = 0.008) patients compared to CN subjects. Reduced glucose metabolism was found in DP_pcu of AD patients compared to CN subjects ( p = 0.038) and in V_pcu of AD patients compared to both MCI patients ( p = 0.045) and CN subjects ( p < 0.001). For both FCS and glucose metabolism, DA_pcu remained relatively unaffected by AD. Moreover, only in V_pcu, disruptions in FCS ( r = 0.498, p = 0.042) and hypometabolism ( r = 0.566, p = 0.018) were significantly correlated with the cognitive decline of AD patients. Our results demonstrated a distinctively disrupted functional and metabolic pattern from ventral to dorsal precuneus affected by AD, with V_pcu and DA_pcu being the most vulnerable and conservative subregion, respectively. Findings of this study extend our knowledge on the differential roles of precuneus subregions in AD.
To investigate whether quantitative T2 mapping is complementary to [18F]FDG PET in epileptogenic zone detection, thus improving the lateralization accuracy for drug-resistant mesial temporal lobe epilepsy (MTLE) using hybrid PET/MR.We acquired routine structural MRI, T2-weighted FLAIR, whole brain T2 mapping, and [18F]FDG PET in 46 MTLE patients and healthy controls on a hybrid PET/MR scanner, followed with computing voxel-based z-score maps of patients in reference to healthy controls. Asymmetry indexes of the hippocampus were calculated for each imaging modality, which then enter logistic regression models as univariate or multivariate for lateralization. Stereoelectroencephalography (SEEG) recordings and clinical decisions were collected as gold standard.Routine structural MRI and T2w-FLAIR lateralized 47.8% (22/46) of MTLE patients, and FDG PET lateralized 84.8% (39/46). T2 mapping combined with [18F]FDG PET improved the lateralization accuracy by correctly lateralizing 95.6% (44/46) of MTLE patients. The asymmetry indexes of hippocampal T2 relaxometry and PET exhibit complementary tendency in detecting individual laterality, especially for MR-negative patients. In the quantitative analysis of z-score maps, the ipsilateral hippocampus had significantly lower SUVR (LTLE, p < 0.001; RTLE, p < 0.001) and higher T2 value (LTLE, p < 0.001; RTLE, p = 0.001) compared to the contralateral hippocampus. In logistic regression models, PET/T2 combination resulted in the highest AUC of 0.943 in predicting lateralization for MR-negative patients, followed by PET (AUC = 0.857) and T2 (AUC = 0.843).The combination of quantitative T2 mapping and [18F]FDG PET could improve lateralization for temporal lobe epilepsy.• Quantitative T2 mapping and18F-FDG PET are complementary in the characterization of hippocampal alterations of MR-negative temporal lobe epilepsy patients. • The combination of quantitative T2 and18F-FDG PET obtained from hybrid PET/MR could improve lateralization for temporal lobe epilepsy.
In this paper, the smear effect and the sand cushion that modifies the permeability of the top boundary are considered equivalently as semipermeable boundaries, to obtain an axisymmetric free-strain consolidation model for unsaturated soils capable of allowing for coupled radial–vertical flow under time-dependent loading. The semianalytical solution is then solved with finite Hankel transform and Laplace transform. This is also verified by comparison with two special cases of axisymmetric consolidation solutions in unsaturated soils. After analysis of the parameters, it is concluded that as the radial or vertical semipermeability factor increases, there is less impediment to the dissipation of excess pore pressures (EPPs); and when it takes values within 0.1–50, it can be used to simulate boundaries with arbitrary permeability from permeable to impermeable. The EPP distribution at different points and times reveals that the effect of the air- and water-phase semipermeability factor on the consolidation of unsaturated soil is different. Furthermore, the contour plots of EPP distribution under free-strain assumption provide a decent reflection of the smear effect and the alteration of the top boundary permeability due to the sand cushion.
Abstract Background: Amnesia in Alzheimer's disease (AD) could be due to disrupted encoding, consolidation dysfunction, or an impairment in the retrieval of stored memory information. The different memory phases relate with different parts of functional brain systems. Methods: We combine task functional magnetic resonance imaging and amyloid positron emission tomography in 72 participants (36 AD and 36 controls), to investigate the relationship between memory performance, memory phase-locked functional connectivity, and cortical β-amyloid deposition. Results: We found that AD was mainly characterized by decreased functional connectivity in a new data-driven Network composed of regions from default mode network, limbic network and frontoparietal network during the memory maintenance and retrieval phase. Within the Network, AD had more regions with reduced connectivity during the retrieval phase than other phases, locating mainly in the medial prefrontal cortex, posterior cingulate cortex, middle temporal and inferior parietal cortex of left hemisphere. Furthermore, functional connectivity in the Network related to memory performance. Crucially, the magnitude of the Network connectivity reduction during retrieval negatively correlated with mean cortical β-amyloid, and this relationship mediated the relationship between cortical β-amyloid and memory performance. Conclusions: Our findings show that memory deficiency in AD relates with decreased connectivity in specific network and cortical β-amyloid only during retrieval phase. These findings help to map impaired functional connectivity during memory phases and explain the relationship between memory deficiency and cortical β-amyloid.
This study proposed a general semianalytical solution for axisymmetric consolidation of unsaturated soil where the unified boundary is extended under electroosmotic and surcharge preloading, allowing for the diversity of permeability at the top boundary of the soil layer. In the coupled electric-flow-mechanic fields, the Laplace transform, decoupling technique, and Laplace inversion were used to derive a semianalytical solution. Then, the proposed solution was examined respectively against the two cases of considering only electroosmosis in saturated soils and only surcharge preloading in unsaturated soils to verify the validity of the solution. The analysis of the factors affecting the consolidation characteristics shows that as the permeability of the top boundary increases, the excess pore pressures dissipate faster, and then the final negative excess pore-water pressure decreases. The electroosmotic-enhanced preloading technique can significantly improve the speed of foundation consolidation and reduce the post-work settlement compared to a single method. Moreover, the excess pore pressures induced by the surcharge preloading dissipate faster as the electrical-to-radial water permeability ratio decreases. It is meritorious to note that the new solution in the present study is applicable to the axisymmetric consolidation model for unsaturated soils under arbitrary time-varying loading and different permeability topsides.
Abstract This study aims to provide substantial theoretical support for employing vacuum preloading‐airbag pressurization (VP‐AP) to enhance soft soil foundations. By integrating the airbags and prefabricated vertical drains (PVDs) within the analytical framework, the consolidation models are developed to accommodate double smear zones and well resistance. Analytical solutions for various airbag pressurization scenarios are derived under the equal‐strain assumption. A model test is subsequently conducted to investigate the settlement process of soft soil using the VP‐AP method. The validity of the proposed theoretical model is corroborated through comparison with existing analytical solutions and experimental data. The accuracy of the predictive model is further substantiated by the model test results. Lastly, this research offers an in‐depth analysis of soil consolidation behavior under diverse influencing factors. The findings indicate that the VP‐AP method demonstrates superior efficacy over conventional vacuum‐surcharge preloading when the airbag pressure matches the external load pressure. Additionally, an increase in the radius of airbags enhances the soil consolidation efficiency. The analytical model presented in this study elucidates the consolidation mechanisms of the VP‐AP method, with experimental research confirming the efficacy of this approach and the predictive model established herein.
To assess predictive value of 68Ga-labeled fibroblast activation protein inhibitor-04 ([68Ga]Ga-DOTA-FAPI-04) PET/MR for late left ventricular (LV) remodeling in patients with ST-segment elevated myocardial infarction (STEMI).Twenty-six patients with STEMI were included in the study. [68Ga]Ga-DOTA-FAPI-04 PET/MR was performed at baseline and at average 12 months after STEMI. LV remodeling was defined as >10% increase in LV end-systolic volume (LVESV) from baseline to 12 months.The LV remodeling group demonstrated higher [68Ga]Ga-DOTA-FAPI-04 uptake volume (UV) at baseline than the non-LV remodeling group (p < 0.001). [68Ga]Ga-DOTA-FAPI-04 UV at baseline was a significant predictor (OR = 1.048, p = 0.011) for LV remodeling at 12 months after STEMI. Compared to clinical information, MR imaging and cardiac function parameters at baseline, [68Ga]Ga-DOTA-FAPI-04 UV demonstrated better predictive ability (AUC = 0.938, p < 0.001) for late LV remodeling, with sensitivity of 100.0% and specificity of 81.3%.[68Ga]Ga-DOTA-FAPI-04 PET/MR is an effective tool to non-invasively quantify myocardial fibroblasts activation, and baseline [68Ga]Ga-DOTA-FAPI-04 UV may have potential predictive value for late LV remodeling.
In addition to contrast-enhanced multiphase computed tomography (CT) and magnetic resonance imaging (MRI), integrated positron emission tomography (PET)/magnetic resonance (MR) is increasingly being used for the preoperative evaluation of pancreatic cancer. The purpose of this study was to explore the value of hybrid
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