| 90131. |
- Lampinen, Björn, et al.
(författare)
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Searching for the neurite density with diffusion MRI : Challenges for biophysical modeling
- 2019
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Ingår i: Human Brain Mapping. - : Wiley. - 1065-9471 .- 1097-0193. ; 40:8, s. 2529-2545
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Tidskriftsartikel (refereegranskat)abstract
- In vivo mapping of the neurite density with diffusion MRI (dMRI) is a high but challenging aim. First, it is unknown whether all neurites exhibit completely anisotropic (“stick-like”) diffusion. Second, the “density” of tissue components may be confounded by non-diffusion properties such as T2 relaxation. Third, the domain of validity for the estimated parameters to serve as indices of neurite density is incompletely explored. We investigated these challenges by acquiring data with “b-tensor encoding” and multiple echo times in brain regions with low orientation coherence and in white matter lesions. Results showed that microscopic anisotropy from b-tensor data is associated with myelinated axons but not with dendrites. Furthermore, b-tensor data together with data acquired for multiple echo times showed that unbiased density estimates in white matter lesions require data-driven estimates of compartment-specific T2 values. Finally, the “stick” fractions of different biophysical models could generally not serve as neurite density indices across the healthy brain and white matter lesions, where outcomes of comparisons depended on the choice of constraints. In particular, constraining compartment-specific T2 values was ambiguous in the healthy brain and had a large impact on estimated values. In summary, estimating neurite density generally requires accounting for different diffusion and/or T2 properties between axons and dendrites. Constrained “index” parameters could be valid within limited domains that should be delineated by future studies.
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| 90132. |
- Lampinen, Björn, et al.
(författare)
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Tensor-valued diffusion MRI differentiates cortex and white matter in malformations of cortical development associated with epilepsy
- 2020
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Ingår i: Epilepsia. - : Wiley. - 0013-9580 .- 1528-1167. ; 61:8, s. 1701-1713
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Tidskriftsartikel (refereegranskat)abstract
- Objective Delineation of malformations of cortical development (MCD) is central in presurgical evaluation of drug-resistant epilepsy. Delineation using magnetic resonance imaging (MRI) can be ambiguous, however, because the conventional T-1- and T-2-weighted contrasts depend strongly on myelin for differentiation of cortical tissue and white matter. Variations in myelin content within both cortex and white matter may cause MCD findings on MRI to change size, become undetectable, or disagree with histopathology. The novel tensor-valued diffusion MRI (dMRI) technique maps microscopic diffusion anisotropy, which is sensitive to axons rather than myelin. This work investigated whether tensor-valued dMRI may improve differentiation of cortex and white matter in the delineation of MCD. Methods Tensor-valued dMRI was performed on a 7 T MRI scanner in 13 MCD patients (age = 32 +/- 13 years) featuring periventricular heterotopia, subcortical heterotopia, focal cortical dysplasia, and polymicrogyria. Data analysis yielded maps of microscopic anisotropy that were compared with T-1-weighted and T-2-fluid-attenuated inversion recovery images and with the fractional anisotropy from diffusion tensor imaging. Results Maps of microscopic anisotropy revealed large white matter-like regions within MCD that were uniformly cortex-like in the conventional MRI contrasts. These regions were seen particularly in the deep white matter parts of subcortical heterotopias and near the gray-white boundaries of focal cortical dysplasias and polymicrogyrias. Significance By being sensitive to axons rather than myelin, mapping of microscopic anisotropy may yield a more robust differentiation of cortex and white matter and improve MCD delineation in presurgical evaluation of epilepsy.
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| 90133. |
- Lampinen, Björn, et al.
(författare)
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Time dependence in diffusion MRI predicts tissue outcome in ischemic stroke patients
- 2021
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Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194 .- 1522-2594. ; 86:2, s. 754-764
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Reperfusion therapy enables effective treatment of ischemic stroke presenting within 4–6 hours. However, tissue progression from ischemia to infarction is variable, and some patients benefit from treatment up until 24 hours. Improved imaging techniques are needed to identify these patients. Here, it was hypothesized that time dependence in diffusion MRI may predict tissue outcome in ischemic stroke. Methods: Diffusion MRI data were acquired with multiple diffusion times in five non-reperfused patients at 2, 9, and 100 days after stroke onset. Maps of “rate of kurtosis change” (k), mean kurtosis, ADC, and fractional anisotropy were derived. The ADC maps defined lesions, normal-appearing tissue, and the lesion tissue that would either be infarcted or remain viable by day 100. Diffusion parameters were compared (1) between lesions and normal-appearing tissue, and (2) between lesion tissue that would be infarcted or remain viable. Results: Positive values of k were observed within stroke lesions on day 2 (P =.001) and on day 9 (P =.023), indicating diffusional exchange. On day 100, high ADC values indicated infarction of 50 ± 20% of the lesion volumes. Tissue infarction was predicted by high k values both on day 2 (P =.026) and on day 9 (P =.046), by low mean kurtosis values on day 2 (P =.043), and by low fractional anisotropy values on day 9 (P =.029), but not by low ADC values. Conclusions: Diffusion time dependence predicted tissue outcome in ischemic stroke more accurately than the ADC, and may be useful for predicting reperfusion benefit.
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| 90134. |
- Lampinen, Björn, et al.
(författare)
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Towards unconstrained compartment modeling in white matter using diffusion-relaxation MRI with tensor-valued diffusion encoding
- 2020
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Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194 .- 1522-2594. ; 84:3, s. 1605-1623
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To optimize diffusion-relaxation MRI with tensor-valued diffusion encoding for precise estimation of compartment-specific fractions, diffusivities, and T2 values within a two-compartment model of white matter, and to explore the approach in vivo. Methods: Sampling protocols featuring different b-values (b), b-tensor shapes (bΔ), and echo times (TE) were optimized using Cramér-Rao lower bounds (CRLB). Whole-brain data were acquired in children, adults, and elderly with white matter lesions. Compartment fractions, diffusivities, and T2 values were estimated in a model featuring two microstructural compartments represented by a “stick” and a “zeppelin.”. Results: Precise parameter estimates were enabled by sampling protocols featuring seven or more “shells” with unique b/bΔ/TE-combinations. Acquisition times were approximately 15 minutes. In white matter of adults, the “stick” compartment had a fraction of approximately 0.5 and, compared with the “zeppelin” compartment, featured lower isotropic diffusivities (0.6 vs. 1.3 μm2/ms) but higher T2 values (85 vs. 65 ms). Children featured lower “stick” fractions (0.4). White matter lesions exhibited high “zeppelin” isotropic diffusivities (1.7 μm2/ms) and T2 values (150 ms). Conclusions: Diffusion-relaxation MRI with tensor-valued diffusion encoding expands the set of microstructure parameters that can be precisely estimated and therefore increases their specificity to biological quantities.
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| 90135. |
- Lampis, Andrea, et al.
(författare)
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Reparation ecology and climate risk in Latin-America: Experiences from four countries
- 2022
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Ingår i: Frontiers in Climate. - : Frontiers Media SA. - 2624-9553. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- IPCC's Sixth Assessment is a landmark in recognizing social justice and local knowledge as imperative for successful climate adaptation; however, taking this new scientific consensus seriously has profound implications. While narratives of fossil fuel companies and closing climate windows often dominate climate politics, there is an urgent need for new thinking frames, especially given that everyday adaptations by the most vulnerable are often hindered by incumbent actors at more local scales. In response, this paper tackles the issue of climate risk and human wellbeing in Latin America from an emerging and innovative perspective: reparation ecology. Reparation is a heuristic category by means of which we systematize converging evidence about the responses of local Latin-American communities to severe socio-environmental crises that are closely connected to climate risks and to long-lasting threats to the wellbeing of human societies and ecosystems. The results focus on a comparative analysis of five case studies on nature-based urban adaptation in two low-income settlements in Brazil; local ecological governance led by actors from the organized civil society in Colombia; agroecological and just innovative food production systems in Ecuador and sustainable urban-rural food markets in Guatemala. Assuming the complexity of climate change from a culturally and geographically located perspective, the paper unveils the non-doomed, ecologically reparative character of these initiatives. It therefore contributes to the recent turn in the debate on climate risk, claiming that diverse groups of people and communities around the world are contributing to radical change, tuning their behaviors and social arrangements in what an emerging scholarship defines as reparation ecology.
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| 90136. |
- Lampousi, Anna Maria, et al.
(författare)
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Antioxidant Nutrients and Risk of Latent Autoimmune Diabetes in Adults and Type 2 Diabetes : A Swedish Case-Control Study and Mendelian Randomization Analysis
- 2023
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Ingår i: Nutrients. - 2072-6643. ; 15:11
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Tidskriftsartikel (refereegranskat)abstract
- Antioxidant vitamins C and E are inversely associated with type 1 diabetes (T1D). We investigated if antioxidants are also associated with latent autoimmune diabetes in adults (LADA), with low (LADAlow) and high (LADAhigh) autoantibody levels, type 2 diabetes (T2D), and estimates of beta cell function (HOMA-B) and insulin resistance (HOMA-IR). We used Swedish case-control data with incident cases of LADA (n = 584) and T2D (n = 1989) and matched population-based controls (n = 2276). Odds ratios (OR) and 95% confidence intervals (CI) were calculated per one standard deviation higher beta-carotene, vitamin C, vitamin E, selenium, and zinc intakes. Two-sample Mendelian randomization (MR) analyses assessed causality between genetically predicted circulating antioxidants and LADA, T1D, and T2D, using summary statistics from genome-wide association studies. Among the antioxidants, vitamins C and E were inversely associated with LADAhigh (OR 0.84, CI 0.73, 0.98 and OR 0.80, CI 0.69, 0.94 respectively), but not with LADAlow or T2D. Vitamin E was also associated with higher HOMA-B and lower HOMA-IR. MR analyses estimated an OR of 0.50 (CI 0.20, 1.25) for the effect of vitamin E on T1D, but did not support causal relationships between antioxidants and either LADA or T2D. In conclusion, vitamin E may have a protective effect on autoimmune diabetes, possibly through preserved beta cell function and less insulin resistance.
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| 90137. |
- Lampousi, Anna Maria, et al.
(författare)
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Interaction between plasma phospholipid odd-chain fatty acids and GAD65 autoantibodies on the incidence of adult-onset diabetes : the EPIC-InterAct case–cohort study
- 2023
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Ingår i: Diabetologia. - : Springer Science+Business Media B.V.. - 0012-186X .- 1432-0428. ; 66:8, s. 1460-1471
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Tidskriftsartikel (refereegranskat)abstract
- Aims/hypothesis: Islet autoimmunity may progress to adult-onset diabetes. We investigated whether circulating odd-chain fatty acids (OCFA) 15:0 and 17:0, which are inversely associated with type 2 diabetes, interact with autoantibodies against GAD65 (GAD65Ab) on the incidence of adult-onset diabetes. Methods: We used the European EPIC-InterAct case–cohort study including 11,124 incident adult-onset diabetes cases and a subcohort of 14,866 randomly selected individuals. Adjusted Prentice-weighted Cox regression estimated HRs and 95% CIs of diabetes in relation to 1 SD lower plasma phospholipid 15:0 and/or 17:0 concentrations or their main contributor, dairy intake, among GAD65Ab-negative and -positive individuals. Interactions between tertiles of OCFA and GAD65Ab status were estimated by proportion attributable to interaction (AP). Results: Low concentrations of OCFA, particularly 17:0, were associated with a higher incidence of adult-onset diabetes in both GAD65Ab-negative (HR 1.55 [95% CI 1.48, 1.64]) and GAD65Ab-positive (HR 1.69 [95% CI 1.34, 2.13]) individuals. The combination of low 17:0 and high GAD65Ab positivity vs high 17:0 and GAD65Ab negativity conferred an HR of 7.51 (95% CI 4.83, 11.69), with evidence of additive interaction (AP 0.25 [95% CI 0.05, 0.45]). Low dairy intake was not associated with diabetes incidence in either GAD65Ab-negative (HR 0.98 [95% CI 0.94, 1.02]) or GAD65Ab-positive individuals (HR 0.97 [95% CI 0.79, 1.18]). Conclusions/interpretation: Low plasma phospholipid 17:0 concentrations may promote the progression from GAD65Ab positivity to adult-onset diabetes. Graphical Abstract: [Figure not available: see fulltext.]
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| 90138. |
- Lamprecht, Ingolf, et al.
(författare)
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Calorimetric investigations of the pollination biology of the thermogenic inflorescences of the dragon lily (Dracunculus vulgaris) and its pollinator (Protaetia cretica) on Crete
- 2013
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Ingår i: Thermochimica Acta. - : Elsevier BV. - 0040-6031. ; 551, s. 84-91
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Tidskriftsartikel (refereegranskat)abstract
- This paper concerns thermometric and direct and indirect investigations of the heat produced by the thermogenic dragon lily (Dracunculus vulgaris) and its main pollinating beetle Protaetia (formerly named Potosia) cretica. The experiments were performed on scented and scentless populations at Panormo, Therisos and Lassithi on the North coast of Crete in the springs of 2007 and 2008. D. vulgaris inflorescences consist of a large spike (spadix) surrounded by a bract (spathe) that forms a floral chamber containing male and female florets, produce a powerful putrid scent and show a triphasic pattern of thermogenesis. The pattern began with a weak heating by the male florets during the night before opening, followed by appendix heating on the next day associated with scent production, and a more powerful male thermogenesis on the next night associated with insects trapped inside. Mass-specific thermogenesis of the scentless variety was identical to that in scented ones, but different insects were attracted. Beetles with a mean weight of 700 mg show heat production rates around 5 mW or 7 mWg(-1) at 25 degrees C. Discontinuous gas exchange cycles (DGCs) were observed calorimetrically at and below 24 degrees C, significantly depending in amplitude and frequency on the experimental temperature. (C) 2012 Elsevier B.V. All rights reserved.
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| 90139. |
- Lamprecht, I, et al.
(författare)
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Discontinuous ventilation in the rhinoceros beetle Oryctes nasicornis. Direct and indirect calorimetry
- 2009
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Ingår i: Journal of Thermal Analysis and Calorimetry. - : Springer Science and Business Media LLC. - 1588-2926 .- 1388-6150 .- 1572-8943. ; 95, s. 743-747
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Tidskriftsartikel (refereegranskat)abstract
- Discontinuous gas exchange cycles (DGCs) are frequently observed with insects, i.e. oxygen take up and carbon dioxide release occur interrupted by periods of a few minutes up to many hours. The paper presents direct and indirect calorimetric experiments on DGCs of the scarabid rhinoceros beetle Oryctes nasicornis. A direct/indirect calorimetric experiment is presented. Total and specific heat production rates amount to 0.56mWand 0.42mWg–1 in the first period without DGCs and to 0.43 mW (0.32 mW g–1 ) in the second phase, resp. The mean DGC amplitude is 0.184 mW and thus between 33 and 66% of the total turnover.
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| 90140. |
- Lamprinakis, Georgios
(författare)
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Structure and dimension of invariant subsets of expanding Markov maps and joint invariance
- 2023
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Ingår i: Dynamical Systems. - : Informa UK Limited. - 1468-9367 .- 1468-9375. ; 38:3, s. 405-426
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Tidskriftsartikel (refereegranskat)abstract
- A long-standing question is what invariant subsets can be shared by two maps acting on the same space. A similar question stands for invariant measures. A particular interesting case are expanding Markov maps of the circle. If the two involved maps are commuting the answer is almost complete. However very little is known in the non-commutative case. A first step is to analyse the structure of the invariant subsets of a single map. For a mapping of the circle of class (Formula presented.), (Formula presented.), we study the topological structure of the set consisting of all compact invariant subsets. Furthermore for a fixed such mapping we examine locally, in the category sense, how big is the set of all maps that have at least one non-trivial joint invariant compact subset. Lastly we show the strong dimensional relation between the maximal invariant subset of a given Markov map contained in a subinterval (Formula presented.) and the set of all right endpoints of its invariant subsets that are contained in the same subinterval, (Formula presented.), as well as the continuous dependence of the dimension on the endpoints of the subinterval (Formula presented.).
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