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| 2. |
- Julkunen, V, et al.
(författare)
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Cortical thickness analysis to detect progressive mild cognitive impairment: a reference to Alzheimer's disease
- 2009
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Ingår i: Dementia and geriatric cognitive disorders. - : S. Karger AG. - 1421-9824 .- 1420-8008. ; 28:5, s. 404-412
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Tidskriftsartikel (refereegranskat)abstract
- <i>Background/Aims:</i> Mild cognitive impairment (MCI) is associated with an increased risk of Alzheimer’s disease (AD). It would be advantageous to be able to distinguish the characteristics of those MCI patients with a high probability to progress to AD if one wishes to monitor the disease development and treatment. <i>Methods:</i> We assessed the baseline MRI and maximum of 7 years clinical follow-up data of 60 MCI subjects in order to examine differences in cortical thickness (CTH) between the progressive MCI (P-MCI) and stable MCI (S-MCI) subjects. CTH was measured using an automatic computational surface-based method. During the follow-up, 15 MCI subjects converted to AD on average 1.9 ± 1.3 years after the baseline examination, while 45 MCI subjects remained stable. <i>Results:</i> The P-MCI group displayed significantly reduced CTH bilaterally in the superior and middle frontal, superior, middle and inferior temporal, fusiform and parahippocampal regions as well as the cingulate and retrosplenial cortices and also in the right precuneal and paracentral regions compared to S-MCI subjects. <i>Conclusions:</i> Analysis of CTH could be used in conjunction with neuropsychological testing to identify those subjects with imminent conversion from MCI to AD several years before dementia diagnosis.
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| 3. |
- Pennanen, C, et al.
(författare)
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The effect of apolipoprotein polymorphism on brain in mild cognitive impairment: a voxel-based morphometric study
- 2006
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Ingår i: Dementia and geriatric cognitive disorders. - : S. Karger AG. - 1420-8008 .- 1421-9824. ; 22:1, s. 60-66
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the effect of apolipoprotein E (ApoE) on the whole brain in 51 individuals with mild cognitive impairment using voxel-based morphometry. Between cases heterozygous for the ApoE Ε4 (n = 15) and those who were ApoE Ε4 noncarriers (n = 28), only the right parahippocampal gyrus, with the entorhinal cortex included, reached the level of statistical significance. In cases homozygous for the Ε4 allele (n = 8) versus noncarriers, the greatest atrophy was located in the right amygdala followed by the right parahippocampal gyrus, the left amygdala and the left medial dorsal thalamic nucleus.
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| 4. |
- Tervo, O., et al.
(författare)
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Distributed Optimization for Coordinated Beamforming in Multicell Multigroup Multicast Systems : Power Minimization and SINR Balancing
- 2018
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Ingår i: IEEE Transactions on Signal Processing. - 1053-587X .- 1941-0476. ; 66:1, s. 171-185
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Tidskriftsartikel (refereegranskat)abstract
- This paper considers coordinated multicast beamforming in a multicell multigroup multiple-input single-output system. Each base station (BS) serves multiple groups of users by forming a single beam with common information per group. We propose centralized and distributed beamforming algorithms for two different optimization targets. The first objective is to minimize the total transmission power of all the BSs while guaranteeing the user-specific minimum quality-of-service targets. The semidefinite relaxation (SDR) method is used to approximate the nonconvex multicast problem as a semidefinite program (SDP), which is solvable via centralized processing. Subsequently, two alternative distributed methods are proposed. The first approach turns the SDP into a two-level optimization via primal decomposition. At the higher level, intercell interference powers are optimized for fixed beamformers, whereas the lower level locally optimizes the beamformers by minimizing BS-specific transmit powers for the given intercell interference constraints. The second distributed solution is enabled via an alternating direction method of multipliers, where the intercell interference optimization is divided into a local and a global optimization by forcing the equality via consistency constraints. We further propose a centralized and a simple distributed beamforming design for the signal-to-interference-plus-noise ratio (SINR) balancing problem in which the minimum SINR among the users is maximized with given per-BS power constraints. This problem is solved via the bisection method as a series of SDP feasibility problems. The simulation results show the superiority of the proposed coordinated beamforming algorithms over traditional noncoordinated transmission schemes, and illustrate the fast convergence of the distributed methods. Index Terms—Alternating direction method of multipliers, distributed optimization, multi-cell coordination, physical layer multigroup multicasting, primal decomposition, SINR balancing, sum power minimization.
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| 5. |
- Tervo, O., et al.
(författare)
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Energy-Efficient Multicell Multigroup Multicasting With Joint Beamforming and Antenna Selection
- 2018
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Ingår i: IEEE Transactions on Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1053-587X .- 1941-0476. ; 66:18, s. 4904-4919
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Tidskriftsartikel (refereegranskat)abstract
- This paper studies the energy efficiency and sum rate tradeoff for coordinated beamforming in multicell multiuser multigroup multicast multiple-input single-output systems. We first consider a conventional network energy efficiency maximization (EEmax) problem by jointly optimizing the transmit beamformers and antennas selected to be used in transmission. We also account for per-antenna maximum power constraints to avoid nonlinear distortion in power amplifiers and user-specific minimum rate constraints to guarantee certain service levels and fairness. To be energy efficient, transmit antenna selection is employed. It eventually leads to a mixed-Boolean fractional program. We then propose two different approaches to solve this difficult problem. The first solution is based on a novel modeling technique that produces a tight continuous relaxation. The second approach is based on sparsity-inducing method, which does not require the introduction of any Boolean variable. We also investigate the tradeoff between the energy efficiency and sum rate by proposing two different formulations. In the first formulation, we propose a new metric, that is, the ratio of the sum rate and the so-called weighted power. Specifically, this metric reduces to EEmax when the weight is 1, and to sum rate maximization when the weight is 0. In the other method, we treat the tradeoff problem as a multiobjective optimization for which a scalarization approach is adopted. Numerical results illustrate significant achievable energy efficiency gains over the method where the antenna selection is not employed. The effect of antenna selection on the energy efficiency and sum rate tradeoff is also demonstrated.
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| 6. |
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| 7. |
- Tervo, S, et al.
(författare)
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Incidence and risk factors for mild cognitive impairment: a population-based three-year follow-up study of cognitively healthy elderly subjects
- 2004
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Ingår i: Dementia and geriatric cognitive disorders. - : S. Karger AG. - 1420-8008 .- 1421-9824. ; 17:3, s. 196-203
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Tidskriftsartikel (refereegranskat)abstract
- <i>Background: </i>Mild cognitive impairment (MCI) has attracted considerable interest as a potential predictor of Alzheimer’s disease (AD). Both the apolipoprotein E (ApoE) Ε4 allele and vascular factors have been associated with a higher risk for AD, recently they have also been linked to the risk of MCI. <i>Objectives: </i>To estimate the incidence of MCI among cognitively healthy elderly subjects during a 3-year follow-up, and to evaluate the impact of demographic and vascular factors as well as the ApoE Ε4 allele on the conversion to MCI. <i>Methods: </i>At baseline, the cognitive abilities of 806 out of 1,150 eligible subjects (aged 60–76 years) from a population-based sample were examined. Cognitively intact subjects (n = 747) were followed for an average of 3 years. <i>Results: </i>66 subjects (8.8%) had converted to MCI. The global incidence rate of MCI was 25.94/1,000 person-years. Persons with higher age (OR 1.08, 95% CI 1.01–1.16), ApoE Ε4 allele carriers (OR 2.04, 95% CI 1.15–3.64) and persons with medicated hypertension (OR 1.86, 95% CI 1.05–3.29) were more likely to convert to MCI than those individuals of lower age and without an ApoE Ε4 allele or medicated hypertension. Persons with high education (OR 0.79, 95% CI 0.70–0.89) were less likely to convert to MCI than persons with low or no education. In subjects with both the ApoE Ε4 allele and medicated hypertension, the crude OR for conversion was 3.92 (95% CI 1.81–8.49). In subjects with cardiovascular disease, the crude OR for conversion was 2.13 (95% CI 1.26–3.60). Gender, elevated blood pressure, diabetes or cerebrovascular disease had no significant effect on the conversion to MCI. <i>Conclusion:</i> Higher age, the presence of at least one ApoE Ε4 allele and medicated hypertension are independent risk factors, but high education is a protective factor for MCI. The results suggest that vascular factors may have an important role in the pathogenesis of MCI.
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