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| 2. |
- Wallin, Anders, 1950, et al.
(författare)
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Alzheimer's disease-subcortical vascular disease spectrum in a hospital-based setting: overview of results from the Gothenburg MCI and dementia studies.
- 2016
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Ingår i: Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism. - : SAGE Publications. - 1559-7016. ; 36:1, s. 95-113
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Forskningsöversikt (refereegranskat)abstract
- The ability to discriminate between Alzheimer's disease (AD), subcortical vascular disease, and other cognitive disorders is crucial for diagnostic purposes and clinical trial outcomes. Patients with primarily subcortical vascular disease are unlikely to benefit from treatments targeting the AD pathogenic mechanisms and vice versa. The Gothenburg mild cognitive impairment (MCI) and dementia studies are prospective, observational, single-center cohort studies suitable for both cross-sectional and longitudinal analysis that outline the cognitive profiles and biomarker characteristics of patients with AD, subcortical vascular disease, and other cognitive disorders. The studies, the first of which started in 1987, comprise inpatients with manifest dementia and patients seeking care for cognitive disorders at an outpatient memory clinic. This article gives an overview of the major published papers (neuropsychological, imaging/physiology, and neurochemical) of the studies including the ongoing Gothenburg MCI study. The main findings suggest that subcortical vascular disease with or without dementia exhibit a characteristic neuropsychological pattern of mental slowness and executive dysfunction and neurochemical deviations typical of white matter changes and disturbed blood-brain barrier function. Our findings may contribute to better healthcare for this underrecognized group of patients. The Gothenburg MCI study has also published papers on multimodal prediction of dementia, and cognitive reserve.Journal of Cerebral Blood Flow & Metabolism advance online publication, 29 July 2015; doi:10.1038/jcbfm.2015.148.
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| 3. |
- Wallin, Anders, 1950, et al.
(författare)
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The Gothenburg MCI study: design and distribution of Alzheimer's disease and subcortical vascular disease diagnoses from baseline to 6-year follow-up.
- 2016
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Ingår i: Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism. - : SAGE Publications. - 1559-7016. ; 36:1, s. 114-131
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Tidskriftsartikel (refereegranskat)abstract
- There is a need for increased nosological knowledge to enable rational trials in Alzheimer's disease (AD) and related disorders. The ongoing Gothenburg mild cognitive impairment (MCI) study is an attempt to conduct longitudinal in-depth phenotyping of patients with different forms and degrees of cognitive impairment using neuropsychological, neuroimaging, and neurochemical tools. Particular attention is paid to the interplay between AD and subcortical vascular disease, the latter representing a disease entity that may cause or contribute to cognitive impairment with an effect size that may be comparable to AD. Of 664 patients enrolled between 1999 and 2013, 195 were diagnosed with subjective cognitive impairment (SCI), 274 with mild cognitive impairment (MCI), and 195 with dementia, at baseline. Of the 195 (29%) patients with dementia at baseline, 81 (42%) had AD, 27 (14%) SVD, 41 (21%) mixed type dementia (=AD+SVD=MixD), and 46 (23%) other etiologies. After 6 years, 292 SCI/MCI patients were eligible for follow-up. Of these 292, 69 (24%) had converted to dementia (29 (42%) AD, 16 (23%) SVD, 15 (22%) MixD, 9 (13%) other etiologies). The study has shown that it is possible to identify not only AD but also incipient and manifest MixD/SVD in a memory clinic setting. These conditions should be taken into account in clinical trials.Journal of Cerebral Blood Flow & Metabolism advance online publication, 15 July 2015; doi:10.1038/jcbfm.2015.147.
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| 4. |
- Eckerström, Carl, et al.
(författare)
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High white matter lesion load is associated with hippocampal atrophy in mild cognitive impairment.
- 2011
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Ingår i: Dementia and geriatric cognitive disorders. - : S. Karger AG. - 1421-9824 .- 1420-8008. ; 31:2, s. 132-8
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Tidskriftsartikel (refereegranskat)abstract
- Mild cognitive impairment (MCI) is a heterogeneous condition suggested as a prodromal state of Alzheimer's disease (AD) and subcortical vascular dementia (SVD). Recent findings suggest that white matter lesions (WML) may be associated with hippocampal atrophy. The objective of the study was to examine hippocampal and WML volumes in MCI patients and to examine if WML were linked to hippocampal atrophy.
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| 5. |
- Olsson, Mattias, 1977-, et al.
(författare)
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Blind OFDM carrier frequency offset estimation by locating null subcarriers
- 2004
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Ingår i: OFDM Workshop 2004,2004.
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Konferensbidrag (refereegranskat)abstract
- We present a novel algorithm for estimating the Carrier Frequency Offset (CFO) in an OFDM receiver. The algorithm is based on locating the spectral minimas within null subcarriers embedded in the spectrum. This is done by using a scaled DFT algorithm to calculate the spectrum of the OFDM symbol around the null subcarrier, followed by averaging the absolute square of the amplitude. The method is suitable for systems with continuous transmission.
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| 6. |
- Olsson, Mattias, 1977-
(författare)
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Contributions to Delay, Gain, and Offset Estimation
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The demand for efficient and reliable high rate communication is ever increasing. In this thesis we study different challenges in such systems, and their possible solutions.A goal for many years has been to implement as much as possible of a radio system in the digital domain, the ultimate goal being so called software defined radio (SDR) where the inner workings of a radio standard can be changed completely by changing the software. One important part of an SDR receiver is the high speed analog-to-digital converter (ADC) and one path to reach this high speed is to use a number of parallel, time-interleaved, ADCs. Such ADCs are, however, sensitive to sampling instant offsets, DC level offsets and gain offsets. This thesis discusses estimators based on fractional-delay filters and one application of these estimmators is to estimate and calibrate the relative delay, gain, and DC level offset between the ADCs comprising the time interleaved ADC.In this thesis we also present a technique for carrier frequency offset (CFO) estimation in orthogonal frequency division multiplexing (OFDM) systems. OFDM has gone from a promising digital radio transmission technique to become a mainstream technique used in several current and future standards. The main attractive property of OFDM is that it is inherently resilient to multipath reflections because of its long symbol time. However, this comes at the cost of a relatively high sensitivity to CFO. The proposed estimator is based on locating the spectral minimas within so-called null or virtual subcarriers embedded in the spectrum.~The spectral minimas are found iteratively over a number of symbols and is therefore mainly useful for frequency offset tracking or in systems where an estimate is not immediately required, such as in TV or radio broadcasting systems. However, complexity-wise the estimator is relatively easy to implement and it does not need any extra redundancy beside a nonmodulated subcarrier. The estimator performance is studied both in a channel with additive white Gaussian noise and in a multipath frequency selective channel environment.Interpolators and decimators are an important part of many systems, e.g. radio systems, audio systems etc. Such interpolation (decimation) is often performed using cascaded interpolators (decimators) to reduce the speed requirements in different parts of the system. In a fixed-point implementation, scaling is needed to maximize the use of the available word lengths and to prevent overflow. In the final part of the thesis, we present a method for scaling of multistage interpolators/decimators using multirate signal processing techniques. We also present a technique to estimate the output roundoff noise caused by the internal quantization.
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| 7. |
- Olsson, Mattias, 1977-
(författare)
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Contributions to Frequency Offset and Time Delay Estimation
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The demand for reliable high rate and efficient communication is ever increasing. In this thesis we look at two different problems in such systems, and their possible solutions.In recent years orthogonal frequency division multiplexing (OFDM) has gone from a promising data transmission technique to become a mainstream technique used in several current and future standards. The main attractive property of OFDM is that it is inherently resilient to multipath reflections because of its long symbol time. However, this comes at the cost of a relatively high sensitivity to carrier frequency offsets (CFOs).In this thesis we present a technique for CFO estimation in OFDM systems that is based on locating the spectral minimas within so-called null or virtual subcarriers embedded in the spectrum.~The spectral minimas are found iteratively over a number of symbols and is therefore mainly useful for frequency offset tracking or in systems where an estimate is not immediately required, such as in TV or radio broadcasting systems. However, complexity wise the estimator is relatively easy to implement and it does not need any extra redundancy beside a nonmodulated subcarrier. The estimator performance is studied both in a channel with additive white Gaussian noise and in a frequency selective channel environment.A goal for many years has been to be able to implement as much as possible of a radio system in the digital domain, the ultimate goal being so called software defined radio (SDR). One important part of an SDR receiver is the high speed analog-to-digital converter(ADC) and one path to reach this goal is to use a number of parallel, time-interleaved, ADCs. Such ADCs are, however, sensitive to sampling instant offsets, DC offset and gain offset.This thesis also discusses iterative time-delay estimators (TDEs) utilizing adjustable fractional-delay filters. The TDEs could for example be used to estimate and calibrate the relative delay between the ADCs comprising the time interleaved ADC. TDEs using a direct correlator and an average squared difference function are compared. Furthermore, an analysis of the effects of the batch length dependence is presented.
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| 8. |
- Olsson, Mattias, 1977-, et al.
(författare)
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Delay Estimation Using Adjustable Fractional Delay All-Pass Filters
- 2006
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Ingår i: Nordic Signal Processing Symposium,2006. - Reykjavik, Iceland : IEEE.
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Konferensbidrag (refereegranskat)abstract
- This paper presents a novel time-delay estimator utilizing an adjustable fractional-delay all-pass filter and Newton-Raphson's method. Solutions using a direct correlator and an average squared difference function are compared. Furthermore, an analysis of the effects of the batch length dependence is presented.
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| 9. |
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| 10. |
- Olsson, Mattias, 1977-, et al.
(författare)
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Scaling and round-off noise in multistage interpolators and decimators
- 2004
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Ingår i: Int. Workshop Spectral Methods Multirate Signal Processing,2004.
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Konferensbidrag (refereegranskat)abstract
- In this paper we present novel methods for scaling and roundoff noise calculation in multistage interpolators and decimators. When a signal is upsampledby $L$ it becomes Cyclo-Wide-Sense Stationary (CWSS) which prevents the use of common design algorithms for scaling. When a signal is downsampled by $M$ the situation is simpler since the stationarity is preserved, however, that case will still be treated for completeness. Finally, we present methods for scaling and noise calculation when the sample rate of a signal is changed by a rational factor $L/M$. The methods are based on multirate identities and polyphase decomposition.
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