| 1. |
- Sjödin, Fredrik, 1978-
(författare)
-
Noise in the preschool : health and preventive measures
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is based on noise recordings and health evaluations carried out at preschools in the northern part of Sweden. Sound level recordings were made on individuals and by use of stationary devices in dining rooms and play halls. Health evaluations were based on ratings by use of questionnaires and by analyses of cortisol.The average equivalent individual noise exposure was 71 dB(A). The average equivalent noise levels in the dining room and playing halls were 64 dB(A). The hearing loss of the employees was significantly higher for the frequencies tested than in an unexposed control group. Symptoms of tinnitus were reported among 31% of the employees. Noise annoyance was rated as somewhat to very annoying, and the voices of the children were the most annoying noise source. The dB(A) level and fluctuations of the noise exposure were significantly correlated with the number of children per department. Stress and energy output were pronounced among the employees. About 30% of the staff experienced strong burnout syndromes. Mental recovery was low as indicated by noise fatigue and high levels of stress after work. Increased cortisol levels during work were associated with higher number of children present at the department.An essential finding of the thesis was that noise and noise sources may impair the pedagogic work, thereby increasing the work load of employees. It is concluded that noise exposure in the preschool, isolated or in combination with other stressors, plays a fundamental role in the building up of acute as well as long term stress. An intervention study implementing six acoustical and seven organizational measures was tested, aimed to improve the noise situation in the departments. Acoustical measures improved the noise situation as well as the rated noise experiences better than the organizational measures.
|
|
| 2. |
- Fraser, Magdalena
(författare)
-
People of the Dolmens and Stone Cists : An archaeogenetic Investigation of Megalithic Graves from the Neolithic Period on Gotland
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The study of ancient genomics of pre-historic human remains has in recent years offered unprecedented knowledge regarding pre-historic migration and population structure on the European continent which has fundamentally altered the current views in the archaeological community. However, the merging of the two fields, archaeology and genetics, is still in its infancy and much work is still needed in order for these fields to integrate. In this thesis I explore how genetic analyses, in combination with contextual radiocarbon dating and isotopic analyses for diet and mobility can be used to investigate demographic events on a local and regional level. This is done through the investigation of people buried in five previously excavated megalithic tombs on the Island of Gotland dated to the Neolithic period. I present the genomic population structure and archaeological background for the pre-historic European reference data and show how this is used to investigate population continuity, demographic shifts, cultural duality, and admixture for local and regional contexts. I present new data and explore the Strontium-baseline for the Gotland biosphere which is used for the mobility analyses. I show that mitochondrial haplogroup data is especially useful in combination with isotopic data, and radiocarbon dating for investigation of demographic shifts on a larger scale. I also show that genomic data gives unique insights into the individuals’ life history which, together with the established demographic background allows for fine scale investigation of population demographic events within and between different archaeological contexts. Finally I show that the different Neolithic contexts on Gotland to a large extent involves immigration of new groups to the island, and that the contextual breaks seen in the archaeological record during the Neolithic period are connected with cultural and population demographic shifts. This dissertation demonstrates that genomic analyses, in combination with archaeology and isotopic analyses, as well as contextual osteological analyses and radiocarbon dating, present unique insights into the life history of the actual people who lived the lives we try to understand.
|
|
| 3. |
- Sundström, Johan, Professor, 1971-, et al.
(författare)
-
Risk factors for subarachnoid haemorrhage : a nationwide cohort of 950 000 adults
- 2019
-
Ingår i: International Journal of Epidemiology. - : Oxford University Press. - 0300-5771 .- 1464-3685. ; 48:6, s. 2018-2025
-
Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Subarachnoid haemorrhage (SAH) is a devastating disease, with high mortality rate and substantial disability among survivors. Its causes are poorly understood. We aimed to investigate risk factors for SAH using a novel nationwide cohort consortium.METHODS: We obtained individual participant data of 949 683 persons (330 334 women) between 25 and 90 years old, with no history of SAH at baseline, from 21 population-based cohorts. Outcomes were obtained from the Swedish Patient and Causes of Death Registries.RESULTS: During 13 704 959 person-years of follow-up, 2659 cases of first-ever fatal or non-fatal SAH occurred, with an age-standardized incidence rate of 9.0 [95% confidence interval (CI) (7.4-10.6)/100 000 person-years] in men and 13.8 [(11.4-16.2)/100 000 person-years] in women. The incidence rate increased exponentially with higher age. In multivariable-adjusted Poisson models, marked sex interactions for current smoking and body mass index (BMI) were observed. Current smoking conferred a rate ratio (RR) of 2.24 (95% CI 1.95-2.57) in women and 1.62 (1.47-1.79) in men. One standard deviation higher BMI was associated with an RR of 0.86 (0.81-0.92) in women and 1.02 (0.96-1.08) in men. Higher blood pressure and lower education level were also associated with higher risk of SAH.CONCLUSIONS: The risk of SAH is 45% higher in women than in men, with substantial sex differences in risk factor strengths. In particular, a markedly stronger adverse effect of smoking in women may motivate targeted public health initiatives.
|
|
| 4. |
- Eklund, Anders, 1981-
(författare)
-
Computational Medical Image Analysis : With a Focus on Real-Time fMRI and Non-Parametric Statistics
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Functional magnetic resonance imaging (fMRI) is a prime example of multi-disciplinary research. Without the beautiful physics of MRI, there wouldnot be any images to look at in the first place. To obtain images of goodquality, it is necessary to fully understand the concepts of the frequencydomain. The analysis of fMRI data requires understanding of signal pro-cessing, statistics and knowledge about the anatomy and function of thehuman brain. The resulting brain activity maps are used by physicians,neurologists, psychologists and behaviourists, in order to plan surgery andto increase their understanding of how the brain works.This thesis presents methods for real-time fMRI and non-parametric fMRIanalysis. Real-time fMRI places high demands on the signal processing,as all the calculations have to be made in real-time in complex situations.Real-time fMRI can, for example, be used for interactive brain mapping.Another possibility is to change the stimulus that is given to the subject, inreal-time, such that the brain and the computer can work together to solvea given task, yielding a brain computer interface (BCI). Non-parametricfMRI analysis, for example, concerns the problem of calculating signifi-cance thresholds and p-values for test statistics without a parametric nulldistribution.Two BCIs are presented in this thesis. In the first BCI, the subject wasable to balance a virtual inverted pendulum by thinking of activating theleft or right hand or resting. In the second BCI, the subject in the MRscanner was able to communicate with a person outside the MR scanner,through a virtual keyboard.A graphics processing unit (GPU) implementation of a random permuta-tion test for single subject fMRI analysis is also presented. The randompermutation test is used to calculate significance thresholds and p-values forfMRI analysis by canonical correlation analysis (CCA), and to investigatethe correctness of standard parametric approaches. The random permuta-tion test was verified by using 10 000 noise datasets and 1484 resting statefMRI datasets. The random permutation test is also used for a non-localCCA approach to fMRI analysis.
|
|
| 5. |
- Knutsson, Erika, 1975-
(författare)
-
Bundling for consumers? : Understanding complementarity and its effect on consumers' preferences and satisfaction
- 2011
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- It is a common market practice to offer two products in a package, so called bundling. While much research investigate how companies can use bundling to increase sales and profit, less is known about how bundling can be beneficial for consumers. There are many advantages with bundling for consumers, as bundles often are offered at a reduced price and provide convenience and reduced risk. But there are also major drawbacks, for example reduced freedom of choice and increased risk of over-consumption. In the present study, the general aim is to increase the understanding of how consumers’ perceive bundle value. To achieve this, focus is turned to bundle composition, more specifically the complementarity between bundle products, as a source of value for consumers. By exploring what complementarity is, how it influences consumer preferences for and satisfaction with bundles and how it interacts with bundle discount insights about the overall value of bundles for consumers is gained. In five scenario-based experiments, the influence of different kinds and different degrees of complementarity on consumers’ perceptions of bundle value is studied and compared to evaluations of separate products. The results show that bundles generally are not preferred over separate products and that they only exceptionally provide more satisfaction. However, the results also highlight the influence of bundle composition on consumer evaluations. Generally, bundle complementarity has a positive effect on preferences and satisfaction, especially when combined with a discount. The results also illustrates that complementarity is a multifaceted concept. Many kinds of relations between bundle products are considered complementary and the degree of complementarity may vary within and between different types of complementarity. Based on the results it is suggested that the notion of complementarity is closely related to consumers’ everyday practices and the value bundles provides in use. When consumers understand the value that bundle products provide in use, the perceived complementarity increases and preferences and satisfaction is positively influenced. It is suggested that bundling can be used as a strategic tool by companies to increase value for customers. By considering their customers’ needs and practices companies can compose bundles that are perceived as complementary and offer value-in-use.
|
|
| 6. |
- Koldestam, Maria, 1968-
(författare)
-
MILO - A Conceptual Learning Model Grounded in a Hermeneutical and a Caritative Caring Perspective : Development and Evaluation
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aim: The overall aim was to develop and evaluate a conceptual learning model grounded in a caritative caring perspective aimed to facilitate undergraduate nursing students’ learning during clinical practice.Methods: This thesis comprises four studies with a descriptive explorative design overall. In the inductively applied research, different designs using both qualitative and quantitative methods, were used. Studies I–III used qualitative methods; data for study I were collected using the Delphi method and analysed using qualitative data analysis. In study II, data were collected using focus group interviews and analysed using latent content analysis. In study III, data were collected using individual interviews and analysed using a phenomenographic approach. Study IV used quantitative methods and data were collected using a questionnaire and analysed using statistical methods.Results: Study I resulted in a conceptual learning model grounded in hermeneutics and a caritative caring perspective. The Model for Improvement in Learning Outcomes (MILO) encompasses eight concepts: four intrapersonal, i.e. the students’ own characteristics, reflecting understanding, and four contextual concepts, i.e. environmental concepts, reflecting structure. Study II showed that students’ learning is facilitated as a result of natural actions and elements that occur in daily life, integrating natural caring with professional caring. Studies III and IV showed that students’ learning was a gain in knowledge and understanding of supportive elements for learning and the perspective of the patients, and a gain in engagement and dedication. Study IV also showed that the intrapersonal concepts were valued more than the contextual concepts in the three different semesters studied. The use of the applications was valued more at the start of the students’ education. Some of the concepts and their applications had not been used in accordance with MILO’s implementation in the region involved.Conclusions: The fundamentals needed to become a professional caring nurse include having compassion and competence. Undergraduate nursing students’ learning during clinical practice needs to be facilitated by a theoretical foundation establishing an ethical bearing, by knowledge and understanding of one self and of the patient as a whole, and by challenged learning using a diversity of tools to achieve the intended outcome of better health and well-being for the patient.
|
|
| 7. |
- Mårtensson, Sophie
(författare)
-
Bridging the gap between caring theory and nursing practice : Learning experiences of undergraduate nursing students in a caring behavior course
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: Healthcare providers are obligated to practice with scientific knowledge in order to deliver high quality and safe care based on patients’ needs. Despite this obligation, complaints from care recipients and their significant others regarding healthcare providers’ lack of compassion and competent care in their professional encounters have increased. In the discipline of nursing, theoretical structures of caring, conceptualized as behaviors, have been established as the heart and core value of guidance in all nursing practice. In nursing education, however, caring has tended to be taught as an intangible aspect of nursing practice, described as hidden curricula, thus, focus more on developing knowledge and psychomotor skills instead of learning caring behaviors. Studies that examine how undergraduate nursing students can learn caring behaviors explicitly are rare. Thus, a stronger emphasis on the learning of caring in the context of a caring behavior course that uses a variety of learning didactics is needed. Without adequate theoretical structures for caring-based observational behavioral instruments assessing verbal and non-verbal caring and non-caring behaviors, there is little evidence to help develop the learning of caring behaviors.Aim: The overall aim of this thesis was to study how a caring behavior course in undergraduate nursing education influenced students’ learning of caring behaviors.Method: This thesis was conducted among undergraduate nursing students at a university in Sweden. The participants attended a 7.5-credit (five-week) Caring Behavior Course (the CBC) in semester four during spring and fall 2018 and spring 2019. The CBC was facilitated through a student-centered learning approach intertwined into reflective practice with the learning didactics of narrative pedagogy and simulation; it comprised six voluntary lectures, five mandatory seminars, and two mandatory caring behavior simulation days and examinations. All data were collected from the students participating in the CBC. Two of the four scientific papers constituting this thesis had a qualitative design based on focus group interviews (paper I) and individual written reflections (paper II). Analyses was conducted using qualitative content analysis. One paper had an instrument development design to develop and test an observational behavioral instrument based on Swanson’s Theory of Caring (paper III). Lastly, one paper had a quantitative observational design using the CBCS on video-recorded observational behavioral data collected in the CBC (paper IV). Analyses was conducted using descriptive statistics and Wilcoxon signed rank test (paper IV).Results: The undergraduate nursing students’ participation in the CBC influenced their learning of caring behaviors. It deepened their understanding and knowledge of caring. The students became aware that learning caring is a task that requires effort because the meaning of caring encompasses nurses’ active engagement in practicing caring behaviors. These findings are also supported through the observational behavioral instrument, through the developed Caring Behavior Coding Scheme based on Swanson’s Theory of Caring; it was found that participation in the CBC influenced the undergraduate nursing students verbal and non-verbal caring and non-caring behaviors.Conclusions: This thesis demonstrated that bridging the gap between caring theory and nursing practice in the CBC using a variety of learning didactics influenced undergraduate nursing students’ learning of caring behaviors. The results contributed to strengthening the knowledge that caring and learning are parallel processes in the undergraduate nursing students’ development into becoming compassionate and competent caring nurses, with the intended outcome of patient healing and well-being.
|
|
| 8. |
- Nordin, Maria, 1967-
(författare)
-
Low social support and disturbed sleep : epidemiological and psychological perspectives
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Swedish work force underwent dramatic changes during an economic crisis in the 1990s. In the aftermath, sick leave increased at an unprecedented rate and stress-related disorders, such as burnout, depression, and sleep disturbances replaced earlier work-related diagnoses. Sleep disturbances have been demonstrated to both precede and succeed mental and physical illnesses, including burnout, depression, anxiety, and cardiovascular disease. Disturbed sleep is also a common complaint in Sweden as well as in the rest of the Western world. Sleep has been shown to easily be disturbed by cognitive, emotional, and physiological arousal (stress). However, several studies have demonstrated that social support has a protective effect against the adverse effects of stress as well as a generally beneficial effect on health. Other studies, though, suggest that lack of social support may increase the risk for mental and physical ill-health. The purpose of this thesis was therefore to investigate the association between social support and disturbed sleep; foremost in working populations.Epidemiological methods were applied to investigate the association between social support and disturbed sleep. Three studies were used; a cross-sectional (MONICA, n = 1,179), a longitudinal (WOLF, n = 2,479), and a case-referent (SHEEP and VHEEP in conjunction, n = 6,231) study. The data was obtained by questionnaires, and social support was operationalized as network and emotional support. Disturbed sleep was defined as difficulties falling asleep, difficulties maintaining sleep, repeated awakenings, and disturbed sleep. Gender was taken into consideration throughout the studies.Foremost, low network support was found to increase the risk for contracting disturbed sleep. Which source the network support was derived from did not alter the association between low network support and disturbed sleep—low network support at work increased the risk for disturbed sleep as did low network outside work. Prolonged low network support and impaired emotional support did also increase the risk for sleep disturbances in men who were under strain at work. Furthermore, open coping buffered against low network support in the association with disturbed sleep five years later in women, whereas low network support increased the risk for developing disturbed sleep at a later date when interacting with covert coping both in women and in men. Moreover, disturbed sleep was shown to mediate low network support in myocardial infarction in women.In conclusion, the association between social support and disturbed sleep is complex and includes both interactions with other personality variables and mediating associations. Previous research on negative effects of low social support was confirmed as was previously observed gender differences in social support.
|
|
| 9. |
- Brun, Anders, 1976-
(författare)
-
Manifolds in Image Science and Visualization
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A Riemannian manifold is a mathematical concept that generalizes curved surfaces to higher dimensions, giving a precise meaning to concepts like angle, length, area, volume and curvature. A glimpse of the consequences of a non-flat geometry is given on the sphere, where the shortest path between two points – a geodesic – is along a great circle. Different from Euclidean space, the angle sum of geodesic triangles on the sphere is always larger than 180 degrees.Signals and data found in applied research are sometimes naturally described by such curved spaces. This dissertation presents basic research and tools for the analysis, processing and visualization of such manifold-valued data, with a particular emphasis on future applications in medical imaging and visualization.Two-dimensional manifolds, i.e. surfaces, enter naturally into the geometric modelling of anatomical entities, such as the human brain cortex and the colon. In advanced algorithms for processing of images obtained from computed tomography (CT) and ultrasound imaging (US), images themselves and derived local structure tensor fields may be interpreted as two- or three-dimensional manifolds. In diffusion tensor magnetic resonance imaging (DT-MRI), the natural description of diffusion in the human body is a second-order tensor field, which can be related to the metric of a manifold. A final example is the analysis of shape variations of anatomical entities, e.g. the lateral ventricles in the brain, within a population by describing the set of all possible shapes as a manifold.Work presented in this dissertation include: Probabilistic interpretation of intrinsic and extrinsic means in manifolds. A Bayesian approach to filtering of vector data, removing noise from sampled manifolds and signals. Principles for the storage of tensor field data and learning a natural metric for empirical data.The main contribution is a novel class of algorithms called LogMaps, for the numerical estimation of logp (x) from empirical data sampled from a low-dimensional manifold or geometric model embedded in Euclidean space. The logp (x) function has been used extensively in the literature for processing data in manifolds, including applications in medical imaging such as shape analysis. However, previous approaches have been limited to manifolds where closed form expressions of logp (x) have been known. The introduction of the LogMap framework allows for a generalization of the previous methods. The application of LogMaps to texture mapping, tensor field visualization, medial locus estimation and exploratory data analysis is also presented.
|
|
| 10. |
- Carlerby, Heidi, 1967-
(författare)
-
Health and Social Determinants Among Boys and Girls in Sweden : Focusing on Parental Background
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The majority of Swedish boys and girls have good psychosomatic health. Despite that the risk of mental health problems such as nervousness, feeling low and sleeping difficulties has increased steadily in recent decades. Moreover, previous surveys on health and well-being indicate that boys and girls of foreign extraction in Sweden are at increased risk of ill health compared to boys and girls of Swedish background. The main aim of this thesis was to analyse health and social determinants among boys and girls of foreign extraction in Sweden. The factors explored in papers I–IV include parental background, family affluence and gender and their associations with subjective health complaints, psychosomatic problems or health risk behaviours. Other included risk factors for ill health were involvement in bullying, low participation and discrimination at school. This thesis takes an intersectional perspective, with ambitions to be able to emphasize the interplay between different power relations (i.e. gender, social class and parental background). Two sets of cross-sectional data were used. Three papers were based on the Swedish part of the World Health Organization’s Health Behaviour in School-Aged Children. The sample consisted of 11,972 children (boys n = 6054; girls n = 5918) in grades five, seven and nine from the measurement years 1997/98, 2001/02 and 2005/06. The response rate varied between 85 and 90%. About one fifth of the included children were of foreign extraction. For the fourth paper regional data from Northern Sweden were used. Boys (n = 729) and girls (n = 798) in grades six to nine answered a questionnaire in 2011 and the response rate was 80%. About 14% of the included children were of foreign extraction. Statistical methods used were chi-square test, correlation analyses, logistic regression analyses, cluster analyses and test of mediating factor. The results showed that girls of foreign background were at increased risk of subjective health complaints (SHC) and boys of mixed background were at increased risk of psychosomatic problems (PSP). Increased risk of allocation to the cluster profile of multiple risk behaviour was shown in boys and girls of mixed background, in girls of foreign background and in girls of low family affluence. Increased risk of allocation to the cluster profile of inadequate tooth brushing was shown in boys and girls of foreign background and in girls of low family affluence. General risk factors for increased risk of ill health for boys and girls in Sweden were: any form of bullying involvement, low family affluence, low participation and discrimination at school, of which the latter also was a mediating factor for ill health. Living with a single parent was a risk factor for ill health among girls. The results can function as a basis for developing health promotion programmes at schools that focus on social consequences of foreign extraction, family affluence, participation as well as health risk behaviours and gender.
|
|
| 11. |
- Eklund, Anders
(författare)
-
Signal Processing for Robust and Real-Time fMRI With Application to Brain Computer Interfaces
- 2010
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- It is hard to find another research field than functional magnetic resonance imaging (fMRI) that combines so many different areas of research. Without the beautiful physics of MRI we would not have any images to look at in the first place. To get images with good quality it is necessary to fully understand the concepts of the frequency domain. The analysis of fMRI data requires understanding of signal processing and statistics and also knowledge about the anatomy and function of the human brain. The resulting brain activity maps are used by physicians and neurologists in order to plan surgery and to increase their understanding of how the brain works.This thesis presents methods for signal processing of fMRI data in real-time situations. Real-time fMRI puts higher demands on the signal processing, than conventional fMRI, since all the calculations have to be made in realtime and in more complex situations. The result from the real-time fMRI analysis can for example be used to look at the subjects brain activity in real-time, for interactive planning of surgery or understanding of brain functions. Another possibility is to use the result in order to change the stimulus that is given to the subject, such that the brain and the computer can work together to solve a given task. These kind of setups are often called brain computer interfaces (BCI).Two BCI are presented in this thesis. In the first BCI the subject was able to balance a virtual inverted pendulum by thinking of activating the left or right hand or resting. In the second BCI the subject in the MR scanner was able to communicate with a person outside the MR scanner, through a communication interface.Since head motion is common during fMRI experiments it is necessary to apply image registration to align the collected volumes. To do image registration in real-time can be a challenging task, therefore how to implement a volume registration algorithm on a graphics card is presented. The power of modern graphic cards can also be used to save time in the daily clinical work, an example of this is also given in the thesis.Finally a method for calculating and incorporating a structural based certainty in the analysis of the fMRI data is proposed. The results show that the structural certainty helps to remove false activity that can occur due to head motion, especially at the edge of the brain.
|
|
| 12. |
- Sjölund, Jens, 1987-
(författare)
-
Algorithms for magnetic resonance imaging in radiotherapy
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Radiotherapy plays an increasingly important role in cancer treatment, and medical imaging plays an increasingly important role in radiotherapy. Magnetic resonance imaging (MRI) is poised to be a major component in the development towards more effective radiotherapy treatments with fewer side effects. This thesis attempts to contribute in realizing this potential.Radiotherapy planning requires simulation of radiation transport. The necessary physical properties are typically derived from CT images, but in some cases only MR images are available. In such a case, a crude but common approach is to approximate all tissue properties as equivalent to those of water. In this thesis we propose two methods to improve upon this approximation. The first uses a machine learning approach to automatically identify bone tissue in MR. The second, which we refer to as atlas-based regression, can be used to generate a realistic, patient-specific, pseudo-CT directly from anatomical MR images. Atlas-based regression uses deformable registration to estimate a pseudo-CT of a new patient based on a database of aligned MR and CT pairs.Cancerous tissue has a different structure from normal tissue. This affects molecular diffusion, which can be measured using MRI. The prototypical diffusion encoding sequence has recently been challenged with the introduction of more general gradient waveforms. One such example is diffusional variance decomposition (DIVIDE), which allows non-invasive mapping of parameters that reflect variable cell eccentricity and density in brain tumors. To take full advantage of such more general gradient waveforms it is, however, imperative to respect the constraints imposed by the hardware while at the same time maximizing the diffusion encoding strength. In this thesis we formulate this as a constrained optimization problem that is easily adaptable to various hardware constraints. We demonstrate that, by using the optimized gradient waveforms, it is technically feasible to perform whole-brain diffusional variance decomposition at clinical MRI systems with varying performance.The last part of the thesis is devoted to estimation of diffusion MRI models from measurements. We show that, by using a machine learning framework called Gaussian processes, it is possible to perform diffusion spectrum imaging using far fewer measurements than ordinarily required. This has the potential of making diffusion spectrum imaging feasible even though the acquisition time is limited. A key property of Gaussian processes, which is a probabilistic model, is that it comes with a rigorous way of reasoning about uncertainty. This is pursued further in the last paper, in which we propose a Bayesian reinterpretation of several of the most popular models for diffusion MRI. Thanks to the Bayesian interpretation it possible to quantify the uncertainty in any property derived from these models. We expect this will be broadly useful, in particular in group analyses and in cases when the uncertainty is large.
|
|
| 13. |
- van den Berg, Johannes, 1962-
(författare)
-
Indicators and predictors of sleepiness
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sleep is a basic need as important as physical fitness and good nutrition. Without enough sleep, we will create a sleep debt and experience sleepiness. Sleepiness can be defined as the inability to stay awake, a condition that has become a health problem in our 24-hour-7-day-a-week society. Estimates suggest that up to one-third of the population suffers from excessive sleepiness. Among other interactions, sleepiness affects our performance, increasing the risk of being involved in accidents. A considerable portion of work related accidents and injuries are related to sleepiness resulting in large costs for the individuals and society. Professional drivers are one example of workers who are at risk of sleepiness related accidents. Up to 40% of heavy truck accidents could be related to sleepiness. A better knowledge about reliable indicators and predictors of sleepiness is important in preventing sleepiness related accidents.This thesis investigates both objective and subjective indicators of sleepiness, how these relate to each other, and how their pattern changes over time. The indicators investigated were electroencephalography, heart rate variability, simple reaction time, head movement, and subjective ratings of sleepiness (Study I-IV). In Study V, a questionnaire study was conducted with professional drivers in northern Sweden. This study mainly deals with predictors of sleepiness. When subjects were sleep deprived both objective and subjective ratings indicated a rapid increase in sleepiness during the first hour of the test followed by a levelling off. This change in pattern was evident for all the indicators except heart rate and heart rate variability. On the other hand, HRV was correlated with the increase of EEG parameters during the post-test sleep period. The changes in pattern of the indicators included in the thesis are analysed in the perspective of temporal patterns and relationships. Of the tested indicators, a subjective rating of sleepiness with CR-10 was considered to be the most reliable indicator of sleepiness. Of the investigated predictors of sleepiness, prior sleep habits were found to be strongly associated to sleepiness and the sleepiness related symptoms while driving. The influences of driving conditions and individual characteristics on sleepiness while driving were lower. A multidisciplinary approach when investigating and implementing indicators and predictors of sleepiness is important. In addition to their actual relations to the development of sleepiness, factors such as technical and practical limitations, work, and individual and situational needs must be taken into account.
|
|
