Dimensionpudotusmenetelmiä fMRI-analyysissä ja visualisoinnissa

The need to model and understand high-dimensional, noisy data sets is common in many domains these day, among them neuroimaging and fMRI analysis. Dimensionality reduction and variable selection are two common strategies for dealing with high-dimensional data, either as a pre-processing step prior to further analysis, or as an analysis step itself. This thesis discusses both dimensionality reduction and variable selection, with a focus on fMRI analysis, visualization, and applications of visualization in fMRI analysis. Three new algorithms are introduced. The first algorithm uses a sparse Canonical Correlation Analysis model and a high-dimensional stimulus representation to find relevant voxels (variables) in fMRI experiments with complex natural stimuli. Experiments on a data set involving music show that the algorithm successfully retrieves voxels relevant to the experimental condition. The second algorithm, NeRV, is a dimensionality reduction method for visualization high-dimensional data using scatterplots. A simple abstract model of the way a human studies a scatterplot is formulated, and NeRV is derived as an algorithm for producing optimal visualizations in terms of this model. Experiments show that NeRV is superior to conventional dimensionality reduction methods in terms of this model. NeRV is also used to perform a novel form of exploratory data analysis on the fMRI voxels selected by the first algorithm; the analysis simultaneously demonstrates the usefulness of NeRV in practice and offers further insights into the performance of the voxel selection algorithm. The third algorithm, LDA-NeRV, combines a Bayesian latent-variable model for graphs with NeRV to produce one of the first principled graph drawing methods. Experiments show that LDA-NeRV is capable of visualizing structure that conventional graph drawing methods fail to reveal.Monilla aloilla esiintyy tarve korkeaulotteisen, kohinaisen datan analysoimiseen. Algorithminen dimensionpudotus tai muuttujanvalinta ovat usein sovellettavia lähestymistapoja, joko muuta analyysiä edeltävänä esikäsittelynä tai itsenäisenä analyysinä. Tässä työssä käsitellään sekä dimensionpudotusta että muuttujanvalintaa, keskittyen erityisesti fMRI-dataaan ja visualisointiin. Työssä esitellään kolme uutta algoritmia. Ensimmäinen algoritmi käyttää harvaa kanonista korrelaaioanalyysi-mallia (CCA) ja koeärsykkeen korkeaulotteista piirre-esitystä olennaisten vokseleiden (muuttujien) valitsemiseen fMRI-kokeissa, joissa koehenkilöt altistetaan monimutkaiselle luonnolliselle ärsykkeelle, kuten esimerkiksi musiikille. Kokeet musiikkia ärsykkeenä käyttävän fMRI-kokeen kanssa osoittavat algoritmin löytävän tärkeitä vokseleita. Toinen algoritmi, NeRV, on dimensionpudotusmenetelmä korkeaulotteisen datan visualisoimiseen hajontakuvion avulla. NeRV pohjautuu yksinkertaiseen abstraktiin malliin ihmisen tavalle tulkita hajontakuviota. Kokeet osoittavat NeRVin olevan perinteisiä menetelmiä parempi tämän visualisointimallin mielessä. Lisäksi NeRViä sovelletaan ensimmäisen algoritmin valitsemien fMRI-vokseleiden visuaaliseen analyysiin; analyysi sekä osoittaa NeRVin hyödyllisyyden käytännössä että tarjoaa uusia näkökulmia vokselinvalintatulosten ymmärtämiseen. Kolmas algoritmi, LDA-NeRV, on NeRViä ja bayesiläistä latenttimuuttujamallia soveltava visualisointimenetelmä graafeille. Kokeet osoittavat LDA-NeRVin kykenevän visualisoimaan rakennetta, jota perinteiset visualisointimenetelmät eivät tuo esiin

Graph visualization with latent variable models

Large graph layout design by choosing locations for the vertices on the plane, such that the drawn set of edges is understandable, is a tough problem. The goal is ill-defined and usually both optimization and evaluation criteria are only very indirectly related to the goal. We suggest a new and surprisingly effective visualization principle: Position nodes such that nearby nodes have similar link distributions. Since their edges are similar by definition, the edges will become visually bundled and do not interfere. For the definition of similarity we use latent variable models which incorporate the user's assumption of what is important in the graph, and given the similarity construct the visualization with a suitable nonlinear projection method capable of maximizing the precision of the display. We finally show that the method outperforms alternative graph visualization methods empirically, and that at least in the special case of clustered data the method is able to properly abstract and visualize the links

The self-organizing map as a visual neighbor retrieval method

We have recently introduced rigorous goodness criteria for information visualization by posing it as a visual neighbor retrieval problem, where the task is to find proximate high-dimensional data based only on a low-dimensional display. Standard information retrieval criteria such as precision and recall can then be used for information visualization. We introduced an algorithm, Neighbor Retrieval Visualizer (NeRV), to optimize the total cost of retrieval errors. NeRV was shown to outperform alternative methods, but the SOM was not included in the comparison. In empirical experiments of this paper the SOM turns out to be comparable to the best methods in terms of (smoothed) precision but not on recall. On a related measure called trustworthiness, the SOM outperforms all others. Finally, we suggest that for information visualization tasks the free parameters of the SOM could be optimized for information visualization with cross-validation

The self-organizing map as a visual neighbor retrieval method

We have recently introduced rigorous goodness criteria for information visualization by posing it as a visual neighbor retrieval problem, where the task is to find proximate high-dimensional data based only on a low-dimensional display. Standard information retrieval criteria such as precision and recall can then be used for information visualization. We introduced an algorithm, Neighbor Retrieval Visualizer (NeRV), to optimize the total cost of retrieval errors. NeRV was shown to outperform alternative methods, but the SOM was not included in the comparison. In empirical experiments of this paper the SOM turns out to be comparable to the best methods in terms of (smoothed) precision but not on recall. On a related measure called trustworthiness, the SOM outperforms all others. Finally, we suggest that for information visualization tasks the free parameters of the SOM could be optimized for information visualization with cross-validation

Urinary metabolite profiling and risk of progression of diabetic nephropathy in 2670 individuals with type 1 diabetes

Aims/hypothesis This prospective, observational study examines associations between 51 urinary metabolites and risk of progression of diabetic nephropathy in individuals with type 1 diabetes by employing an automated NMR metabolomics technique suitable for large-scale urine sample collections. Methods We collected 24-h urine samples for 2670 individuals with type 1 diabetes from the Finnish Diabetic Nephropathy study and measured metabolite concentrations by NMR. Individuals were followed up for 9.0 +/- 5.0 years until their first sign of progression of diabetic nephropathy, end-stage kidney disease or study end. Cox regressions were performed on the entire study population (overall progression), on 1999 individuals with normoalbuminuria and 347 individuals with macroalbuminuria at baseline. Results Seven urinary metabolites were associated with overall progression after adjustment for baseline albuminuria and chronic kidney disease stage (p < 8 x 10(-4)): leucine (HR 1.47 [95% CI 1.30, 1.66] per 1-SD creatinine-scaled metabolite concentration), valine (1.38 [1.22, 1.56]), isoleucine (1.33 [1.18, 1.50]), pseudouridine (1.25 [1.11, 1.42]), threonine (1.27 [1.11, 1.46]) and citrate (0.84 [0.75, 0.93]). 2-Hydroxyisobutyrate was associated with overall progression (1.30 [1.16, 1.45]) and also progression from normoalbuminuria (1.56 [1.25, 1.95]). Six amino acids and pyroglutamate were associated with progression from macroalbuminuria. Conclusions/interpretation Branched-chain amino acids and other urinary metabolites were associated with the progression of diabetic nephropathy on top of baseline albuminuria and chronic kidney disease. We found differences in associations for overall progression and progression from normo- and macroalbuminuria. These novel discoveries illustrate the utility of analysing urinary metabolites in entire population cohorts.Peer reviewe