Stühler, Elisabeth


Suchergebnisse Publikationen

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Dementia-Related Features in Longitudinal MRI : Tracking Keypoints over Time

2014-12-10, Stühler, Elisabeth, Berthold, Michael R.

We aim at developing new dementia-related features based on longitudinal MRI in order to differentiate various stages of Alzheimer’s disease.

Current methods for dementia classification rely heavily on the quality of MRI preprocessing, especially on prior registration. We propose to avoid a possibly unsuccessful and always time-consuming non-rigid registration by employing local invariant features which are independent of image scale and orientation, and can be tracked over time in longitudinal studies. We detect and track such keypoints based on scale-space theory in an automatized image processing workflow, and test it on a standardized MRI collection made available by the Alzheimer’s Disease Neuroimaging Initiative (ADNI).

Our approach is very efficient for processing very large datasets collected from different sites and technical devices, and first results show that characteristic scale and movement of keypoints and their tracks differ significantly between controls and diseased subjects.


Multiple Discriminant Analysis of SPECT Data for Alzheimer’s Disease, Frontotemporal Dementia and Asymptomatic Controls

2011-10, Stühler, Elisabeth, Platsch, Günther, Weih, Markus, Kornhuber, Johannes, Kuwert, Torsten, Merhof, Dorit

Multiple discriminant analysis (MDA) is a generalization of the Fisher discriminant analysis (FDA) and makes it possible to discriminate more than two classes by projecting the data onto a subspace. In this work, it was applied to technetium- 99methylcysteinatedimer (99mTc-ECD) SPECT datasets of 10 Alzheimer’s disease (AD) patients, 11 frontotemporal dementia (FTD) patients and 11 asymptomatic controls (CTR). Principal component analysis (PCA) was used for dimensionality reduction, followed by projection of the data onto a discrimination plane via MDA. In order to separate the different groups, linear boundaries were calculated by applying FDA to two classes at a time (linear machine). By executing the F-test for different numbers of principal components and examining the corresponding classification accuracy, an optimal discrimination plane based on the first three principal components was determined. In order to further assess the method, another dataset comprising patients with early-onset AD and FTD (beginning or suspected disease) was projected by the same method onto this discrimination plane, resulting in a correct classification for most cases. The successful iscrimination of another dataset on the same plane indicates that the model is well suited to account for
disease-specific characteristics within the classes, even for patients with early-onset AD and FTD.

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Classification of neurodegenerative dementia by Gaussian Mixture Models applied to SPECT images

2012-10, Stühler, Elisabeth, Platsch, Günther, Weih, Markus, Kornhuber, Johannes, Kuwert, Torsten, Merhof, Dorit

Gaussian mixture (GM) models can be applied for statistical classification of various types of dementia. As opposed to linear boundaries, they do not only provide the class membership of a case, but also a measure of its probability. This enables an improved interpretation and classification of neurodegenerative dementia datasets which comprise various stages of the disease, and also mixed forms of dementia. In this work, GM models are applied to a total number of 103 technetium-99methylcysteinatedimer (99mTc-ECD) SPECT datasets of asymptomatic controls (CTR), as well as Alzheimer’s disease (AD) and frontotemporal dementia (FTD) patients in early or moderate stages of the disease. Prior to classification, multivariate analysis is applied: Principal component analysis (PCA) is used for dimensionality reduction, followed by a differentiation of the datasets via multiple discriminant analysis (MDA). A GM model on the resulting discrimination plane is constructed by computing the GM distribution associated with the underlying training set. The posterior probabilities of each case indicate its class membership probability. The performance of GM models for classification is assessed by bootstrap resampling and cross validation. Accuracy and robustness of the method are evaluated for different numbers of principal components (PCs), and furthermore the detection rate of dementia in early stages is calculated. The GM model outperfomes classification with linear boundaries in both predicted accuracy and detection rate of early dementia, and is equally robust.

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Skeleton-based gyri sulci separation for improved assessment of cortical thickness

2012-05, Richter, Mirco, Bishop, Courtney A., Dukart, Jürgen, Stühler, Elisabeth, Müller, Karsten, Schroeter, Matthias L., Merhof, Dorit

In order to improve classification of neurological diseases involving cortical thinning, this work proposes an approach for separating gyral and sulcal regions of the human cortex. Using data from magnetic resonance imaging, the skeleton of the brain's white matter was reconstructed and a geodesic distance measure was applied to separate gyri and sulci. Cortical thickness per subregion was measured for the entire cortex and for gyri and sulci individually in 21 patients with Alzheimer's disease, 10 patients with frontotemporal lobar degeneration composed of two subgroups and 13 control subjects. For discrimination using logistic regressions, which was assessed using leave-one-out cross-validation, improved results were obtained in five out of six group comparisons when cortical thickness measurements were constrained to gyral or sulcal regions.