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Haegler, Katrin (2011): Similarity Search in Medical Data. Dissertation, LMU München: Faculty of Mathematics, Computer Science and Statistics
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Abstract

The ongoing automation in our modern information society leads to a tremendous rise in the amount as well as complexity of collected data. In medical imaging for example the electronic availability of extensive data collected as part of clinical trials provides a remarkable potentiality to detect new relevant features in complex diseases like brain tumors. Using data mining applications for the analysis of the data raises several problems. One problem is the localization of outstanding observations also called outliers in a data set. In this work a technique for parameter-free outlier detection, which is based on data compression and a general data model which combines the Generalized Normal Distribution (GND) with independent components, to cope with existing problems like parameter settings or implicit data distribution assumptions, is proposed. Another problem in many modern applications amongst others in medical imaging is the efficient similarity search in uncertain data. At present, an adequate therapy planning of newly detected brain tumors assumedly of glial origin needs invasive biopsy due to the fact that prognosis and treatment, both vary strongly for benign, low-grade, and high-grade tumors. To date differentiation of tumor grades is mainly based on the expertise of neuroradiologists examining contrast-enhanced Magnetic Resonance Images (MRI). To assist neuroradiologist experts during the differentiation between tumors of different malignancy we proposed a novel, efficient similarity search technique for uncertain data. The feature vector of an object is thereby not exactly known but is rather defined by a Probability Density Function (PDF) like a Gaussian Mixture Model (GMM). Previous work is limited to axis-parallel Gaussian distributions, hence, correlations between different features are not considered in these similarity searches. In this work a novel, efficient similarity search technique for general GMMs without independence assumption is presented. The actual components of a GMM are approximated in a conservative but tight way. The conservativity of the approach leads to a filter-refinement architecture, which guarantees no false dismissals and the tightness of the approximations causes good filter selectivity. An extensive experimental evaluation of the approach demonstrates a considerable speed-up of similarity queries on general GMMs. Additionally, promising results for advancing the differentiation between brain tumors of different grades could be obtained by applying the approach to four-dimensional Magnetic Resonance Images of glioma patients.