A Visual Analytics Approach for Comparing Cohorts in Single-Voxel Magnetic Resonance Spectroscopy Data.

Single-voxel proton magnetic resonance spectroscopy (H-MRS) is a non-invasive in-vivo technology to measure metabolic concentrations in selected regions of interest in a tissue, e.g., the brain. H-MRS generates spectra of signals with different frequencies and specific intensities which can be assigned to respective metabolites in the investigated tissue and quantified. In studies designed to detect biomarkers of a specific disorder or dysfunction, the overall goal is not just to analyze a single H-MRS data set, but to compare patient cohorts against healthy controls. We propose a visual analytics tool for the comparative analyses of cohorts, i.e., sets of data sets. Each data set can be regarded as a multivariate data sample, in which each variable represents the concentration of a metabolite. While a standard workflow for comparative analyses of two cohorts is routinely deployed by analyzing metabolites individually, our tool allows for comparative cohort analysis in a multivariate setting. Our top-down analysis strategy uses multidimensional data visualization methods combined with statistical plots and statistical analyses. We document and evaluate the effectiveness of our approach for the interactive analysis of metabolite concentrations in three brain regions for a comparative study of an alcohol-dependent patient cohort and a healthy control group.