title: Spatial Autocorrelation in Mass Spectrometry Imaging.
abstract: Mass spectrometry imaging (MSI) is a powerful molecular imaging technique. In microprobe MSI, images are created through a grid-wise interrogation of individual spots by mass spectrometry across a surface. Classical statistical tests for within-sample comparisons fail as close-by measurement spots violate the assumption of independence of these tests, which can lead to an increased false-discovery rate. For spatial data, this effect is referred to as spatial autocorrelation. In this study, we investigated spatial autocorrelation in three different matrix-assisted laser desorption/ionization MSI data sets. These data sets cover different molecular classes (metabolites/drugs, lipids, and proteins) and different spatial resolutions ranging from 20 to 100 μm. Significant spatial autocorrelation was detected in all three data sets and found to increase with decreasing pixel size. To enable statistical testing for differences in mass signal intensities between regions of interest within MSI data sets, we propose the use of Conditional Autoregressive (CAR) models. We show that, by accounting for spatial autocorrelation, discovery rates (i.e., the ratio between the features identified and the total number of features) could be reduced between 21% and 69%. The reliability of this approach was validated by control mass signals based on prior knowledge. In light of the advent of larger MSI data sets based on either an increased spatial resolution or 3D data sets, accounting for effects due to spatial autocorrelation becomes even more indispensable. Here, we propose a generic and easily applicable workflow to enable within-sample statistical comparisons.
authors.affiliation: Department of Methodology and Statistics, Maastricht University , 6200 MD Maastricht, The Netherlands.
authors.forename: Alberto
authors.initials: A
authors.lastname: Cassese
authors.affiliation: Maastricht MultiModal Molecular Imaging Institute (M4I), Maastricht University , Universiteitssingel 50, P.O. Box 616, 6200 MD Maastricht, The Netherlands.
authors.forename: Shane R
authors.initials: SR
authors.lastname: Ellis
authors.affiliation: Maastricht MultiModal Molecular Imaging Institute (M4I), Maastricht University , Universiteitssingel 50, P.O. Box 616, 6200 MD Maastricht, The Netherlands.
authors.forename: Nina
authors.initials: N
authors.lastname: Ogrinc Potočnik
authors.affiliation: Department of Internal Medicine II, Medical Faculty Mannheim, Heidelberg University , 68167 Mannheim, Germany.
authors.forename: Elke
authors.initials: E
authors.lastname: Burgermeister
authors.affiliation: Department of Internal Medicine II, Medical Faculty Mannheim, Heidelberg University , 68167 Mannheim, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Ebert
authors.affiliation: Research Unit Analytical Pathology, Helmholtz Zentrum München , 85764 Oberschleißheim, Germany.
authors.forename: Axel
authors.initials: A
authors.lastname: Walch
authors.affiliation: Departments of Human Genetics and Neurology, Leiden University Medical Center , 2333 ZC Leiden, The Netherlands.
authors.forename: Arn M J M
authors.initials: AM
authors.lastname: van den Maagdenberg
authors.affiliation: Fondazione Pisana per la Scienza ONLUS , 56121 Pisa, Italy.|Center for Proteomics and Metabolomics, Leiden University Medical Center , 2333 ZC Leiden, The Netherlands.|Department of Pathology, Leiden University Medical Center , 2333 ZA Leiden, The Netherlands.
authors.forename: Liam A
authors.initials: LA
authors.lastname: McDonnell
authors.affiliation: Maastricht MultiModal Molecular Imaging Institute (M4I), Maastricht University , Universiteitssingel 50, P.O. Box 616, 6200 MD Maastricht, The Netherlands.
authors.forename: Ron M A
authors.initials: RM
authors.lastname: Heeren
authors.affiliation: Maastricht MultiModal Molecular Imaging Institute (M4I), Maastricht University , Universiteitssingel 50, P.O. Box 616, 6200 MD Maastricht, The Netherlands.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Balluff