title: Robust data processing and normalization strategy for MALDI mass spectrometric imaging.
abstract: Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) provides localized information about the molecular content of a tissue sample. To derive reliable conclusions from MSI data, it is necessary to implement appropriate processing steps in order to compare peak intensities across the different pixels comprising the image. Here, we review commonly used normalization methods, and propose a rational data processing strategy, for robust evaluation and modeling of MSI data. The approach includes newly developed heuristic methods for selecting biologically relevant peaks and pixels to reduce the size of a data set and remove the influence of the applied MALDI matrix. The methods are demonstrated on a MALDI MSI data set of a sagittal section of rat brain (4750 bins, m/z = 50-1000, 111 × 185 pixels) and the proposed preferred normalization method uses the median intensity of selected peaks, which were determined to be independent of the MALDI matrix. This was found to effectively compensate for a range of known limitations associated with the MALDI process and irregularities in MS image sampling routines. This new approach is relevant for processing of all MALDI MSI data sets, and thus likely to have impact in biomarker profiling, preclinical drug distribution studies, and studies addressing underlying molecular mechanisms of tissue pathology.
authors.affiliation: Biomolecular Medicine, Department of Surgery and Cancer, Faculty of Medicine, Imperial College London, Sir Alexander Fleming Building, South Kensington, London SW7 2AZ, United Kingdom.
authors.forename: Judith M
authors.initials: JM
authors.lastname: Fonville
authors.forename: Claire
authors.initials: C
authors.lastname: Carter
authors.forename: Olivier
authors.initials: O
authors.lastname: Cloarec
authors.forename: Jeremy K
authors.initials: JK
authors.lastname: Nicholson
authors.forename: John C
authors.initials: JC
authors.lastname: Lindon
authors.forename: Josephine
authors.initials: J
authors.lastname: Bunch
authors.forename: Elaine
authors.initials: E
authors.lastname: Holmes
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D001921:Brain / Q000473:pathology; D004353:Drug Evaluation, Preclinical; D007091:Image Processing, Computer-Assisted / Q000379:methods* / Q000592:standards; D025341:Principal Component Analysis; D051381:Rats; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D015415:Biomarkers