imaging mass spectrometry matrix-assisted laser desorption-ionisation imaging mass spectrometry matrix-assisted laser desorption/ionization imaging mass spectroscopy CHMO:0000054 MALDI-MS imaging MALDI-IMS The collection of spatially resolved mass spectra of a sample during microscopy where a pulse laser is used to produce both ionisation and vapourisation and the sample is held in a matrix (such as dihydrobenzoic acid) to protect it from direct laser illumination and to separate the sample molecules. The spectra are used to visualise the spatial distribution of (typically) biomolecules by their molecular masses.