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Imaging time-of-flight-secondary ion mass spectrometry (TOF-SIMS) was used to analyse the lateral distributions of lipids on the surface of freeze-dried mouse brain sections. Tissue sections (14μm thick) were prepared by cryosectioning, placed on glass or Si substrates and desalinated by submersion in NH₃HCOO solution. Immediately prior to analysis, the samples were freeze-dried by thawing the sample in vacuum. TOF-SIMS analysis was carried out using 25keV Au₃⁺ or Bi₃⁺ primary ions, always keeping the accumulated ion dose below 4×10¹²ions/cm². Positive and negative ion images over the entire mouse brain section and of analysis areas down to 100μm×100μm show characteristic distributions of various lipids. The signals from cholesterol and sulfatides are primarily located to white matter regions, while the phosphocholine and phosphatidylinositol signals are strongest in grey matter regions. By …