1. National Centre of Excellence in Mass Spectrometry Imaging, National Physical Laboratory, Hampton Road, Teddington TW11 0LW, U.K.
2. Department of Metabolism, Digestion and Reproduction, Imperial College London, South Kensington Campus, London SW7 2AZ, U.K.
3. Rosalind Franklin Institute, Harwell Campus, Didcot OX11 0FA, U.K.