Fig. 2.

The workflow is shown here in chronological order. First, mice are fed 8% deuterated water over a course of different time periods to increase their deuterium concentration in the lipids within their bodies. Then the mice are euthanized, their organs are sliced to 50 μm thick, and the slices are thaw mounted on glass slides. The DESI source is rastered over each tissue slice over a period of approximately 2 h. The mass spectral data files are converted initially from .d files to a MATLAB data cube. Individual m/z peaks are selected to see the spatial and regioselective nature of individual lipids. Isotope ratio images reveal differing lipid turnover rates within the organ structure for individual lipids, which are measured using incorporation curves.