1. A method for generating a mass spectral image of a tissue sample, comprising steps of: establishing a tissue imaging border based on operator input; performing a first scan at relatively low spatial resolution by irradiating a first set of target regions that span the area bound by the tissue imaging border and acquiring mass spectral data at each target region of the first set of target regions; analyzing the mass spectral data from the first scan using a processing unit by calculating spatial gradients in the values of the mass spectral data to identify at least one area of interest within the tissue sample having a relatively highly spatially differentiated abundance of ions having a selected mass-to-charge ratio; performing a second scan at relatively high spatial resolution by irradiating a second set of target regions located within the at least one identified area of interest and acquiring mass spectral data at each target region of the second set of target regions; combining the mass spectral data from the first and second scans; and using the combined mass spectral data, displaying an image representing the spatial distribution across the tissue sample of at least one ion having a selected mass-to-charge ratio, wherein the displayed image is highly spatially resolved within a region corresponding to the at least one identified area of interest relative to regions corresponding to areas of the tissue lying outside of the at least one identified area of interest.