For cells, I think washing steps on slides should try to be avoided, once it was washed, the location of cells changed, though afterwards you can do immunofluorescence, to align images from MSI and images from fluorescence will be challenging and meaningless.

First, you may need to optimize the Matrix application and MSI condition to have a nice signal with low laser energy(less damage to the cell).

Second, you may rinse and immerse the sample with 100% Methanol to remove of matrix, meanwhile to fix the sample. Based on our experiences, that will be no significant movement for the cells, normally, like the laser shot(too strong laser power) will be observed as a result in the incomplete structure of the cell.