An x-ray gives a clear image of the internal morphology of the seed or fruit. The x-rays are generated using very low voltages (much lower than are used for most medical applications) and the method is safe with the appropriate precautions. However, because there is a very small risk of genetic damage, the sub-sample is either discarded or used for germination testing.
The seed samples to be x-rayed are laid out in Petri dishes or plastic grids with machine-punched holes set in a regular pattern, backed with waxed paper. The Millennium Seed Bank uses a Faxitron digital x-ray machine.