Living, untreated cells are very radiation-sensitive when exposed to soft X-rays, which creates problems for microscopy. Using increased soft X-ray fluence (and hence reduced exposure times) or fixation of cells with glutaraldehyde did not provide realistic solutions. However, rapid freezing of samples preserved structural integrity, increased radiation resistance (up to
or more) and enhanced the resolution and contrast of the image. Oxygen mapping was also achieved by sequential imaging of a frozen cell either side of the oxygen edge.