You don't need that many photons for a diagnostic imaging machine since they typically use hard x-rays (20-70 keV) that are very penetrating. Very soft x-rays/

You don't need that many photons for a diagnostic imaging machine since they typically use hard x-rays (20-70 keV) that are very penetrating. Very soft x-rays/EUV is amongst the hardest regions in which to work as the photons are just the right energy to be strongly absorbed by most materials, so as the article states, losses to the optics are significant, i.e. you lose ~half your photons in every mirror.