Slight detour

I am still planning to follow up my previous post on environmental negligence and will write a post about CFCs in the near future. However, I saw this YouTube video recently and found it harrowing. The British government had known about the consequences of acute radiation poisoning, but chose to perform these tests anyhow. In addition to the lives irreversibly changed, there is also the remarkable fact that these people were able to see live images of bones and blood vessels with their eyes. Does anyone have a good explanation as to how this would even be possible?