Actually at least in the USA there are geographic portions of the USA where radon gases via what the house foundation was built on are more of a threat than tracked medical imaging as obviously if the house is not tested than we have no way of determining whether radon gas is a threat.

EPA map of radon gas zones, Zone 3 is the high risk level: http://www.epa.gov/radon/pdfs/zonemapcolor.pdf

and no sarcastic comments about it also being the bible belt please..:)