you should be fine going through if its so infrequent.
But i did read up some time ago that there was a some complaints from people in the US who are very frequent flyers that they were suffering higher than normal incidences of equipment failure.
This may have been down to useage of older x-ray machines which would have pumped out a lot more radiation or more mechanical abuse by groundstaff throwing bags about.
(the choice is light fingered or heavy handed ground staff, thiefrow is infamous for it)
oh only exception will be the big X-RAY machines they use to see inside trucks and the like, those ones WILL be able to see straight through the block of a big engine and probably through most stainless steel exhaust boxes.
try not to be left in the vehicle if your going through one of those, the long term risks are unknown, and probably not pleasant
(i'd rather a intimate pat down by an ugly goon than go through one of those again - ever).