The x-ray cars are the ones that some of the railways are contracting from Sperry, which are actually able to detect some defects within the rail, whereas the other one is what we call a track geometry car, which mostly measures the geometry of the track, and the railway owns these cars. There are companies that also provide leases on those cars, but CN and CP own a few of these cars.
On December 11th, 2007. See this statement in context.