The interesting parts of the explanation:
…In 2004, more ED visits included imaging procedures than in 1995 (43% versus 38% of visits, respectively). During 1995-2004, the number of MRI or CAT scans nearly quadrupled, and the number of ultrasounds more than doubled. The overall number of ED visits increased by 14%.
I see this as more access to technology more than anything else. The rule today: if there’s a test for it, just get the test.