It all comes down to money, although I find this statement amusing:

The most cutting comment at Tuesday’s hearing came from Rep. Charles Norwood, R-Ga., who said the imaging reimbursement cuts in the Deficit Reduction Act should be eliminated: He said the representatives from the Medicare Payment Advisory Commission, or MedPAC, and the Centers for Medicare and Medicaid Services, or CMS, who testified Tuesday “have no idea what they are talking about,” when they asserted medical imaging services have been overused.

There is clear overuse of imaging services. The reasons for this are legion, but can be boiled down to defensive tests and the lack of disincentive to test.