UnitedHealthCare recently published this notification:

Radiology Notification Program: Process for Rendering Providers when Services are Ordered by Non-Participating Physicians

For claims with dates of service September 7, 2010 and thereafter, UHC requires rendering providers to submit notification for services ordered by non-participating physicians when no notification is on file, in accordance with the Radiology Notification protocol for commercial benefit plans set forth in the UnitedHealthcare Physician, Health Care Professional, Facility and Ancillary Provider Administrative Guide. If the rendering provider does not provide notification for services ordered by a non-participating physician, the rendering provider’s claim will be denied for failure to provide notification and the member cannot be billed. Furthermore, UnitedHealthcare will uphold on appeal any claims denied for failure to provide notification that are appealed on the basis that the ordering physician is a non-participating provider.

If the ordering physician is a participating provider, the rendering provider should not provide notification to UnitedHealthcare. This is the responsibility of the participating ordering physician.

For additional information, here is a link to their web site.