Medicare has specific physician supervision requirements for diagnostic tests.  Each CPT® code that represents a diagnostic test is given a supervision indicator in the Medicare Fee Schedule.  From Chapter 15, of the Medicare Benefit Policy Manual describes these levels of supervision:

General Supervision - means the procedure is furnished under the physician’s overall
direction and control, but the physician’s presence is not required during the performance
of the procedure.  Under general supervision, the training of the nonphysician personnel
who actually performs the diagnostic procedure and the maintenance of the necessary
equipment and supplies are the continuing responsibility of the physician.
 
Direct Supervision - in the office setting means the physician must be present in the
office suite and immediately available to furnish assistance and direction throughout the
performance of the procedure.  It does not mean that the physician must be present in the
room when the procedure is performed.
 
Personal Supervision - means a physician must be in attendance in the room during the
performance of the procedure.

The complete list of indicators is in Section 80 of the manual, but the first ones are:

One of the following numerical levels is assigned to each CPT® or HCPCS code in the
Medicare Physician Fee Schedule Database:
 
0 Procedure is not a diagnostic test or procedure is a diagnostic test which is not
subject to the physician supervision policy.
1 Procedure must be performed under the general supervision of a physician.
2 Procedure must be performed under the direct supervision of a physician.
3 Procedure must be performed under the personal supervision of a physician.

A physician or coder can look up individual CPT® codes on the Medicare website at:

http://www.cms.hhs.gov/pfslookup/02_PFSsearch.asp?agree=yes&next=Accept

Or download the entire Medicare Fee Schedule at:

http://www.cms.hhs.gov/PhysicianFeeSched/