In response to the widespread concern about the increasing use of diagnostic imaging and the concern that a significant portion of the diagnostic imaging being performed is not helpful in patient management and therefore not necessary [1], the ACR has developed and continues to refine the ACR Appropriateness Criteria® [2] to assist referring physicians in ordering the most appropriate diagnostic imaging in given clinical situations. As with all clinical practice guidelines, referral guidelines for diagnostic imaging such as the ACR Appropriateness Criteria, should be evidence- based [3].