OBJECTIVES: (1) To describe a unique initiative to implement a standardized system of electronic decision support for ambulatory orders for hightech diagnostic imaging (HTDI) statewide, and (2) to evaluate the impact of a pilot version of that system, plus prior notification on the volume of such orders. STUDY DESIGN: Description of the initiative and analysis of aggregated claims data. METHODS: Claims data for HTDI studies were aggregated from the main health plans in the state from 2003 to 2010 by the regional quality improvement collaborative that also facilitated the pilot and subsequent initiative being implemented in 2011 throughout Minnesota. RESULTS: Aggregate ambulatory statewide orders for HTDI tests increased from 32 to 41 per 1000 members from 2003 to 2006 (9% per year) at which point the rate leveled off through 2010. This trajectory change was simultaneous with implementation of an electronic medical record-based decision-support system for all ambulatory HTDI orders from 45% of the physicians in the state, as well as a prior notification/authorization approach by payers for the rest of the HTDI orders. CONCLUSIONS: Although it is not possible to disentangle the effects of these separate approaches, the much greater physician acceptance of the decision support system has led payers to financially support the creation of a unique statewide implementation of a version of this system to replace prior notification/authorization approaches.