BACKGROUND: The use of diagnostic imaging with computed tomography (CT) has risen significantly, increasing cumulative life-time exposure to ionizing radiation for patients and raising concerns about increased cancer risk. Lowering the doses would reduce concerns about associated cancer risks. PURPOSE: To determine organizational leaders' perceptions of barriers to optimizing radiation dose in CT. MATERIALS AND METHODS: An observational study using semistructured interviews conducted with 26 organizational leaders from 19 health care systems in the United States, Europe, and Japan. Interviews focused on approaches the organizations used to optimize radiation dose and barriers encountered. Data were analyzed using a directed content analysis approach. RESULTS: Analysis identified six primary barriers to dose optimization: (1) resistance to change, (2) limited time and resources, (3) complex organizational structure, (4) lack of leadership support, (5) variations in CT equipment, and (6) variability in CT protocols. CONCLUSION: Barriers to optimizing CT dose across diverse health care organizations were described by organizational leaders tasked with implementing and improving CT imaging. They identified six consistent themes that reflected barriers to optimizing radiation dose at the organizational level. These barriers impeded efforts by health care organizations to optimize radiation doses to patients from CT imaging. Identifying barriers early in any improvement process is an important first step in making meaningful and sustained change.