Background Contrast media agents are essential for computed tomography-based diagnoses. However, they can cause fatal adverse effects such as anaphylaxis in patients. Although it is rare, the chances of anaphylaxis increase with the number of examinations. Thus, we aimed to design a quality-improvement initiative to reduce patient risk to these agents. Methods We analysed computed tomography processes using contrast iodine in a tertiary-care academic hospital that performs approximately 14,000 computed tomography scans per year in Japan. We applied a combination of failure modes and effects analysis and cause–effect analysis to reduce the risk of patients developing allergic reactions to iodine-based contrast agents during computed tomography imaging. Results Our multidisciplinary team comprising seven professionals analysed the data and designed a 56-process flowchart of computed tomography imaging with iodine. We obtained 177 failure modes, of which 15 had a risk-probability number higher than 100. We identified the two riskiest processes and developed cause-and-effect diagrams for both: one was related to exchange of information between the radiation and hospital information system regarding the patient’s allergy, the other was due to education and structural deficiencies in observation following the exam. Conclusion The combined method of failure mode effect analysis and cause-and-effect analysis reveals high-risk processes and suggests measures to reduce these risks. Failure modes and effects analysis is not well-known in healthcare but has significant potential for improving patient safety. Our findings emphasise the importance of adopting new techniques to reduce patient risk and carry out best practices in radiology.