In a method and a computer for identifying a group of persons, from a number of persons, to whom at least one contrast agent has been applied during an examination which was carried out in an imaging system with which medical images of each of the number of persons were produced, existing examination data provided for each of the number of persons are used to determine to which of those persons the at least one contrast agent was applied. The persons to whom at least one contrast agent was applied during the examination are identified as a group of persons. For each person in the group, person-specific contrast agent data are determined that include at least identification information identifying the person to whom the at least one contrast agent was applied, and contrast agent information identifying the fact that the at least one contrast agent was applied. A designation of each person in the group of persons is stored with that person's corresponding person-specific contrast agent data in a register.