Objective: To evaluate emergency department patients' knowledge of radiation exposure and subsequent risks from computed tomography (CT) and magnetic resonance imaging (MRI) scans.
Methods: This is a cross-sectional survey study of adult, English-speaking patients from June to August 2011 at 2 emergency departments--1 academic and 1 community-based--in the upper Midwest. The survey consisted of 2 sets of 3 questions evaluating patients' knowledge of radiation exposure from medical imaging and subsequent radiation-induced malignancies and was based on a previously published survey. The question sets paralleled each other, but one pertained to CT and the other to MRI. Questions in the survey ascertained patients' understanding of (1) the relative amount of radiation exposed from CT/MRI compared with a single chest x-ray; (2) the relative amount of radiation exposed from CT/MRI compared with a nuclear power plant accident; and (3) the possibility of radiation-induced malignancies from CT/MRl. Sociodemographic data also were gathered. The primary outcome measure was the proportion of correct answers to each survey question. Multiple logistic regression then was used to examine the relationship between the percentage correct for each question and sociodemographic variables, using odds ratios with 95% confidence intervals. P-values less than 0.05 were considered statistically significant.
Results: There were 500 participants in this study, 315 from the academic center and 185 from the community hospital. Overall, 14.1% (95% CI, 11.0%-17.2%) of participants understood the relative radiation exposure of a CT scan compared with a chest x-ray, while 22.8% (95% CI, 18.9%-26.7%) of respondents understood the lack of ionizing radiation use with MRI. At the same time, 25.6% (95% CI, 21.8%- 29.4%) believed that there was an increased risk of developing cancer from repeated abdominal CTs, while 55.6% (95% CI, 51.1%-60.1%) believed this to be true of abdominal MRI. Higher educational level and identification as a health care professional were associated with correct responses. However, even within these groups, a significant majority gave incorrect responses to all questions.
Conclusion: Patients did not demonstrate understanding of the degree of radiation exposure from CT scans and the subsequent risks associated with this exposure, namely radiation-induced malignancies. Moreover, they did not understand that MRI scans do not expose them to ionizing radiation and therefore lack this downstream effect. While patient preference is integral to patient-centered care, physicians should be aware of the significant lack of knowledge as it pertains to the selection of medical imaging tests.