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Background
A core facet of radiology training involves gaining familiarity of relative radiation dosages from common radiologic procedures. In doing so, radiologists gain the foundations essential for counselling patients on the benefits and potential risks that may arise from undergoing imaging studies. In the publicly available resources and much of the available literature, radiation dose from medical procedures is compared to background radiation and exposure from natural sources.

Educational Goals / Teaching Points
To review how radiation exposure is expressed (i.e., effective dose in rem/Sieverts [Sv]) and how these values are used in determining the relative risks imposed by different imaging studies when compared to common encounters humans may be exposed to throughout their lives. To do this, we convert the radiation dose from common X-Ray, computed tomography (CT), and fluoroscopic examinations to the expected change in life expectancy related to increased cancer risk from radiation (i.e., stochastic effects). We used a range of conversion factors provided by the Nuclear Regulatory Commission (NRC), centered on an expected loss of 1.5 days of life expectancy for every 1 rem (10 mSv) of radiation exposure. We then compare these expected values to similar values from exposures commonly encountered on a day-to-day basis. Rough estimates are based under the presumption of a linear, no threshold risk of cancer from radiation exposure.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Head CT (1.6 mSv) has expected loss of life expectancy of 1.5 hours. A CT abdomen pelvis is estimated to impart a loss of life expectancy of approximately 18.5 hours. Chest radiograph has loss of life expectancy of 15 minutes. Overall, medical imaging has slightly higher than expected loss of life expectancy than known risks from everyday activities. Yearly background radiation (approximately 3mSv) equates to approximately 8 hours of loss of life per year. For comparison, loss of life expectancy from eating a hot dog: 36 minutes; 1 hour of driving: 20 minutes; smoking 1 cigarette: 5-11 minutes.

Conclusion
In almost all circumstances where ionizing radiation is used from medical imaging, the benefits of diagnosis will outweigh the risks. However, radiation exposure needs to be considered as a meaning impact on long-term outcomes. Conversion of dosages to this easily understandable scale facilitates understanding and counseling surrounding the use of medical imaging.