The environmental cost of unwarranted variation in the use of magnetic resonance imaging and computed tomography scans.

Background: Pollution is a major threat to global health, and there is growing interest on strategies to reduce emissions caused by health care systems. Unwarranted clinical variation, i.e. variation in the utilization of health services unexplained by differences in patient illness or preferences, may be an avoidable source of CO2 when related to overuse. Our objective was to evaluate the CO2 emissions attributable to unwarranted variation in the use of MRI and CT scans among countries of the G20-area.

Methods: We selected seven countries of the G20-area with available data on the use of CT and MRI scans from the organization for Economic Co-operation and Development repository. Each nation's annual electric energy expenditure per 1000 inhabitants for such exams (T-En) was calculated and compared with the median and lowest value. Based on such differences we estimated the national energy and corresponding tons of CO2 that could be potentially avoided each year.

Results: With available data we found a significant variation in T-En (median value 1782 kWh, range 1200-3079 kWh) and estimated a significant amount of potentially avoidable emissions each year (range 2046-175120 tons of CO2). In practical terms such emissions would need, in the case of Germany, 71900 and 104210 acres of forest to be cleared from the atmosphere, which is 1.2 and 1.7 times the size of the largest German forest (Bavarian National Forest).

Conclusion: Among countries with a similar rate of development, unwarranted clinical variation in the use of MRI and CT scan causes significant emissions of CO2.