The Relationship Between Climate Change and Emergency Medical Imaging Utilization

Academic Background

Climate change and related environmental exposures have significantly impacted human health, leading to increased demand for healthcare services. High-temperature exposure and poor air quality are closely associated with increased emergency department visits and hospital admissions. As global temperatures continue to rise, the frequency and intensity of heatwaves are expected to further increase. Climate change and its root causes contribute to air quality degradation in two ways: first, the burning of fossil fuels and other human activities release harmful pollutants into the atmosphere, resulting in greenhouse gas emissions; second, the impacts of climate change, such as rising ambient temperatures and more frequent wildfires, also increase air pollution, including fine particulate matter (PM2.5) and ground-level ozone. PM2.5, with an aerodynamic diameter of 2.5 micrometers or less, can be inhaled due to its small size, posing a significant threat to human health.

Radiology plays a central role in complex healthcare systems. On one hand, the delivery of medical imaging generates substantial greenhouse gas emissions, necessitating mitigation efforts to improve environmental sustainability. On the other hand, adaptation strategies are needed to address the current and future impacts of climate change. However, data on the relationship between climate-related environmental exposures and short-term imaging utilization remain scarce, hindering emergency planning in radiology departments. Therefore, this study aims to determine the association between short-term exposure to high ambient temperatures and particulate air pollution with emergency department medical imaging utilization.

Source of the Paper

This study was conducted by Dr. Kate Hanneman and her team from the Department of Medical Imaging at the University of Toronto, with contributions from scholars at the Harvard T.H. Chan School of Public Health, the University Health Network in Toronto, and other institutions. The paper was published in November 2024 in the journal Radiology, titled Increased Emergency Department Medical Imaging: Association with Short-Term Exposures to Ambient Heat and Particulate Air Pollution.

Study Design and Methods

Study Design

This retrospective time-stratified case-crossover study analyzed daily imaging utilization data from the emergency departments of four academic hospitals in downtown Toronto (Toronto General Hospital, Toronto Western Hospital, Mount Sinai Hospital, and St. Michael’s Hospital) between January 2013 and December 2022. The data were linked to local daily environmental data, including PM2.5 and ambient temperature. The case-crossover design controlled for all known and unknown individual and regional covariates (e.g., age, sex, race, and behavioral risk factors) to reduce confounding effects. The time-stratified approach further accounted for temporal trends in environmental exposures, allowing for simultaneous control of long-term trends, unmeasured time-varying confounders, and the influence of the day of the week.

Data Sources

Daily imaging utilization data were based on direct documentation of imaging tests requested and performed for patients in the emergency departments. Daily emergency department visit counts (patient volumes) were also recorded. Imaging utilization data were stratified by modality (CT, X-ray, ultrasound, and MRI) and organ system (chest, abdomen, neuroimaging, and musculoskeletal imaging). Environmental exposure data included daily mean ambient temperature and PM2.5 concentrations, sourced from publicly available historical direct measurement data.

Statistical Analysis

Conditional Poisson regression models were used to assess the association between daily imaging utilization and environmental exposures, controlling for the day of the week, month, and year. Results were expressed in terms of excess relative risk and excess absolute risk, based on incidence rate ratios (IRRs) and their 95% confidence intervals. Moving averages of mean daily PM2.5 and temperature were calculated to account for lagged exposure effects. Imaging utilization data were stratified by modality and organ system.

Results

Emergency Department Imaging Utilization

Between 2013 and 2022, a total of 1,666,420 imaging studies were performed across the four emergency departments, with an average of 428 studies per day. These included 790,619 X-rays, 508,950 CT scans, 187,289 ultrasound scans, and 15,953 MRI scans. The average daily emergency department visit count was 659. Imaging volumes and emergency department visits declined in 2020 but subsequently recovered.

Environmental Exposures

From 2013 to 2022, the mean daily ambient temperature was 9.0°C, and the mean daily PM2.5 concentration was 7.9 μg/m³. There were 602 heat exposure days (mean temperature >20°C) and 552 air pollution exposure days (mean PM2.5 >12 μg/m³) during the study period.

Heat Exposure and Imaging Utilization

Mean ambient temperature was significantly associated with imaging utilization on the day of exposure (lag 0) and the subsequent 1 to 4 days (lag 1-4), with the largest effect on the day of exposure. A 10°C increase in the 2-day moving average of mean temperature was associated with a 5.1% increase in overall imaging utilization (IRR=1.051). Heat exposure days (mean temperature >20°C) were associated with a 2.0% increase in same-day imaging utilization.

Air Pollution Exposure and Imaging Utilization

Mean PM2.5 concentration was significantly associated with imaging utilization on the day of exposure and the subsequent 1 to 5 days, with the largest effect on the day after exposure (lag 1). A 10 μg/m³ increase in the 3-day moving average of PM2.5 was associated with a 4.0% increase in overall imaging utilization (IRR=1.040). Air pollution exposure days (mean PM2.5 >12 μg/m³) were associated with a 2.4% increase in same-day imaging utilization.

Stratified Analysis by Modality and Organ System

Heat and air pollution exposure were significantly associated with increased utilization of X-ray and CT but not ultrasound or MRI. Stratified by organ system, heat and air pollution exposure were significantly associated with increased utilization of chest, neuroimaging, and musculoskeletal imaging, while air pollution exposure was also associated with increased utilization of abdominal imaging.

Discussion and Conclusion

Extreme climate exposures are closely linked to increased healthcare demand, including emergency department visits. However, data on the relationship between environmental exposures and imaging utilization remain limited. This time-stratified case-crossover study found that short-term exposure to high temperatures and PM2.5 was significantly associated with increased emergency department imaging utilization, particularly for X-ray and CT. Although individual daily effects are modest, the cumulative impact is substantial. These findings provide a foundation for future research to explore the long-term effects of climate change on medical imaging and to develop response strategies.

Highlights of the Study

1. Key Findings: Short-term exposure to high temperatures and particulate air pollution is significantly associated with increased utilization of X-ray and CT in emergency departments.
2. Methodological Innovation: The use of a time-stratified case-crossover design effectively controlled for confounding factors, providing reliable data on the relationship between environmental exposures and imaging utilization.
3. Practical Implications: The study results provide a basis for radiology departments to prepare for surges in imaging demand related to climate change, aiding in emergency planning.

Significance of the Study

This study is the first to systematically explore the relationship between short-term environmental exposures and emergency department imaging utilization, filling a gap in the field. The findings not only have significant scientific value but also provide data support for emergency planning in healthcare systems and the formulation of environmental policies. As climate change and air pollution issues intensify, these findings will help healthcare systems better address future challenges.