Date of Award

January 2012

Document Type


Degree Name

Medical Doctor (MD)



First Advisor

Howard P. Forman

Subject Area(s)

Medicine, Medical imaging and radiology, Public health


Computed tomography (CT) utilization in Emergency Departments (EDs) has increased dramatically over the last decade, sparking concerns about costs and radiation-induced malignancies. A cross-border comparison of trends could enhance our understanding of factors underlying the increase.

We performed a retrospective population-based study of ED visits from 2003-2008 using a systematic survey in the US (NHAMCS) and administrative databases in Ontario, Canada. Sampled visits in the US were weighted to produce national estimates. CT utilization rates were determined over time and by patient and visit characteristics. Rates were also compared for four pre-specified clinical conditions for which CT is commonly used: headache, abdominal pain, chest pain/shortness of breath, and "complex abdominal pain".

The overall CT rate was 11.4% (95%CI 10.8-12.0) in the US versus 5.9% (95%CI 5.9-5.9) in Ontario (p<0.0001). The rate for children was 4.7% (95%CI 4.3-5.1) in the US versus 1.4% (95%CI 1.4-1.4) in Ontario (p<0.0001). Rates increased faster from 2003-2008 in the US (OR 2.00, 95%CI 1.81-2.21) than Ontario (OR 1.69, 95%CI 1.68-1.70) (p=0.001). US-Ontario differences in CT rates were significant for patients seen for headache, abdominal pain, and chest pain/shortness of breath. Rates for complex abdominal pain were indistinguishable: 45.8% in the US (95%CI 39.9-51.7) versus 44.7% (95%CI 44.4-45.0) in Ontario (p=0.7).

Overall US ED CT rates were nearly double those in Ontario, and for children the rates were more than triple. Rates of imaging increased in both regions, but faster in the US. However, cross-jurisdiction CT utilization was similar when clinical indications were more clear-cut. It is likely that factors besides clinical appropriateness are important drivers of CT rates.