The diagnostic reference levels (DRLs) for the 10 most common adult CT exams performed in the U.S. match those of many other countries, according to an article published online January 19 in the Journal of the American College of Radiology.
In a follow-up study, first author Priscilla Butler and colleagues compared U.S. DRLs previously reported by Kanal et al with DRLs from different countries, including Japan, Australia, Canada, several individual countries in the European Union, and the European Union as a whole. The researchers found the DRLs to be similar among these nations.
The U.S. DRLs never ranked as the highest for any of the primary adult CT exams studied, and the country's average CT dose index volume (CTDIvol) was lowest among all countries for noncontrast head CT exams.
![Axial images from unenhanced calcium score cardiac CT (left) and curved planar reformation images from CT angiography (right) show that higher long-term exposure to air pollution is associated with greater coronary artery calcium and more obstructive coronary artery disease (CAD). Top row: Images in a 68-year-old male patient with higher 10-year mean ambient air pollution exposure (7.9 μg/m3 for particulate matter measuring ≤2.5 μm in diameter [PM2.5] and 17.4 parts per billion [ppb] for NO2) with extensive CAD (coronary artery calcium score [CACS] >1,000 and obstructive CAD [≥70% diameter stenosis]). Bottom row: Images in a 57-year-old female patient with lower 10-year mean ambient air pollution exposure (6.3 μg/m3 for PM2.5 and 4.6 ppb for NO2) with no CAD (CACS = 0 and no obstructive stenosis).](https://img.auntminnie.com/mindful/smg/workspaces/default/uploads/2026/06/hanneman.r6SMLzkezo.png?auto=format%2Ccompress&dpr=2&fit=crop&h=167&q=70&w=250)
