AJR: Prospective ECG triggering, not retrospective gating, may lower CT dose
For long-z-axis whole-chest 64-multidetector CT of emergency department patients with nonspecific chest pain, the use of prospective ECG triggering may result in substantially lower patient radiation doses and better coronary artery image quality than is achieved with retrospective ECG gating, according to a study in the June issue of the American Journal of Roentgenology.

William P. Shuman, MD, from the department of radiology at the University of Washington School of Medicine in Seattle, and colleagues consecutively registered emergency department patients with nonspecific low-to-moderate-risk chest pain underwent whole-chest CT with retrospective gating (41) or prospective triggering (31).

The researchers estimated and compared the effective patient radiation doses. Two independent reviewers scored the quality of images of the coronary arteries, and compared the scores by use of ordinal logistic regression.

According to the investigators, age, heart rate, body mass index and z-axis coverage were not statistically different between the two groups.

For retrospective gating, the mean effective radiation dose was 31.8 mSv; for prospective triggering, the mean effective radiation dose was 9.2 mSv (prospective triggering 71 percent), the authors wrote. They reported that two of 512 segments imaged with retrospective gating were nonevaluable (0.4 percent), and two of 394 segments imaged with prospective triggering were nonevaluable (0.5 percent).

Shuman and colleagues reported that the prospectively triggered images were 2.2 times as likely as retrospectively gated images to receive a high image quality score for each segment after adjustment for segment differences.

Based on their findings, the authors concluded that the "benefits of prospective triggering of whole-chest CT must be weighed against two current reported limitations: Imaging at heart rates greater than 75 beats/min is not recommended and information about cardiac function is not produced."