CHICAGO—Cardiac CT is a dose reduction success story, according to a presentation Nov. 25 at the annual meeting of the Radiological Society of North America (RSNA).

James P. Earls, MD, of Fairfax Radiological Consultants in Fairfax, Va., explained that as cardiac CT technology has advanced, the amount of dose has increased. He cited the PROECTION I study, published in 2007, which recorded a mean dose of 12 mSv for cardiac CT angiography exams. The researchers also concluded that the dose range was too variable among various scanners and that dose reduction protocols were underutilized.

Dose reduction is a multi-pronged strategy. “Putting all of the pieces together can reduce dose 90 percent,” Earls said. Standard dose reduction tools include:

• ECG dose modulation with retrospective gating, which allows for a 30 to 50 percent dose reduction;
• Weight adjusted mA;
• Limiting z-axis coverage to required cardiac structures; and
• Lowering kVp from 120 to 100 kVP.

According to Earls, 100 kVp has emerged as the new standard for cardiac CT studies for most patients, and reduces dose 30 to 40 percent, while maintaining image quality. For some thinner patients, 80 kVp studies can be performed, which reduces dose 60 to 70 percent compared with 120 kVp exams.

Recently introduced technology has delivered additional dose reductions. Studies of prospective triggering show it provides a 70 to 80 percent dose reduction. Iterative reconstruction reduces image noise to improve the signal-to-noise ratio and enable reduced dose exams.

Fairfax Radiological Consultants has utilized these techniques to drop its cardiac CT dose from a mean high of 20mSv to a current average in the mid 1 mSv range, according to Earls.

For more about CT dose reduction, please read “Image Gently in action: San Diego practice cuts dose up to 90%."