Report from NASCI: Low-dose dual-source coronary CTA technique can be reproduced on any scanner

Researchers using a dual-source CT scanner have developed a method to reduce radiation dose by up to 30%. They say the strategy is not vendor specific and can be used on any scanner, according to a study presented at the 2007 North American Society for Cardiac Imaging meeting.

Dr. Pal Suranyi, a first-year resident at the Medical University of South Carolina, cited a study published in the July 18 American Medical Association that indicated that routine cardiac CT angiography scans put younger patients, particularly women, at a high lifetime risk of developing cancer.

This led Suranyi and colleagues to explore the utility of using a calcium scoring scan preceding CTA to identify the optimal cardiac phase for reconstruction. They also sought to assess the potential effect on radiation dose if the full dose ECG-pulsing window had only been applied during this pre-selected cardiac phase.

Researchers retrospectively reviewed raw data from 30 patients who underwent coronary calcium scoring and dual-source coronary CTA. Two observers identified in consensus the phase with the least cardiac motion on coronary calcium scoring. They did the same using the CTA data, but in a blinded fashion.

They calculated the potential radiation dose savings by assuming the use of full tube current only during the phase of least cardiac motion as determined by the calcium scoring scan.

The standard CTA scan involved full radiation dose applied between 35% and 75% of the R-R interval for heart rates faster than 65 bpm (n = 14) and between 55% and 75% of the R-R interval for heart rates under 65 bpm (n = 16).

Investigators calculated the mean CT dose index volume values for CTA to be 57.5 mGy, while the mean dose for the narrow ECG-pulsing window was significantly lower at 40.8 mGy, a dose savings of 16.7 mGy, or 29%.

The cardiac motion phase determined at coronary calcium scoring coincided with that of coronary CTA scanning in more than 93% of the cases. The optimal cardiac motion phases for pre- and postcontrast scans did not match in two patients. However, their coronary calcium scoring tests were diagnostic and their contrast-enhanced CTA scans showed even better image quality, Suranyi said.

"Coronary calcium scoring scans can reliably predict the phase of least cardiac motion at dual-source CT angiography and guide the positioning of the ECG-pulsing window," he said. "Radiation exposure could be reduced by applying ECG-pulsing only during the most suitable cardiac phase, determined precontrast."

There are caveats, however. As the findings suggest, the postcontrast phase may not always match the precontrast estimates. A potential solution is to adjust tube current to widen the potential window of reconstruction, Suranyi said.

"We are so excited about these results that we actually started doing this in practice on the patients," he said.

The paper won honorable mention in the American Heart Association Young Investigator awards.

For more information from the Diagnostic Imaging archives:

Dose reduction tips fit 64-slice, dual-source CT scanners

Dose-saving strategies play catch up to greater CT use

Cardiac CTA reveals significant incidental disease beyond the heart

Dual-source CT excels in segment-by-segment diagnosis of coronary artery disease