Radiology: Volume scans during CCTA can reduce dose by 91%

While coronary CT angiography (CCTA) can assist in the diagnosis of coronary artery disease (CAD), the radiation dose exposure  during an exam has been a problem. Using volume scans rather than helical scans has the potential to reduce dose by 91 percent, a study published in the March issue of Radiology found.

Andrew J. Einstein, MD, PhD, of Columbia University Medical Center in New York City, and colleagues compared the radiation dose associated with the use of a 320-slice volume scanner and a 64-slice helical scanner.

The traditional 64-slice scanners acquire data from the “most cranial to the most caudal portion of the heart,” the authors wrote. In contrast, “because of the brief duration during which the x-ray tube needs to be left on (as little as 0.35 seconds, i.e., a full gantry rotation), volume scanning offers the theoretic possibility of markedly decreasing radiation dose in comparison with traditional helical scanning."

Einstein et al compared radiation exposure of six different scan modes during CCTA with a 64-slice scanner and the Toshiba America Medical Systems Aquilion One 320-slice CT scanner (volume scanning). For imaging purposes, researchers positioned metal oxide-semiconductor field-effect transistor (MOSFET) detectors in anthropomorphic phantoms simulating both the male and female bodies.

According to the authors, “For volume scanning, the middle 280-detector rows were used, attaining 14 cm craniocaudal coverage, which is greater than the median scan length used in practice and usually sufficient for cardiac scanning."

Results showed that with use of the 320-slice CT volume scanner, effective dose was reduced by 91 percent, from 35.4 mSv -- without the use of ECG-synchronized tube current modulation -- to 4.4 mSv with the use of 100 kVp volume scanning during simulated CCTA. 

“64-section helical CCTA has been associated with some of the highest radiation doses of any diagnostic radiologic procedure and, specifically, higher radiation doses than those from any generation of scanners preceding it,” said the authors. “It is widely recognized that improved scanners, affording comparable or improved diagnostic performance at lower cost in terms of radiation exposure, are needed.”

In addition, researchers found that during a simulated CCTA helical scan via a 64-detector row scanner, the male and female heart absorbed a dose of 113.2 mGy and 96.1 mGy, respectively. 

In contrast, the hearts of male and female phantoms that underwent CCTA via the 320-slice scanner at 100 kVp  at the optimized exposure time absorbed 15.8 and 13.5 mGy, respectively.

“CCTA can be performed by using volume scanning to decrease radiation dose to patients with no meaningful change in image noise, with effective doses of 4.4 mSv at 100 kVp and 5.8 mSv at 120 kVp,” the authors said.

Einstein said that careful attention must be paid to using the correct scan mode in order to obtain diagnostic images at a low dose.

“Given volume scanning’s potential for low radiation dose, further studies evaluating its diagnostic accuracy, efficacy and impact on patient-important outcomes are needed,” the authors concluded.