Tech upgrade pushes sub-mSv CCTA envelope

The median radiation dose among a cohort of 107 patients undergoing coronary CT angiography (CCTA) fell to 0.93 mSv using a second-generation, 320-slice system, according to a study published online Jan. 22 in Radiology.

As the drumbeat to curb radiation exposure has amplified, pressure on providers and manufacturers has mounted. One second-generation, 320-slice CT system incorporates multiple advances designed to reduce exposure: a gantry rotation time of 275 ms, wide volume coverage, iterative reconstruction, automatic exposure control and a larger x-ray power generator.

Marcus Y. Chen, MD, from the advanced cardiovascular imaging laboratory at the National Institutes of Health in Bethesda, Md., and colleagues devised a study to compare radiation exposure and image quality of this second-generation system with a first-generation, 320-slice scanner.

The researchers enrolled 107 consecutive patients undergoing CCTA from July to October 2012 with the scanner and compared estimated radiation exposure and image quality with those from 100 consecutive patients who underwent CCTA with a first-generation system.

The mean patient age of the 107 patients was 55.4 years; 53.3 percent were men. Mean body mass index was 27.3 kg/m2, and 71 patients were overweight, obese or morbidly obese.

Radiation dose was estimated by multiplying the dose-length product by a conversion factor of 0.014 mSv/mGy, and size-specific dose estimates were obtained on the basis of individual patient diameter measured on scout images.

Two cardiovascular imaging physicians rated image quality in four categories (coronary motion artifact, image noise, contrast material enhancement and fine detail) on a four-point scale. A score of 4 corresponded to excellent with no significant artifacts; and 1 signified unevaluable.

A total of 97 of the 107 patients were imaged at 100 kV tube potential; 104 patients underwent CT with a single-volume acquisition; and prospective gating was used on 106 patients.

Chen and colleagues reported estimated median effective dose at 0.93 mSv for all 107 patients. “[T]his represents at least a 75 percent reduction compared with previous reports from the first-generation, 320-detector row CT scanner. This level of dose exposure was achieved by means of a combination of B-blockers to help slow the resting heart rate and carefully controlling cranial-caudal scan range.”

Overall dose was less than 0.5 mSv in 23 patients, less than 1 mSv in 58 patients and less than 4 mSv in 103 patients.

The two readers agreed that all 107 CT exams were of diagnostic quality, and most exams achieved a score of 4 in all categories.

“This technology could further facilitate CT stress perfusion, contrast attenuation gradients across atherosclerotic lesions and noninvasive fractional flow reserve computed from coronary CT angiography,” concluded Chen and colleagues.