Large dose reductions possible in calcium scoring

Dose exposures during CT calcium scoring procedures can be reduced substantially without sacrificing scoring accuracy, according to studies presented Saturday by German and U.S. researchers.

Using both phantom and human subjects and three separate scoring strategies, the researchers found that the higher noise produced at lower dose levels had an insignificant impact on scoring accuracy for smaller subjects. Accuracy declined at lower doses among larger subjects with two scoring methods - Agatston and calcium volume - but was within acceptable limits at low dose levels and for all body types using the calcium mass scoring method.

A third study presented Saturday found that Agatston and volumetric calcium scores tended to be highly dependent on reconstruction intervals. The research, conducted at the University of Essen, Germany, concluded that accurate quantification seems to require analysis of reconstructions covering the entire cardiac cycle.

The dose studies were undertaken at the University of Aachen in Germany and Brigham and Women's Hospital in Boston, with support from Siemens. The phantom study examined various kV and mA settings in small, medium, and large phantoms. Using both 120 kVp and 80 kVp settings, all three scoring methods were found to be within 10% of higher dose settings in the smaller phantom, allowing a reduction of dose exposure from 2 mSv to 0.6 mSv at 120 kVp and to 0.2 mSv at 80 kVp. Low-dose performance declined for the larger phantoms using the other two scoring methods, but remained consistently good with calcium mass scoring.

In a study of 20 human subjects, the researchers correlated body habitus with dose levels. A computer program was used to add noise to the calcium images, stimulating lower dose levels. As with the phantom studies, the calcium mass index was most robust at lower dose levels for both large and small bodies. The mean body mass index was 29.72. With decreasing radiation dose, the Agatston and calcium volume scores generally increased, the researchers said.