Radiation in cardiac CT: predictors of higher dose and its reduction over time

Cardiac CT provides noninvasive information on cardiac anatomy, particularly in coronary artery disease. However, exposure to radiation has been identified as a limitation of this exam. The aim of this study was to evaluate variations in radiation dose over time and to identify variables associated with use of higher radiation doses.

A prospective registry of 643 patients who underwent 64-slice dual source cardiac CT scan (Dual source CT--Somaton Definition, Siemens-Medical) during 2007 and 2008 was analyzed.

The sample was divided into quartiles according to the chronological order of the exams. There was a progressive reduction in median radiation dose in the quartiles analyzed (Q1: 8.9 [5.9-14.1], Q2: 6.6 [5.5-10.7], Q3: 6.4 [5.3-8.7], Q4: 6.1 [5.2-7.9] mSv), significant when the first quartile was compared with the others (p < 0.05). Along with this reduction, was a progressive increase in the use of a tube voltage of 100 kV (p < 0.001). Predictors of a higher radiation dose were higher body mass index, previous cardiac surgery, atrial fibrillation during acquisition, longer acquisition time and use of a tube voltage of 120 kV. When one or more of these variables were present (one third of the population), the radiation dose was significant higher (12.1 [9.5-14.8] vs. 5.7 [5.0-6.7] mSv, p < 0.001).