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

INTRODUCTION

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.

METHODS

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.

RESULTS

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).