The impact of iodine contrast agent on radiation dose of heart and blood: a comparison between coronary CT angiography and cardiac calcium scoring CT

Background Iodine contrast agent (CA) is widely used in cardiac computed tomography (CT). The CA can increase the organ radiation doses due to the photoelectric effect. Purpose To investigate the impact of CA on radiation dose in cardiac CT by comparing the radiation dose between contrast coronary CT angiography (CCTA) and non-contrast calcium scoring CT (CSCT). Material and Methods Radiation doses were computationally calculated for 30 individual patients who received CSCT and CCTA in the same exam session. The geometry and acquisition parameters were modeled in the simulations based on individual patient CT images and acquisitions. Doses in the presence and absence of CA were obtained in the aorta, left ventricle (LV), right ventricle (RV), and myocardial tissue (MT). The dose values were normalized by size-specific dose estimate (SSDE). The dose enhancement factors (DEF SSDE ) were calculated as the ratio of doses in CCTA over doses in CSCT. Results Compared to the CSCT scans, doses increase in the CCTA scans in the aorta (DEF SSDE = 2.14 ± 0.20), LV (DEF SSDE = 1.78 ± 0.26), and RV (DEF SSDE = 1.31 ± 0.22). A linear relation is observed between the local CA concentrations and the dose increase in the heart; DEF SSDE = 0.07*I(mg/mL) + 0.80 (R 2 = 0.8; p < 0.01). The DEF SSDE in the MT (DEF SSDE = 0.96 ± 0.08) showed no noticeable impact of CA on the dose in this tissue. In addition, patient variability in the dose distributions was observed. Conclusion A linear causal relation exists between local CA concentration and increase in radiation dose in cardiac CT. For the same CT exposure, dose to the heart is on average 55% higher in contrast cardiac CT.