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 (DEFSSDE) 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 (DEFSSDE = 2.14 ± 0.20), LV (DEFSSDE = 1.78 ± 0.26), and RV (DEFSSDE = 1.31 ± 0.22). A linear relation is observed between the local CA concentrations and the dose increase in the heart; DEFSSDE = 0.07*I(mg/mL) + 0.80 (R2 = 0.8; p < 0.01). The DEFSSDE in the MT (DEFSSDE = 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.

The presence of contrast agent increases organ radiation dose in contrast-enhanced CT.

OBJECTIVES: Routine dosimetry calculations do not account for the presence of iodine in organs and tissues during CT acquisition. This study aims to investigate the impact of contrast agent (CA) on radiation dose. METHODS: First, relation between absorbed radiation dose and iodine concentrations was investigated using a cylindrical water phantom with iodine-saline dilution insertions. Subsequently, a retrospective study on abdominal dual-energy CT (DECT) patient data was performed to assess the increase of the local absorbed radiation dose compared to a non-contrast scan. Absorbed doses were estimated with Monte Carlo simulations using the individual CT voxel data of phantom and patients. Further, organ segmentations were performed to obtain the dose in liver, liver parenchyma, left kidney, right kidney, aorta, and spleen. RESULTS: In the phantom study, a linear relation was observed between the radiation dose normalized by computed tomography dose index (CTDI) and CA concentrations Iconc (mg/ml) for three tube voltages; [Formula: see text] = 0.14 × Iconc + 1.02, [Formula: see text] = 0.16 × Iconc + 1.21, [Formula: see text] = 0.16 × Iconc + 1.24, and for DECT acquisition; [Formula: see text] = 0.15 × Iconc + 1.09. Similarly, a linear relation was observed between the dose increase and the organ iodine contents (R2 = 0.86 and pvalue < 0.01) in the patient study. The relative doses increased in the liver (21 ± 5%), liver parenchyma (20 ± 5%), right kidney (37 ± 7%), left kidney (39 ± 7%), aorta (34 ± 6%) and spleen (26 ± 4%). In addition, the local dose distributions changed based on patient's anatomy and physiology. CONCLUSIONS: Compared to a non-contrast scan, the organ doses increase by 30% in contrast-enhanced abdominal CT. This study suggests considering CA in dosimetry calculations, epidemiological studies, and organ dose estimations while developing new CT protocols. KEY POINTS: • The presence of contrast media increases radiation absorption in CT, and this increase is related to the iodine content in the organs. • The increased radiation absorption due to contrast media can lead to an average 30% increase in absorbed organ dose. • Iodine should be considered in CT radiation safety studies.