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

Abstract

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 I_conc (mg/ml) for three tube voltages; [Formula: see text] = 0.14 × I_conc + 1.02, [Formula: see text] = 0.16 × I_conc + 1.21, [Formula: see text] = 0.16 × I_conc + 1.24, and for DECT acquisition; [Formula: see text] = 0.15 × I_conc + 1.09. Similarly, a linear relation was observed between the dose increase and the organ iodine contents (R² = 0.86 and p_value < 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.

Keywords: Humans; Iodine; Phantoms, Imaging; Radiation dosage; Tomography, X-ray Computed.

Fig. 1

a CT image of the experimental phantom, and (b) the reconstructed virtual phantom

Fig. 2

a CTDI_vol normalized dose versus iodine concentration in the ROI in syringes for 80, 120, 140 kVp, and DECT. b Dose in the ROI in the iodine syringes versus iodine concentration for virtual model and experimental phantom for DECT. Horizontal bars indicate uncertainty in the solutions and vertical bars indicate the uncertainty in the simulated dose (6.3%)

Fig. 3

D_SSDE in the presence and in the absence of CA in (a) liver, (b) liver parenchyma, (c) aorta, (d) right kidney, (e) left kidney, and (f) spleen in the 20 patients

Fig. 4

a A Pearson correlation test shows a linear agreement between %D_SSDE increase and iodine content in all the organs of the patient study. b D_SSDE in the segmented organs and iodine solutions with respect to their iodine content

Fig. 5

Parametric dose maps of three patients in the absence (left column) and presence (right column) of CA. a 23-year-old female administered to 370 mg I/ml (Iopromide), (b) 35-year-old female administered to 350 mg I/ml (Iomeprol), (c) 76-year-old male administered to 350 mg I/ml (Iomeprol), Abbreviations: I_adm, administered iodine