Presence of contrast agent has an impact on the absorbed radiation dose:
The absorbed dose (D) in the region of interest of syringes rises with the increase in the iodine concentration (Fig.
2).
In the clinical range of iodine concentrations (< 20 mg/ml),
the increase in dose can be accurately described by a linear function; however,
the trend deviates from the linear behavior as the iodine concentration increases.
For the clinical range of iodine concentrations following equations were obtained; for 80 kVp; D = 0.35 × I (mg/ml) + 2.66,
r2=0.99,
for 120 kVp; D = 1.27 × I (mg/ml) + 9.83,
r2=0.99 and for 140 kVp; 1.82 × I (mg/ml) + 15.05,
r2=0.99.
Obtained simulated doses from experimental and virtual aorta models are not statistically different:
Fig.
3 shows the simulation results for 120 kVp and 120 mAs for both experimental and virtual aorta models.
Dose values obtained from virtual and experimental aorta models are in good agreement and not statistically different (p = 0.75,
a = 0.05),
which can demonstrate the reliability of our simulations.
The amount of iodine concentration has an effect on spatial dose uniformity:
Fig.
4 shows the dose profiles in virtual images across the phantom’s diameter for 5 different concentrations of 2,
9.7,
18.8,
27.4,
and 35.8 mg/ml.
As it is seen,
the dose profiles show a cupping-shaped dose distribution in the aorta (iodine syringe) and to a lower extent also in the surrounding tissue (water). The cupping shape in the dose profile of the iodine syringe is much more pronounced for high iodine concentrations,
which is likely due to the high beam absorption at the periphery of the tube,
and consequently a lower beam intensity in the center of the tube. This can explain the non-linear increase of dose versus iodine concentration for the high concentrations.
Dose enhancement factors (DEFs) in the clinical range of iodine concentrations:
Compared to a non-enhanced scan,
clinically relevant iodine mixtures of 5 mg/ml (132 HU),
10 mg/ml (243 HU),
15 mg/ml (353 HU),
and 20 mg/ml (463 HU) in the aorta,
increases the dose respectively by factors of 1.65±0.15,
2.29±0.20,
2.94±0.26,
and 3.59±0.32 for 120 kVp.
Fig.
5 shows the dose enhancement factors in the clinical range of iodine concentrations (< 20 mg/ml).
Results of statistical test on the DEFs showed that DEFs of 80 - 120 kVp (P = 0.92,
a = 0.05),
80 - 140 kVp (P = 0.81,
a = 0.05),
and 120 – 140 kVp (P = 0.75,
a = 0.05) are not statistically different.