Monte Carlo dosimetry of iodine contrast objects in a small animal microCT

Small animal microcomputed tomography (microCT) studies with iodine-based contrast media are commonly used in preclinical research. While the use of contrast media improves the quality of the images, it can also result in an increase in the absorbed dose to organs with high concentration of the contrast agent, which might cause radiation damage to the animal. In this work we present the results of a Monte Carlo investigation of a microCT dosimetry study using mouse-sized cylindrical water phantoms with iodine contrast insets for different X-ray spectra (Mo and W targets, 30−80 kVp), iodine concentrations (0, 5, 10 and 15 mg mL−1) and contrast object sizes (3 and 10 mm diameter). Our results indicate an absorbed dose increase in the contrast-inset regions with respect to the absorbed dose distribution within a reference uniform water phantom. The calculated spatial absorbed dose distributions show large gradients due to beam hardening effects, and large absorbed dose enhancement as the mean energy of the beam and iodine concentration increase. We have found that absorbed doses in iodine contrast objects can increase by a factor of up to 12 for a realistic 80 kVp X-ray spectra and an iodine concentration of 15 mg mL−1.