The Effect of Contrast Material on Radiation Dose at CT: Part II. A Systematic Evaluation across 58 Patient Models

Abstract

Purpose To estimate the radiation dose as a result of contrast medium administration in a typical abdominal computed tomographic (CT) examination across a library of contrast material-enhanced computational patient models. Materials and Methods In part II of this study, first, the technique described in part I of this study was applied to enhance the extended cardiac-torso models with patient-specific iodine-time profiles reflecting the administration of contrast material. Second, the patient models were deployed to assess the patient-specific organ dose as a function of time in a typical abdominal CT examination using Monte Carlo simulation. In this hypothesis-generating study, organ dose refers to the total energy deposited in the unit mass of the tissue inclusive of iodine. Third, a study was performed as a strategy to anticipate the biologically relevant dose (absorbed dose to tissue) in highly perfused organs such as the liver and kidney. The time-varying organ-dose increment values relative to those for unenhanced CT examinations were reported. Results The results from the patient models subjected to the injection protocol indicated up to a total 53%, 30%, 35%, 54%, 27%, 18%, 17%, and 24% increase in radiation dose delivered to the heart, spleen, liver, kidneys, stomach, colon, small intestine, and pancreas, respectively. The biologically relevant dose increase with respect to the dose at an unenhanced CT examination was in the range of 0%-18% increase for the liver and 27% for the kidney across 58 patient models. Conclusion The administration of contrast medium increases the total radiation dose. However, radiation dose, while relevant to be included in estimating the risk associated with contrast-enhanced CT, may still not fully characterize the total biologic effects. Therefore, given the fact that many CT diagnostic decisions would be impossible without the use of iodine, this study suggests the need to consider the effect of iodinated contrast material on the organ doses to patients undergoing CT studies when designing CT protocols. ^© RSNA, 2017 Online supplemental material is available for this article.

Figure 1:

Graph shows intravenous contrast medium injection function, which was a uniphasic injection function of 125 mL of contrast agent (320 mg I/mL) at 5 mL/sec.

Figure 2:

Graph shows tissue contribution of radiation dose increase due to the presence of iodine in different components of a vessels network. The distribution was approximated by the probability of the secondary electrons generated inside the iodine being deposited outside the vessel by using a Monte Carlo simulation of a simplified organ model.

Figure 3:

Graphs show simulated iodine concentration curves for different organs (spleen, liver, kidneys, stomach, small intestine, colon, and pancreas) across a library of XCAT models for a contrast-enhanced abdominal CT examination.

Figure 4:

Graphs show results of Monte Carlo simulation of the organ dose to the heart, spleen, liver, kidneys, stomach, colon, small intestine, and pancreas as a function of time across the XCAT models for a contrast-enhanced abdominal CT examination. The organ doses are normalized by CTDI_vol.

Figure 5:

Graphs show distribution of the maximum dose increment (as a percentage) in the heart, spleen, liver, kidney, stomach, colon, small intestine, and pancreas due to the administration of contrast medium across the XCAT models.

Figure 6:

Graphs show potential range of radiation dose alteration for, A, liver and, B, kidney. The impact of iodine on radiation dose increase varies as the iodinated blood circulates through the vascular system. A normal distribution was assumed for the impact of iodine on dose increase, as the blood enters the arteries and flows through the capillaries in which it experiences the maximum proximity to the tissue cells and washes out subsequently through the veins.