How do concentration and dosage of the contrast agent affect the signal change in perfusion-weighted magnetic resonance imaging? A computer simulation.

In this study we investigated the effect of varying both concentration and dosage of an intravenously administered MR contrast agent on the concentration-time curve in brain tissue. Aside from injection time and injection rate, our model considers the distribution of transit-time between injection site and brain but it is independent from pulse rate, heart volume or other circulation parameters. The width of the transit-time distribution and the concentration-time course in the brain were computed according to indicator dilution theory. We found that increasing the dosage of the administered contrast agent raises the maximum concentration of the agent in the brain, particularly if the injection time is short. Increasing the concentration of the agent (at fixed dosage and injection rate) also increases maximum concentration in the brain capillaries, particularly if the injection time is long. This increase, however, is less than that achieved by raising the dosage.