Bolus dynamics: theoretical and experimental aspects.

This paper analyses the arterial enhancement produced by short intravenous boluses of iodinated contrast medium, with particular attention to the differences between various types of contrast media. A theoretical discussion is presented, followed by a small experimental study. The characteristics of the arterial time-attenuation curve are a function of the rate of contrast medium transit to the extracellular fluid (ECF), osmolality driven transit of water from the ECF into the plasma, direct effects on the heart and pulmonary circulation, the distribution of transit times in the cardiopulmonary circulation and recirculation. Theory predicts that while differences in peak arterial attenuation/peak height (PH) will be small, alterations in the areas under the time-attenuation curve (AUC) will reflect early-phase rate constants in the absence of major inotropic effects. The AUC should be higher for non-ionic than ionic media reflecting these lower rate constants. An experimental study on three healthy dogs confirmed these theoretical observations, with a slightly higher PH (6.5% higher) using a non-ionic medium but a substantially higher AUC (22% higher). (Differences significant at the 5% level, two-tailed paired t-test.) Our theoretical predictions and experimental findings suggest non-ionic media produce superior vascular enhancement, particularly shortly after injection. Possible clinical implications, particularly in dynamic enhanced computed tomography, are discussed.