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Corot C, Violas X, Robert P, Port M. Pharmacokinetics of three gadolinium chelates with different molecular sizes shortly after intravenous injection in rabbits: Relevance to MR angiography. Invest Radiol 2000;35:213–218.To mimic an MR angiographic protocol, an experimental model was developed in rabbits to determine gadolinium concentrations in blood early after injection. Contrast agents with different molecular sizes were compared.The influence of injection parameters (injection rate, duration of injection, volume of injection, dose) was assessed, and two blood pool agents (P760, P717) were compared with the low-molecular-weight Gd-DOTA under similar conditions.Two main phases were identified: bolus and postbolus. Injection parameters strongly influenced the pattern of the bolus phase, but the postbolus phase was sensitive only to the injected dose. The blood pool agents presented a bolus phase profile similar to that of Gd-DOTA, but 45 seconds after injection, 84% of P717 molecules were still present in the blood compartment, compared with 65% of P760 molecules and only 51% of Gd-DOTA molecules.Blood pool agents are useful for MR angiographic protocols involving the postbolus phase. In protocols in which only the bolus phase is imaged, blood pool agents provide similar data to Gd-DOTA, provided that the injection rate, iso-T1 efficiency dose, and volume are similar.