Determination of optimal injection parameters for intraarterial gadolinium-enhanced MR angiography

PURPOSE: Rapid vascular depiction with use of a minimum of gadolinium (Gd) contrast agent will be required to generate roadmap vascular images for mag netic resonance (MR) imaging-guided endovascular interventions. The objecti ve of this study was to optimize intraarterial injections of MR contrast ag ent during magnetic resonance angiography (MRA), obtained during interventi ons, by determining the optimal Gd vascular concentration ([Gd]) for vessel depiction. MATERIALS AND METHODS: The authors derived theoretical expressions to estim ate the [Gd] resulting in maximal signal in blood. A model was developed to account for flow dilution to estimate [Gd] given the injected Gd concentra tion, injection rate, and the blood flow rate. Experiments in four animals (three dogs, one pig) were conducted to verify this model with use of both time-resolved two-dimensional (2D) thick-slab and single-phase three-dimens ional (3D) MRA acquisitions. The authors also determined the optimal [Gd] r equired for vessel depiction in animal models. RESULTS: The theoretical expressions yielded optimal [Gd] of 10.2 mmol/L in blood. The animal experiments used the flow dilution model and examined si gnal enhancement in the aorta and the renal and iliac arteries. Maximal enh ancement occurred at [Gd] = 16.2 +/- 4.0 mmol/L (mean +/- SE). CONCLUSIONS: The theoretically predicted values for [Gd](optimal) and the f low dilution model were successfully validated. The relationship between in jected [Gd], injection rate, and blood flow rate permits rapid intraarteria l administration of contrast material, using less overall contrast material than with standard intravenous Gd-enhanced MRA.