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

Rapid vascular depiction with use of a minimum of gadolinium (Gd) contrast agent will be required to generate road-map vascular images for magnetic resonance (MR) imaging-guided endovascular interventions. The objective of this study was to optimize intraarterial injections of MR contrast agent during magnetic resonance angiography (MRA), obtained during interventions, by determining the optimal Gd vascular concentration ([Gd]) for vessel depiction.

The authors derived theoretical expressions to estimate the [Gd] resulting in maximal signal in blood. A model was developed to account for flow dilution to estimate [Gd] given the injected Gd concentration, 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-dimensional (3D) MRA acquisitions. The authors also determined the optimal [Gd] required for vessel depiction in animal models.

The theoretical expressions yielded optimal [Gd] of 10.2 mmol/L in blood. The animal experiments used the flow dilution model and examined signal enhancement in the aorta and the renal and iliac arteries. Maximal enhancement occurred at [Gd] = 16.2 +/- 4.0 mmol/L (mean +/- SE).

The theoretically predicted values for [Gd]optimal and the flow dilution model were successfully validated. The relationship between injected [Gd], injection rate, and blood flow rate permits rapid intraarterial administration of contrast material, using less overall contrast material than with standard intravenous Gd-enhanced MRA.