Low-dose intra-arterial contrast-enhanced MR aortography in patients based on a theoretically derived injection protocol

Multiple intra-arterial contrast agent injections are necessary during MR-guided endovascular interventions. In respect to the approved limits of maximum daily gadolinium dose, a low-dose injection protocol is mandatory. The objective of this study was to derive and apply a low-dose injection protocol for intra-arterial 3D contrast-enhanced MR aortography in patients. Injection rate (Q_inj), concentration of injected gadolinium [Gd]_inj and aortal blood flow rate (Q_blood) were included for the theoretical evaluation of signal intensity (SI) of the arterial lumen. SI simulations were carried out at Q_inj=2 versus 4 ml/s in the [Gd]_inj range between 0–500 mM. Q_inj and [Gd]_inj with SI above the 75% threshold of the maximal SI were regarded as optimal injection parameters. [Gd]_inj=50 mM and Q_inj=4 ml/s were considered as optimal and were administered in five patients for 3D MR aortography. All images revealed clear delineation of the abdominal aorta and its major branches. Mean±SD of contrast-to-noise ratios of the abdominal aorta, common iliac and renal artery were 70.2±15.2, 58.6±12.3 and 67.4±12.3. Approximately seven intra-aortal injections would be permissible in patients during MR-guided interventions without exceeding the maximal dose of gadolinium.