Frank L. Goerner

In vitro T2 relaxivities of the Gd-based contrast agents (GBCAs) in human blood at 1.5 and 3 T

Background The availability of data in the medical literature for the T2 relaxivities of the Gd-based contrast agents (GBCAs) is limited. A comprehensive comparison between the agents available commercially (other than in Europe) is lacking, with no data available that most closely reflect the clinic, which is in human whole blood at body temperature. Purpose To complement the existing literature by determining T2 relaxivity data for eight GBCAs in vitro. Material and Methods The relaxivities of eight GBCAs diluted in human whole blood at 1.5 and 3 T were determined at 37 ± 0.5 °C. Gd was in the range of 0–4 mM. Multi-echo sequences with variable echo times were acquired using a phantom containing a dilution series with each agent, and SigmaPlot 12.0 was used to calculate the R2 relaxation rate and finally r2. Statistical comparisons between agents and field strengths were conducted. Results The relationship between R2 vs. Gd was observed to be linear at 1.5 and 3 T, with a mild increase in r2 from 1.5 to 3 T for all GBCAs. T2 relaxivity data were compared with prior results. The GBCAs are closely clustered into two groups, with higher r2 noted for the two lipophilic (those with partial hepatobiliary excretion) compounds. Conclusion The r2 values at 1.5 and 3 T, determined for the eight GBCAs still clinically available (other than in Europe), provide a definitive baseline for future evaluations, including theoretical calculations of signal intensity and their clinical impact on T2-weighted scans.

46 Contrast-Enhanced MRA: Basics; Renal, Abdomen

Fig. 46.1A demonstrates the abdominal aorta and common iliac arteries, with moderate to severe stenosis noted at the origin of the left renal artery (arrow). Figure 46.1B demonstrates extensive atherosclerotic disease involving the aorta, with severe stenosis at the origin of the left renal artery. Both studies were performed at 1.5 T. The study presented in Fig. 46.2 (reprinted with permission from U. Kramer, Invest Radiol 2007;42:747) illustrates the feasibility of high spatial resolution contrastenhanced MRA at 3 T, providing a further improvement in evaluation of the renal artery and its branches. Early branching is demonstrated, involving both renal arteries, in this potential, living, related kidney donor. The voxel size was 1 mm3, the contrast dose 0.1 mmol/kg injected at 2 mL/sec and the scan time 16 sec (with a parallel imaging factor of 3 employed). An additional advantage of this type of acquisition is the ability to reconstruct high-resolution images in any desired plane, given the high spatial resolution and isotropic voxel dimensions. Such reformatted images are similarly advantageous for the evaluation of renal artery stenosis. In this application, 3 T offers substantial advantages compared with 1.5 T, largely due to the inherent increase in SNR. Improved suppression of background tissue, due to the prolongation of T1 at 3 T, aids as well by further increasing CNR. Contrast-enhanced MRA (CE-MRA) has become the exam of choice for evaluation of the abdominal aorta and renal arteries. The standard imaging sequence is a fast 3D