Contrast-Enhanced Magnetic Resonance Angiography: Evaluation of the High Relaxivity Low Diffusible Gadolinium-Based Contrast Agent P846 in Comparison With Gadoterate Meglumine in Rabbits at 1.5 Tesla and 3.0 Tesla

Evaluation of the Contrast Enhancement Performance of Gadopiclenol for Magnetic Resonance Angiography in Healthy Rabbits and Pigs

OBJECTIVES

Unexpected accumulations of gadolinium in various organs were reported after the administration of gadolinium-based contrast agents, making desirable to reduce the dose while maintaining equivalent diagnostic performance. The aim of this study was to evaluate the contrast enhancement performance of high relaxivity gadopiclenol compared with gadoterate meglumine in abdominal contrast-enhanced magnetic resonance angiography (CE-MRA).

MATERIALS AND METHODS

In a first study in healthy rabbits, axial 3D gradient echo sequences were applied at 4.7 T to study arterial enhancement as a function of gadopiclenol dose (0.025, 0.05, 0.075, and 0.1 mmol Gd/kg) or gadoterate meglumine at 0.1 mmol Gd/kg (n = 5-6/group). The increase in signal-to-noise ratio (ΔSNR) in the aorta at the first pass was measured and compared. In a second, crossover study in 6 healthy pigs, abdominal CE-MRA sequences were acquired at 3 T with gadopiclenol at 0.05 mmol Gd/kg or gadoterate meglumine at 0.1 mmol Gd/kg at a 1-week interval. Quantitatively on the maximum intensity projection (MIP) images, the mean MIP SNR within the aorta of both groups was compared. Qualitatively, a blinded comparison of the angiograms was performed by an experienced radiologist to determine the preferred contrast agent.

RESULTS

In the rabbit, ∆SNR is linearly correlated with the gadopiclenol dose (P = 0.0010). Compared with gadoterate meglumine 0.1 mmol Gd/kg, an increase in the ∆SNR is observed after 0.05, 0.075, and 0.1 mmol Gd/kg of gadopiclenol (+63% P = 0.0731, +78% P = 0.0081, and +72% P = 0.0773, respectively), whereas at 0.025 mmol Gd/kg, ∆SNR is in the same range as with gadoterate meglumine 0.1 mmol Gd/kg (+15% P > 0.9999). In pigs, contrast enhancement after gadopiclenol at 0.05 mmol/kg is +22% superior to MIP SNR after gadoterate meglumine at 0.1 mmol Gd/kg (P = 0.3095). Qualitatively, a preference was shown for gadopiclenol images (3/6) over the gadoterate meglumine examinations (1/6), with no preference being shown for the remainder (2/6).

CONCLUSIONS

First-pass CE-MRA is feasible with gadopiclenol at 0.05 mmol Gd/kg with at least the same arterial signal enhancement and image quality as gadoterate meglumine at 0.1 mmol Gd/kg.

Whole cancer-region enhancement using meglumine-gadopentetate-glucose solution and 7.0-T magnetic resonance imaging

To visualize whole cancerous region including hypoxic cancer without radiation exposure, we developed meglumine-gadopentetate-glucose solution for 7.0-T magnetic resonance imaging. The infusion solution consists of meglumine-gadopentetate and glucose solutions, and these solutions are mixed before the vein drip infusion. We used readily available solutions, and the concentrations of the meglumine-gadopentetate and glucose solutions were 37.14 and 5.0%, respectively. In the first and second experiments, vein infusions were conducted from a rabbit ear using meglumine-gadopentetate-saline and meglumine-gadopentetate-glucose solutions, and T1 weighted imaging was performed to visualize cancerous region. Using the meglumine-gadopentetate saline, it was not difficult to image cancer-growth regions with new blood vessels. Using the meglumine-gadopentetate-glucose solution, the signal intensity of whole cancerous region including hypoxic cancer substantially increased. The visualizing duration for the meglumine gadopentetate glucose was beyond 90 min, and the rabbit survived after the infusion. The signal intensity in the hypoxic cancer was increasing until 90 min using the meglumine-gadopentetate-glucose solution, since the meglumine-gadopentetate molecules were absorbed into almost the whole cancerous region along with glucose-molecule flows.

Contrast-enhanced magnetic resonance angiography in rabbits: evaluation of the gadolinium-based agent p846 and the iron-based blood pool agent p904 in comparison with gadoterate meglumine

OBJECTIVES

: To evaluate the performance of a gadolinium-based contrast compound (P846) as well as an ultra-small particle of iron oxide agent (P904) in contrast-enhanced magnetic resonance angiography (MRA) in rabbits and to compare those agents with gadoterate meglumine (Gd-DOTA) for first pass and steady state imaging.

MATERIALS AND METHODS

: A total of 6 rabbits underwent contrast-enhanced MRA of the aorta and its branches at 3 different time points. All examinations were performed on a 1.5T MR (Siemens HealthCare, Magnetom Espree), and the contrast agents were applied in random order. Image data were acquired using a time-resolved MRA sequence (time-resolved angiography with stochastic trajectories) during the first pass to assess the bolus phase and a high-resolution MRA sequence followed by repetitive measurements over the next 10 minutes for all 3 agents to evaluate the postbolus phase. Two radiologists reviewed the images in consensus blinded to the contrast agent used. Signal-to-noise ratio and contrast-to-noise ratio for three-dimensional high-resolution MRA were calculated for each time point and agent. Image quality was consensually evaluated on a 4-point Likert scale. A Wilcoxon-Mann-Whitney U test was used for comparison with P < 0.05 as level of statistical significance.

RESULTS

: All agents led to diagnostic MR angiograms in all 6 rabbits. The time-resolved angiography with stochastic trajectories datasets provided detailed information about the bolus phase for all the 3 agents. During the first pass, P904 and P846 proved to be superior to Gd-DOTA with the highest peak enhancement for P846. In the postbolus phase up to 10 minutes postcontrast injection, P904 proved to be superior to the other agents. All the agents led to excellent image quality, with no statistical difference to a maximum of 3 minutes postinjection, whereas thereafter images with Gd-DOTA and P846 were assessed as nondiagnostic.

CONCLUSIONS

: P846 and P904 proved to be superior to Gd-DOTA for time-resolved MRA. The ultra-small particle of iron oxide compound P904 showed continuous high signal over 10 minutes and seems to be best suited for first pass and steady-state imaging.

A quantitative comparison of the influence of individual versus population-derived vascular input functions on dynamic contrast enhanced-MRI in small animals

For quantitative analysis of dynamic contrast enhanced magnetic resonance imaging data, the time course of the concentration of the contrast agent in the blood plasma, or vascular input function (VIF), is required. We compared pharmacokinetic parameters derived using individual and population-based VIFs in mice for two different contrast agents, gadopentetate dimeglumine and P846. Eleven mice with subcutaneous 4T(1) breast cancer xenografts were imaged at 7 T. A precontrast T(1) map was acquired along with dynamic T(1) -weighted gradient echo images before, during, and after a bolus injection of contrast agent delivered via a syringe pump. Each animal's individual VIF and derived population-averaged VIF were used to extract parameters from the signal-time curves of tumor tissue at both the region of interest and voxel level. The results indicate that for both contrast agents, K(trans) values estimated using population-averaged VIF have a high correlation (concordance correlation coefficient > 0.85) with K(trans) values estimated using individual VIF on both a region of interest and voxel level. This work supports the validity of using of a population-based VIF with a stringent injection protocol in preclinical dynamic contrast enhanced magnetic resonance imaging studies.

Monitoring blood-brain barrier status in a rat model of glioma receiving therapy: dual injection of low-molecular-weight and macromolecular MR contrast media

PURPOSE

To evaluate the sequential injection of a low-molecular-weight (gadoterate meglumine [Gd-DOTA], 0.5 kDa) and a macromolecular (P846, 3.5 kDa) contrast media in monitoring the effect of antitumor therapies (antiangiogenic therapy and/or microbeam radiation therapy [MRT]) on healthy brain tissue and implanted tumors.

MATERIALS AND METHODS

Animal use was compliant with official French guidelines and was assessed by the local Internal Evaluation Committee for Animal Welfare and Rights. Eighty male rats bearing 9L gliosarcoma were randomized into four groups: untreated, antiangiogenic (sorafenib) therapy, MRT, and both treatments. Magnetic resonance (MR) imaging was performed 1 day before and 1, 5, and 8 days after the start of the treatment. At all time points, vascular integrity to a macromolecular contrast medium (P846) and, 11 minutes 30 seconds later, to low-molecular-weight contrast medium (Gd-DOTA) was evaluated by using a dynamic contrast material-enhanced MR imaging approach. To quantify vessel wall integrity, areas under the signal intensity curves were computed for each contrast medium. Unpaired t tests and one-way analysis of variance were used for statistical analyses.

RESULTS

Tumor vessels receiving antiangiogenic therapy became less permeable to the macromolecular contrast medium, but their permeability to the low-molecular-weight contrast medium remained unchanged. Healthy double-irradiated vessels became permeable to the low-molecular-weight contrast medium but not to the macromolecular contrast medium.

CONCLUSION

Antiangiogenic therapy and MRT generate different effects on the extravasation of contrast medium in tumoral and healthy tissues. This study indicates that the use of a low-molecular-weight contrast medium and a macromolecular contrast medium provides complementary information and suggests that the use of two contrast media within the same MR imaging session is feasible.

Brain tumor enhancement in magnetic resonance imaging at 3 tesla: intraindividual comparison of two high relaxivity macromolecular contrast media with a standard extracellular gd-chelate in a rat brain tumor model

OBJECTIVES

The aim of this study was to evaluate lesion enhancement (LE) and contrast-to-noise ratio (CNR) properties of P846, a new intermediate sized, high relaxivity Gd-based contrast agent at 3 Tesla in a rat brain glioma model, and to compare this contrast agent with a high relaxivity, macromolecular compound (P792), and a standard extracellular Gd-chelate (Gd-DOTA).

MATERIALS AND METHODS

Seven rats with experimental induced brain glioma were evaluated using 3 different contrast agents, with each MR examination separated by at least 24 hours. The time between injections assured sufficient clearance of the agent from the tumor, before the next examination. P792 (Gadomelitol, Guerbet, France) and P846 (a new compound from Guerbet Research) are macromolecular and high relaxivity contrast agents with no protein binding, and were compared with the extracellular agent Gd-DOTA (Dotarem, Guerbet, France). T1w gradient echo sequences (TR/TE 200 milliseconds/7.38 milliseconds, flip angle = 90 degrees , acquisition time: 1:42 minutes:sec, voxel size: 0.2 x 0.2 x 2.0 mm, FOV = 40 mm, acquisition matrix: 256 x 256) were acquired before and at 5 consecutive time points after each intravenous contrast injection in the identical slice orientation, using a dedicated 4-channel head array animal coil. The order of contrast media injection was randomized, with however Gd-DOTA used either as the first or second contrast agent. Contrast agent dose was adjusted to compensate for the different T1 relaxivities of the 3 agents. Signal-to-noise ratio, CNR, and LE were evaluated using region-of-interest analysis. A veterinary histopathologist confirmed the presence of a glioma in each subject, after completion of the imaging study.

RESULTS

P792 showed significantly less LE as compared with Gd-DOTA within the first 7 minutes after contrast agent injection (P < 0.05) with, however, reaching comparable LE values at 9 minutes after injection (P = 0.07). However, P792 provided significantly less CNR as compared with Gd-DOTA (P < 0.05) for all examination time points. P846 provided comparable but persistent LE as compared with Gd-DOTA (P < 0.05) and demonstrated significantly greater LE and CNR when compared with P792 (P < 0.05). No statistically significant differences between CNR values for Gd-DOTA and P846 were noted for all examination time points (P < 0.05), with P846 administered at one-fourth the dose as compared with Gd-DOTA.

CONCLUSION

The intravascular contrast medium P792 showed significantly less LE and CNR in comparison to Gd-DOTA and P846, suggesting that it does not show marked extravasation from tumor neocapillaries and does not significantly cross the disrupted blood brain-barrier in this rat glioma model. In distinction, P846 provides comparable enhancement properties at a field strength of 3 Tesla to the extracellular contrast agent Gd-DOTA, using the adjusted dose, suggesting that it crosses the disrupted blood-brain-barrier and tumor capillaries, most likely based on the decreased molecular weight as compared with P792. At the same time, the high relaxivity of this compound allows for decreasing the injected gadolinium dose by a factor of 4 whereas providing comparable enhancement properties when compared with a standard extracellular Gd-chelate (Gd-DOTA) at a dose of 0.1 mmol/kg body weight.

Advances in magnetic resonance (2008)

Current advances in magnetic resonance, as a diagnostic modality, are discussed in the context of publications from Investigative Radiology during 2007 and 2008. The articles relating to this topic, published during the past 2 years, are reviewed by anatomic region. The discussion concludes with a consideration of magnetic resonance contrast media, focusing on studies published in the journal, and examining in particular the potential impact of nephrogenic systemic fibrosis.