Pierre Loubeyre

CARBOXYMETHYL-DEXTRAN-GADOLINIUM-DTPA AS A BLOOD-POOL CONTRAST AGENT FOR MAGNETIC RESONANCE ANGIOGRAPHY : EXPERIMENTAL STUDY IN RABBITS

RATIONALE AND OBJECTIVES The authors evaluate the efficiency of various doses of a paramagnetic macromolecular contrast agent, a gadolinium (Gd)-DTPA-dextran conjugate, as a blood-pool contrast media, in a transverse three-dimensional time-of-flight (TOF) magnetic resonance (MR) angiography sequence of the abdominal aorta in rabbits. METHODS Imaging experiments were performed on a 1.5-T magnet, using a transverse three-dimensional TOF tilted optimized nonsaturating excitation (TONE) sequence. The macromolecular contrast media used was a carboxymethyl-dextran-Gd-DTPA (CMD-Gd-DTPA). Different concentrations of CMD-Gd-DTPA (0.005, 0.01, 0.03, 0.05 mmol Gd/kg) were evaluated. A comparative study using Gd-DOTA (0.01 and 0.1 mmol/kg) was performed. A visual analysis based on the gain in the visualized length of small arteries (renal arteries), and a quantitative analysis based on the percent contrast enhancement of the aorta plotted against distance in the slab from the top edge of the acquisition volume were obtained. RESULTS A signal-to-noise ratio enhancement of the distal part of the aorta and an improvement in the visualized length of the renal arteries were noted for concentrations of CMD-Gd-DTPA ranging form 0.01 to 0.05 mmol Gd/kg. Venous enhancement was noted for concentrations greater than 0.01 mmol Gd/kg when using CMD-Gd-DTPA or Gd-DOTA. CONCLUSION Carboxymethyl-dextran-Gd-DTPA reduced, in part, the saturation effect in a three-dimensional transverse TOF TONE MR angiography in rabbits. To prevent venous enhancement, observed with the higher concentrations used in this study, a decrease in the polydispersity of the polymer should be a goal in the future. Rapid extravasation of the low-molecular weight fraction of the polymer could explain the venous enhancement.

Contrast-enhanced magnetic resonance tomoangiography: A new imaging technique for studying thoracic great vessels

The authors propose a new imaging approach for studying thoracic great vessels, using high-speed MR imaging combined with intravenous rapid bolus injection of a paramagnetic contrast media. The decrease of the T1 relaxation time of flowing blood induced by the contrast agent (Gd-DOTA) caused an increased signal intensity within the vessel lumen for a time period allowing multiplanar imaging of various vascular structures. The intraluminal signal enhancement is mainly related to the blood concentration of the contrast agent as in conventional X-ray angiography. Information on the aorta and pulmonary arteries obtained by the so-called contrast-enhanced magnetic resonance tomoangiography appears complementary to that obtained with other vascular MR imaging procedures such as cine-MRI and magnetic resonance angiography (MRA).

Comparison of iron oxide particles (AMI 227) with a gadolinium complex (Gd-DOTA) in dynamic susceptibility contrast MR imagings (FLASH and EPI) for both phantom and rat brain at 1.5 Tesla

The goal of the study was to compare, in phantom and normally perfused rat brain tissue, a superparamagnetic iron oxide particle‐based contrast agent (AMI 227) with a low‐molecular‐weight gadolinium chelate, gadolinium tetraazacyclododecanetetraacetic acid (Gd‐DOTA), in two susceptibility contrast magnetic resonance imaging (MRI) modes [fast low‐angle shot sequence (FLASH) and echoplanar imaging (EPI)]. A phantom consisting of dilution series of both contrast agents was manufactured. Dilutions were obtained with isotonic serum from the available agent solutions (0.5 mmol Gd/mL Gd‐DOTA; 350 μmol Fe/mL AMI 227). Eighteen rats were studied. Contrast agent (0.1 mL) was bolus injected in each rat, and dynamic MRI was performed (first pass of the contrast agent) in rat brain. The doses of AMI 227 injected were extrapolated from the phantom experiment: 0.2 mmol/kg body weight of Gd‐DOTA and 7, 14, and 28 μmol Fe/kg body weight of AMI 227 were injected.

Three-dimensional phase contrast MR cerebral venography with zero filling interpolation in the slice encoding direction

The purpose of this study was to evaluate the magnetic resonance (MR) cerebral venography findings of a three-dimensional phase contrast MR sequence with zero filling interpolation of the data in the slice encoding direction. Fifty volunteers were enrolled in the study. Images were obtained on a 1.5 MR imaging system with acquisition time of 12 min. MIP images were reconstructed throughout the entire imaging volume. A grading scale system was used to assess dural venous sinuses, major deep veins, cortical, and cortical eponymic veins. Inferior group of dural venous sinuses, inferior sagittal sinus, and cortical eponymic veins were poorly demonstrated. Score of the superior sagittal sinus, the straight sinus, the confluence of the superior sinus group, the right transverse and sigmoid sinuses, the internal veins, and the vein of Galen was excellent. The score of the left transverse and sigmoid sinuses was good. In conclusion, when using zero filling interpolation of the data in a three-dimensional phase contrast MR cerebral venography sequence, the superior group of dural venous sinuses and main major deep veins are demonstrated with good conspicuity.

ASSESSMENT OF IRON OXIDE PARTICLES (AMI 227) AND A GADOLINIUM COMPLEX (Gd-DOTA) IN DYNAMIC SUSCEPTIBILITY CONTRAST MR IMAGINGS (FLASH AND EPI) IN A TUMOR MODEL IMPLANTED IN RATS

The objective of our study was to assess the feasibility of dynamic susceptibility contrast MR technique after bolus injection of SPIO and Gd-DOTA in a tumor model implanted in rats. Tumors were subcutaneously implanted in 24 rats. A FLASH sequence and EPI were evaluated. Different doses of AMI 227 and Gd-DOTA were assessed. Mean signal intensity vs. time curves were plotted. Well-shaped curves of the first pass of the contrast agent were only obtained with Gd-DOTA. According to these results it appears difficult to assess tumor blood volume with USPIO dynamic susceptibility contrast imaging.

Dynamic contrast-enhanced MR tomoangiography of major pulmonary arteries

We evaluated the use of contrast-enhanced MR tomoangiography of the major pulmonary arteries in patients with suspected pulmonary embolism and hilar lung carcinoma. Patients with acute pulmonary emboli of the major pulmonary arteries, pulmonary hypertension (n = 11), and hilar lung carcinoma with suspected infiltrated pulmonary artery (n = 4), underwent MRI after selective digital subtraction pulmonary angiography (DSA). Subsecond contrast-enhanced MR tomoangiograms were obtained in the long axis of each pulmonary artery after bolus injection of a paramagnetic MR contrast agent. All proximal thrombi visualized using DSA (n = 13) were depicted using contrast-enhanced MR tomoangiography. Pulmonary artery obstruction (n = 2) or stenosis (n = 2) by the tumor were similarly assessed by DCMRA and DSA. Contrast-enhanced MR tomoangiography allows a reproducible, fast, dynamic, and multiplanar good quality imaging of the major pulmonary arteries and their proximal branches. This technique may be useful in patients with pulmonary hypertension for whom DSA is dangerous, and in the diagnosis of malignant involvement of central pulmonary arteries.