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 tetraa zacyclododecanetetraacetic acid (Gd-DOTA), in two susceptibility contrast m agnetic 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 isotoni c serum from the available agent solutions (0.5 mmol Gd/mL Gd-DOTA; 350 pmo l Fe/mL AMI 227), Eighteen rats were studied. Contrast agent (0.1 mt) was b olus 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 extrapola ted from the phantom experiment: 0.2 mmol/kg body weight of Gd-DOTA and 7, 14, and 28 mu mol Fe/kg body weight of AMI 227 were Injected. For both sequences, signal-to-noise ratios (S/N) were measured on each tube of the phantom and on rat brain from each image of the dynamic imaging, S/ N was plotted versus contrast dilution (phantom) and versus time (rats), In the FLASH sequence, a well-shaped curve (S/N decrease, S/N peak decrease, S/N increase) of the first pass of the contrast agent was demonstrated for Gd-DOTA and for AMI 227 (7 mu mol Fe/kg body weight), In the EPI sequence, a well-shaped curve was demonstrated for Gd-DOTA, and a plateau effect was noted for both concentrations of AMI 227, With the FLASH technique, dynamic susceptibility contrast imaging of rat brain can be performed with very lo w concentrations of AMI 227 compared with the Gd-DOTA concentration (0.2 mm ol Gd/kg body weight) used in clinical practice. This could be of interest in perfusion imaging, because it may allow for first-pass susceptibility im aging after administration of a small volume in a narrow bolus, (C) 1999 Wi ley-Liss, Inc.