ULTRASMALL SUPERPARAMAGNETIC IRON-OXIDE PARTICLES (AMI-227) AS A BLOOD-POOL CONTRAST AGENT FOR MR-ANGIOGRAPHY - EXPERIMENTAL-STUDY IN RABBITS

The purpose of this study was to evaluate the contribution of an ultra small superparamagnetic iron oxide particles (USPIOs) based contrast a gent (AMI 227), in a transverse three-dimensional time-of-night TONE M R angiography sequence of abdominal aorta in rabbits. The main goal wa s to assess improvement in the visualization of small arteries such as renal arteries, when using such a sequence. Imaging experiments were performed on a 1.5 T magnet, using a transverse 3D time-of-flight (TOF ) tilted optimized nonsaturating excitation (TONE) sequence with magne tization transfer suppression. The contrast media used were composed o f a USPIO core surrounded by a dextran-surfactant (AMI 227), Different concentrations of AMI 227 were evaluated in 12 rabbits. Concentration s varied within the range 8.5-34 mu mol Fe/kg-bw: 8.5 mu mol Fe/kg (th ree rabbits); 17 mu mol Fe/kg (three rabbits); 25.5 mu mol Fe/kg (thre e rabbits): 34 mu mol Fe/kg (three rabbits). A visual analysis based o n the improvement of visualization of small arteries (renal arteries) on MIP images and a quantitative analysis based on the percentage of c ontrast enhancement of the aorta plotted against distance in the slab from the top edge of the acquisition volume were obtained. A signal-to -noise ratio enhancement of the distal part of the aorta and only impr ovement in the delineation of the renal arteries were noted when using low concentrations of the contrast media. A loss of signal-to-noise r atio of the aorta and a decrease in arterial visualization were respec tively noted with higher concentration of contrast media. In this expe rimental study, using a transverse three-dimensional TOF TONE MR angio graphy sequence of renal arteries, in which sequence the saturation ef fect is minimized, the use of AMI 227 allows only improvement in the d elineation of small arteries when using low concentrations of contrast media.