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The purpose of this study was to evaluate the contribution of an ultrasmall superparamagnetic iron oxide particles (USPIOs) based contrast agent (AMI 227), in a transverse three-dimensional time-of-flight TONE MR angiography sequence of abdominal aorta in rabbits. The main goal was 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 magnetization transfer suppression. The contrast media used were composed of a USPIO core surrounded by a dextran-surfactant (AMI 227). Different concentrations of AMI 227 were evaluated in 12 rabbits. Concentrations varied within the range 8.5-34 micromol Fe/kg - bw: 8.5 micromol Fe/kg (three rabbits); 17 micromol Fe/kg (three rabbits); 25.5 micromol Fe/kg (three rabbits); 34 micromol Fe/kg (three rabbits). A visual analysis based on the improvement of visualization of small arteries (renal arteries) on MIP images and a quantitative analysis based on the percentage of contrast 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 improvement in the delineation of the renal arteries were noted when using low concentrations of the contrast media. A loss of signal-to-noise ratio of the aorta and a decrease in arterial visualization were respectively noted with higher concentration of contrast media. In this experimental study, using a transverse three-dimensional TOF TONE MR angiography sequence of renal arteries, in which sequence the saturation effect is minimized, the use of AMI 227 allows only improvement in the delineation of small arteries when using low concentrations of contrast media.

The authors suggest that ultra-small paramagnetic iron oxide (USPIO) particles used as blood pool contrast agents may increase the sensitivity of midfield MRI (i.e., less than 1.5 Tesla) to physiological variations in cerebral blood volume. This hypothesis was tested on a rabbit model of apnea which increases pCO2 and cerebral blood volume. Using Sinerern as the USPIO at a blood concentration of 60 mumol Iron/kg body weight, an 8% T2*-weighted signal decrease could be observed at 1.0 T with 25-33% increase in pCO2. Comparatively, in the absence of USPIO, T2*-weighted signal dropped only 4% during apnea and after mild hyperoxygenation beforehand, due to increased deoxyhemoglobin content. These preliminary data suggest that USPIOs could play an important role in functional MRI at midfield strength, by sensitizing the signal to cerebral blood volume changes.

Enhanced-MR imaging in combination with ultrasmall superparamagnetic iron oxide (USPIO) was used in the glycerol-induced model of acute renal failure (ARF) in the rabbit to detect renal perfusion abnormalities. A control group (n = 5) and an ARF group (n = 5) were studied after intramuscular injection of glycerol (10 ml/kg) with T2-weighted spin-echo sequence at 1.5 T and a 27 mumol/kg IV dose of iron. The signal intensity (SI) was quantified in the cortex, the outer medulla (OM), and the inner medulla (IM). In control rabbits, the maximum SI decrease after USPIO injection was in the OM (76% +/- 3.6), as this is the region of maximal vascular density, then in the IM (73.4% +/- 2.9). In the glycerol group, SI loss in the OM (61% +/- 12.6) and the IM (45.2% +/- 16.24) was significant less than in the control group (p < .05). Pathology results showed fibrinous thrombus in the efferent arterioles and congestive aspect of the vasa recta in the medulla. We argue that a reduced medullary concentration of USPIO in the renal failure group is indicative of medullary hypoperfusion.