RES-specific imaging of the liver and spleen with iron oxide particles designed for blood pool MR-angiography

The purpose of this study was to determine the dependency of liver- and spl een-enhancement on particle size and dose of bolus-injectable iron oxides d esigned for blood-pool MR-angiography (MRA). The superparamagnetic iron oxi de SHU 555 A [particle size 65 nm (group 1)] and three derivatives designed for blood-pool MRA (groups 2-4) with smaller hydrodynamic diameters (46/33 /21 nm) were i.v, injected in New Zealand White rabbits at doses of 10, 20, or 40 mu mol Fe/kg bw, MRI was performed before, 2, and 24 hours after con trast application using T1-weighted SE and T2-weighted TSE sequences, In ad dition splenic tissue was harvested post mortem and scanned ex vivo, All ir on oxides significantly decreased the SI of liver and spleen in T1- and Ta- weighted images at 2 and 24 hours after application of contrast media (P < 0.01), The signal intensity was inversely related to the dose applied. Decr easing particle size resulted in a lower signal enhancement in liver and sp leen, However, ultra-small superparamagnetic iron oxides suited for blood-p ool MRA(USPIOs, group 4) still revealed a significant signal enhancement in the liver and spleen even 24 hours after contrast application (< - 60%, 40 mu mol Fe/kg bw), They might thus be used for comprehensive abdominal stud ies including contrast enhanced MR-angiography and RES specific imaging, (C ) 1999 Wiley-Liss, Inc.