USPIO-enhanced direct MR imaging of thrombus: preclinical evaluation in rabbits.
OBJECTIVE
To test the hypothesis that ultrasmall superparamagnetic iron oxide (USPIO) particles may diffuse into nonendothelialized fresh thrombi and thus allow for direct magnetic resonance (MR) imaging of a thrombus.


METHODS
Stagnation thrombi of different thrombus ages (1, 3, 5, 7, and 9 days) were induced in the external jugular veins of 25 rabbits. Direct MR imaging of thrombi was performed by using a fat-saturated T1-weighted gradient-echo sequence (three-dimensional [3D] magnetization prepared rapid acquisition gradient echo) before and 24 hours after intravenous administration of USPIO (particle size, 25 nm; 200 micromol per kilogram of body weight). Thrombus length on 3D reconstruction images was compared with that depicted on a radiographic venogram and with histologic findings (joint reference standard). In addition, T2*-weighted gradient-echo images were acquired and scored semiquantitatively.


RESULTS
The hyperintensity of the thrombus segment depicted on T1-weighted images (thrombus length determined with 3D reconstruction images divided by true thrombus length) increased significantly after administration of contrast medium at a thrombus age of 3 days (0.6 +/- 0.4 [SD] to 0.8 +/- 0.4; P =.02), 5 days (0.1 +/- 0.1 to 1.0 +/- 0.1; P <.001), and 7 days (0 to 0.6 +/- 0.4; P =.02), but not at an age of 1 and 9 days. No significant change in the thrombus signal intensity was observed on T2*-weighted images.


CONCLUSIONS
The animal model showed that direct MR imaging of the thrombus improved 24 hours after USPIO administration with a T1-weighted sequence. No improvement was seen with the T2*-weighted sequence.
Schmitz
S A
SA
Department of Radiology and Nuclear Medicine, Universitätsklinikum Benjamin Franklin, Freie Universität Berlin, Hindenburgdamm 30, 12200 Berlin, Germany. s.schmitz@medizin.fu-berlin.de
Winterhalter
S
S
Schiffler
S
S
Gust
R
R
Wagner
S
S
Kresse
M
M
Coupland
S E
SE
Semmler
W
W
Wolf
K J
KJ
D000818:Animals; D003287:Contrast Media; D003911:Dextrans; D004195:Disease Models, Animal; D005260:Female; D052203:Ferrosoferric Oxide; D007501:Iron; D008279:Magnetic Resonance Imaging / Q000379:methods*; D058185:Magnetite Nanoparticles; D008297:Male; D010087:Oxides; D010690:Phlebography; D011817:Rabbits; D013927:Thrombosis / Q000473:pathology*
D003287:Contrast Media; D003911:Dextrans; D058185:Magnetite Nanoparticles; D010087:Oxides; C097921:ferumoxtran-10; D007501:Iron; D052203:Ferrosoferric Oxide