A targeted contrast agent for magnetic resonance imaging of thrombus: implications of spatial resolution.
A preparation of ultra-small superparamagnetic iron oxide (USPIO) particles coupled to an RGD peptide (RGD-USPIO) was investigated as an MR contrast agent, targeted to activated platelets, in both ex vivo and in vivo thrombus models. Thrombus visualization ex vivo was compared using RGD-USPIO and a non-targeted UPSIO. The influence of thrombus visualization on thrombus exposure time to RGD-USPIO (ex vivo) and on the spatial resolution of the MR image (ex vivo and in vivo) was assessed. RGD-USPIO resulted in better thrombus visualization than non-targeted USPIO ex vivo, and maximum enhancement was achieved after approximately one hour exposure time of the thrombus to RGD-USPIO. The ability to visualize the clots was highly dependent on the spatial resolution of the image. In vivo, an in-plane resolution of less than 0.2 x 0.2 mm(2) was required for good clot visualization after contrast enhancement. It is concluded that the achievable resolution and sensitivity is a potential limitation to the usefulness of active vascular targeting in MRI.
Uppsala University Hospital, Uppsala, Sweden. lars.johansson@radiol.uu.se
L O
LO
Johansson
A
A
Bjørnerud
H K
HK
Ahlström
D L
DL
Ladd
D K
DK
Fujii
D000818:Animals; D003287:Contrast Media; D003911:Dextrans; D052203:Ferrosoferric Oxide; D006801:Humans; D007501:Iron; D008279:Magnetic Resonance Imaging / Q000379:methods*; D058185:Magnetite Nanoparticles; D009842:Oligopeptides; D010087:Oxides; D019047:Phantoms, Imaging; D012680:Sensitivity and Specificity; D013552:Swine; D013927:Thrombosis / Q000175:diagnosis*
D003287:Contrast Media; D003911:Dextrans; D058185:Magnetite Nanoparticles; D009842:Oligopeptides; D010087:Oxides; C097921:ferumoxtran-10; C047981:arginyl-glycyl-aspartic acid; D007501:Iron; D052203:Ferrosoferric Oxide