title: Enhancement of gas-filled microbubble R2* by iron oxide nanoparticles for MRI.
abstract: Gas-filled microbubbles have the potential to become a unique intravascular MR contrast agent due to their magnetic susceptibility effect, biocompatibility, and localized manipulation via ultrasound cavitation. However, microbubble susceptibility effect is relatively weak when compared with other intravascular MR susceptibility contrast agents. In this study, enhancement of microbubble susceptibility effect by entrapping monocrystalline iron oxide nanoparticles (MIONs) into polymeric microbubbles was investigated at 7 T in vitro. Apparent T2 enhancement (DeltaR2*) induced by microbubbles was measured to be 79.2+/-17.5 sec(-1) and 301.2+/-16.8 sec(-1) for MION-free and MION-entrapped polymeric microbubbles at 5% volume fraction, respectively. DeltaR2* and apparent transverse relaxivities (r2*) for MION-entrapped polymeric microbubbles and MION-entrapped solid microspheres (without gas core) were also compared, showing the synergistic effect of the gas core with MIONs. This is the first experimental demonstration of microbubble susceptibility enhancement for MRI application. This study indicates that gas-filled polymeric microbubble susceptibility effect can be substantially increased by incorporating iron oxide nanoparticles into microbubble shells. With such an approach, microbubbles can potentially be visualized with higher sensitivity and lower concentrations by MRI.
authors: Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Pokfulam, Hong Kong.
authors: April M
authors: AM
authors: Chow
authors: Kannie W Y
authors: KW
authors: Chan
authors: Jerry S
authors: JS
authors: Cheung
authors: Ed X
authors: EX
authors: Wu
mesh_terms: D052203:Ferrosoferric Oxide / Q000737:chemistry; D005740:Gases / Q000737:chemistry; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D045423:Microbubbles; D053758:Nanoparticles / Q000737:chemistry*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D005740:Gases; C499827:monocrystalline iron oxide nanoparticle; D052203:Ferrosoferric Oxide