Thermoacoustic molecular tomography with magnetic nanoparticle contrast agents for targeted tumor detection

Purpose: The primary feasibility steps of demonstrating the ability of microwave-induced thermoacoustic (TA) in phantoms have been previously reported. However, none were shown to target a diseased site in living subjects in thermoacoustic tomography (TAT) field so far. To determine the expressions of oncogenic surface molecules, it is quite necessary to image tumor lesions and acquire pathogenic status on them via TAT.Methods: Compared to biological tissues, iron oxide nanoparticles have a much higher microwave absorbance. Fe₃O₄/polyaniline (PANI) nanoparticles were prepared via polymerization of aniline in the Fe₃O₄ superparamagnetic fluids. Then Fe₃O₄/PANI was conjugated to folic acid (FA), which can bind specifically to the surface of the folate receptor used as a tumor marker. FA-Fe₃O₄/PANI targeted tumor was irradiated by pulsed microwave at 6 GHz for thermoacoustic detection and imaging.Results: The effect of the Fe₃O₄/PANI superparamagnetic nanoparticles for enhancing TAT images was successfully investigated in ex vivo human blood and in vivo mouse tail. Intravenous administration of the targeted nanoparticles to mice bearing tumors showed fivefold greater thermoacoustic signal and much longer elimination time than that of mice injected with nontargeted nanoparticles in the tumor. The specific targeting ability of FA-Fe₃O₄/PANI to tumor was also verified on fluorescence microscopy.Conclusions: Fabricated iron oxide nanoparticles conjugated with tumor ligands for targeted TAT tumor detection at the molecular level was reported for the first time. The results indicate that thermoacoustic molecular imaging with functionalized iron oxide nanoparticles may contribute to targeted and functional early cancer imaging. Also, the modified iron oxide nanoparticles combined with suitable tumor markers may also be used as novel nanomaterials for targeted and guided cancer thermal therapy. ©2010 American Association of Physicists in Medicine