RT Journal Article SR Electronic T1 Facile synthesis of 69Ge-labeled nanoparticles for dual-modality PET/MRI JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 1049 OP 1049 VO 55 IS supplement 1 A1 Chakravarty, Rubel A1 Valdovinos, Hector A1 Chen, Feng A1 Ellison, Paul A1 Nickles, Robert A1 Cai, Weibo YR 2014 UL http://jnm.snmjournals.org/content/55/supplement_1/1049.abstract AB 1049 Objectives 69Ge (t1/2=39.1 h, 21% β+, Emax=1205 keV) is a novel and desirable PET isotope. However, due to complex coordination chemistry of Ge ions, it is challenging to prepare 69Ge-based tracers using chelator-based approaches. Our goal is to develop a chelator-free strategy to label superparamagnetic iron oxide nanoparticles (SPION) with 69Ge for dual-modality PET/MRI. Methods 69Ge was produced by bombarding a Ga/Ni alloy target (thickness: 45 mg/cm2) with 11 MeV protons at 15 μA for 1 h. It was chemically separated and used for labeling poly(acrylic acid) (PAA)-coated SPION at pH 7-8. Specificity of 69Ge labeling to SPION was confirmed by incubation of control nanoparticles (e.g. copper sulfide and silica-coated SPION) with 69Ge under the same conditions. In vitro stability of 69Ge-SPION was assessed in mouse serum, whereas in vivo stability and biodistribution pattern were studied with both PET and MRI using BALB/c mice. Results 69Ge could be readily produced at activity of >65 MBq. Radiolabeling yield of 69Ge-SPION was ~60% after 3 h incubation at 37 °C, which increased to >80% after 24 h of incubation. In contrast, no radiolabeling of control nanoparticles was observed under the same conditions, demonstrating the specificity of SPION towards 69Ge ions. After 24 h of incubation of 69Ge-SPION in mouse serum, only <30% of 69Ge was found to have leached out of SPION, indicating good stability. Upon i.v. injection of 69Ge-SPION into mice, strong liver uptake was observed in PET imaging and biodistribution studies over a period of 36 h, which showed that 69Ge-SPION could retain its integrity in vivo. These results were confirmed by MRI where darkening of the liver (but not kidney) was observed, as expected for i.v. injected nanoparticles. Conclusions We have developed a chelator-free approach to use 69Ge for in vivo PET imaging, which takes advantage of the strong affinity between SPION and 69Ge. This is the first in vivo PET/MRI study with a 69Ge-based agent, which holds potential for future multimodality molecular imaging after surface conjugation of various targeting ligands.