Comparison of ¹⁸F PET and ^99mTc SPECT imaging in phantoms and in tumored mice

Our objective was to compare the performance of a micro-single photon emission computed tomography (micro-SPECT) with that of a micro-positron emission tomography (microPET) in a Her2+ tumored mice using an anti-Her2 nanoparticle radiolabeled with ^99mTc and ¹⁸F. Camera performance was first compared using phantoms; then a tumored mouse administered the ^99mTc-nanoparticle was imaged on a Bioscan NanoSPECT/CT, while another tumored mouse received the identical nanoparticle, labeled now with ¹⁸F, and was imaged on a Philips Mosaic HP PET camera. The nanoparticle was radiolabeled with ^99mTc via MAG₃ chelation and with ¹⁸F via SFB as an intermediate. Phantom imaging showed that the resolution of the SPECT camera was clearly superior, but even with 4 heads and multipinhole collimators, detection sensitivity was 15-fold lower. Radiolabeling of the nanoparticle by chelation with ^99mTc was considerably easier and safer than manual covalent attachment of ¹⁸F. Both cameras provided accurate quantitation of radioactivity over a broad range. In conclusion, when deciding between ^99mTc vs ¹⁸F, an advantage rests with the chelation of ^99mTc over covalent attachment of ¹⁸F, achieved manually or otherwise, but with these small animal cameras, this choice also results in trading lower sensitivity for higher resolution.