Direct imaging of radionuclide-produced electrons and positrons with an ultrathin phosphor

Current electron detectors are either unable to image in vivo or lack sufficient spatial resolution because of electron scattering in thick detector materials. This study was aimed at developing a sensitive high-resolution system capable of detecting electron-emitting isotopes in vivo. Methods: The system uses a lens-coupled charge-coupled-device camera to capture the scintillation light excited by an electron-emitting object near an ultrathin phosphor. The spatial resolution and sensitivity of the system were measured with a 3.7-kBq ⁹⁰Y/⁹⁰Sr b-source and a 70-μm resin bead labeled with ^99mTc. Finally, we imaged the ^99mTc-pertechnetate concentration in the mandibular gland of a mouse in vivo. Results: Useful images were obtained with only a few hundred emitted β particles from the ⁹⁰Y/⁹⁰Sr source or conversion electrons from the ^99mTc bead source. The in vivo image showed a clear profile of the mandibular gland and many fine details with exposures of as low as 30 s. All measurements were consistent with a spatial resolution of about 50 μm, corresponding to 2.5 detector pixels with the current camera. Conclusion: Our new electron-imaging system can image electron-emitting isotope distributions at high resolution and sensitivity. The system is useful for in vivo imaging of small animals and small, exposed regions on humans. The ability to image β particles, positrons, and conversion electrons makes the system applicable to most isotopes.