VECTor: A Preclinical Imaging System for Simultaneous

neously at high resolutions but require 2 separate imaging systems. This paper introduces a Versatile Emission Computed Tomography system (VECTor) for radionuclides that enables simultaneous submillimeter imaging of single-photon and pos-itron-emitting radiolabeled molecules. Methods: g-photons produced both by electron–positron annihilation and by sin-gle-photon emitters are projected onto the same detectors by means of a novel cylindric high-energy collimator containing 162 narrow pinholes that are grouped in clusters. This collima-tor is placed in an existing SPECT system (U-SPECT-II) with 3 large-field-of-view g-detectors. From the acquired projections, PET and SPECT images are obtained using statistical image re-construction that corrects for energy-dependent system blurring. Results: For PET tracers, the tomographic resolution obtained with a Jaszczak hot rod phantom was less than 0.8 mm, and 0.5-mm resolution images of SPECT tracers were acquired si-multaneously. SPECT images were barely degraded by the si-multaneous presence of a PET tracer, even when the activity concentration of the PET tracer exceeded that of the SPECT tracer by up to a factor of 2.5. Furthermore, we simultaneously acquired fully registered 3- and 4-dimensional multiple functional images from living mice that, in the past, could be obtained only sequentially. Conclusion: High-resolution complementary in-formation about tissue function contained in SPECT and PET tracer distributions can now be obtained simultaneously using a fully integrated imaging device. These combined unique capa-bilities pave the way for new perspectives in imaging the bi-ologic systems of rodents