Discrete NaI(TI) crystal detector optimization for small animal SPECT molecular imaging

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Dual-modality imaging instrumentation has allowed the noninvasive analysis of preclinical models of human disease. A combined microSPECT/CT unit (Siemens) equipped with dual discrete crystal SPECT detectors was under performance evaluation in our laboratory for SPECT molecular imaging. The CT component consists of a CCD x-ray detector and a micro-focus x-ray source (40 [mu] m focal spot). MicroSPECT performance was assessed thru characteristics measurements and high resolution phantoms. Gamma camera SPECT properties investigated using Tc-99m included system photon sensitivity, detection efficiencies, detector uniformity, spectral energy resolution, spatial resolution (FWHM), count rate, and tomograhic pre-clinical performance employing a 3D-OSEM algorithm with geometrical misalignment corrections. Camera gamma-ray sensitivity was calculated to be 3.5, 37 and 73 cps/[mu] Ci for the 0.5, 2 and 3 mm pinhole apertures, respectively. Intrinsic uniformity for the central field of view was 1.42% differential and 2.99% integral. Energy spectral resolution (FWHM) at 140 keVwas 14.3% [plus or minus]1.5 %. Volumetric spatial resolution of 1.2 mm was achieved with a hot-rod Tc-99m SPECT micro-phantom. Camera count rate linearity was achieved up to 1 mCi. In-vivo osteoblastic bone lesions 0.6 mm in diameter measured by CT were also detectable with SPECT Tc-99m-HDP imaging. Spatial resolution (FWHM) results suggest that the microCAT II® SPECT unit is capable of sub-millimeter resolution, however, photon sensitivity improvements either by employing multi-pinhole collimation and/or larger crystal elements will significantly enhance the SPECT pre-clinical performance of the unit.