188Re image performance assessment using small animal multi-pinhole SPECT/PET/CT system

Purpose: The goal of this study was to investigate the performance of a pre-clinical SPECT/PET/CT system for Re-188 imaging. Methods: Phantom experiments were performed aiming to assess the characteristics of two multipinhole collimators: ultra-high resolution collimator (UHRC) and high-energy ultra high resolution collimator (HE-URHC) for imaging Re-188. The spatial resolution, image contrast and contrast-to-noise ratio (CNR) were investigated using micro-Jaszczak phantoms. Additionally, the quantification accuracy of Re-188 images was evaluated using two custom-designed phantoms. The Re-188 images were compared to those obtained with Tc-99m (gold standard); the acquired energy spectra were analyzed and MonteCarlo simulations of the UHRC were performed. To verify our findings, a C57BL/6-mouse was injected with Re-188-microspheres and scanned with both collimators. Results: The spatial resolution achieved in Re-188 images was comparable to that of Tc-99m. Acquisitions using HE-UHRC yielded Re-188 images with higher contrast and CNR than UHRC. Studies of quantitative accuracy of Re-188 images resulted in <10% errors for both collimators when the activity was calculated within a small VOI around the object of interest. Similar quantification accuracy was achieved for Tc-99m. However, Re-188 images showed much higher levels of noise in the background. Monte-Carlo simulations showed that Re-188 imaging with UHRC is severely affected by down-scattered photons from high-energy emissions. The mouse images showed similar biodistribution of Re-188-microspheres for both collimators. Conclusions: VECTor/CT provided Re-188 images quantitatively accurate and with quality comparable to Tc-99m. However, due to large penetration of UHRC by high-energy photons, the use of the HE-UHRC for imaging Re-188 in VECTor/CT is recommended. (C) 2016 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.