High-resolution clustered pinhole 131Iodine SPECT imaging in mice

Introduction: High-resolution pre-clinical I-131 SPECT can facilitate development of new radioiodine therapies for cancer. To this end, it is important to limit resolution-degrading effects of pinhole edge penetration by the high-energy gamma-photons of iodine. Here we introduce, optimize and validate I-131 SPECT performed with a dedicated high-energy clustered multi-pinhole collimator. Methods: A SPECT-CT system (VECTor/CT) with stationary gamma-detectors was equipped with a tungsten collimator with clustered pinholes. Images were reconstructed with pixel-based OSEM, using a dedicated I-131 system matrix that models the distance- and energy-dependent resolution and sensitivity of each pinhole, as well as the intrinsic detector blurring and variable depth of interaction in the detector. The system performance was characterized with phantoms and in vivo static and dynamic I-131-NaI scans of mice. Results: Reconstructed image resolution reached 0.6 mm, while quantitative accuracy measured with a I-131 filled syringe reaches an accuracy of +3.6 +/- 3.5% of the gold standard value. In vivo mice scans illustrated a clear shape of the thyroid and biodistribution of I-131 within the animal. Pharmacokinetics of I-131 was assessed with 15-s time frames from the sequence of dynamic images and time-activity curves of I-131-NaI. Conclusions: High-resolution quantitative and fast dynamic I-131 SPECT in mice is possible by means of a high-energy collimator and optimized system modeling. This enables analysis of I-131 uptake even within small organs in mice, which can be highly valuable for development and optimization of targeted cancer therapies. (C) 2016 Elsevier Inc. All rights reserved.