ABSTRACT
PURPOSE: The goal of this study was to investigate the performance of a pre-clinical SPECT/PET/CT system for 188Re imaging. METHODS: Phantom experiments were performed aiming to assess the characteristics of two multi-pinhole collimators: ultra-high resolution collimator (UHRC) and high-energy ultra high resolution collimator (HE-URHC) for imaging 188Re. The spatial resolution, image contrast and contrast-to-noise ratio (CNR) were investigated using micro-Jaszczak phantoms. Additionally, the quantification accuracy of 188Re images was evaluated using two custom-designed phantoms. The 188Re images were compared to those obtained with 99mTc (gold standard); the acquired energy spectra were analyzed and Monte-Carlo simulations of the UHRC were performed. To verify our findings, a C57BL/6-mouse was injected with 188Re-microspheres and scanned with both collimators. RESULTS: The spatial resolution achieved in 188Re images was comparable to that of 99mTc. Acquisitions using HE-UHRC yielded 188Re images with higher contrast and CNR than UHRC. Studies of quantitative accuracy of 188Re 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 99mTc. However, 188Re images showed much higher levels of noise in the background. Monte-Carlo simulations showed that 188Re imaging with UHRC is severely affected by down-scattered photons from high-energy emissions. The mouse images showed similar biodistribution of 188Re-microspheres for both collimators. CONCLUSIONS: VECTor/CT provided 188Re images quantitatively accurate and with quality comparable to 99mTc. However, due to large penetration of UHRC by high-energy photons, the use of the HE-UHRC for imaging 188Re in VECTor/CT is recommended.
