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

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.

Keywords: (188)Re; Image quality; Image quantification; Small-animal SPECT.