Development of a clear sub-millimeter small animal PET scanner by reducing the influence of the non-collinearity effect

Abstract

Small animal PET plays a major role in studying molecular processes in vivo. However, the spatial resolution of small animal PET is limited by physical effects like positron range, photon non-collinearity, and object scattering. The aim of this project was to minimize the influence of the non-collinearity effect by reducing the distance between the coincidence detectors leading to an improved spatial resolution. A multi-wire proportional chamber-based high-resolution PET scanner (quadHIDAC) was used, offering a spatial resolution of nearly 1 mm FWHM. By removing two opposite detector banks of the 4-detector-setup, the inner distance between the two remaining detector plates could be reduced from 180 mm to 40 mm. List mode acquisitions of a small point source (22Na) experiment were performed, images were reconstructed (0.25 mm voxel size) using a one-pass list-mode EM algorithm and the FWHM in the radial, tangential, and axial directions was calculated. In addition, a Jaszczak phantom (hole sizes of 0.7 up to 1.2 mm) was acquired with both scanners. The prototype high-resolution PET scanner showed improved spatial resolution in radial (0.9 mm FWHM), tangential (0.9 mm FWHM), and axial (0.8 mm FWHM) direction compared to the quadHIDAC scanner (1.x mm, 1.x mm, 1.x mm), respectively offering clear sub-millimeter imaging. Blurring effects due to photon non-collinearity could be reduced by minimizing the detector distance.