The Multi-Module, Multi-Resolution SPECT System: A Tool for Variable-Pinhole, Small-Animal Imaging

Abstract

The multi-module, multi-resolution SPECT system (M3R) was developed and evaluated at the University of Arizona's Center for Gamma-Ray Imaging (CGRI). The system consists of four modular gamma cameras stationed around a Cerrobend shielding assembly. Slots machined into the shielding allow for the easy interchange of pinhole apertures, providing M3R with excellent hardware flexibility. Motivation for the system included serving as a prototype for a tabletop, small-animal SPECT system, acting as a testbed for image quality by enabling the experimental validation of imaging theory, and aiding in the development of techniques for the emerging field of adaptive SPECT imaging.Development of the system included design and construction of the shielding assembly and pinhole apertures. The issue of pinhole design and evaluation represents a recurring theme of the presented work. Existing calibration methods were adapted for use with M3R. A new algorithm, the contracting grid-search algorithm, that is capable of being executed in hardware was developed for use in position estimation. The algorithm was successfully applied in software and progress was made in hardware implementation. Special equipment and interpolation techniques were also developed to deal with M3R unique system design and calibration requirements. A code library was created to simplify the many image processing steps required to realize successful analysis of measured image and calibration data and to achieve reconstruction.Observer studies were performed using both projection data and reconstructed images. These observer studies sought to explore signal-detection and activity estimation for various pinhole apertures. Special attention was paid to object variability, including the development and statistical analysis of a phantom capable of generating multiple realizations of a random, textured background. The results of these studies indicate potential for multiple-pinhole, multiplexed apertures but reemphasize the need for careful design and implementation of such complicated imaging elements. Several other techniques were investigated for the evaluation of pinhole apertures. These techniques are less quantitative than rigorous objective methods but offer rapid insight into an aperture's resolution, artifact, and sensitivity characteristics and may find use as predictors of observer performance for certain tasks or in the rapid aperture assessment necessary for successful adaptive SPECT imaging.