TITLE: Investigation of Multi-Pinhole Collimator Designs and Imaging Reconstruction Methods for Imaging Small Animals with Different Sizes using a SPECT/CT Imaging System


AUTHORS: G.S.P. Mok, Y. Wang, J. Li, D. J. Wagenaar and B.M.W. Tsui


PURPOSE: The purpose of this study is to investigate multi-pinhole (MPH) collimator designs and SPECT imaging reconstruction methods for imaging small animals with different sizes using a Gamma Medica-Ideas X-SPECT small animal SPECT/CT system.


METHODS AND MATERIALS: Both Monte Carlo simulation and experimental methods were used to evaluate the effects of MPH collimator design and imaging geometry on the reconstructed image quality.  Monte Carlo simulation methods were used to generate MPH projection data from a digitized Defrise phantom and a realistic 4D digital mouse whole body (MOBY) phantom using MPH collimators with different pinhole numbers, hole patterns and imaging geometries. The X-SPECT small animal imaging system was fitted with a prototype MPH collimator system with interchangeable pinhole patterns and adjustable magnification optimized for small animals of different sizes.  Experimental projection data were acquired from a physical Defrise phantom, an ultra-resolution SPECT phantom and mice injected with Tc-99m MDP. All MPH projection data were reconstructed using an iterative 3D OS-EM based MPH image reconstruction method with accurate correction for system misalignments.  The 3D MPH reconstructed images from the simulation study were compared to the phantom images and were evaluated in terms of normalized mean square error and normalized standard deviation over selected regions-of-interests (ROIs) to assess the reconstructed image quality and artifacts.  Those from the experimental studies were compared to the corresponding single pinhole (SPH) images for image artifact generation and image noise reduction.


RESULTS: Our results indicate that MPH SPECT provides increased detection efficiency and lower image noise[a1]  as compared to SPH with concomitant increased image artifacts and distortions which are also dependent on the pinhole pattern.  The imaging of small animals with different sizes requires different imaging geometries



CONCLUSIONS: We conclude that MPH SPECT with significant increase in detection efficiency and minimal artifacts and distortions is feasible with careful considerations of the different contributing factors.



FUNDING SOURCES: This work is supported by the NIH research grant EB001558




 [a1]Lower image noise or increased signal-to-noise ratio? I thought more pinholes means more noise, but with increased S/N ratio, the image quality is improved. Correct me if I misunderstood.