ANALYSIS OF THE RECONSTRUCTIBILITY AND NOISE PROPERTIES OF SCATTERED PHOTONS IN TC-99M SPECT

Since scattered photons carry degraded spatial information, scatter is typically considered a source of contamination in SPECT. However, wit h the advent of scatter modelling methods and reconstruction-based sca tter compensation (RBSC), it may be possible to utilize scattered data in a productive manner. in this work we analyse the reconstructibilit y of scattered photon projection data and investigate the potential fo r using scattered photons to reduce the noise levels of SPECT images. We have simulated projection data for an elliptical phantom containing three cold rods in a uniform background of Tc-99m activity. A variety of photopeak and scatter energy windows were formed, as well as corre sponding RBSC transfer matrices. Each statistically weighted matrix wa s decomposed using SVD and analysed in terms of reconstructibility and noise properties. Results indicate that scattered photons contain suf ficient information to reconstruct the source activity, but the scatte r-only matrices are very poorly conditioned. We have also evaluated se veral methods of utilizing scattered events via RBSC, and compared the m with other, idealized methods of handling scatter. It was found that scattered photons can be used productively when photopeak and non-pho topeak data are separated through the use of multiple energy windows. The RBSC methods outperformed ideal scatter subtraction, but fell shor t of methods which assume perfect discrimination between scattered and primary events. The knowledge gained by this study may help guide fut ure research and lead to better approaches to handling scatter in SPEC T.