Application of reconstruction-based scatter compensation to Tl-201 SPECT

Scatter compensation in Tl-201 SPECT presents an interesting challenge because of the multiple emission energies and relatively large proportion of scattered photons. Reconstruction-based scatter compensation (RBSC), in which the scatter response function is modeled during the reconstruction, can improve quantitative accuracy and contrast while maintaining or even reducing image noise levels. In this work we investigate methods of applying RBSC to Tl-201 SPECT and study the noise levels resulting from each method. We have applied RBSC to a simulated phantom experiment using a variety of single and multiple energy window schemes. The RBSC methods were also compared with other methods of handling scatter. Singular value decomposition (SVD) of the system transfer matrix was used to analyze the noise levels of each method in a regularization-independent manner. Results indicate that inclusion of higher energy gamma peak data leads to reduced noise over using only X-ray emission data. In addition, using a different window for each emission energy gives better performance than acquiring into a single wide energy window. Non-photopeak window data can also be included to reduce image noise. These results are supported by analysis of iteratively reconstructed MLEM images.