The relative importance of energy resolution for quantitative Tc-99m SPECT imaging

We seek to determine the desired energy resolution for quantitative SPECT imaging. As the energy resolution of the sytem is improved, the relative error due to scatter decreases. Yet, at some point the improvement becomes inconsequential since the scatter error is small compared to the other physical perturbations in the radionuclide measurement. In order to estimate the energy resolution at which this condition becomes true, we used a Monte Carlo code to simulate the emission data from a myocardial perfusion phantom. The data were reconstructed using a maximum likelihood code, and the images were analyzed to determine the relative effects of attenuation correction, collimator response compensation, noise, and scatter rejection on image quantitation. The simulations showed that improving the system energy resolution beyond 5 keV offers little benefit for myocardial perfusion studies as judged by the noise in a 9-pixel ROI. The relevance of this result to other applications is also discussed.