Reduction of contribution of scattered photons by optimization of energy window settings in 201Tl SPECT imaging: a simulation study

Abstract

Introduction and Objectives: detection of Compton scattered photons is one of the effective factors in reducing the quality of SPECT images. The aim of this study is to reduce the contribution of scattered counts included in the main energy window for 201Tl SPECT imaging in two steps: first step, by determining the location and width of the optimal main energy window, and second step, by using the optimal correction methods.Materials and Methods: in this study, the Monte Carlo program is used to simulate the required phantoms (a cylindrical phantom consist of two small cylinders with different diameters and a simple cardiac phantom), and to produce the projections related to different energy windows.Results: according to the simulation results, among the 13 investigated energy windows, the 30%-wide window with the central energy of 75 keV is determined as the optimal main window for 201Tl SPECT imaging. Also, from the results of this study, two energy window settings are proposed as the most suitable settings for scatter correction of 201Tl SPECT images. In the first case, a second energy window (a 34%-wide window centered at 51 keV) with counts approximately equal to the scattered counts of the optimal main window, and in the second case, two narrow windows (a 8%-wide window centered at 56 keV and a 6%-wide window centered at 92 keV) on both sides of the optimal main window and at a certain distance from two sides of this window are determined as the most suitable energy window settings for these methods.Conclusion: using the optimal main window together with the optimal scatter correction settings proposed in this study leads to a significant improvement of the contrast of 201Tl SPECT images with an acceptable noise level.