The impact of two scatter correction methods on I-131 AC-SPECT images using an anthropomorphic phantom with variable sizes of thyroid remnants

Differentiated thyroid cancer treatment typically involves surgical removal of the whole or the largest part of the thyroid gland and a subsequent radioiodine therapy. It is important in diagnostic postsurgical SPECT/CT imaging to provide information on the actual presence and sizes of thyroid remnants. The aim of this work is to assess the impact of two scatter correction methods, the dual energy window (DEW) and the triple energy window (TEW), on the quality of the I-131 SPECT/CT images. Acquisitions were performed using an anthropomorphic neck-thyroid phantom with two thyroid remnants of 1.5 and 3 mL. Activity could be injected in the remnants and the background area. For the first set of acquisitions, the counts in each thyroid remnant from the non-scatter (NSC) and scatter corrected (DEW and TEW) attenuation corrected SPECT (AC-SPECT) images for different administered activity were calculated. For the second set of acquisitions, the image quality in terms of Contrast-to-Noise (CNR), Signal-to-Noise (SNR) ratios and Noise from the NSC, DEW and TEW corrected images were calculated for different remnants-to-background activity ratios. The DEW scatter correction method removed more photons than the TEW one. Even though both scatter correction methods improved image quality, especially for lower background activities and for higher volumes of remnants, this improvement is more profound when applying the TEW method. In addition, two experienced nuclear medicine physicians in a visual evaluation, without having a prior knowledge on any imaging parameters, considered that the TEW scatter corrected AC-SPECT images presented better image quality than the DEW ones. In this study, the qualitative and quantitative comparison of the two scatter correction methods indicated the effectiveness of the TEW method in diagnostic postsurgical thyroid I-131 SPECT/CT imaging.