Improving image quality in terbium-161 phantom imaging: Quantitative evaluation of DEW and TEW scatter correction...

Terbium-161 (Tb-161) emits gamma rays and beta radiation, enabling both therapeutic and imaging applications. However, the multiple gamma emissions of ¹⁶¹Tb can affect image quality by increasing the scattering rate during SPECT imaging. To improve image quality, appropriate scatter correction methods, such as Dual-Energy Window (DEW) and Triple-Energy Window (TEW) need to be optimized. Although these methods are used in clinical practice, studies investigating the efficacy of spectral analysis approaches for next-generation radionuclides with multiple gamma emissions, such as ¹⁶¹Tb, are limited.

This study aims to evaluate the effects of DEW and TEW scatter correction methods on image quality and quantitative accuracy in ¹⁶¹Tb SPECT imaging compared to uncorrected images.

Three distinct reference geometries were utilized to determine the gamma camera calibration factor (CF) and to evaluate the image quality parameters. Five image protocols were used, each with different combinations of main photopeak and scatter energy windows. Image quality parameters (CF, contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR), spatial resolution) and activity bias (%) were compared using LifeX software in both uncorrected and corrected SPECT images.

The CF calculated in images acquired with an energy window of 48.9 keV was found to be higher than that calculated in an energy window of 74.6 keV. The best CNR was calculated for images acquired in air with a photopeak of 48.9 keV ± 10% and a scatter window of 6%. In scattered media, it was observed in images obtained with a photopeak of 74.6 keV ± 10% and a scatter window of 6%. When scatter correction was applied, the images' SNR values decreased slightly, ranging from 1.188 to 1.724 across all media. Scatter correction techniques reduced the FWHM values for all protocols except the air medium, thereby improving spatial resolution. Activity bias results showed an overestimation in uncorrected protocols including the 48.9 keV peak. Conversely, utilizing the 74.6 keV peak with TEW correction improved quantitative accuracy to a 3.7%-4.2% absolute bias.

Our results show that both DEW and TEW correction approaches improve spatial resolution and increase CNR by reducing scattering contributions and background noise. However, as expected with the subtraction of scattered effects, these enhancements are accompanied by a slight decrease in SNR. The TEW method performed better than the DEW method in terms of quantitative accuracy under scattering conditions. In SPECT imaging using therapeutic amounts of Tb-161, high image quality can be achieved with an energy window of 74.6 keV ± 10%.