Attenuation correction in single-photon emission computed tomography for NURBS-based cardiac-torso phantom using dual-energy acquisition

Hossein Rajabi; Hadi Taleshi Ahangari; Iraj Mohammadi; Alireza Mohammadkarim; Mohammad Ali Tajik-Mansoury

doi:10.4103/wjnm.WJNM_55_19

Attenuation correction in single-photon emission computed tomography for NURBS-based cardiac-torso phantom using dual-energy acquisition

World J Nucl Med. 2020 Aug 22;19(3):211-219. doi: 10.4103/wjnm.WJNM_55_19. eCollection 2020 Jul-Sep.

Authors

Hossein Rajabi¹, Hadi Taleshi Ahangari², Iraj Mohammadi^{3

4}, Alireza Mohammadkarim², Mohammad Ali Tajik-Mansoury²

Affiliations

¹ Department of Medical Physics, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran.
² Department of Medical Physics, Faculty of Medicine, Semnan University of Medical Sciences, Semnan, Iran.
³ Department of Basic Sciences, Faculty of Medicine, Sari Branch, Islamic Azad University, Sari, Iran.
⁴ Institute of Biophysics and Biomedical Engineering, Faculty of Sciences, University of Lisbon, Lisbon, Portugal.

Abstract

Single photon emission tomography is widely used to detect photons emitted from the patient. Some of these emitted photons suffer from scattering and absorption because of the attenuation occurred through their path in patient's body. Therefore, the attenuation is the most important problem in single-photon emission computed tomography (SPECT) imaging. Some of the radioisotopes emit gamma rays in different energy levels, and consequently, they have different counts and attenuation coefficients. Calculation of the parameters used in the attenuation equation N _out=αN_in = e^- ^μ ^l N_in by mathematical methods is useful for the attenuation correction. Nurbs-based cardiac-torso (NCAT) phantom with an adequate attenuation coefficient and activity distribution is used in this study. Simulations were done using SimSET in 20-70 and 20-167 keV. A total of 128 projections were acquired over 360°. The corrected and reference images were compared using a universal image quality index (UIQI). The simulation repeated using NCAT phantom by SimSET. In the first group, no attenuation correction was used, but the Zubal coefficients were used for attenuation correction in the second image group. After the image reconstruction, a comparison between image groups was done using optimized UIQI to determine the quality of used reconstruction methods. Similarities of images were investigated by considering the average sinogram for every block size. The results showed that the proposed method improved the image quality. This study showed that simulation studies are useful tools in the investigation of nuclear medicine researches. We produced a nonattenuated model using Monte Carlo simulation method and compared it with an attenuated model. The proposed reconstruction method improved image resolution and contrast. Regional and general similarities of images could be determined, respectively, from acquired UIQI of small and large block sizes. Resulted curves from both small and large block sizes showed a good similarity between reconstructed and ideal images.

Keywords: Attenuation correction; SimSET; nurbs-based cardiac-torso phantom; single photon emission computed tomography; universal image quality index.