Study on High Density Scintillators and Multi-energy Windows for Improving I-131 Gamma Image Quality: Monte Carlo Simulation Approach

• Published in: Journal of the Korean Physical Society Vol. 74; no. 3; pp. 305 - 311
• Main Authors: Kim, Minho, Bae, Jae Keon, Hong, Bong Hwan, Kim, Kyeong Min, Lee, Wonho
• Format: Journal Article
• Language: English
• Published: Seoul The Korean Physical Society 01.02.2019; Springer Nature B.V; 한국물리학회
• Subjects: Collimation; Collimators; Computer simulation; Energy; Feasibility studies; Gamma rays; Image contrast; Image degradation; Image quality; Mathematical and Computational Physics; Monte Carlo simulation; Particle and Nuclear Physics; Performance indices; Physics; Physics and Astronomy; Scattering; Scintillation counters; Spatial resolution; Theoretical; 물리학; Gamma-camera; GAGG; Iodine-131; Monte Carlo simulation; Scatter-Correction
• ISSN: 0374-4884; 1976-8524
• DOI: 10.3938/jkps.74.305

An energy window with a gamma peak centered at 364 keV (86%) is usually used for I-131 imaging. However, the image performance indexes such as image count, scatter fraction (SF), spatial resolution (SR) obtained using a conventional gamma camera, which uses a 3/8-in sodium iodide scintillator, are poor mainly due to its low detection efficiency. In this study, we investigated the feasibility of using a higher energy peak (637 and 723 keV) for the energy window to obtain a better imaging performance compared with the conventional I-131 imaging method. GATE (v7.0), which is based on Monte Carlo method, was used for performing simulations. A clinical gamma camera, SYMBIA-T2 (Siemens), was mounted on a NaI scintillator in the simulation. A GAGG scintillator was also realized for effective detection of high energy gamma, in addition to using high energy (HE) and ultrahigh energy (UHE) collimators. We obtained I-131 planar images through the conventionally used window method (364 keV ± 10%). The high-energy gamma ray of I 131 (637 and 723 keV) have been additionally used for improving image performance. The scatter correction method was applied to images for suppressing scatter due to high-energy gamma rays. Various indexes are used for validating image performance such as SR, SF, and contrast-to-noise ratio. High-energy gamma rays could be used to increase the image counts, but the other image performances were degraded compared to the scatter-corrected 364 keV images (SF of 6.33 - 27.73%; SR of 0.93 - 6.02%). The UHE collimator was useful in obtaining a better spatial resolution and suppressing scatter components compared with the HE collimator. However, it did not exhibit a sufficient image performance to be considered as a replacement for the HE collimator. In order to use the high-energy gamma rays of I-131 (637 and 723 keV), it is necessary to design a new collimator to control penetration and improve resolution, instead of using a UHE collimator. Furthermore, scatter correction methods also need to be optimized.