Monte Carlo Simulation of Characteristics of Discovery NM/CT 670 Pro SPECT System for Routinely Used Diagnostic and Therapeutic Radionuclides.

The collimator in the SPECT imaging system is a critical component that uniquely influences image quality. Collimator selection for the imaging of the specific isotope is of the utmost importance. This study used Monte Carlo simulations to evaluate the response of different collimators for commonly used radionuclides in SPECT imaging. Methods: The Simulating Medical Imaging Nuclear Detectors Monte Carlo program was used to simulate the Discovery NM/CT 670 Pro SPECT system equipped for a collimator-radionuclide pair to optimize the selection of the collimator for SPECT imaging. Low-energy high-resolution (LEHR), medium-energy general-purpose (MEGP), and high-energy general-purpose (HEGP) collimators were simulated with ^99mTc, ¹⁷⁷Lu, and ¹³¹I point sources (1 MBq) to evaluate spatial resolution, sensitivity, scatter fraction, and septal penetration. The results were analyzed for the optimization of the collimator-radionuclide pair. Results: For ^99mTc (γ-energy, 140 keV), the resolution (full width at half maximum), sensitivity, scatter fraction, and septal penetration for LEHR, MEGP, and HEGP were 7.03 mm, 189 counts per minute (cpm)/μCi, 3.50%, and 2.65%; 9.3 mm, 184 cpm/μCi, 2.32%, and 1.35%; and 11.3 mm, 224 cpm/μCi, 2.05%, and 1.27%, respectively. For ¹⁷⁷Lu (γ-energy, 113 and 208 keV), the respective values were 7.5 mm, 62.52 cpm/μCi, 22.22%, and 18.56%; 9.6 mm, 20 cpm/μCi, 3.36%, and 2.19%; and 12.03 mm, 25 cpm/μCi, 2.88%, and 1.89%. For ¹³¹I (γ-energy, 364 keV), the respective values were 11.5 mm, 6,027 cpm/μCi, 28.80%, and 49.78%; 11.3 mm, 152 cpm/μCi, 43.49%, and 32.89%; and 14.08 mm, 86 cpm/μCi, 23.85%, and 17.96%. Conclusion: The study highlighted the need to understand collimator characteristics as a function of photon energy, where quantitative evaluation is the main aspect. The study suggests that the collimators that had optimal characteristics for imaging with ^99mTc, ¹⁷⁷Lu, and ¹³¹I were the LEHR, MEGP, and HEGP collimators, respectively.