Monte Carlo Simulations of the GE Signa PET/MR for Different Radioisotopes

Abstract

NEMA characterization of PET systems is generally based on 18 F because it is the most relevant radioisotope for the clinical use of PET. 18 F has a half-life of 109.7 min and decays into stable 18 O via β+ emission with a probability of over 96% and a maximum positron energy of 0.633 MeV. Other commercially available PET radioisotopes, such as 82 Rb and 68 Ga have more complex decay schemes with a variety of prompt gammas, which can directly fall into the energy window and induce false coincidence detections by the PET scanner. Methods: Aim of this work was threefold: (A) Develop a GATE model of the GE Signa PET/MR to perform realistic and relevant Monte Carlo simulations (B) Validate this model with published sensitivity and Noise Equivalent Count Rate (NECR) data for 18 F and 68 Ga (C) Use the validated GATE-model to predict the system performance for other PET isotopes including 11 C, 15 O, 13 N, 82 Rb, and 68 Ga and to evaluate the effect of a 3T magnetic field on the positron range. Results: Simulated sensitivity and NECR tests performed with the GATE-model for different radioisotopes were in line with literature values. Simulated sensitivities for 18 F and 68 Ga were 21.2 and 19.0 /kBq, respectively, for the center position and 21.1 and 19.0 cps/kBq, respectively, for the 10 cm off-center position compared to the corresponding measured values of 21.8 and 20.0 cps/kBq for the center position and 21.1 and 19.6 cps/kBq for the 10 cm off-center position. In terms of NECR, the simulated peak NECR was 216.8 kcps at 17.40 kBq/ml for 18 F and 207.1 kcps at 20.10 kBq/ml for 68 Ga compared to the measured peak NECR of 216.8 kcps at 18.60 kBq/ml and 205.6 kcps at 20.40 kBq/ml for 18 F and 68 Ga, respectively. For 11 C, 13 N, and 15 O, results confirmed a peak NECR similar to 18 F with the effective activity concentration scaled by the inverse of the positron fraction. For 82 Rb, and 68 Ga, the peak NECR was lower than for 18 F while the corresponding activity concentrations were higher. For the higher energy positron emitters, the positron range was confirmed to be

Comparison of image quality and spatial resolution between 18F, 68Ga, and 64Cu phantom measurements using a digital Biograph Vision PET/CT

“…The more precise measurements also offer new possibilities for analyses of the impact of different radionuclides and their physical properties on image quality and detectability of small lesions. The maximum positron energy and thus the mean range in tissue differ between 68 Ga, 18 F, and 64 Cu: Positrons arising from the decay of 68 Ga feature an endpoint energy three times higher than those of 18 F or 64 Cu and therefore have a much greater mean range in tissue ( 68 Ga: 3.5 mm; 18 F: 0.6 mm; 64 Cu: 0.7 mm) (Table 1 ) [ 6 ]. This degrades the spatial resolution of 68 Ga-PET.…”

“…The individual impact of different physical properties of PET nuclides on PET image quality and spatial resolution has already been studied in detail, including the use of preclinical PET/CT scanners with a higher intrinsic spatial resolution than clinical PET/CT scanners [ 7 – 10 ]. In addition, different simulations have been performed on this topic [ 6 , 10 – 12 ]. However, no analyses have been performed on PET data recorded on PET/CT scanners of the newest generation, which allow for more accurate PET measurements by applying time-of-flight (ToF) measurements and point spread function (PSF) reconstruction.…”

Implementation of a Spatially-Variant and Tissue-Dependent Positron Range Correction for PET/CT Imaging

“…Deviations can be attributed to the use of different physics definitions within the MC simulation frameworks (containing the positron cross sections, step size) and the definition of the materials (composition and mass density), as well as the radioactive source definitions. The largest deviation was −36% for 18 F in bone material when comparing the PR to the published values by Caribé et al (2020) . For PRs in water, the same values were calculated for both 18 F and 68 Ga.…”

The effect of magnetic field strength on the positron range and projected annihilation artifact in integrated PET/MR systems: A GATE Monte Carlo study

“…15 Caribé et al used GATE MC simulations to predict sensitivity and noise equivalent count rate (NECR) performance of GE Signa PET/MR for 11 C, 13 N, 15 O, 18 F, 68 Ga, and 82 Rb radioisotopes. 16 Aside from these technology defectives, PET/MR presents other challenges in the practice. The attenuation correction with MR information is one of the most challenging topics in hybrid imaging now.…”

“…Caribé et al. used GATE MC simulations to predict sensitivity and noise equivalent count rate (NECR) performance of GE Signa PET/MR for 11 C, 13 N, 15 O, 18 F, 68 Ga, and 82 Rb radioisotopes 16 …”