Image quality analysis of 44Sc on two preclinical PET scanners: a comparison to 68Ga

Abstract

Background: 44 Sc has been increasingly investigated as a potential alternative to 68 Ga in the development of tracers for positron emission tomography (PET). The lower mean positron energy of 44 Sc (0.63 MeV) compared to 68 Ga (0.83 MeV) can result in better spatial image resolutions. However, high-energy γ-rays (1157 keV) are emitted at high rates (99.9%) during 44 Sc decay, which can reduce image quality. Therefore, we investigated the impact of these physical properties and performed an unbiased performance evaluation of 44 Sc and 68 Ga with different imaging phantoms (image quality phantom, Derenzo phantom, and three-rod phantom) on two preclinical PET scanners (Mediso nanoScan PET/MRI, Siemens microPET Focus 120). Results: Despite the presence of high-energy γ-rays in 44 Sc decay, a higher image resolution of small structures was observed with 44 Sc when compared to 68 Ga. Structures as small as 1.3 mm using the Mediso system, and as small as 1.0 mm using the Siemens system, could be visualized and analyzed by calculating full width at half maximum. Full widths at half maxima were similar for both isotopes. For image quality comparison, we calculated recovery coefficients in 1-5 mm rods and spillover ratios in either air, water, or bone-equivalent material (Teflon). Recovery coefficients for 44 Sc were significantly higher than those for 68 Ga. Despite the lower positron energy, 44 Sc-derived spillover ratio (SOR) values were similar or slightly higher to 68 Ga-derived SOR values. This may be attributed to the higher background caused by the additional γ-rays. On the Siemens system, an overestimation of scatter correction in the central part of the phantom was observed causing a virtual disappearance of spillover inside the three-rod phantom. Conclusion: Based on these findings, 44 Sc appears to be a suitable alternative to 68 Ga. The superior image resolution makes it an especially strong competitor in preclinical settings. The additional γ-emissions have a small impact on the imaging resolution but cause higher background noises and can effect an overestimation of scatter correction, depending on the PET system and phantom.

Dual-Time Point [68Ga]Ga-PSMA-11 PET/CT Hybrid Imaging for Staging and Restaging of Prostate Cancer

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Diagnosis of Pancreatic Ductal Adenocarcinoma by Immuno-Positron Emission Tomography

“…In addition to its short half-life, a key advantage of 68 Ga or 44 Sc is that they can be produced from a commercially available 68 Ge/ 68 Ga or 44 Ti/ 44 Sc generator allowing their production to be cyclotron-independent, making it accessible to any PET center and at a lower economic cost [ 77 , 78 , 79 ]. With regards to 44 Sc, as it emits prompt gamma-rays right after the positron emission, it can be distinguished from standard positron emitters like 68 Ga or 18 F, enabling multiplexed PET (mPET) imaging [ 80 , 81 , 82 ]. This technique allows for the accurate simultaneous non-invasive imaging of two different radiotracers with preclinical and clinical PET scanners [ 82 ].…”

Production of scandium radionuclides for theranostic applications: towards standardization of quality requirements

“…The impact of physical properties of 44g Sc on image quality has been studied by Bunka et al (Bunka et al 2016) and recently evaluated by Rosar et al (Rosar et al 2020) in comparison to 68 Ga with different imaging phantoms. The lower mean positron energy of 44g Sc (0.63 MeV) compared to 68 Ga (0.83 MeV) can result in better spatial image resolutions.…”