Presentation Small lesion imaging performance of a novel helmet-neck PET prototype: a phantom study

Akamatsu, Go  ,  Tashima, Hideaki  ,  Iwao, Yuma  ,  Wakizaka, Hidekatsu  ,  Maeda, Takamasa  ,  Yoshida, Eiji  ,  Yamashita, Taichi  ,  Yamaya, Taiga

Objectives: Brain PET imaging is frequently used in clinical practice and research. A high lesion detectability is required in neuro-oncology field because the brain tumor extent is clinically relevant. Therefore, we have developed a brain-dedicated high-resolution and high-sensitivity PET prototype. In this study, we evaluated the small lesion imaging performance of the brain PET prototype using a small sphere phantom. Materials and methods: The helmet-neck PET is our original brain PET system, in which 47 four-layer depth-of-interaction detectors are used to form a hemisphere and 7 of them are placed on the neck part. The phantom had six small spheres (Inner diameters: 22, 17, 13, 10, 8, and 5 mm), which were filled with three times higher radioactivity concentration of the background. The background radioactivity was 1.32kBq/mL, which was generally half radioactivity level compared with clinical neuro-oncology PET. PET data were acquired for 20-min and were reconstructed with ordered-subsets expectation-maximization algorithm. The %contrast in each sphere and coefficient-of-variation on the background area (CVBG) were calculated to evaluate lesion detectability and image quality. Results: On the images reconstructed with 8-iterations and 8-subsets, the 8-mm-sphere was clearly observed. The %contrast of the 8-mm-sphere was 35.8% and the CVBG was 16.0%. The %contrast obviously achieved the criteria described by the previous report (%contrast >13%). Conclusion: The novel helmet-neck PET showed great small lesion detectability even though the radioactivity level was a lower condition. Therefore, the helmet-neck PET has a potential to not only improve small lesion detectability but also reduce injection activity or scanning duration.

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