量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum Science and Technology.
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Purpose: Brain PET imaging is useful for clinical practice and molecular imaging research. High-resolution and high-sensitivity PET systems are highly required for accurate brain functional imaging. Therefore, we have developed a brain-dedicated PET prototype, in which depth-of-interaction (DOI) detectors are arranged to form a hemisphere. On the other hand, some of standardized performance evaluation methods, which are originally proposed for whole-body PET systems, may not be suitable for a next-generation hemispherical brain PET system. Therefore, in this paper, we extended conventional performance evaluation methods so as to be applied to a hemispherical brain PET system.
\nMaterials and Methods: The NEMA NU-2 performance evaluation protocol was applied to the prototype, but the NEMA image quality phantom did not fit the prototype. In addition, the Hoffman 3-dimensional brain phantom, which is often used for imaging performance evaluation, did not fit the hemispherical detector arrangement. Therefore, we made a small image quality phantom and a hemispherical Hoffman phantom based on the original phantoms so as not to largely change activity distribution. Then, we experimentally evaluated imaging performance of the prototype, which had 54 four-layer DOI detectors (47 detectors for the hemisphere and the other 7 detectors placed at the back of the neck). We evaluated image quality using our developed small image quality phantom (Six spheres inner diameters: 22, 17, 13, 10, 8 and 5 mm) and hemispherical Hoffman brain phantom. The hot-sphere-to-background activity ratio was 3 which simulating brain tumor PET imaging. We then measured hot-sphere-to-background percent contrast (%contrast) and evaluated gray-to-white matter contrast in comparison with the digital Hoffman phantom.
\nResults: The NEMA NU-2 performance evaluation protocol was partially and successfully modified to the prototype. The %contrast of the 8-mm-sphere was 46.9%. The gray-to-white matter contrast was visually better than that of the digital phantom smoothed with 8-mm FWHM Gaussian filter, which has been often used as a reference resolution image.
\nConclusion: Standardized performance evaluation methods were successfully extended to hemispherical brain PET scanners by using our newly developed phantoms. We confirmed high imaging performance of our brain PET system.
Standardized performance evaluation of a brain-dedicated PET scanner with hemispherical detector arrangement
