Presentation Standardized performance evaluation of a brain-dedicated PET scanner with hemispherical detector arrangement

赤松, 剛  ,  田島, 英朗  ,  岩男, 悠真  ,  脇坂, 秀克  ,  前田, 貴雅  ,  吉田, 英治  ,  山下, 大地  ,  山谷, 泰賀

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. Materials 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. Results: 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.Conclusion: 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.

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