Initial clinical test of the first Helmet-Chin PET prototype for highly sensitive brain imaging

254 Objectives With progress in clinical studies on recently developed diagnostic medicine approaches for dementia, there is an emerging demand for dedicated brain PET scanners to provide early diagnosis of the disease. Therefore, we have proposed the Helmet-Chin PET, a novel geometry for highly sensitive brain imaging based on a hemispheric arrangement of detectors. For a proof-of-concept, last year we developed the first prototype using 4-layered depth-of-interaction (DOI) detectors. Following successful realization of phantom imaging, we conducted the first clinical test which we describe in this paper. Methods The Helmet-Chin PET prototype was developed using 54 DOI detectors, each of which consisted of 16×16×4 Zr-doped GSO crystals (2.8×2.8×7.5 mm3) and a high sensitivity 64-channel flat-panel photomultiplier tube. In the prototype, 47 detectors were used to form a hemisphere of 25 cm inner diameter and 50 cm outer diameter, and 7 detectors were used for the chin detector. First of all, we compared sensitivity for the brain region with a commercial scanner to determine injection activity. We measured the count rate performance of the prototype and that of a whole-body PET, Biograph mCT Flow 64-4R PET/CT system (Siemens Medical Solutions USA, Inc.). The mCT consisted of four detector rings 84 cm in diameter, having 192 detectors, each of which consisted of 13×13 LSO crystals (4×4×20 mm3). We made a pool phantom with a shape of hemisphere with inner diameter of 20 cm filled with 18F solution. The phantom was measured with the prototype and the mCT for 5 min. Following the sensitivity assessment, we conducted the initial clinical test using the prototype. A healthy volunteer was measured for 18 min beginning 85 min after 18F-FDG injection of 70 MBq. For attenuation correction, the separately scanned CT image was registered. Results The measured sensitivity for the brain region was 17.4 kcps/MBq for the Helmet-Chin PET prototype and 9.3 kcps/MBq for the mCT, where the energy windows were 400-600 keV and 435-650 keV, respectively. The sensitivity of the Helmet-Chin PET for the brain region was almost twice as high as that of the mCT, even though the number of detectors was less than 30% that of the mCT. For the initial clinical test, we could obtain a clear image of the brain with low radioactivity injection. Conclusions Our initial clinical test using the first prototype showed that the Helmet-Chin PET has promising performance for highly sensitive brain imaging.