The Engineering and Initial Results of a Transformable Low-cost High-Resolution PET Camera

We have developed a high-resolution transformable positron emission tomography (PET) camera that can be configured into either a whole-body mode (83-cm detector ring diameter, 13-cm axial field-of-view (AFOV)) or a brain/breast/axilla (54-cm detector ring diameter, 21-cm AFOV) mode. The camera has 12 rectangular detector modules, and the detector gap between adjacent modules is very small and remains constant for each configuration. Each module has a large detection area (13 cm times 21 cm) and 38016 bismuth germanate (BGO) detector crystals of 2.7 times 2.7 times 18 mm
³
with built-in front-end electronics. To improve spatial sampling, the gantry on which the camera is mounted can be rotated 30deg with a fine step size of 1deg, and the high-speed electronics and detector modules also rotate along with the gantry. This system uses only 924 photomultiplier tubes (PMT) by applying a low-cost high-resolution PMT-quadrant-sharing detector design. To compensate for the slower scintillation timing of BGO detectors, the camera is equipped with the "HYPER", high-yield pile-up event recovery front-end electronics. A fast light-emitting diode (LED) cross-reference PMT tuning method is used to maintain the PMT gain balance. The system has been constructed and tested for preliminary imaging characteristics. The system sensitivity is 4.2% for whole-body and 9.2% for brain/breast/axilla mode measured with Na-22 at center of field of view (FOV). For brain/breast/axilla modes, the transaxial image resolutions at 0 and 10 cm were found to be 2.7 and 4.0 mm, respectively, while for whole-body mode, the image resolutions were 3.3 and 3.9 mm. The slice thickness resolution ranged from 2.6 to 3.3 mm for middle 7 detector rings in brain/breast/axilla modes. High quality Hoffman brain phantom images were obtained in both brain and whole-body modes.