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The conceptual design of a high-resolution positron emission tomography (PET) camera is presented. This PET has a transformable transaxial and axial fields of view to facilitate oncology applications. The photomultiplier-quadrant-sharing (PQS) detector design is used to achieve very high resolution with lower cost. It has 38 016 small bismuth germanate crystals (2.68 × 2.68 × 18 mm3, 2.68 × 3.06 × 18 mm3) and 924 photomultipliers (PMTs). The second-generation PQS detectors will be used for this high-resolution-oncologic-transformable PET (HOTPET). Monte Carlo simulations showed that image resolution would vary from 1.8 to 3.0 mm depending on the operating mode (detector ring diameter). The detector ring is made of 12 detector modules. Inside each module, the detector packing fraction is very high, 98.5% in both axial and transaxial dimensions to increase coincidence sensitivity to compensate for the loss from its narrower 13 cm wholebody axial field of view (AFOV) designed to reduce production cost and scatter and accidentals in 3-D imaging. The detector-ring diameter can change from 24 to 83 cm with no gaps between modules. For radiotherapy treatment planning, the ring expands to 100 cm creating an 80 cm patient port (17% detection gap). In the body modes, HOTPET has 44 detector rings (87 image planes). In the brain/breast modes, the detector diameter becomes 53 cm with a large AFOV (21 cm) with 72 detector rings (143 image planes). In the 24-cm mouse mode, coincidence nonlinearity may be reduced to yield a resolution of 1.8-2.2 mm for mouse/rat; it would have 21 cm AFOV providing a 3-7 × higher geometrical coincidence sensitivity over a similar mouse-PET with 8 cm AFOV (no septa). The front-end electronics use the high-yield-pileup-event-recovery electronics to increase the count-rate performance and an automatic PMT gain-equalization for quality control.