FIGURE 18-18 PET scanner geometries based on discrete scintillator elements (top row) or continuous scintillator plates (bottom row). A, Full ring of modular block detectors. B, Partial ring of modular block detectors. C, Hexagonal array of quadrant-sharing panel detectors. D, Dual-headed gamma camera with coincidence circuitry. E, Hexagonal array of gamma camera detectors. F, Continuous detectors using curved plates of NaI(Tl). A complete set of profiles can be acquired without motion with systems shown in A. C, E, and F, whereas detector motion is required with systems shown in B and D.