a two-dimensional array of elongated scintillation crystals to be positioned on a detector ring, wherein the two-dimensional array of elongated scintillation crystals includes M rows of elongated scintillation crystals in an axial direction of the detector ring and N columns of elongated scintillation crystals in a transaxial direction of the detector ring, where M and N are each an integer value,

wherein each elongated scintillation crystal includes a proximal end-face, a distal end-face to be oriented into the detector to receive a gamma photon, and four lateral faces, including an axially oriented first lateral face, an axially oriented second lateral face, a transaxially oriented third lateral face, and a transaxially oriented fourth lateral face;

an array of photosensors positioned along the axially oriented first lateral face of each scintillation crystal to detect scintillation photons; and

a reflective material positioned on the proximal end-face, the distal end-face, and the second, third, and fourth lateral faces of each scintillation crystal to internally reflect scintillation photons,

such that a given elongated scintillation crystal and an axially adjacent elongated scintillation crystal are separated from one another in the axial direction by (i) the photosensors on the axially oriented first lateral face of the given elongated scintillation crystal and (ii) the reflective material on the axially oriented second lateral face of the axially adjacent elongated scintillation crystal, and

such that the given elongated scintillation crystal and a transaxially adjacent elongated scintillation crystal are separated from one another in the transaxial direction by the reflective material.