Development and Performance Evaluation of an Ultra-High-Resolution Self-Collimation SPECT System for Small Animal Imaging

We have recently introduced a novel self-collimation (SC) concept for SPECT imaging, which utilizes detectors also as collimators to overcome the resolution-sensitivity trade-off innate to mechanical collimators. In this work, we report a prototype SC-SPECT system dedicated for high-resolution small animal imaging.The prototype consists of four concentric detector rings with spatially separated scintillators and a high-aperture-ratio tungsten ring, where each detector ring is collimated by other inner detector rings and the tungsten ring. The four detector rings have inner diameters of 260 mm, 390 mm, 520 mm, and 650 mm, and consist of 480, 720, 960, and 1,200 GAGG(Ce) scintillators, respectively. The scintillators are 0.84 mm (tangential) × 6 mm (radial) × 20 mm (axial) in size, evenly separated by a 0.84 mm gap in the tangential direction. The four detector rings are constructed with 40 detector modules, each covering a 9° angular region and comprising 42 detector units. In each detector unit, two scintillators are optically coupled to four SiPMs on the axial ends to determine photons’ axial interaction position with the depth-of-interaction technique; the decay time constants of the two scintillators are 90 ns and 200 ns, respectively, allowing for crystal identification with pulse shape discrimination. The tungsten ring has an inner diameter of 75 mm, an axial length of 290 mm, and a thickness of 2.5 mm, with 200 circular apertures (D = 0.4 mm) evenly distributed on the central transverse plane with a center-to-center distance of 1.2 mm.Preliminary results show that the prototype has a sensitivity of 0.064% at the center of the field-of-view. In the transverse plane, it can clearly resolve 5 × 5 point sources with a diameter of 0.36 mm and a center-to-center distance of 0.36 mm. Axially, it can clearly resolve point sources with a diameter of 0.4 mm and a center-to-center distance of 0.6 mm. A comprehensive performance evaluation is currently underway.