Focused scintillator array for high resolution gamma ray imaging

The spatial resolution in small animal pinhole SPECT cameras is limited by parallax errors in the scintillator, particularly towards the edge of the field of view. We have developed a method to overcome the parallax errors in pinhole gamma cameras using a focused cut scintillator. A KrF (λ = 248 nm) excimer laser was used to cut very fine grooves in CsI (Tl) scintillator crystals of thickness between 1 mm to 3 mm. The cuts were made in a manner to form structured columns, oriented focused towards the pinhole collimator, and thereby towards the incoming gamma rays. The thickness of the groves averaged 30 μm which is much thinner than that which can be achieved by a wire saw. Individual pixel columns of thickness between 250 μm and 500 μm were cut. Scanning electron micrographs of the samples the CsI:Tl walls after laser ablation are smooth, and free of debris resulting from ablated particles. This reduces the risk of post-processing damage that might occur during debris removal, and encourages complete coverage by reflective coatings in the grooves. The laser optics and the operating parameters were optimized to achieve such deep and thin cuts and are discussed in this paper. Fixturing apparatus was developed in order to cut the pixels in the desired shape. We also present the performance characteristics of the laser ablated scintillators and data from their use in a multipinhole SPECT system.