A preclinical SPECT camera with depth-of-interaction compensation using a focused-cut scintillator

Preclinical SPECT offers a powerful means to understand the molecular pathways of metabolic activity in animals. SPECT cameras using pinhole collimators offer high resolution that is needed for visualizing small structures in laboratory animals. One of the limitations of pinhole geometries is that increased magnification causes some rays to travel through the scintillator detector at steep angles, introducing parallax errors due to variable depth-of-interaction in the scintillator, especially towards the edges of the detector field of view. These parallax errors ultimately limit the resolution of pinhole preclinical SPECT systems, especially for higher energy isotopes that can easily penetrate through millimeters of scintillator material. A pixellated, focused-cut scintillator, with its pixels laser-cut so that they are collinear with incoming rays, can potentially compensate for these parallax errors and thus open up a new regime of sub-mm preclinical SPECT. We have built a 4-pinhole prototype gamma camera for preclinical SPECT imaging, using an EMCCD camera coupled to a 3 mm thick CsI(Tl) scintillator whose pixels are focused towards each 500 μm-diameter pinhole aperture of the four pinholes. The focused-cut scintillator was fabricated using a laser ablation process that allows for cuts with very high aspect ratios. We present preliminary results from our phantom experiments.