Depth-of-interaction compensation using a focused-cut scintillator for a pinhole gamma camera

Preclinical SPECT can potentially be a powerful platform to study fundamental biological processes and drug interactions in small animals. Gamma cameras for such SPECT systems require high spatial resolutions in order to adequately map the uptake of radioisotopes in small animals. Pinhole collimators offer one of the best technically feasible ways to achieve a high resolution. However, pinhole geometry introduces parallax errors, particularly toward the edge of the field of view, limiting the system spatial resolution. The parallax errors arise from the variable depth of interaction (DOI) of gammaray/scintillator events, especially when gamma rays enter a scintillator at steep angles. There have been several efforts to address parallax errors in pinhole SPECT, including algorithm-based DOI modeling and correction and the use of a curved fiber bundle to collimate light from a curved scintillator. Another way to overcome parallax errors in a pinhole gamma camera is to use a focused-cut scintillator, which is pixellated so that the pixels are focused towards the pinhole of a collimator. Thus, the path of a primary ray that has passed through the pinhole only intersects with a single pixel in the scintillator. Here, we experimentally test a pinhole gamma camera with a focused-cut (FC) scintillator. We measure the resolution across a continuous scintillator and across a straight-cut (SC) pixellated scintillator and show that the thicker FC scintillator has comparable parallax error in comparison with a thinner SC scintillator (3 mm vs. 1 mm). Thus, FC scintillators are shown to offer both the high resolution of thin pixellated scintillators and the high sensitivity of thicker scintillators.