Photon-counting gamma camera based on columnar CsI(Tl) optically coupled to a back-illuminated CCD

摘要

Recent advances have been made in a new class of CCD-based, single-photon-counting gamma-ray detectors which offer sub-100 μm intrinsic resolutions.These detectors show great promise in small-animal SPECT and molecular imaging and exist in a variety of configurations. Typically, a columnar CsI(Tl) scintillator or a radiography screen (Gd_2O_2S:Tb) is imaged onto the CCD. Gamma-ray interactions are seen as clusters of signal spread over multiple pixels. When the detector is operated in a charge-integration mode, signal spread across pixels results in spatial-resolution degradation. However, if the detector is operated in photon-counting mode, the gamma-ray interaction position can be estimated using either Anger (centroid) estimation or maximum-likelihood position estimation resulting in a substantial improvement in spatial resolution. Due to the low-light-level nature of the scintillation process, CCD-based gamma cameras implement an amplification stage in the CCD via electron multiplying (EMCCDs) or via an image intensifier prior to the optical path. We have applied ideas and techniques from previous systems to our high-resolution LumiSPECT detector. LumiSPECT is a dual-modality optical/SPECT small-animal imaging system which was originally designed to operate in charge-integration mode. It employs a cryogenically cooled, high-quantum-efficiency, back-illuminated large-format CCD and operates in single-photon-counting mode without any intermediate amplification process. Operating in photon-counting mode, the detector has an intrinsic spatial resolution of 64 μm compared to 134 μm in integrating mode.