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

Abstract

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. [1][2][3][4][5][6][7] 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 2 O 2 S:Tb) is imaged onto the CCD. Gammaray 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 maximumlikelihood position estimation resulting in a substantial improvement in spatial resolution. 2 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) [8][9][10] or via an image intensifier prior to the optical path. 1 We have applied ideas and techniques from previous systems to our high-resolution LumiSPECT detector. 11,12 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-photoncounting 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.

Modular platform for low-light microscopy

“…Moreover, a technique known as radioluminescence microscopy (RLM) has been recently developed to quantify the biological transport of small molecules tagged with radionuclides in real-time [9,10]. The mechanism of RLM is similar to previously developed gamma cameras, in which the scintillator is coupled to the sensor via two camera lenses [11,12], but the unique magnification of RLM allows it to detect radionuclides on the single cell level. The principle of RLM is to label cells cultured in vitro with radionuclides and collect radioactive decay data by positioning a scintillating crystal in close proximity to the cell surface.…”

Statistical characterization of radiological images: basic principles and recent progress

“…Fig. 2 shows an example from the work of Miller et al, 22 who used a lens with a high numerical aperture to couple the light from a columnar CsI scintillator to a low-noise CCD detector. Shown on the left is a single frame of image data with a 99m Tc gamma-ray source.…”

“…From the pixel values associated with individual events, it is possible to estimate the coordinates of the initial interaction and the energy of the photon. Researchers at the University of Arizona 15,16 have been using this approach with integrating arrays of cadmium zinc telluride (CZT) semiconductor detectors for over a decade, and more recently it has been shown by several groups [17][18][19][20][21][22] that the method also works well with scintillation detectors. Fig.…”

“…Further improvement in performance can be obtained by performing maximum-likelihood (ML) processing 16,21,22 on each cluster of pixels. Fig.…”

Imaging and spectroscopy using a scintillator-coupled EMCCD

“…Such a system has the potential for use in a variety of applications, namely in small animal Single Photon Emission Computed Tomography (SPECT) [10] in which, through the use of different isotopes, a multi-label imaging system could be developed. The main aims of this study are to highlight methods by which the imaging and spectrographic qualities of a scintillator-coupled EMCCD can potentially be improved through the use of novel image analysis techniques and the use of Geant4 as an investigative tool.…”