From Event: SPIE Optical Engineering + Applications, 2016
Pixelated Cadmium Zinc Telluride (CZT) detectors provide the opportunity to perform spectroscopic imaging for
discriminating one radioactive material from another. Although Compton interactions provide a means for imaging high
energy gamma sources, identification of materials emitting lower energy signatures are better suited to collimator
imaging techniques. This paper specifically considers a multiple pinhole method for its simplicity of pinhole focusing
combined with straightforward processing methods for incorporating multiple apertures to reduce photon collection time
while retaining image resolution. Multiple pinhole image detections are combined using an iterative Maximum-
Likelihood Expectation-Maximization (MLEM) synthetic imaging algorithm. To enable subsequent field operations, the
imaging system matrix is computed using an imaging model with adjustable parameters rather than one experimentally
acquired from point sources. The system model includes an object space, a multiple pinhole collimator plane, and a
pixelated detection plane. The modeled object space is implemented in two dimensions to reduce image reconstruction
burden since 3D imaging is not practical for single view stand-off imaging. Focusing is modeled by a function
computing photon trajectory and passage through the pinhole patterned barrier plane. Results show that a MLEM
processed image will achieve resolution approaching that of a single pinhole imaged onto the full detector. The multiple
pinhole advantages of simple implementation with shorter focal lengths combined with the availability of portable CZT
detectors would be useful in short stand-off applications. Work is currently in progress to experimentally quantify spatial
resolution and imaging timelines using an eV Products D-Matrix 4x4 array of pixelated CZT modules.
Paul J. DeRego, Adam A. Hecht, Kenya Moore Dias da Cunha, and Phoenix Baldez, "A model-based multiple-pinhole synthetic imager for stand-off range gamma-emitting objects," Proc. SPIE 9968, Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XVIII, 996813 (Presented at SPIE Optical Engineering + Applications: August 31, 2016; Published: 30 September 2016); https://doi.org/10.1117/12.2239948.
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