Real-Time 3D Compton Imaging using Incremental Iterative Algorithm and Environmental Information (#1210)
J. Chu1, Y. Liu2, D. Shy1, Z. He1
1 University of Michigan, Nuclear Engineering and Radiological Sciences, Ann Arbor, Michigan, United States of America
Compton imaging uses multi-interaction Compton scattering events to reconstruct radiation distribution images around gamma-ray detectors. With the information of the detector position and orientation, it is possible to locate the back-projected Compton cones and estimate the source distribution in a 3D imaging space. However, since the mesh size of a typical 3D imaging space and the number of collected events are both very large, the speed of reconstruction is limited and the memory usage is not practical for iterative algorithms. To accelerate the 3D reconstruction, an incremental iterative algorithm was applied, which provides real-time reconstruction speed while preserving reasonable statistics, and environmental information was fused to exclude voxels in the air and build a sparse 3D imaging space. A recent detector system was built using two 3×3 arrays of 2×2×1.5 cm3 CdZnTe crystals with pixelated 11×11 array anodes and a planer cathode. A simultaneous localization and mapping (SLAM) system with two cameras was mounted on the radiation detector to provide environmental information. With the incremental iterative algorithm and environmental information, the 3D Compton imaging in a sparse space is achievable in real-time.
Keywords: Compton imaging, 3D reconstruction, incremental iterative algorithm
Evaluation of Compton Imaging Efficiency Degradation Factors in Large Volume, Pixelated CdZnTe Sensors (#2145)
B. Williams1, Z. He1
1 University of Michigan, Department of Nuclear Engineering and Radiological Sciences, Ann Arbor, Michigan, United States of America
Compton imaging efficiency for radiation detection systems featuring large volume, pixelated CdZnTe sensors is systematically overestimated by the efficiency predicted in simulations. In order to reduce model mismatch in simulated event data, predictive efficiency models are constructed in order to identify and discard improbable simulated events. These models are constructed from a single calibration measurement, and they account for sensor-specific Compton scattering event loss mechanisms in pixelated CdZnTe detectors. These mechanisms include anode trigger threshold rejection, charge-sharing between adjacent pixels and programmatic event reconstruction errors. The accuracy of these models are validated with measurements, and the impact of these individual efficiency loss mechanisms is quantified by comparing raw simulation data to filtered data. Results indicate that charge-sharing and depth reconstruction errors account for the majority of the efficiency loss to Compton scattering events. The degree to which these mechanisms degrade the efficiency varies as a function of the incident gamma ray direction.
Keywords: Compton Imaging, CdZnTe Detectors
Investigation of Anti-perovskite Hg3Se2I2 for Room Temperature Hard Radiation Detection (#2191)
Y. He1, O. Y. Kontsevoi4, C. C. Stoumpos1, Z. Liu2, S. Das2, J. - I. Kim2, B. W. Wessels2, 3, M. G. Kanatzidis1
1 Northwestern University, Department of Chemistry, Evanston, Illinois, United States of America
In this work, we describe a mercury-based compound Hg3Se2I2 which is a very promising candidate for X- and γ-ray semiconductor detectors. This compound has a defect anti-perovskite structure with ordered Hg vacancies. Its optical, electrical, and good mechanical properties match well for the fundamental requirements for radiation detection at room temperature. It also possesses a high density ( 7.38 g/cm3) and wide bandgap (2.12 eV), showing strong stopping power for hard radiation and high intrinsic electrical resistivity at room temperature, over 1011 Ω×cm. Large single crystals are grown using the vapor transport method. Detectors made from thin Hg3Se2I2 crystals show reasonable response under a series of radiation sources and spectroscopic resolution is achieved for both 241Am α particles (5.49 MeV) and 241Am γ-rays (59.5 KeV), with full widths at half maximum (FWHM, in percentage) of 19% and 50%, respectively. The electron mobility-lifetime μτ product for Hg3Se2I2 detectors is achieved of ~10-5 cm2/V. The electron mobility for Hg3Se2I2 is estimated to be 104±12 cm2/(V×s), confirming its strong potential as materials for X- and g-ray detection.
Keywords: Anti-perovskite, Hg3Se2I2, crystal growth, radiation detection
Orthogonal Strip TlBr Detectors for PET (#2488)
G. Ariño-Estrada1, J. Du1, H. Kim2, L. J. Cirignano2, K. S. Shah2, S. R. Cherry1, G. S. Mitchell1
1 University of California Davis, Department of Biomedical Engineering, Davis, California, United States of America
We are building orthogonal strip TlBr detectors for PET with a goal of high 3-D segmentation, good energy resolution, and acceptable coincidence time resolution. We measured the energy and timing resolution of a planar TlBr detector of 0.89 mm thickness and operated at -400 V and at room temperature. We achieved a 6.8% energy resolution at 511 keV and a timing resolution of 27.8 ns FWHM in coincidence with an LYSO scintillation crystal and PMT detector when events with energy close to 511 keV were selected. A setup able to digitize and process the signal from multiple TlBr strips in parallel with 16 µs shaping time was used for a detector with seven 0.4 mm-width strips (0.5 mm pitch) on the one electrode and four 2-mm width strips (2.5 mm pitch) on the opposite electrode. Submillimeter intrinsic spatial resolution is well established for TlBr detectors with small strip pitch. The detector was 0.35 mm thick and was operated at -100 V and at room temperature. The energy resolution on the strips was better than 8% at 511 keV. We studied the correlation between the energies readout by strips in opposite electrodes, and the energy resolution improved from 7.4% to 6.0% at 511 keV when only events with similar energy in both strips were selected. Studies of charge sharing among strips, depth of interaction estimation, and k-edge escape peak reconstruction are under way as well as timing measurements with individual strips. Work to achieve better timing capabilities includes manufacturing TlBr detectors able to hold higher bias voltages.
Keywords: TlBr, Strip detectors, PET, timing resolution, spatial resolution, DOI, charge sharing
Characterisation of an epitaxial silicon strip detector for microbeam radiation therapy (#2841)
A. Dipuglia1, J. Davis1, 2, M. Cameron1, M. Petasecca1, 2, A. Rosenfeld1, 2, V. Perevertaylo3, M. Lerch1, 2
1 University of Wollongong, CMRP, Wollongong, NSW, Australia
The emergence of synchrotron X-ray microbeam radiation therapy as a potential treatment modality for inoperable brain tumours has initiated a need for customised dosimeters to handle the conditions that are unique to this radiation oncology modality. This modality differs from conventional megavoltage radiotherapy treatments firstly in the manner of radiation production and secondly in the purposeful fractionation of the radiation field to create quasi parallel micron sized x-ray beams, 50 mm wide. Silicon strip detectors are a promising candidate technology to fulfil this need having the necessary radiation hardness and dynamic range required to measure the large range of dose that is delivered in the central peak of the microbeams to the valley regions that lie in between. Our previous generation silicon strip device demonstrated the proof of principle of these detectors, however misalignment of the sensitive volume relative to the microbeams compromised the intrinsic spatial resolution and led to dose averaging effects, making them less ideal for quality assurance of the microbeams. In this study, a second generation silicon strip detector aimed at addressing these issues has been characterised through the use of ion beam induced charge collection studies, supported by Technology Computer-Aided Design simulations. The detector performance for microbeam radiation therapy dosimetry was then evaluated at the imaging and medical beam line at the Australian synchrotron using two independent data acquisition systems. An immediate and significant improvement on the previous generation of detector was observed in the measured profiles of the X-ray microbeams.
Keywords: Dosimeter, Silicon, Quality Assurance, Microbeam Radiation Therapy
Ternary Bismuth Halide: New Semiconductors for Radiation Detection (#3450)
D. Y. Chung1, F. Meng1, Y. Xu2, A. S. Botana1, M. R. Norman1, M. G. Kanatzidis2, 1
1 Argonne National Laboratory, Materials Science Division, Argonne, Illinois, United States of America
Highly sensitive hard radiation detectors operating at room temperature are greatly desired for national security, non-proliferation, and medical applications. Semiconductors with wide band gaps and high densities provide higher energy resolution than scintillator materials. We investigated the 2-D structured semiconducting A3Bi2Br9 (A = Rb, Cs) family as a new class of semiconductors promising for cost-effective X-ray and g-ray radiation detector applications. They possess a wide band gap (2.5 – 2.7 eV), high density (>4.5 g/cm3), and a good thermal behavior with low melting temperature (<650 oC) which are required for good candidate materials for radiation detection. We synthesized them by a stoichiometric reaction of two binary precursors, RbBr/CsBr and Bi2O3 in a corresponding haloic acid solution. Purification of the materials was performed by sublimation, bromination, filtration of molten materials, and zone refining, and followed by crystal growth using the Bridgman method. Yellow transparent single crystal boules with typical dimensions of 10 mm diameter and 100 mm length were grown. The resistivity for these materials is in the order of 1013 - 1014 W∙cm. The mobility-lifetime products (μτ) are in the order of ~10-4 cm2/V for both electron and hole carriers. The crystal structure, optical property, defect analysis, charge transport, photoconductivity, and X-ray and γ-ray spectroscopy are also discussed.
Keywords: bismuth halides, detector material, gamma ray, x ray, crystal growth, radiation detection