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Portable Active Collimation Imager Using URA Patterned Scintillator
Taewoong Lee,Wonho Lee IEEE 2014 IEEE transactions on nuclear science Vol.61 No.1
<P>A portable active collimator using systematically patterned scintillators was constructed and its performance evaluated. In the conventional passive radiation collimation method, single or multiple holes are used to limit radiation reaching a detector while radiation scattered in the collimator is not used. However in active collimation where one replaces the passive collimator with a radiation detector, both the radiation that passes through the holes and radiation scattered in the collimator can be used. The active collimator was composed of uniformly redundant array (URA)-patterned Bi4Ge3O12 (BGO) scintillators with a CsI(Na) detector planar array positioned behind the collimator. Images using radiation passing through the holes of the URA collimator were reconstructed using the correlation method of conventional coded apertures, while the radiation scattered in the active collimator and detected in the planar detector, was imaged using a Compton imaging technique. Since the active collimation method uses both Compton scattered events and photoelectric absorption events, its detection efficiency and energy range are inherently higher than those of conventional collimation methods. The reconstructed images of the portable active collimation methods for various energy sources were obtained and compared with those of conventional methods.</P>
High-Performance Compton SPECT Using Both Photoelectric and Compton Scattering Events
Taewoong Lee,Younghak Kim,Won Ho Lee 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.9
In conventional single-photon emission computed tomography (SPECT), only the photoelectric events in the detectors are used for image reconstruction. However, if the 131I isotope, which emits high-energy radiations (364, 637, and 723 keV), is used in nuclear medicine, both photoelectric and Compton scattering events can be used for image reconstruction. The purpose of our work is to perform simulations for Compton SPECT by using the Geant4 application for tomographic emission (GATE). The performance of Compton SPECT is evaluated and compared with that of conventional SPECT. The Compton SPECT unit has an area of 12 cm 12 cm with four gantry heads. Each head is composed of a 2-cm tungsten collimator and a 4040 array of CdZnTe (CZT) crystals with a 33 mm2 area and a 6-mm thickness. Compton SPECT can use not only the photoelectric effect but also the Compton scattering effect for image reconstruction. The correct sequential order of the interactions used for image reconstruction is determined using the angular resolution measurement (ARM) method and the energies deposited in each detector. In all the results of simulations using spherical volume sources of various diameters, the reconstructed images of Compton SPECT show higher signal-to-noise ratios (SNRs) without degradation of the image resolution when compared to those of conventional SPECT because the effective count for image reconstruction is higher. For a Derenzo-like phantom, the reconstructed images for different modalities are compared by visual inspection and by using their projected histograms in the X-direction of the reconstructed images.
Single-Photon-Emission Computed Tomography with Neutron Activation for Material Inspection
Taewoong Lee,Minho Kim,Younghak Kim,Kyeong Min Kim,Wonho Lee 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.7
A single-photon-emission computed tomography (SPECT) system with a lanthanum-bromide (LaBr3:Ce) scintillator was proposed and simulated to detect neutron-activated prompt -rays from suspicious materials. The optimized parameters of the SPECT system were calculated to achieve the best performance. Under the optimized conditions, energy spectra, spatial images, and elemental ratios were obtained and employed to identify hidden materials. The carbon-to-oxygen ratios of the materials calculated through the simulations were consistent with the corresponding theoretical values while the calculated nitrogen-to-oxygen ratios were slightly different from the corresponding theoretical values. In the proposed system, not only the energy spectrum of each element but also the characteristic intensity ratios obtained using the reconstructed images were used to identify the unknown elements of hidden materials in the three-dimensional spatial domain. These results demonstrate the feasibility of using the SPECT system in field applications.