Optimal Optical Conditions and Positioning Scheme for an Ultrahigh-Resolution Silicon Drift Detector-Based Gamma Camera

JOUNG, Jinhun,LEE, Kisung,HENSELER, Debora,METZGER, Wilhelm,CHOI, Yong,AHN, Young Bok,KIM, Yongkwon Atomic Energy Society of Japan 2008 Journal of nuclear science and technology Vol.45 No.12

<P>In this study, we optimized the optical conditions and associated positioning scheme for an ultrahigh-spatial-resolution, solid-state gamma detector. The detector module consisted of an array of seven hexagonal silicon drift detectors (SDDs) packed hexagonally and coupled to a single slab of crystal via a light guide glass. Because the optical behavior and requirements of the detector module and noise characteristics of the SDD sensor are different from those of conventional photomultiplier tube (PMT)-based detectors, the following parameters were studied to determine the optimum condition: scintillator selection, the effect of cooling on signal-to-noise ratio (SNR), the depth dependence of the scintillation light distribution, and optimum shaping time. To that end, a modified, Anger-style positioning algorithm with a denoise scheme was also developed to address the estimation bias (pincushion distortion) caused by the excessively confined light distribution and the leakage current induced by the SDD sensor. The results of this study proved that the positioning algorithm, together with the optimized optical configuration of the detector module, improves the positioning accuracy of the prototype detector. Our results confirmed the ability of the prototype to achieve a spatial resolution of about 0.7 mm in full width at half maximum (FWHM) for 122 keV gamma rays under the equivalent noise count (ENC) of 100 (e- rms) per SDD channel. The results also confirmed NaI(Tl) to be a more desirable scintillator for our prototype with an energy resolution performance of about 8%.</P>

Feasibility study of a non-destructive assay system for certifying identified isotopes and their activity concentrations for radioactive waste in a large container

Joung Jinhun,Nguyen Hung M.,Kim Yongkwon,Lee Mi-hyun,Cho Hang-rae,Park Kyung-Rok,Lee Ji-Hoon,Dho Ho-seog,Cho Chun-Hyung 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.78 No.1

We have generated a system concept for a non-destructive assay (NDA) system to certify identified isotopes and their activity concentrations for radioactive waste in a large container. Various optimization studies have evaluated the system performance in terms of the MDA (minimum detectable activity) results using the Monte Carlo simulation in conjunction with experimental studies. The proposed system consists of a total of eight HPGe (high-pressure germanium) detectors: four detectors on the top and the other four detectors on the bottom. The top and the bottom detector arrays are aligned and face each other. This detector arrangement has advantages in employing the attenuation correction as proposed by T. Chang [IEEE Trans. Nucl. Sci. NS-25, 638 (1978)]. We also found that the UFOV (useful field of view) of the detector highly influences the system efficiency, which leads to an improvement in the MDA performance. However, while the wider FOV of the detector improves the detection efficiency by allowing incoming radiation from other segmented volumes, it may suffer from nonuniform performance or increased errors in estimating an activity concentration for each segmented volume. To prevent such potential errors in employing the wider FOV, we have proposed an activity estimation algorithm, a so-called ‘fine volume reconstruction’, based on a back-projection method that estimates the activity concentration of each segmented volume. We demonstrate the feasibility of the conceptual system for use as a free release assay system for ISO containers up to a size of 2.4 × 6.0 × 1.3 m3 (W x L x H). The detector efficiency was about four times higher than those of typical commercial systems. Future studies include fine-tuning of the activity reconstruction algorithm and a validation study on various materials and non-uniform activity concentrations.

Non-destructive System and its Calibration Method for Isotope Identification and Quantification of Radio-waste From Decommissioning

Jinhun Joung,Hung Nyguen,Yongkwon Kim,Hoseog Dho,Junki Baik,Sukwon Joung 한국방사성폐기물학회 2021 한국방사성폐기물학회 학술논문요약집 Vol.2021 No.11

Investigation of the Optimal Design Parameters of a Bar Detector for Nuclear Medicine Applications

이기성,Jinhun Joung,Yongkwon Kim,John C. Engdahl 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.3

This study examined the optimal design parameters for a bar detector that allows 3-dimensional position decoding of impinging gamma rays. Simulation studies were carried out to determine the optimum design parameters of a bar detector. Experimental measurements were carried out to validate the simulation. The bar detector simulator consisted of a long scintillation crystal, ranging in size from 5 cm to 20 cm and with a relatively small cross section (4 × 4 mm2), that was coupled to two photo sensors, one on each end. A statistics-based positioning (SBP) scheme was used to improve the positioning accuracy. This method mapped the event characterization vectors to the associated position based on the chi-square error. The simulation showed that a 5-cm-, 10-cm-,and 20-cm-long NaI(Tl) bar detector could achieve a full width at half maximum(FWHM) spatial resolution of 0.9 mm, 1.7 mm and 3.3 mm for 511 keV gamma photons, respectively. There was approximately a 20% improvement in the performance of the SBP scheme over the conventional linear estimate. The simulation also showed that the grounded surface treatment was important for providing optimum performance with respect to the spatial resolution and spatial uniformity. For the experimental studies, average spatial resolutions of 3.0 mm and 8.5 mm FWHM, were achieved for the 5-cm- and 10-cm-long CsI(Na) bar scintillators with a 57Co source, respectively. This investigation demonstrated that the proposed bar detector could be used as a gamma-ray imaging detector, particularly for PET applications in the field of nuclear medicine, with many advantages over conventional detector configurations.

Development of Correction Schemes for a Small Field of View Gamma Camera

Nguyen Manh Hung,이기성,Jinhun Joung,Yongkwon Kim 대한의용생체공학회 2012 Biomedical Engineering Letters (BMEL) Vol.2 No.4

Purpose The goal of this study is to develop data correction schemes for a small field of view (SFOV) high resolution gamma camera detector for a small organ dedicated system such as breast, thyroid and joints. Methods The gamma camera contains PMTs coupled with single slap of NaI(TI) plate crystal. Correction schemes including energy, linearity and uniformity correction were developed. Energy and linearity correction was performed with 57Co sheet by utilizing same dot pattern phantom used for look up table (LUT) generation. Energy correction aligns the energy peaks of energy spectrum to reference energy by linear transformation. Linearity correction removes spatial distortions based on LUT of X, Y directions. Uniformity correction was executed with 99mTc flood source to redistribute counts in the image. This correction was based on pixel addition and subtraction for each event. Results The results showed calibration measure for dot pattern image acquired with 57Co sheet and flood field image obtained with 99mTc. This system acquired with 99mTc provided 17.54% FWHM energy resolution and 2.5% integral uniformity within a useful field of view (UFOV). Conclusions The correction schemes in this paper showed good results about linearity and uniformity. The measured energy resolution of the system is not as high as what we had expected due to the limitation of the current version of DAQ in the prototype system. In the future, we will revise the hardware so that we can maximize the performance of the proposed methods.

Development of correction schemes for a small field of view gamma camera

Hung, Nguyen Manh,Joung, Jinhun,Lee, Kisung,Kim, Yongkwon Springer-Verlag 2012 Biomedical Engineering Letters (BMEL) Vol.2 No.4

Design and Performance Investigation of a Multi-pinhole Collimator for a Small Field of View Gamma Imaging System

배재건,배승빈,이기성,최용,Yongkwon Kim,Jinhun Joung 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.7

The aim of this study is to design a collimator for a gamma imaging system that has a smallfootprint,a fast-scan-time, and a organ-specific applicability. To achieve such features, the collimatormust have a high resolution, a high sensitivity, and a gantry with a simple geometry. Forensuring high resolution and high sensitivity, we designed a multi-pinhole collimator. For realizinga simplified gantry, we carried out studies with limited angle reconstruction. On the designed multipinholecollimator has eight-pinholes, whose diameters are 2 mm. Limited-angle reconstruction hasbeen conducted with angle intervals of 3, 6, 9, and 12 and with an angle coverage of 60, 90, 120,150, and 180 . The reconstruction of an image was separately developed based on the ray-drivenand voxel-driven methods in order to overcome the sampling problem and to reduce the amount ofcomputation required. To evaluate the performance of the designed system, performed studies onthree spherical phantoms and a heart phantom by using the Geant4 application for tomographicemission (GATE) simulation tool. The results showed that the full width at half maximum (FWHM)of the center source were 6.25 mm and 7.18 mm for single-pinhole and multi-pinhole collimators,respectively. Moreover, limited angle reconstruction resulted in a higher efficiency of the imagingsystem because it overcame the limitation of the gantry geometry. Limited-angle reconstructionwas optimized at an angle coverage of 120 with an angle interval of 6 , then reconstructed imagewas shown a 12.18 mm FWHM. This suggests that the designed system needs only one-third thenumber of projections to acquire a reconstructed image with a slight degradation in image quality. This also suggests that our proposed multi-pinhole collimator is suitable for applications requiringa small-footprint, a fast-scan-time, and organ-specificity.

Experimental Evaluation of a Multi-Pinhole Collimator for a Small Organ by Using a Small-Field-of-View Gamma Camera

배재근,배승빈,정영준,이기성,김용권,Jinhun Joung,김경민,김희정 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.4

The aim of this study is to design and evaluate a multi-pinhole (MP) collimator for a gamma imaging system that requires a high sensitivity, organ-specific, and small footprint. To ensure these requirements, we designed an eight-hole collimator that can be integrated into a small field-of-view gamma camera for imaging the thyroid or relatively sized organs. Each pinhole was designed to have a cylindrical shape with a 2-mm diameter. Experiments were performed with both a two-sphere phantom and a four-rod phantom. An image reconstruction based on the maximum likelihood expectation maximization with the distance-driven method was used for obtaining a 3-dimensional image. For improving the uniformity of the reconstruction image, we modeled the sensitivity of the cylindrical pinhole by calculating the area of the overlapped circle. The results show that the full width at half maximum values of the two-sphere phantom and the four-rod phantom were 7.56 mm (5-mm-diameter source) and 6.84 mm (5-mm-diameter rod), respectively. The scanning time can be reduced by up to 20 minutes in small-organ applications by using developed MP collimator. Thus, the results indicate that the proposed MP collimator is suitable for a fast scan time, as well as for organ-specific and small-footprint applications.

Two-level multi-pinhole collimator for SPECT imaging using a small-field-of-view gamma camera

Bae, Jaekeon,Bae, Seungbin,Lee, Soo-young,Lee, Kisung,Kim, Yongkwon,Joung, Jinhun,Kim, MinHo,Kim, Kyeong Min 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol. No.

Implementation of a Coded Aperture Imaging System for Gamma Measurement and Experimental Feasibility Tests

Kwangdon Kim,Hakjae Lee,Jinwook Jang,Yonghyun Chung,Donghoon Lee,Chanwoo Park,Jinhun Joung,Yongkwon Kim,Kisung Lee 대한전자공학회 2017 IEIE Transactions on Smart Processing & Computing Vol.6 No.1

Radioactive materials are used in medicine, non-destructive testing, and nuclear plants. Source localization is especially important during nuclear decommissioning and decontamination because the actual location of the radioactive source within nuclear waste is often unknown. The coded-aperture imaging technique started with space exploration and moved into X-ray and gamma ray imaging, which have imaging process characteristics similar to each other. In this study, we simulated 21x21 and 37x37 coded aperture collimators based on a modified uniformly redundant array (MURA) pattern to make a gamma imaging system that can localize a gamma-ray source. We designed a 21x21 coded aperture collimator that matches our gamma imaging detector and did feasibility experiments with the coded aperture imaging system. We evaluated the performance of each collimator, from 2 mm to 10 mm thicknesses (at 2 mm intervals) using root mean square error (RMSE) and sensitivity in a simulation. . In experimental results, the full width half maximum (FWHM) of the point source was 5.09° at the center and 4.82° at the location of the source was 9°. We will continue to improve the decoding algorithm and optimize the collimator for high-energy gamma rays emitted from a nuclear power plant.