Feasibility study of multiplexing method using digital signal encoding technique

Radiation imaging systems consisting of a large number of channels greatly benefit from multiplexing methods to reduce the number of channels with minimizing the system complexity and development cost. In conventional pixelated radiation detector modules, such as anger logic, is used to reduce a large number of channels that transmit signals to a data acquisition system. However, these methods have limitations of electrical noise and distortion at the detector edge. To solve these problems, a multiplexing concept using a digital signal encoding technique based on a time delay method for signals from detectors was developed in this study. The digital encoding multiplexing (DEM) method was developed based on the time-over-threshold (ToT) method to provide more information including the activation time, position, and energy in one-bit line. This is the major advantage of the DEM method as compared with the traditional ToT method providing only energy information. The energy was measured and calibrated by the ToT method. The energy resolution and coincidence time resolution were observed as 16% and 2.4 ns, respectively, with DEM. The position was successfully distributed on each channel. This study demonstrated the feasibility that DEM was useful to reduce the number of detector channels.ope

Serial line multiplexing method based on bipolar pulse for PET

Although the individual channel readout method can improve the performance of PET detectors with pixelated photo-sensors, such as silicon photomultiplier (SiPM), this method leads to a significant increase in the number of readout channels. In this study, we proposed a novel multiplexing method that could effectively reduce the number of readout channels to reduce system complexity and development cost. The proposed multiplexing circuit was designed to generate bipolar pulses with different zero-crossing points by adjusting the time constant of the high-pass filter connected to each channel of a pixelated photo-sensor. The channel position of the detected gamma-ray was identified by estimating the width between the rising edge and the zero-crossing point of the bipolar pulse. In order to evaluate the performance of the proposed multiplexing circuit, four detector blocks, each consisting of a 4 × 4 array of 3 mm × 3 mm × 20 mm LYSO and a 4 × 4 SiPM array, were constructed. The average energy resolution was 13.2 ± 1.1% for all 64 crystal pixels and each pixel position was accurately identified. A coincidence timing resolution was 580 ± 12 ps. The experimental results indicated that the novel multiplexing method proposed in this study is able to effectively reduce the number of readout channels while maintaining accurate position identification with good energy and timing performance. In addition, it could be useful for the development of PET systems consisting of a large number of pixelated detectors.ope

Feasibility study of SiPM based scintillation detector for dual-energy X-ray absorptiometry

Dual-energy x-ray absorptiometry (DXA) is the noninvasive method to diagnose osteoporosis disease characterized by low bone mass and deterioration of bone tissue. Many global companies and research groups have developed the various DXA detectors using a direct photon-counting detector such as a cadmium zinc telluride (CZT) sensor. However, this approach using CZT sensor has some drawback such as the limitation of scalability by high cost and the loss of efficiency due to the requirement of a thin detector. In this study, a SiPM based DXA system was developed and its performance evaluated experimentally. The DXA detector was composed of a SiPM sensor coupled with a single LYSO scintillation crystal (3 × 3 × 2 ㎣). The prototype DXA detector was mounted on the dedicated front-end circuit consisting of a voltage-sensitive preamplifier, pulse shaping amplifier and constant fraction discriminator (CFD) circuit. The SiPM based DXA detector showed the 34% (at 59 keV) energy resolution with good BMD accuracy. The proposed SiPM based DXA detector showed the performance comparable to the conventional DXA detector based on CZT.ope

Metallic Component Preserving Algorithm Based on the Cerebral Computed Tomography Angiography in Aneurysm Surgery

The purpose of this study was to investigate the viability of the proposed method in preventing the loss of metallic components including the clip and coil in cerebral computed tomography angiography (CTA). Forty patients undergoing surgery for aneurysms carried metallic materials. The proposed method is based on conventional bone subtraction CTA (BS-CTA) system. Briefly, the position of metal components was determined using the threshold value and a region of interest (ROI). An appropriate threshold was used to separate the background from the target materials based on the Otsu method. A three-dimensional (3D) rendering was performed from the proposed BS-CTA data carrying the extracted target information. The accuracy of clip and coil region measured using the dice similarity coefficient (DSC) and bidirectional Hausdorff distance (HD) is reported. The metallic components of the proposed BS-CTA were significantly visualized in various patient cases. Quantitative evaluation using the proposed method is based on the mean DSC of 0.93 with a standard deviation (SD) of ±0.05 (e.g., maximum value = 0.99, minimum value = 0.75, 95% confidence interval (CI) = 0.91 to 0.95, and all p < 0.05). The mean HD was 1.50 voxels with an SD of ± 0.58 (e.g., maximum value = 5.95, minimum value = 0.12, 95% CI = 1.10 to 1.90, and all p < 0.05). The proposed method demonstrates effective segmentation of the metallic component and application to the existing conventional BS-CTA system.ope

Preliminary results of a single photon emission computed tomography (SPECT) detector for inspection of spent fuel assembly

SPECT systems are being used by international safeguards organizations for the measurement for structural evaluation of spent fuel assemblies. However, the low sensitivity still limits the verification of spent fuel assemblies within a short measurement time (1–2 h per assembly). In this study, the SPECT detector was optimized and evaluated to identify the structure of spent fuel. The detector module consists of 64 one-dimensional (1-D) multi-slit collimators and 1-D pixelated scintillators coupled to SiPMs. We evaluated and optimized the light collection efficiency and energy resolution according to the shape of scintillator (Trapezoid, Rectangular), and reflector materials (Paint, Teflon tape, BaSO4) by Geant4 Application for Tomographic Emission (GATE) simulation and experiment. As a result, the trapezoidal scintillator coated with BaSO4 showed the highest light collection efficiency among the six models in GATE simulation and in experiments. The spent fuel rods were imaged using trapezoidal scintillator coated with BaSO4, and 1-D projections and line profiles were obtained in order to distinguish the source location. In this study, the scintillator structure and reflector material variables were optimized using Monte Carlo simulation to measure 662 keV gamma-ray of 137Cs for inspection of spent fuel assembly using the SPECT system. In order to confirm the imaging potential of the spent fuel assembly, the detector performance was evaluated using unused fuel rods for testing. The performance of the detector for fuel rod identification has been proven, and we expect that the optimized detector module will contribute to the rapid verification of the spent fuel assembly compared to conventional systems.restrictio

Development of a muon detector based on a plastic scintillator and WLS fibers to be used for muon tomography system

Muon tomography is a useful method for monitoring special nuclear materials (SNMs) such as spent nuclear fuel inside dry cask storage. Multiple Coulomb scattering of muons can be used to provide information about the 3-dimensional structure and atomic number(Z) of the inner materials. Tomography using muons is less affected by the shielding material and less harmful to health than other measurement methods. We developed a muon detector for muon tomography, which consists of a plastic scintillator, 64 long wavelength-shifting (WLS) fibers attached to the top of the plastic scintillator, and silicon photomultipliers (SiPMs) connected to both ends of each WLS fiber. The muon detector can acquire X and Y positions simultaneously using a position determination algorithm. The design parameters of the muon detector were optimized using DETECT2000 and Geant4 simulations, and a muon detector prototype was built based on the results. Spatial resolution measurement was performed using simulations and experiments to evaluate the feasibility of the muon detector. The experimental results were in good agreement with the simulation results. The muon detector has been confirmed for use in a muon tomography system. © 2022 Korean Nuclear Society, Published by Elsevier Korea LLC. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).restrictio

차실-트렁크 연성계의 연성경로 및 음향모드 특성에 관한 연구

Thesis (master`s)--서울대학교 대학원 :기계항공공학부,2001.Maste

(A) study on the wave characteristics of the periodic structures for the vibration attenuation in a rotating ring

학위논문(석사) - 한국과학기술원 : 기계공학과, 2022.2,[vi, 57 p. :]본 연구는 주기적인 구조의 파동 특성을 이용하여 많은 기계의 주요 동력 전달 요소인 회전 고리의 진동을 감쇠시키는 방법을 제안한다. 회전 원환 구조는 보강재 형태의 주기적인 구조가 배열된 Euler-Bernoulli 가정을 만족하는 휘어진 보로 모델링된다. 이러한 구조에 대한 파동 전파 모델을 개발하기 위해, 먼저 직선 빔과 회전하지 않는 원형 링에서 주기적으로 보강재가 있는 구조물의 진동 음향 특성을 연구한다. 파동의 전파 상수는 전달 행렬법과 Floquet 정리를 사용하는 고유값 문제를 해결함으로써 얻어진다. 대칭 또는 비대칭 보강재가 주기적으로 부착되면, 굽힘파 또는 종파의 전파의 저지 대역은 단위 셀의 공명 주파수에서 나타난다. 원형 링의 경우 일부 주파수 대역에서 굽힘파와 종파가 결합되어 추가적인 저지 대역이 생성된다. 이러한 파동 결합에 의한 저지 대역은 단위 셀의 공명과는 무관하기 때문에 공명으로 인한 저지 대역 외에 고리의 진동을 감쇠시키는 데 도움이 된다. 회전 고리의 경우 Coriolis 힘과 Doppler 효과 때문에 파동 전파의 특성이 전진 또는 후진 방향에 따라 달라지는 것을 볼 수 있다. 도플러 효과는 전진파와 후진파의 비대칭 저지 대역을 발생시킨다. 이러한 특성은 주기적인 구조를 가진 회전 고리에 가해지는 가진으로 인해 전파되는 구조파의 저지 대역의 대역폭을 증가시키는데 도움이 된다.한국과학기술원 :기계공학과

Performance evaluation of an adjustable gantry PET (AGPET) for small animal PET imaging

A rectangular-shaped PET system with an adjustable gantry (AGPET) has been developed for imaging small animals. The AGPET system employs a new depth of interaction (DOI) method using a depth dependent reflector patterns and a new digital time pickoff method based on the pulse reconstruction method. To evaluate the performance of the AGPET, timing resolution, intrinsic spatial resolution and point source images were acquired. The timing resolution and intrinsic spatial resolution were measured using two detector modules and Na-22 gamma source. The PET images were acquired in two field of view (FOV) sizes, 30 mm and 90 mm, to demonstrate the characteristic of the AGPET. As a result of in the experiment results, the timing resolution was 0.9 ns using the pulse reconstruction method based on the bi-exponential model. The intrinsic spatial resolution was an average of 1.7 mm and the spatial resolution of PET images after DOI correction was 2.08 mm and 2.25 mm at the centers of 30 mm and 90 mm FOV, respectively. The results show that the proposed AGPET system provided higher sensitivity and resolution for small animal imaging.restrictio