Resolution Recovery 기반의 Astonish 영상 재구성 기법의 평가

승종민,이형진,김진의,김현주,김중현,이재성,이동수,Seung, Jong-Min,Lee, Hyeong-Jin,Kim, Jin-Eui,Kim, Hyun-Joo,Kim, Joong-Hyun,Lee, Jae-Sung,Lee, Dong-Soo 대한핵의학기술학회 2011 핵의학 기술 Vol.15 No.1

SPECT 영상에서의 resolution recovery를 기반으로 하는 3D 재구성 기법은 detector면으로부터 거리에 의한 공간적 blur를 보상하여 높은 spatial resolution과 contrast를 가지는 특징이 있다. 본 논문에서는 이러한 재구성 기법 중의 하나인 Philips사의 Astonish 프로그램을 phantom 실험을 통하여 기존의 재구성 기법과 비교, 평가하고 임상적 유용성을 높이고자 하였다. Skylight SPECT system (Philips)에서 NEMA IEC PET body phantom과 Flanges Jaszczak phantom (Data Spectrum corp.)을 이용하여 시간과 거리에 따른 4가지의 다른 입력 조건에서 실험을 실시하였다. 가까운 거리와 먼 거리 (짧은 거리보다 10 cm 더해진 거리)에서 각각 full time (40 kcts/frame)과 half time (full time의 절반)을 적용하여 영상을 얻고, iteration 수에 변화를 주어 MLEM, 3D-OSEM, Astonish로 영상을 재구성하였다. NEMA IEC PET body phantom의 각 sphere에서 background variability에 따른 contrast ratio의 변화양상을 확인하고 각 재구성 기법에서의 최적의 iteration 수를 찾아보았다. 이로부터 얻은 최적의 iteration 수를 Jaszczak phantom 영상의 재구성에 적용하여 비교해보고 실제 환자의 myocardial SPECT data에 대하여 육안적 평가를 실시하였다. 전반적인 contrast ratio는 Astonish가 MLEM과 3D-OSEM보다 높았다. 직경 37 mm의 가장 큰 hot sphere에서 짧은 거리에서는 Astonish가 MLEM과 3D-OSEM보다 각각 27.1%와 17.4%의 더 높은 contrast ratio를 보였고, 먼 거리에서는 40.5%와 32.6%로 더 높았다. 그러나 시간에 따른 변화의 차이는 크게 나타나지 않았다. 또한, 육안적 평가에서 Astonish가 다른 두 재구성 기법에 비하여 더 좋은 영상을 보였다. 이 실험에서는 정량적 분석 및 육안적 평가를 통하여 Astonish가 기존의 영상 재구성 기법인 MLEM과 3D-OSEM에 비하여 시간을 단축시켜 업무의 효율성을 높일 뿐만 아니라 질적으로도 우수한 영상을 구현하여 임상적으로 신뢰성이 높은 검사 결과를 제공할 수 있음을 확인하였다. Objective: The 3-dimensional reconstruction method with resolution recovery modeling has advantages of high spatial resolution and contrast because of its precise modeling of spatial blurring according to the distance from detector plane. The aim of this study was to evaluate one of the resolution recovery reconstruction methods (Astonish, Philips Medical), compare it to other iterative reconstructions, and verify its clinical usefulness. Materials and Methods: NEMA IEC PET body phantom and Flanges Jaszczak ECT phantom (Data Spectrum Corp., USA) studies were performed using Skylight SPECT (Philips) system under four different conditions; short or long (2 times of short) radius, and half or full (40 kcts/frame) acquisition counts. Astonish reconstruction method was compared with two other iterative reconstructions; MLEM and 3D-OSEM which vendor supplied. For quantitative analysis, the contrast ratios obtained from IEC phantom test were compared. Reconstruction parameters were determined by optimization study using graph of contrast ratio versus background variability. The qualitative comparison was performed with Jaszczak ECT phantom and human myocardial data. Results: The overall contrast ratio was higher with Astonish than the others. For the largest hot sphere of 37 mm diameter, Astonish showed about 27.1% and 17.4% higher contrast ratio than MLEM and 3D-OSEM, in short radius study. For long radius, Astonish showed about 40.5% and 32.6% higher contrast ratio than MLEM and 3D-OSEM. The effect of acquired counts was insignificant. In the qualitative studies with Jaszczak phantom and human myocardial data, Astonish showed the best image quality. Conclusion: In this study, we have found out that Astonish can provide more reliable clinical results by better image quality compared to other iterative reconstruction methods. Although further clinical studies are required, Astonish would be used in clinics with confidence for enhancement of images.

Rule Induction Considering Implication Relations Between Conclusions

Inuiguchi, Masahiro,Inoue, Masanori,Kusunoki, Yoshifumi Korean Institute of Industrial Engineers 2011 Industrial Engineeering & Management Systems Vol.10 No.1

In rough set literatures, methods for inducing minimal rules from a given decision table have been proposed. When the decision attribute is ordinal, inducing rules about upward and downward unions of decision classes is advantageous in the simplicity of obtained rules. However, because of independent applications of the rule induction method, inclusion relations among upward/downward unions in conclusion parts are not inherited to the condition parts of obtained rules. This non-inheritance may debase the quality of obtained rules. To ensure that inclusion relations among conclusions are inherited to conditions, we propose two rule induction approaches. The performances of the proposed approaches considering the inclusion relations between conclusions are examined by numerical experiments.

Rule Induction Considering Implication Relations Between Conclusions

Masahiro Inuiguchi,Masanori Inoue,Yoshifumi Kusunoki 대한산업공학회 2011 Industrial Engineeering & Management Systems Vol.10 No.1

In rough set literatures, methods for inducing minimal rules from a given decision table have been proposed. When the decision attribute is ordinal, inducing rules about upward and downward unions of decision classes is advantageous in the simplicity of obtained rules. However, because of independent applications of the rule induction method, inclusion relations among upward/downward unions in conclusion parts are not inherited to the condition parts of obtained rules. This non-inheritance may debase the quality of obtained rules. To ensure that inclusion relations among conclusions are inherited to conditions, we propose two rule induction approaches. The performances of the proposed approaches considering the inclusion relations between conclusions are examined by numerical experiments.

Development of image reconstruction algorithm with iterative method using maximum-likelihood expectation-maximization (MLEM) for chest digital tomosynthesis (CDT) X-ray system

Lee, S.,Kang, S.H.,Heo, Y.C.,Lee, Y. Wissenschaftliche Verlagsgesellschaft m. b. H 2017 OPTIK -STUTTGART- Vol.150 No.-

<P>Digital tomosynthesis system (DTS) has been increasingly used in chest X-ray imaging with a limited-projection angle image reconstruction method. Image reconstruction methods in chest digital tomosynthesis (CDT) have fundamental impacts on image characteristics. Among these methods, iterative algorithm provides the additional benefits of chest X-ray imaging. However, there is almost no research that maximum-likelihood expectation-maximization (MLEM) method in CDT system. Thus, the purpose of this study was (1) to develop MLEM reconstruction algorithm based on CDT system and (2) to quantitatively compare the image characteristics with respect to the total angular range and iteration number as applied this system. For that purpose, we performed both simulation using MATLAB program and experimental studies. Tomography was performed linearly with a maximum +/- 30 degrees total angular range and then we acquired Shepp-Logan and PMMA-Aluminum (Al) phantom images using 120 kVp X-ray source for simulation and experiment, respectively. We evaluated and compared the MLEM reconstructed image characteristics using root-mean-square error (RMSE) and signal difference-to-noise ratio (SDNR) with various total angular ranges and iteration numbers. According to the results, we can acquire improved image characteristics as the number of iterations and the number of projections increased. Also, we found optimized iteration number for 20 iteration numbers in our CDT system geometry because there were few changes of image characteristics over 20 iteration numbers. In conclusion, we have presented usefulness and effectiveness of developed CDT image reconstruction algorithm. (C) 2017 Elsevier GmbH. All rights reserved.</P>

An Inner-Crystal Neutron-Scatter Camera: Monte Carlo Simulation

Ajin Jo,Won Ho Lee 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.68 No.9

Neutron energy emitted from special nuclear materials (SNMs) can be measured by using neutronproton scattering; also, the scattering angle can be calculated from the ratio of the scattered energy to the incident energy. By using position and energy information, we can image the original source position by using the backprojection and list-mode maximum-likelihood expectation maximization (MLEM) method. In this paper, we propose an inner-crystal neutron scatter camera system in which the detectors are not separated to obtain interactions at a variety of scatter angles; based on this system, we analyzed the characteristics of the corresponding neutron-scattering camera. The factors that affected the neutron-scatter image were the neutron velocity after scattering, the cut-off level of the time of flight (ToF), and the width of the cones used for image reconstruction. To determine the optimal point for the reconstruction of an image, we estimated the performance of the system by using the figure of merit (FoM). The optimal neutron-velocity (d/ToF) was 0.3 × 107 m/s according to our simulation result, while the optimal cut-off level of the ToF was 4 ns as the latter minimized the noise while maintaining the required efficiency. The widths of the cones (") also affected the full width at half maximum (FWHM) and the noise of the image. In terms of a simple source-geometry, whereby concepts such as “point source” were used, a large " value was suitable to achieve noise reduction; however, regarding the complicated source geometry, a small " value was favorable for precise reconstruction of the original source geometry for both the backprojection and the list-mode MLEM methods.

Estimate of the 225Ac Radioactive Isotope Distribution by Means of DOI Compton Imaging in Targeted Alpha Radiotherapy: A Monte Carlo Simulation

Yoon Changyeon,Jo Seongmin,Cho Yongho,Kim Nakjeom,Lee Taewoong 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.10

For successful targeted alpha radiotherapy (TAT), verifying the accurate position and distribution of a targeted radiotherapeutic agent in a patient or phantom is important. This paper, describes our investigation of depth-of-interaction (DOI) Compton imaging for the two γ-rays emitted during TAT with the 225Ac radioactive isotope. We optimized the design parameters of the DOI Compton camera, for example, the inter-detector distance, based on the figure of merit (FOM). The performance of DOI Compton imaging for TAT was improved because Doppler broadening and the energy uncertainty are inversely proportional to the radiation energy and the position uncertainty of the depth information is decreased. After the contrast phantom and the resolution phantom had been designed, two reconstruction algorithms, the filtered back-projection (FBP) algorithm and the maximum-likelihood expectation maximization (MLEM) algorithm, were applied to each reconstructed phantom image, and the qualities of the reconstructed images for the two γ-rays (218 keV and 440 keV) were compared. In the quantitative evaluation of the reconstructed images, the MLEM reconstruction algorithm performed better than the FBP algorithm. Based on Monte Carlo simulation studies, the DOI Compton images of the 225Ac radioactive isotope emitting two γ-rays demonstrated the capability of imaging a targeted radiotherapeutic agent in TAT.

CT 선량감소를 위한 결정론적(FBP) 및 확률적(MLEM) 영상재구성 방법의 비교

이형건,이원호 대한방사선방어학회 2012 대한방사선방어학회 학술발표회 논문요약집 Vol.2012 No.11

High performance γ-ray imager using dual anti-mask method for the investigation of high-energy nuclear materials

Lee, Taewoong,Lee, Wonho Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.7

As the γ-ray energy increases, a reconstructed image becomes noisy and blurred due to the penetration of the γ-ray through the coded mask. Therefore, the thickness of the coded mask was increased for high energy regions, resulting in severely decreased the performance of the detection efficiency due to self-collimation by the mask. In order to overcome the limitation, a modified uniformly redundant array γ-ray imaging system using dual anti-mask method was developed, and its performance was compared and evaluated in high-energy radiation region. In the dual anti-mask method, the two shadow images, including the subtraction of background events, can simultaneously contribute to the reconstructed image. Moreover, the reconstructed images using each shadow image were integrated using a hybrid update maximum likelihood expectation maximization (h-MLEM). Using the quantitative evaluation method, the performance of the dual anti-mask method was compared with the previously developed collimation methods. As the shadow image which was subtracted the background events leads to a higher-quality reconstructed image, the reconstructed image of the dual anti-mask method showed high performance among the three collimation methods. Finally, the quantitative evaluation method proves that the performance of the dual anti-mask method was better than that of the previously reconstruction methods.

Compact hybrid gamma camera with a coded aperture for investigation of nuclear materials

Lee, T.,Lee, W. North-Holland 2014 Nuclear Instruments & Methods in Physics Research. Vol.767 No.-

Mechanical collimation commonly uses the photoelectric effect to reconstruct radiation images. Electronic collimation (i.e. Compton camera) using Compton scattering has been developed to reconstruct radiation images without utilizing mechanical collimators. Generally, for radiation imaging, electronic and mechanical collimation methods are used individually. In order to increase the quality of imaging and the efficiency of radiation detection, we combined both collimation methods in a single system. Our compact hybrid gamma camera comprised a modified uniformly redundant array (MURA) and a Compton camera, and the information from each modality was obtained simultaneously. The entire system formed a radial shape with detector modules which comprising CsI(Na) scintillators coupled with position-sensitive photomultiplier tubes (PSPMTs) whose anodes were connected to custom-made circuits. For various energy sources, the reconstructed images produced using this hybrid method were obtained and compared with reconstructed images from the two aforementioned methods. The maximum likelihood expectation maximization (MLEM) algorithm was applied for the reconstruction method. Compared with individual imagers at intermediate energies, the hybrid imager showed equal or better performance.

2×2 virtual Frisch-grid CZT 배열 기반 Compton camera 개발

김영학,이원호 대한방사선방어학회 2021 대한방사선방어학회 학술발표회 논문요약집 Vol.2021 No.11