Filtered Backprojection에서 정착자를 사용한 고주파 감쇠

이수진,김용호,Lee, Soo-Jin,Kim, Yong-Hoh 배재대학교 공학연구소 1997 공학논문집 Vol.2 No.1

Emission computed tomography에 있어서 Bayesian방법에 근거한 통계학적 영상 재구성법이 수년간에 걸쳐 중요한 관심사로 대두되어 왔다. 이는 Bayesian 접근 방법을 사용할 경우 영상 재구성 알고리즘에 재구성하고자 하는 영상에 대한 사전정보를 포함시킬 수 있기 때문이었다. 이러한 방법은 경우에 따라 향상된 성능을 보이고 있으나, 막대한 계산시간으로 인해 실제 임상에 적용되기가 매우 어려운 상황이다. 한편, filtered backprojection(FBP)은 알고리즘 자체가 간단하고 계산시간도 매우 단축되므로 대부분의 임상에 널리 적용되고 있다. 본 연구에서는 Bayesian 영상 재구성에서 매우 유용하게 사용되는 spline 모델을 FBP의 고주파 감쇠를 위한 정칙자로 사용함으로써 FBP 영상 재구성에 Bayesian 방법과 유사한 효과를 얻을 수 있음을 보인다. In emission computed tomography, statistical reconstruction methods in the context of a Bayesian framework have been a topic of interest over the last decade. This was mainly due to the fact that Bayesian approaches can incorporate a priori information into the reconstruction algorithm. Although these approaches can exhibit good performance, their applications to the clinic is hindered mainly by their high computational cost. On the other hand, the speed and simplicity of the filtered backprojection (FBP) algorithm have led to its widespread use in most clinical applications. In this work, we use spline models, which have been quite useful in Bayesian reconstruction, as regularizers for high-frequency apodization in FBP algorithm and show that the effects of using spline models as priors in Bayesian reconstruction can also be achieved in FBP reconstruction.

Digital Tomosynthesis in Cone-beam Geometry for Industrial Applications: Feasibility and Preliminary Study

조민국,김호경,윤한빈,장선영,이석,한명철 한국정밀공학회 2012 International Journal of Precision Engineering and Vol.13 No.9

We introduce a cone-beam computed tomography with insufficient projections obtained from a limited-angle scan, the so-called digital tomosynthesis, and demonstrate its feasibility for the industrial applications by implementing to the reconstruction of internal slice images of a multilayer printed circuit board. The image reconstruction algorithm is based on the filtered-backprojection approach for the cone-beam geometry with isocentric linear motion in the scanning trajectory of the X-ray source and imaging detector pair. Although the slice image reconstructed at the plane of interest was affected by the structures outside, we could reconstruct the plane of interest with the total scan angle less than 20 degrees and 11 projections. The digital tomosynthesis is expected to be practical for industrial tomography restricted to the limited-angle scan.

A Spline-Regularized Sinogram Smoothing Method for Filtered Backprojection Tomographic Reconstruction

Lee, S.J.,Kim, H.S. The Korean Society of Medical and Biological Engin 2001 의공학회지 Vol.22 No.4

Statistical reconstruction methods in the context of a Bayesian framework have played an important role in emission tomography since they allow to incorporate a priori information into the reconstruction algorithm. Given the ill-posed nature of tomographic inversion and the poor quality of projection data, the Bayesian approach uses regularizers to stabilize solutions by incorporating suitable prior models. In this work we show that, while the quantitative performance of the standard filtered backprojection (FBP) algorithm is not as good as that of Bayesian methods, the application of spline-regularized smoothing to the sinogram space can make the FBP algorithm improve its performance by inheriting the advantages of using the spline priors in Bayesian methods. We first show how to implement the spline-regularized smoothing filter by deriving mathematical relationship between the regularization and the lowpass filtering. We then compare quantitative performance of our new FBP algorithms using the quantitation of bias/variance and the total squared error (TSE) measured over noise trials. Our numerical results show that the second-order spline filter applied to FBP yields the best results in terms of TSE among the three different spline orders considered in our experiments.

Image Reconstruction for Digital Breast Tomosynthesis (DBT) by Using Projection-angle-dependent Filter Functions

박연옥,박철규,조효성,제의규,홍대기,이민식,조희문,최성일,구양서 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.5

Digital breast tomosynthesis (DBT) is considered in clinics as a standard three-dimensionalimaging modality, allowing the earlier detection of cancer. It typically acquires only 10-30 projectionsover a limited angle range of 15 − 60 with a stationary detector and typically uses acomputationally-efficient filtered-backprojection (FBP) algorithm for image reconstruction. However,a common FBP algorithm yields poor image quality resulting from the loss of average imagevalue and the presence of severe image artifacts due to the elimination of the dc component ofthe image by the ramp filter and to the incomplete data, respectively. As an alternative, iterativereconstruction methods are often used in DBT to overcome these difficulties, even though they arestill computationally expensive. In this study, as a compromise, we considered a projection-angledependentfiltering method in which one-dimensional geometry-adapted filter kernels are computedwith the aid of a conjugate-gradient method and are incorporated into the standard FBP framework. We implemented the proposed algorithm and performed systematic simulation works toinvestigate the imaging characteristics. Our results indicate that the proposed method is superiorto a conventional FBP method for DBT imaging and has a comparable computational cost, whilepreserving good image homogeneity and edge sharpening with no serious image artifacts.

Tc-99m-MIBI 심근 SPECT에서 재구성필터의 차단주파수에 의한 인위적 관류결손의 정량적 평가

곽철은,정준기,이명철,Kwark, Cheol-Eun,Chung, June-Key,Lee, Myung-Chul 대한의용생체공학회 1995 의공학회지 Vol.16 No.2

Tc-99m-MIBI 심근 SPECT에서 심근조직에 비하여 간섭취가 상대적으로 높고 이들이 서로 가까이에 위치해 있는 경우 단축단면상의 하위부 또는 하위중격부에서 발생하는 인위적 관류결손의 정도와 여과기의 차단주파수의 관계를 분석하였다. 이러한 영향은 단축단면상 뿐만 아니라 심근 극성지도에서도 관찰되는데, 심근단층상에서 계수분포가 균일하지 못하고 간과 같이 특정부위에 방사능의 집적도가 높은 경우 단층상 재구성시 차단 파수의 적절한 설정에 따라 이 효과를 줄일 수 있는 방법을 제안하였다. 본 연구에서 분석에 사용된 여과기는 저역통과여과기로 이를 사용하는 경우에는 차단주파수를 0.4Nyquist 이상으로 하면 인위적 관류결손의 정도를 충분히 줄일 수 있었다. 그러나 높은 차단주파수에서는 심근영상의 균일도가 떨어지고 배후방사능 및 기타 잡음요인이 효과적으로 제거되지 않기 때문에 적절한 차단주파수의 설정이 중요하며, 본 연구에 사용된 영상에서 여과방법에 따른 원주프로필의 변화가 미세하여 후처리방법을 사용하여 분석하였다. 또한 역투사방법이 비선형적이므로 특정 영상보다는 다양한 간-심근 방사능비에 따른 영상을 분석하여 비선형성을 배제한 연구가 향후 진행되어야 한다. Tc-99m-MIBI (Sestamibi) myocardial SPECT along with TI-201 tomographic Imaging has demonstrated wide application and high image quality sufficient for the diagnosis of myocardial perfusion defect, which consequently reflects regional myocardial blood flow. The qualitative values of myocardial SPECT with Tc-99m-MIBI as well ds the quantitative cases depend in some degree on the reconstruction techniques of multiple projections. Filtered backprojection (FBP) Is the common standard method for reconstruction rather than the complicated and time-consuming arithmetic methods. In FBP it is known that the distribution of radioactivity in reconstructed transverse slices varies with the selected litter parameters such as cutoff frequencies and order (Butterworth case) The cutoff frequencies used in clinicAl practice partially remove and decrease the true radioactive distribution and alter the pixel counts, which lead to underestimation of true counts in specific myocardial regions. In this study, we have investigated the effect of cutoff frequencies of reconstruction filter on the artifactually induced perfusion defects, which are often demonstrated near inferior and/or inferoseptal cardiac walls due to the intense hepatic uptake of Tc-99m-MIBI. A computerized method for Identifying the relative degree of artifactual perfusion defect and for comparing those degrees along with the relative amount of hepatic uptake to myocardium was developed and patient images were studied to observe the quantitative degree of underestimation of myocardial perfusion, and to propose some reasonable threshold of cutoff frequency in the diagnosis of perfusion defect quantitatively. We concluded that from the quantitative viewpoint cutoff frequencies may be used as high as possible with the sacrifice of homogeneity of image quality, and those frequencies lower than the common 0.3 Wyquist frequency would reveal severe degradation of radioactive distribution near inferior and/or inferoseptal myocardium when applying Butterworth or low pass filter.

Image Reconstruction Using Filtered Backprojection and Maximum Likelihood Expectation Maximization Methods

Altansukh Sengee,Nyamlkhagva Sengee,Heung-Kook Choi,Myung-Ja Tak,Sae-Hong Cho 한국멀티미디어학회 2011 한국멀티미디어학회 국제학술대회 Vol.2011 No.-

This study objective was to compare popular image reconstruction methods which are the filtered backprojection (FBP) and maximum likelihood expectation maximization (MLEM) on some medical and phantom images with noise. Peak signal noise ratio (PSNR) is used to evaluate the methods. Experimental result shows that FBP and MLEM are closely similar result but MLEM is better than FBP in noisy images.

컴프턴 카메라를 위한 재배열 기반 확정론적 영상재구성법

이미노,이수진,서희,Lee, Mi-No,Lee, Soo-Jin,Seo, Hee,Nguyen, Van-Giang 대한의용생체공학회 2011 의공학회지 Vol.32 No.1

While Compton imaging is recognized as a valuable 3-D technique in nuclear medicine, reconstructing an image from Compton scattered data has been of a difficult problem due to its computational complexity. The most complex and time-consuming computation in Compton camera reconstruction is to perform the conical projection and backprojection operations. To alleviate the computational burden imposed by these operations, we investigate a rebinning method which can convert conical projections into parallel projections. The use of parallel projections allows to directly apply the existing deterministic reconstruction methods, which have been useful for conventional emission tomography, to Compton camera reconstruction. To convert conical projections into parallel projections, a cone surface is sampled with a number of lines. Each line is projected onto an imaginary plane that is mostly perpendicular to the line. The projection data rebinned in each imaginary plane can then be treated as the standard parallel projection data. To validate the rebinning method, we tested with the representative deterministic algorithms, such as the filtered backprojection method and the algebraic reconstruction technique. Our experimental results indicate that the rebinning method can be useful when the direct application of existing deterministic methods is needed for Compton camera reconstruction.

Simulation of the Digital Image Processing Algorithm for the Coating Thickness Automatic Measurement of the TRISO-coated Fuel Particle

Kim, Woong-Ki,Lee, Young-Woo,Ra, Sung-Woong Korea Information Processing Society 2005 Journal of information processing systems Vol.1 No.1

TRISO (Tri-Isotropic)-coated fuel particle is widely applied due to its higher stability at high temperature and its efficient retention capability for fission products in the HTGR (high temperature gas-cooled reactor), one of the highly efficient Generation IV reactors. The typical ball-type TRISO-coated fuel particle with a diameter of about 1 mm is composed of a nuclear fuel particle as a kernel and of outer coating layers. The coating layers consist of a buffer PyC, inner PyC, SiC, and outer PyC layer. In this study, a digital image processing algorithm is proposed to automatically measure the thickness of the coating layers. An FBP (filtered backprojection) algorithm was applied to reconstruct the CT image using virtual X-ray radiographic images for a simulated TRISO-coated fuel particle. The automatic measurement algorithm was developed to measure the coating thickness for the reconstructed image with noises. The boundary lines were automatically detected, then the coating thickness was circularly by the algorithm. The simulation result showed that the measurement error rate was less than 1.4%.

Sparse-view CT Imaging of Trabecular Bones: Comparison of Image Reconstruction Methods

이수열,Hye Sun Kim,조민형 대한의용생체공학회 2011 Biomedical Engineering Letters (BMEL) Vol.1 No.3

Purpose In longitudinal in-vivo imaging studies of trabecular bones using a micro-CT, sparse-view imaging is highly desired to reduce x-ray dose to the animals under study and to reduce the scan time. Sparse-view imaging, i.e., imaging with reduced number of views in the CT scan, may result in severe streak artifacts in the reconstructed images degrading the image quality. We compare image reconstruction methods in terms of final image quality in CT imaging of trabecular bones. Methods We have compared three image reconstruction methods, the conventional filtered backprojection method and two iterative image reconstruction methods, i.e., SIRT and TV-minimization methods, in trabecular bone imaging with sparse-view CT scans. After acquiring projection data from sparse-view scanning of a chicken bone using a micro-CT, we have calculated relative image errors and edge preservation metrics from the images reconstructed by the three different methods. Results We have observed that the TV-minimization method outperforms the other methods in trabecular bone imaging in terms of edge preservation and relative image error. Conclusions TV-minimization-based iterative image reconstruction methods may be greatly used for low-dose CT imaging of trabecular bones with reduced number of views.

Compressed-sensing (CS)-based Digital Breast Tomosynthesis (DBT) Reconstruction for Low-dose, Accurate 3D Breast X-ray Imaging

박연옥,조효성,Uikyu Je,홍대기,이민식,박철규,조희문,최성일,구양서 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.4

In practical applications of three-dimensional (3D) tomographic techniques, such as digital breasttomosynthesis (DBT), computed tomography (CT), etc., there are often challenges for accurateimage reconstruction from incomplete data. In DBT, in particular, the limited-angle and few-viewprojection data are theoretically insufficient for exact reconstruction; thus, the use of commonfiltered-backprojection (FBP) algorithms leads to severe image artifacts, such as the loss of theaverage image value and edge sharpening. One possible approach to alleviate these artifacts mayemploy iterative statistical methods because they potentially yield reconstructed images that are inbetter accordance with the measured projection data. In this work, as another promising approach,we investigated potential applications to low-dose, accurate DBT imaging with a state-of-the-artreconstruction scheme based on compressed-sensing (CS) theory. We implemented an efficientCS-based DBT algorithm and performed systematic simulation works to investigate the imagingcharacteristics. We successfully obtained DBT images of substantially very high accuracy by usingthe algorithm and expect it to be applicable to developing the next-generation 3D breast X-rayimaging system.