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Subsets and overrelaxation in iterative image reconstruction

PHYSICS IN MEDICINE AND BIOLOGY 1999年第5期44卷 1385-1396页

作者： Schmidlin, P Bellemann, ME Brix, G Deutsch Krebsforschungszentrum Forsch Schwerpunkt Radiol Diagnost & Therapie D-6900 Heidelberg Germany

A number of iterative image reconstruction algorithms were integrated into one formula characterizing each algorithm by only two parameters: overrelaxation and number of subsets. From the formula it follows that the ordered-subsets iteration (OS-EM) is equivalent to iteration with overrelaxation, where the OS level corresponds to the overrelaxation parameter. Algorithms represented by the formula were studied with respect to speed of convergence and image characteristics. In particular, OS-EM was compared with a single-projection iteration procedure using an optimized sequence of overrelaxation parameters (HOSP) which combines rapid convergence with reduced storage requirements. As a result, OS-FM with a constant number of subsets either needed more iteration steps than HOSP or provoked additional noise, depending on the number of subsets used during iteration. OS-FM can be improved by using decreasing OS levels, imitating the decreasing overrelaxation parameters used for HOSP. The resulting OS-FM may be slightly more rapid than HOSP, due to the increasing number of projections used simultaneously.

关键词：算法生物物理学现象生物物理学评价研究(主题) 图像处理计算机辅助/方法图像处理计算机辅助/统计学和数值数据体模显象术体层摄影术发射型计算机/统计学和数值数据体层摄影术发射型计算机单光子/统计学和数值数据人类

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A slice-by-slice blurring model and kernel evaluation using the Klein-Nishina formula for 3D scatter compensation in parallel and converging beam SPECT

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PHYSICS IN MEDICINE AND BIOLOGY 2000年第5期45卷 1275-1307页

作者： Bai, CY Zeng, GSL Gullberg, GT Univ Utah Dept Radiol Salt Lake City UT 84108 USA

Converging collimation increases the geometric efficiency for imaging small organs, such as the heart, but also increases the difficulty of correcting far the physical effects of attenuation, geometric response and scatter in SPECT. In this paper, 3D first-order Compton scatter in non-uniform scattering media is modelled by using an efficient slice-by-slice incremental blurring technique in both parallel and converging beam SPECT. The scatter projections are generated by first forming an effective scatter source image (ESSI), then forward-projecting the ESSI. The Compton scatter cross section described by the Klein-Nishina formula is used to obtain spatial scatter response functions (SSRFs) of scattering slices which are parallel to the detector surface. Two SSRFs of neighbouring scattering slices are used to compute two small orthogonal 1D blurring kernels used for the incremental blurring from the slice which is further from the detector surface to the slice which is closer to the detector surface. First-order Compton scatter point response functions (SPRFs) obtained using the proposed model agree well with those of Monte Carlo (MC) simulations for both parallel and fan beam SPECT. Image reconstruction in fan beam SPECT MC simulation studies shows increased left ventricle myocardium-to-chamber contrast (LV contrast) and slightly improved image resolution when performing scatter compensation using the proposed model. Physical torso phantom fan beam SPECT experiments show increased myocardial uniformity and image resolution as well as increased LV contrast. The proposed method efficiently models the 3D first-order Compton scatter effect in parallel and converging beam SPECT.

关键词：生物物理学现象生物物理学心脏/诊断显像图像处理计算机辅助/方法图像处理计算机辅助/统计学和数值数据模型理论蒙特卡罗法体模显象术光子散射辐射体层摄影术发射型计算机单光子/方法体层摄影术发射型计算机单光子/统计学和数值数据人类

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Evaluating the exposure and disease relationship with adjustment for different types of exposure misclassification: A regression approach

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STATISTICS IN MEDICINE 1999年第20期18卷 2795-2808页

作者： Kosinski, AS Flanders, WD Emory Univ Rollins Sch Publ Hlth Dept Biostat Atlanta GA 30322 USA Emory Univ Rollins Sch Publ Hlth Dept Epidemiol Atlanta GA 30322 USA

Misclassification of exposure can lead to biased results in the epidemiologic research. Available methods accounting for misclassification often require the use of a gold standard or assume non-differential misclassification of exposure. We present a regression approach which can detect and account for different types of misclassification when estimating the exposure and disease relationship. This approach uses two imperfect measures of a dichotomous exposure and does not require a gold standard. Standard statistical packages with a logistic regression module can be used for estimation of parameters through the EM algorithm process. Two examples are used to illustrate the methodology. Copyright (C) 1999 John Wiley & Sons, Ltd.

关键词：算法血管成形术气囊冠状动脉/统计学和数值数据冠状动脉分流术/统计学和数值数据冠心病/治疗运动试验/统计学和数值数据似然函数随机对照试验(主题) 回归分析体层摄影术发射型计算机单光子/统计学和数值数据女(雌)性人类男(雄)性

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Independent and incremental value of coronary artery calcium for predicting the extent of angiographic coronary artery disease - Comparison with cardiac risk factors and radionuclide perfusion imaging

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JOURNAL OF THE AMERICAN COLLEGE OF CARDIOLOGY 1999年第3期34卷 777-786页

作者： Schmermund, A Denktas, AE Rumberger, JA Christian, TF Sheedy, PF Bailey, KR Schwartz, RS Mayo Clin & Mayo Fdn Div Cardiovasc Dis & Internal Med Rochester MN 55905 USA Mayo Clin & Mayo Fdn Biostat Sect Rochester MN 55905 USA Univ Texas Sch Med Dept Internal Med Div Cardiol Houston TX USA

OBJECTIVES The study was done to test the ability to predict the extent of angiographically determined coronary artery disease (CAD) by quantification of coronary calcium using electron-beam computed tomography (EBCT) and to compare it with more conventional parameters for delineating the angiographic extent of CAD, that is, cardiovascular risk factors and radionuclide single-photon emission computed tomography (SPECT). BACKGROUND The angiographic extent of CAD is a powerful predictor of subsequent events. Use of EBCT may be able to define it by virtue of its ability to determine plaque burden. METHODS We examined 308 patients presenting with suspected but not previously known CAD who underwent selective coronary angiography. As measures of the angiographic extent of CAD, coronary artery greater even 20 (CAGE greater than or equal to 20) and CAGE greater than or equal to 50 scores represented the total number of coronary segments with greater than or equal to 20% or greater than or equal to 50% stenoses, respectively. The EBCT derived total calcium scores were obtained in 291 patients, risk factors as defined by the National Cholesterol Education Program in 239 patients, and SPECT scans in 136 patients. RESULTS Using multiple linear regression analysis, total calcium scores were better independent predictors of both CAGE greater than or equal to 20 and CAGE greater than or equal to 50 scores than either a SPECT-derived radionuclide perfusion score or the risk factors age, male gender and ratio of total/high density lipoprotein (HDL) cholesterol. The association between EBCT and angiographic scores remained highly significant after excluding the influence of all interrelated risk factors and SPECT variables (r = 0.65;p < 0.001 for CAGE greater than or equal to 20 scores, r = 0.50;p < 0.001 for CAGE greater than or equal to 50 scores). CONCLUSIONS Coronary calcium predicts the angiographic extent of CAD in symptomatic patients and provides independent and incremental

关键词：钙质沉着症/诊断显像冠状血管造影术/方法冠状血管造影术/统计学和数值数据冠心病/诊断显像冠状血管/诊断显像运动试验/方法运动试验/统计学和数值数据线性模型预后放射性药物危险因素 99m锝甲氧基异丁基异腈铊放射性同位素体层摄影术发射型计算机单光子/方法体层摄影术发射型计算机单光子/统计学和数值数据体层摄影术 X线计算机/方法体层摄影术 X线计算机/统计学和数值数据老年人女(雌)性人类男(雄)性中年人

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