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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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Determination of water absorbed dose in a carbon ion beam using thimble ionization chambers

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PHYSICS IN MEDICINE AND BIOLOGY 1999年第5期44卷 1193-1206页

作者： Hartmann, GH Jäkel, O Heeg, P Karger, CP Kriessbach, A German Canc Res Ctr Dept Med Phys D-69009 Heidelberg Germany Univ Heidelberg Radiol Hosp D-69120 Heidelberg Germany

The method to measure absorbed dose to water in a field of carbon ions as applied for the heavy ion therapy project at the Heavy Ion Research Laboratory in Darmstadt (GSI), Germany, is described in detail. Thimble ionization chambers with a water absorbed calibration factor are applied. The dose obtained with this method was compared with that obtained at the heavy ion therapy facility HIMAC at the National Institute of Radiological Sciences in Chiba, Japan, using the Japanese code of practice. The agreement found was better than 1%. The combined uncertainty of the determination of absorbed dose to water was estimated to amount to 5%.

关键词：空气生物物理学现象生物物理学碳评价研究(主题) 肿瘤/放射疗法辐射剂量放射测量术/仪器和设备放射测量术/统计学和数值数据放射治疗计划计算机辅助/统计学和数值数据水人类

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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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Three-dimensional echocardiography: assessment of inter- and intra-operator variability and accuracy in the measurement of left ventricular cavity volume and myocardial mass

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PHYSICS IN MEDICINE AND BIOLOGY 2000年第5期45卷 1255-1273页

作者： Nadkarni, SK Boughner, DR Drangova, M Fenster, A John P Robarts Res Inst Adv Imaging Res Labs London ON N6A 5K8 Canada Univ Western Ontario Dept Med Biophys London ON N6A 5C1 Canada London Hlth Sci Ctr London ON N6A 5A5 Canada

Accurate left ventricular (LV) volume and mass estimation is a strong predictor of cardiovascular morbidity and mortality. We propose that our technique of 3D echocardiography provides an accurate quantification of LV volume and mass by the reconstruction of 2D images into 3D volumes, thus avoiding the need for geometric assumptions. We compared the accuracy and variability in LV volume and mass measurement using 3D echocardiography with 2D echocardiography, using in vitro studies. Six operators measured the LV volume and mass of seven porcine hearts, using both 3D and 2D techniques. Regression analysis was used to test the accuracy of results and an ANOVA lest was used to compute variability in measurement. LV volume measurement accuracy was 9.8% (3D) and 18.4% (2D);LV mass measurement accuracy was 5% (3D) and 9.2% (2D). Variability in LV volume quantification with 3D echocardiography was %SEMinter = 13.5%, %SEMintra = 11.4%, and for 2D echocardiography was %SEMinter = 21.5%, %SEMintra, = 19.1%. We derived an equation to predict uncertainty in measurement of LV volume and mass using 3D echocardiography, the results of which agreed with our experimental results to within 13%. 3D echocardiography provided twice the accuracy for LV volume and mass measurement and half the variability for LV volume measurement as compared with 2D echocardiography.

关键词：方差分析生物物理学现象生物物理学超声心动描记术/方法超声心动描记术/统计学和数值数据超声心动描记术三维/方法超声心动描记术三维/统计学和数值数据心脏/解剖学和组织学心室/解剖学和组织学图像处理计算机辅助/方法图像处理计算机辅助/统计学和数值数据观察者偏差猪动物人类

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A study on virtual source position for electron beams from a Mevatron MD linear accelerator

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PHYSICS IN MEDICINE AND BIOLOGY 1999年第5期44卷 1309-1315页

作者： Ravindran, BP Christian Med Coll & Hosp Dept Radiat Oncol Vellore 632004 Tamil Nadu India

The virtual source position (VSP) for electron beams of energies 5, 7, 9 10, 12 and 14 MeV and for the applicators (cones) available in the department have been measured for a Mevatron MD class linear accelerator. Different methods of obtaining the virtual source position for electron beams have been investigated in the present study. The results obtained have been compared with those of other workers. It is observed that the VSP is very much machine dependent and needs to be measured for each linear accelerator. The effect of shielding on virtual source position for the type of applicators available in the department has also been investigated.

关键词：空气生物物理学现象生物物理学电子肿瘤/放射疗法粒子加速器/仪器和设备放射治疗计划计算机辅助/统计学和数值数据放射疗法高能/仪器和设备人类

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Methods for separation of contributions from two radionuclides in autoradiography with a silicon strip detector

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PHYSICS IN MEDICINE AND BIOLOGY 2000年第5期45卷 1183-1193页

作者： Kvinnsland, Y Skretting, A Norwegian Radium Hosp Dept Nucl Med N-0310 Oslo Norway

Two methods have been developed for the separation of contributions from two different nuclides in an autoradiography picture. Both approaches, a modified least squares (LS) and a maximum likelihood (ML) algorithm, are based on the position and energy information available from a digital detector. Tests and comparisons, using artificially as well as measured data, demonstrate that the ML approach performs slightly better, but is much more computationally demanding than the LS method.

关键词：算法放射自显影术/方法放射自显影术/统计学和数值数据生物物理学现象生物物理学图像处理计算机辅助/方法图像处理计算机辅助/统计学和数值数据最小二乘法分析似然函数磷放射性同位素硅硫放射性同位素动物

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Multispectral imaging approach in the diagnosis of cutaneous melanoma: potentiality and limits

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PHYSICS IN MEDICINE AND BIOLOGY 2000年第5期45卷 1243-1254页

作者： Farina, B Bartoli, C Bono, A Colombo, A Lualdi, M Tragni, G Marchesini, R Ist Nazl Studio & Cura Tumori I-20133 Milan Italy

In an attempt to overcome the subjectiveness of clinical observation in the diagnosis of cutaneous melanoma, a computerized method is proposed. Reflectance images of 237 pigmented lesions (67 melanomas and 170 non-melanomas) were analysed using a telespecificphotometric technique. This device consists of a CCD camera with 17 interference filters. Images were acquired at selected wavelengths, from 420 to 1040 nm. Morphological and reflectance related parameters were extracted from the wavelength-dependent images of the lesions. The most significant features in the comparison between benign and malignant lesions were: lesion dimension (P < 10(-8) at 578 nm);mean value (P < 10(-7) at 940 nm) and standard deviation(P < 10(-4) at 904 nm) of lesion reflectance;lesion roundness (P < 10(-5) at 461 nm);and border irregularity (P < 10-4 at 461 nm). Based on these parameters, a discriminant function between the two populations of lesions (naevi and melanomas) was obtained. By using the results of the analysis of the recruited lesions as 'training data', discriminant functions enabled the assignment of a score, or a 'risk probability', to each studied lesion. By imposing a sensitivity of 80% (a figure that mimics the diagnostic capability of an experienced clinician), entering or not entering the lesion dimension as input data in the discriminant analysis led to a specificity of 51% or 46% respectively. The high number of false-positive cases, which is a consequence of the selection criteria of the lesions, is, at present, the major limitation of the current technique. Nevertheless, our results suggest that an imaging-based computer-assisted device could be capable of discriminating malignant lesions mainly by evaluation of reflectance, especially in the infrared region, and shape properties. The dimension of a lesion should not be essential in the diagnosis of melanoma and, in our opinion, small melanomas should be recognized by a computer system as well as they are on clinica

关键词：生物物理学现象生物物理学诊断计算机辅助/统计学和数值数据判别分析假阳性反应图像处理计算机辅助黑色素瘤/诊断痣色素/诊断 ROC曲线敏感性与特异性皮肤肿瘤/诊断分光光度法青少年成年人老年人老年人 80以上儿童女(雌)性人类男(雄)性中年人

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The problem of the missing wavelet

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PERCEPTUAL AND MOTOR SKILLS 1999年第2期88卷 496-502页

作者： Brigner, WL Appalachian State Univ Boone NC 28607 USA

A block face was generated by dividing a drawn face into a matrix of rectangular cells and then making the brightness of each cell equal to the average of the brightnesses within the facial area circumscribed by a cell. A wavelet analysis was performed on the numbers representing the brightnesses of the cells in each rom of the matrix, and from each row, the wavelet was deleted which corresponded to the fundamental or the lowest frequency sine wave of a complex wave. The appearance of the block face uas not substantially altered by the deletion of the wavelet corresponding to the fundamental.

关键词：算法面部形状知觉傅里叶分析图像处理计算机辅助/统计学和数值数据光数学人类

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The Mackworth Clock Test: A computerized version

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JOURNAL OF PSYCHOLOGY 2000年第2期134卷 153-161页

作者： Lichstein, KL Riedel, BW Richman, SL Univ Memphis Dept Psychol Memphis TN 38152 USA

The Mackworth Clock Test (MCT;N. H. Mackworth, 1948) was developed to evaluate vigilance in British Air Force radar technicians during World War II. Homemade versions of the MCT have since varied with respect to both the characteristics of the device and the procedures of its administration;This article is a report on a computerized version of the MCT developed by the authors to closely emulate Mackworth's test. MCT data were collected from 25 undergraduate students;their performance was found to be equivalent to Mackworth's participants' data. This is the first MCT version that has been validated against the original.

关键词：注意力诊断计算机辅助/统计学和数值数据心理学试验/统计学和数值数据心理测定学精神运动性行为反应时间可重复性结果软件学生/心理学青少年成年人女(雌)性人类男(雄)性

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Intensity modulated photon beams subject to a minimal surface smoothing constraint

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PHYSICS IN MEDICINE AND BIOLOGY 2000年第5期45卷 N49-N52页

作者： Alber, M Nüsslin, F Univ Tubingen Radiol Uniklin Abt Med Phys D-72076 Tubingen Germany

A method to smooth intensity-modulated photon beams is presented which can be applied in conjunction with any optimization algorithm. The method employs an additional soft constraint to minimize the area of the surfac... 详细信息

关键词：算法生物物理学现象生物物理学肿瘤/放射疗法光子/治疗应用放射治疗计划计算机辅助/方法放射治疗计划计算机辅助/统计学和数值数据放射疗法适形/方法放射疗法适形/统计学和数值数据人类

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