Method For Changes Research Articles

Impact of CT attenuation correction by SPECT/CT in brain perfusion images

The aim of this study was to elucidate the regional differences between brain perfusion single photon emission computed tomography (SPECT) images reconstructed with a uniform attenuation correction using Chang's method (AC-Chang) and a non-uniform attenuation correction with CT using SPECT/CT (AC-CT). SPECT images of a phantom with and without head holder were obtained, and reconstructed images of AC-Chang and AC-CT were compared. Twenty-eight consecutive patients with brain disease examined by SPECT/CT brain perfusion imaging were selected, and images were reconstructed with AC-Chang and AC-CT. The AC-Chang and AC-CT reconstructed images were then compared by voxel-based analysis using three-dimensional stereotactic surface projections. Counts in the frontal area of the AC-Chang phantom image with head holder were higher than those in the posterior area. Counts in the frontal area of the AC-Chang clinical images were significantly higher than those in the AC-CT images, while the counts in the margin of the frontal lobe and posterior margin of the parietal, occipital cortices and cerebellum of the AC-Chang images were significantly lower. Relative frontal perfusion was 5.0% higher and relative cerebellar perfusion was 4.6% lower in the AC-Chang images relative to the AC-CT images, on average. We demonstrated the frontal dominant hyper-perfusion and parieto-occipital and cerebellar hypo-perfusion in brain SPECT images reconstructed with AC-Chang compared to those reconstructed with AC-CT. We suggest that to obtain an accurate attenuation-corrected brain perfusion SPECT image, attenuation correction by Chang's method is inadequate.

A modal coupling procedure to improve residual modal effects based on experimentally generated data

In this paper a modal coupling procedure is developed to improve residual modal effects based on experimentally generated data. While showing that Craig–Chang's proposed approximation function for higher frequency modes does not compare well with the exact function, a new procedure is developed in order to re-express the dynamic residuals. For this purpose, all frequency dependent terms of the Maclaurin series in Craig–Chang's proposed method are replaced by a general compatible function, which includes the neglected higher order terms. However, this function no longer appears in final equation of motion. Results from case studies for the discrete, continuous and experimental models are presented to verify the procedure and to show the capabilities of the proposed method.

A NEW FUZZY MULTI CRITERIA DECISION MAKING MODEL FOR OPEN PIT MINES EQUIPMENT SELECTION

Nowadays, the capital cost of open-pit mining equipment is very high so any mistake in the selection of quantity, type and capacity of equipment may cause irreparable impact on the net present value of mining project. Mine planning engineers generally use their intuition and experience in decision making even though equipment selection is a complex multi criteria decision problem. Considering the tangible along with intangible factors in the mine equipment selection problem, this paper proposes a new method of multi criteria decision making (MCDM) that makes it possible to select the optimal equipment that satisfies the decision maker. In a real-world situation, because of incomplete or non-obtainable information, the data (attributes) are often not deterministic but they are usually fuzzy-imprecise. Our proposed model considers objective, critical, and subjective factors as the three main common factors in equipment selection analysis. The last two factors, critical and subjective factors, are defined by decision maker's judgments for more adoption with real world problems. A case study is presented to illustrate the use of the proposed model and to demonstrate the capability of the model. The result of this study shows significant reduction of time consumption of calculation and good precision compared to customary methods such as Chang's fuzzy AHP method.

Inverse Halftoning Based on the Bayesian Theorem

This study proposes a method which can generate high quality inverse halftone images from halftone images. This method can be employed prior to any signal processing over a halftone image or the inverse halftoning used in JBIG2. The proposed method utilizes the least-mean-square (LMS) algorithm to establish a relationship between the current processing position and its corresponding neighboring positions in each type of halftone image, including direct binary search, error diffusion, dot diffusion, and ordered dithering. After which, a referenced region called a support region (SR) is used to extract features. The SR can be obtained by relabeling the LMS-trained filters with the order of importance. Moreover, the probability of black pixel occurrence is considered as a feature in this work. According to this feature, the probabilities of all possible grayscale values at the current processing position can be obtained by the Bayesian theorem. Consequently, the final output at this position is the grayscale value with the highest probability. Experimental results show that the proposed method offers better visual quality than that of Mese-Vaidyanathan's and Chang et al's methods in terms of human-visual peak signal-to-noise ratio (HPSNR). In addition, the memory consumption is also superior to Mese-Vaidyanathan's method.

A fuzzy-AHP-based framework for prioritising benchmarks in the service sector

Benchmarking as an improvement tool has been acknowledged in almost all sectors of the business world, including the service sector. However, the available literature on benchmarking is apparently lacking attention on the issue of prioritisation of benchmarks in the service sector, especially when there are clear constraints on time and resources that can be spent on an elaborate benchmarking endeavour. This paper presents a comprehensive fuzzy-AHP-based framework using Chang's extent analysis method for prioritising benchmarks in the service sector. The framework is based on a philosophy wherein the viewpoint of all the stakeholders of a given business set-up is taken into account for progressive improvement.

A lossless data embedding technique by joint neighboring coding

Information hiding methods are currently exploited by many researchers for various applications. Proposing an efficient and feasible information hiding method is valuable. This paper presents a new reversible information hiding method for vector quantization (VQ)-compressed grayscale images by using joint neighboring coding (JNC) technique. The proposed method embeds secret data by using the difference values between the current VQ-compressed index and left or upper neighboring indices. The experimental results show that the proposed method achieves the best visual quality of reconstructed images compared with the two related works. In addition, the proposed method obtains as high embedding capacity as Lin and Chang's method, followed by Yang et al.'s method. As for execution speed, Yang et al.'s method is fastest, followed by the proposed method, and then Lin and Chang's method. With respect to bit rate, the proposed method has a little higher bit rate in comparison with the two related works.

A HIGH-RESOLUTION SPACE–TIME CONSERVATIVE METHOD FOR NON-LINEAR HYPERBOLIC CONSERVATION LAWS

We present a second-order scheme for the numerical solution of hyperbolic systems which treats space and time in a unified manner. The flow variables and their slopes are the basic unknowns in the scheme. The scheme utilizes the advantages of the space–time conservation element and solution element (CE/SE) method of Chang [1995] as well as central schemes of Nessyahu and Tadmor [1990]. However, unlike the CE/SE method the present scheme is Jacobian-free and hence like the central schemes can also be applied to any hyperbolic system. In Chang's method, a finite difference approach is being used for the slope calculation in case of non-linear hyperbolic equations. We propose to propagate the slopes by a scheme even in the case of non-linear systems. By introducing a suitable limiter for the slopes of flow variables, we can apply the same scheme to linear and non-linear problems with discontinuities. The scheme is simple, efficient and has a good resolution especially at contact discontinuities. We derive the scheme for one- and two-space dimensions. In two-space dimensions we use structured triangular meshes. The second-order accuracy of the scheme has been verified by numerical experiments. Several numerical tests presented in this article validate the accuracy and robustness of the present scheme.

Représentations de la société et pratiques éducatives en contexte de disparité culturelle : les choix de scolarisation de l'enfant chez des parents sénégalais

The purpose of this study, including the socio-cultural context of Senegal, is to show how society and social change's representations affect the choice to attend school or not. Representations of the society and of the social change have been apprehended during half directive talks, accomplished with twenty subjects (parents of Senegalese children) and put in evidence by statistical analyses, both lexical and morphosyntactical. It emerges from the results that important changes concerning representations of the society and of the social change - especially according to school attendance's modes - can be observed. Parent's positions on the social change - sometimes ambivalents – underline incoherence of link between society and social change's representations and school attendance's methods in a cross-cultural context.

Technical note – On optimization approach for multidisk vertical allocation problems

Multidisk vertical allocation (MDVA) problems intend to find an allocation of relations to disks such that the expected query cost is minimized. Recently, Chang [European Journal of Operational Research 143 (2002) 210] modified Rotem et al.'s [IEEE Transactions on Knowledge and Data Engineering 5 (1993) 882] method for solving an MDVA problem using a smaller number of binary variables. Chang's method however is unable to treat MDVA problems with possible replication of relations. This paper proposes another method to solve MDVA problems, which is more effective than Rotem et al.'s and is able to treat replication problems insolvable by Chang's method.

Characterization of ordered-subsets expectation maximization with 3d post-reconstruction gauss filtering and comparison with filtered backprojection in99mTc SPECT

To characterize ordered-subset expectation maximization algorithm with a fixed 3D Gauss post-reconstruction filtering (OSEM) in 99mTc SPECT as for noise, contrast and spatial resolution with varying number of subset and iteration and to compare OSEM with an optimized set of parameters, with filtered backprojection (FBP) with filter parameters typical of brain and myocardial SPECT, both with and without Chang's method of attenuation correction (AC). SPECT images of a Jaszczak phantom with cold rod inserts, hot and cold spheres and capillary line sources were acquired. Different background activity concentrations of the phantom were simulated as well as different lesion-to-background activity ratios. OSEM reconstructions were halted after 5, 10 and 15 iterations using 4, 8 and 16 subsets. The effect of subset and iteration number over noise is additive: thus, it is possible to define an EM-equivalent iteration number that indicates the product between the subset and the iteration numbers. Noise increases linearly with increasing EM-equivalent iteration number. For each level of nominal contrast, the measured contrast after OSEM shows a little increase with increasing iteration number and saturates after 80 EM-equivalent iterations. The application of AC leads to diminished contrast values both in FBP and OSEM. The contrast of cold lesions after OSEM increases with increasing number of EM-equivalent iteration number: after 80 iterations the contrast values with OSEM overtake the ones obtained with FBP; contrast values diminished as background concentration raised. Resolution values did not change with increasing EM-equivalent iteration number and were higher than those obtained with FBP. The major findings of the present work are the demonstration of additivity of subset and iteration in OSEM over noise, with the possibility of defining an EM equivalent iteration number, and the superiority of OSEM with respect to FBP in terms of spatial resolution.

Impact of image-based scatter correction for 123IMP-SPECT and SPM analysis

Recently, techniques for converting site-specific normal databases to other databases have been required for SPECT image statistical analysis. To implement scatter correction, we developed an image conversion technique named image-based scatter correction (IBSC). Furthermore, we evaluated the applicability of IBSC for SPM analysis. SPECT studies were performed on 28 normal volunteers and 10 patients with Alzheimer's disease (AD) using 123I-IMP. Two sets of scatter uncorrected images, I AC μb , and a corrected image by TEW, I TEW, were reconstructed with attenuation correction using Chang's method. Scatter corrected images by IBSC, I IBSC, were generated from I AC μb . Normal databases of I AC μb , I TEW and I IBSC were compared by SPM analysis. The Z-score (=(mean−AD)/S.D.) of I TEW was compared with that of I AC μb . Significant differences ( p<0.05) between normal databases of I AC μb and I TEW observed at the global posterior cingulate and precuneus regions almost disappeared when I TEW and I IBSC were compared . The Z-score at the posterior cingulate by I TEW was increased compared with that of I AC μb . We conclude that for SPM analysis of IMP-SPECT, IBSC can convert a normal database of scatter uncorrected images into corrected images, which is equivalent to correction by a conventional TEW method. Scatter correction may improve the ability to detect AD.

Thermal degradation kinetics of uncapped and end-capped poly(propylene carbonate)

In order to improve its thermal stability, poly(propylene carbonate)(PPC) was end-capped by different active agents. Thermogravimetric data show that the degradation temperature of uncapped PPC was lower than that of end-capped PPC. The kinetic parameters of thermal degradation of uncapped and end-capped PPC were calculated according to Chang's method. The results show that different mechanisms operate during the whole degradation temperature range for uncapped PPC. In the first stage, chain unzipping dominates the degradation. With increasing temperature, competing multi-step reactions occur. In the last stage, random chain scission plays an important role in degradation. For end-capped PPC, random chain scission dominates the whole degradation process.

A NEW METHOD FOR CHANGE POINT DETECTION DEVELOPED FOR SLEEP STAGE RECONSTRUCTION FROM HEART BEAT STATISTICS

Article A NEW METHOD FOR CHANGE POINT DETECTION DEVELOPED FOR SLEEP STAGE RECONSTRUCTION FROM HEART BEAT STATISTICS was published on January 1, 2003 in the journal Biomedical Engineering / Biomedizinische Technik (volume 48, issue s1).

On the assessment of tolerance limits under inverse gaussian distribution

Inverse Gaussian distribution has been used in a wide range of applications in modeling duration and failure phenomena. In these applications, one-sided lower tolerance limits are employed, for instance, for designing safety limits of medical devices. Tang and Chang (1994) proposed lowersided tolerance limits via Bonferroni inequality when parameters in the inverse Gaussian distribution are unknown. However, their simulation results showed conservative coverage probabilities, and consequently larger interval width. In their paper, they also proposed an alternative to construct lesser conservative limits. But simulation results yielded unsatisfactory coverage probabilities in many cases. In this article, the exact lower-sided tolerance limit is proposed. The proposed limit has a similar form to that of the confidence interval for mean under inverse Gaussian. The comparison between the proposed limit and Tang and Chang's method is compared via extensive Monte Carlo simulations. Simulation results suggest that the proposed limit is superior to Tang and Chang's method in terms of narrower interval width and approximate to nominal level of coverage probability. Similar argument can be applied to the formulation of two-sided tolerance limits. A summary and conclusion of the proposed limits is included.

A METHOD FOR DETERMINING MOLECULAR WEIGHT OF COPOLYMERS BY GPC

In this paper, a method is described that makes easier application of Chang's method for the determination of molecular weight of copolymers by GPC. Determinations of molecular weight of EP-copolymers have been performed with this method. The values of the resultant weight- and number-average molecular weight are rather close to the experimental data, and the values of intrinsic viscosity [η]c are close to the values measured with Ubbelodhe viscometers [η]d.

Iodine-123 iodobenzofuran (I-123 IBF) SPECT in patients with parkinsonism.

I-123 IBF is a dopaminergic antagonist which is suitable for SPECT imaging of D2 receptors. The purpose of this study is to evaluate the potential usefulness of semi-quantitative parameters obtained from brain SPECT data of I-123 IBF for differential diagnosis in patients with parkinsonism (PN). Subjects were 10 patients with PN: 2 patients with striato-nigral degeneration (SND), 5 patients with Parkinson's disease (PD), 2 patients with progressive supranuclear palsy (PSP) and one patient with olivo-ponto-cerebellar atrophy (OPCA). The data were acquired with a triple-head gamma camera at 2 hours after intravenous injection of 167 MBq of I-123 IBF. Transverse images were reconstructed by means of filtered backprojection, and attenuation correction was performed by Chang's method (mu = 0.08). The basal ganglia-to-frontal cortex ratio (GFR) and the basal ganglia-to-occipital cortex ratio(GOR) on slices of 5 different thicknesses were calculated. The GFR and GOR were lower in the SND group than in the other disease groups in all slices with different thicknesses (7.2 mm, 14.4 mm, 21.6 mm, 28.8 mm and 43.2 mm). The semiquantitative parameters (GFR and GOR) obtained from brain SPECT data at 2 hours after intravenous injection of I-123 IBF may be useful for differential diagnosis in patients with PN.

A multiresolution restoration method for cardiac SPECT imaging

In this study we present a multiresolution based method for restoring cardiac SPECT projections. Original projections were decomposed into a set of sub-band frequency images by using analyzing functions localized in both the space and frequency domain. This representation allows a simple denoising and restoration procedure by discarding high-frequency channels and performing inversion only in low frequencies. The method was evaluated in bull's eye reconstructions of a realistic cardiac chest phantom with a custom-made liver insert and 99mTc liver-to-heart activity ratios (LHAR) of 0:1, 1.5:1, 2.5:1, and 3.5:1. The cardiac phantom in free air was used as the reference standard. Reconstructions were performed by filtered backprojection using (1) no correction; (2) restoration without attenuation correction; (3) attenuation correction without restoration; and (4) restoration and attenuation correction. The attenuation correction was carried out with the Chang's method for one iteration. Results were compared with those obtained using an optimized prereconstruction Metz filter. Quantitative analysis was performed by calculating the normalized chi-square measure and mean +/- s.d. of bull's eye counts. In reconstructions with high liver activity (LHAR > 2), attenuation correction without restoration severely distorted the polar maps due to the spill-over of liver activity into the inferior myocardial wall. Both restoration methods when combined with an attenuation correction compensated this artifact and yielded uniform polar maps similar to that of the standard reference. There was no visual or quantitative difference between the performance of Metz filtering and multiresolution restoration. However, the main advantage of the multiresolution method is that it states a more concise and straightforward approach to the restoration problem. Multiresolution based methods does not require information about the object image or optimization processes, such as in conventional nuclear medicine restoration filters. In addition, the method is easy to implement using DFT techniques and potentially can be extended to noniterative spatially shift-invariant restorations in SPECT.

ROC evaluation of SPECT myocardial lesion detectability with and without single iteration non-uniform Chang attenuation compensation using an anthropomorphic female phantom

The purpose of this work was to evaluate lesion detectability with and without nonuniform attenuation compensation (AC) in myocardial perfusion SPECT imaging in women using an anthropomorphic phantom and receiver operating characteristics (ROC) methodology. Breast attenuation causes artifacts in reconstructed images and may increase the difficulty of diagnosis of myocardial perfusion imaging in women. The null hypothesis tested using the ROC study was that nonuniform AC does not change the lesion detectability in myocardial perfusion SPECT imaging in women. The authors used a filtered backprojection (FBP) reconstruction algorithm and Chang's (1978) single iteration method for AC. In conclusion, with the authors' proposed myocardial defect model nuclear medicine physicians demonstrated no significant difference for the detection of the anterior wall defect; however, a greater accuracy for the detection of the inferior wall defect was observed without nonuniform AC than with it (P-value=0.0034). Medical physicists did not demonstrate any statistically significant difference in defect detection accuracy with or without nonuniform AC in the female phantom.

Space-Time Conservation Method Applied to Saint Venant Equations

A new numerical technique by Chang is described and used to solve the one-dimensional (1D) and two-dimensional (2D) Saint Venant equations. This new technique differs from traditional numerical methods (i.e., finite-difference, finite-element, finite-volume, spectral methods, etc.). Chang's method treats space and time on the same footing, so that space and time are unified—a key characteristic that distinguishes the new method from other techniques. This method is explicit, uses a staggered grid, enforces flux conservation in space and time, and does not require upwinding, flux-splitting, flux limiters, evaluation of eigenvalues, or the addition of artificial viscosity. Furthermore, the scheme is simple, easy to implement (see Appendix I), and can be extended to higher dimensions. First, the new technique, as developed by Chang, is introduced, explained, and applied to the 1D Saint Venant equations. To illustrate its effectiveness, an idealized dam-break and a hydraulic jump in a straight rectangular channel are simulated. The numerical results obtained using the new method are compared with results from other, more conventional techniques of similar complexity, experimental data, and an analytical solution. Next, Chang's scheme is extended for solution of the 2D Saint Venant (i.e., shallow water or depth-averaged) equations. The writers do not follow Chang's 2D development but instead employ Strang's method of fractional steps, which transforms the 2D problem into two 1D problems. The new 2D scheme is applied to an oblique hydraulic jump, and the results are compared with an analytical solution.

Multiple-prototype classifier design

Five methods that generate multiple prototypes from labeled data are reviewed. Then we introduce a new sixth approach, which is a modification of Chang's (1974) method. We compare the six methods with two standard classifier designs: the 1-nearest prototype (1-np) and 1-nearest neighbor (1-nn) rules. The standard of comparison is the resubstitution error rate; the data used are the Iris data. Our modified Chang's method produces the best consistent (zero-error) design. One of the competitive learning models produces the best minimal prototypes design (five prototypes that yield three resubstitution errors).