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PubMedDate not supplied

Optimized acquisition and processing protocols for I-123 cardiac SPECT imaging.

BACKGROUND: Deconvolution of septal penetration (DSP) has been developed to improve quantification so as to allow the use of low-energy high-resolution collimators for iodine 123 cardiac single photon emission computed tomography (SPECT) imaging. The purpose of this study is to optimize its acquisition and processing protocols. METHODS AND RESULTS: Planar images of a 9-compartment phantom loaded with variable radioactive concentrations were acquired to derive optimal scatter compensation scaling factors for 20% and 15% photopeak energy window configurations, respectively. A cardiac phantom, loaded with high and low heart-to-calibration ratios (HCRs), respectively, was imaged with both configurations. Repeated acquisitions were done for medium-energy all-purpose collimators for comparison. Critical frequencies for Butterworth filtering were optimized by use of defect contrast and normal short-axis uniformity as selection indices. HCRs were calculated with planar projection and different reconstruction methods, respectively, and then compared with the true HCRs. SPECT produced more accurate HCRs than planar imaging. With the optimized parameters for scatter compensation and filtering, the 2 energy window configurations yielded similar results. Iterative reconstructions with DSP yielded more accurate HCRs than other reconstructions without DSP. CONCLUSION: The optimized protocols based on DSP show promise that quantification of I-123 cardiac SPECT imaging can be achieved with the widely available low-energy high-resolution collimators.

Algorithms↗

PubMedDate not supplied

Effects of optimization and image processing in digital chest radiography: an ROC study with an anthropomorphic phantom.

A digital system for chest radiography based on a large image intensifier was compared to a conventional film-screen system. The digital system was optimized with regard to spatial and contrast resolution and dose. The images were digitally processed for contrast and edge enhancement. A simulated pneumothorax and two simulated nodules were positioned over the lungs and the mediastinum of an anthropomorphic phantom. Observer performance was evaluated with ROC analysis. Five observers assessed the processed digital images and the conventional full-size radiographs. The time spent viewing the full-size radiographs and the digital images was recorded. For the simulated pneumothorax, the results showed perfect performance for the full-size radiographs and detectability was high also for the processed digital images. No significant difference in the detectability of the simulated nodules was seen between the two imaging systems. The results for the digital images showed a significantly improved detectability for the nodules in the mediastinum as compared to a previous ROC study where no optimization and image processing was available. No significant difference in detectability was seen between the former and the present ROC study for small nodules in the lung. No difference was seen in the time spent assessing the conventional full-size radiographs and the digital images. The study indicates that processed digital images produced by a large image intensifier are equal in image quality to conventional full-size radiographs for low-contrast objects such as nodules.

Evaluation Studies as Topic↗

PubMed1993

[The optimization of the process of instrumental learning with a low intensity of the conditioned stimulus].

The influence of the intensity of conditional stimulation on the speed of instrumental teaching of rats at different probabilities of casual fulfillment of the reaction under development (VSPR) was investigated. The VSPR value significantly affects the number of positive and negative confirmations in the early period of teaching and, finally, the informational individuum-environment interaction. Therefore, with the existing choice of VSPR values the dependence of the speed of teaching upon different unfavourable factors lessens, which may be used for optimization of the process of instrumental teaching at a low intensity of the conditional signal.

Acoustic Stimulation↗

PubMed2002

Diagnosing and optimizing water treatment processes by using particle counter: a case study in Korea.

The goal of the flocculation process is to change the particle size distribution to best suit the subsequent processes. Although several methods exist to evaluate the flocculation process, no single universally accepted method has yet to be developed. The purpose of this paper is to present experiences whereby particle counting was used in the diagnosis and optimization of the flocculation process. A commercially available on-line continuous particle counter has been used in evaluating the design and the operation of this process at two conventional Water Treatment Plants. The evaluation is based on particle dynamics, i.e., the change of the number of small and large particles. Some design deficiencies in the distribution channel and flocculation process have been identified from this method, and thus some operational parameters are suggested for optimum performance. Because the optimum condition may be site-specific, the method presented in this paper will be beneficial in the evaluation of the flocculation process at other water treatment plants.

Facility Design and Construction↗

PubMed1993

Toward a theory of optimal hearing aid processing.

An ideal hearing aid for a peripheral hearing loss would process the incoming signal in order to give a perfect match between the cochlear outputs of the impaired ear and a reference normal ear. As a first step toward this objective, a model of the normal and impaired peripheral auditory system was used to derive the optimal hearing-aid processing filter based on a minimum mean-squared error criterion. The auditory model includes the compression and suppression effects of the cochlear mechanics and the sensitivity of the neural transduction process. Simplifying assumptions were then incorporated into the processing to yield a practical frequency-dependent adaptive gain system. Processing examples of several individual speech sounds are presented for a flat hearing loss, and the results indicate that a three-channel compression system with adjustable gains and band edges will be close to the optimal solution for this case.

Adaptation, Physiological↗

PubMed2003

Optimal operation of batch processes via the tracking of active constraints.

This paper presents a new measurement-based optimization framework for batch processes whereby optimal operation can be achieved via the tracking of active constraints. It is shown that, under mild assumptions and to a first-order approximation, tracking the necessary conditions of optimality is equivalent to tracking active constraints (both during the batch and at the end of the batch). Thus the optimal input trajectories can be adjusted using measurements without the use of a model of the process. When only batch-end measurements are available, the proposed method leads itself to an efficient batch-to-batch optimization scheme. The approach is illustrated via the simulation of a semibatch reactor under uncertainty.

Chemical Industry↗

PubMed2001

[Pharmacodynamics study of suanzaoren decoction extracted by different technological process].

OBJECTIVE: To select the optimal technological process for Suanzaoren decoction. METHOD: The effects of extracts from different technological processes on spontaneous motion and sleep time in mice induced by pentobarbital sodium (subthreshold dosage) were studied. RESULTS: Both the decoction and 95% alcohol extract of Suanzaoren possess sedative and hypnotic effects. CONCLUSION: Suanzaoren aqueous decoction was selected as the optimal technological process.

Animals↗

PubMed1997

Does Escherichia coli optimize the economics of the translation process?

The codon translation rate is usually assumed to be proportional to the cellular concentration of the cognate tRNA, but synonymous codons sharing the same cognate tRNA may be translated at rather different rates. To account for the latter observation, we assume that the translation process is optimized in two respects: (i), the codon demand is optimized with respect to the supply of cognate tRNAs (composition of the tRNA pool); and (ii), for synonymous codons sharing the same cognate tRNA, the usage frequency of each codon correlates optimally with the stability of the codon-anticodon complex. These assumptions allow us to compute the relative rate constants of synonymous codons. Highly expressed genes, which produce 80-90% of the protein mass in the E. coli cell, appear to have selected codons which make an optimal use of the tRNA pool. Assuming the optimization criteria were valid, a list of codon translation times (in ms) were derived from available experimental data.

Codon, Terminator↗

PubMed2004

Optimization of ultrafiltration/diafiltration processes for partially bound impurities.

Ultrafiltration and diafiltration processes are used extensively for removal of a variety of small impurities from biological products. There has, however, been no experimental or theoretical analysis of the effects of impurity- product binding on the rate of impurity removal during these processes. Model calculations were performed to account for the effects of equilibrium binding between a small impurity and a large (retained) product on impurity clearance. Experiments were performed using D-tryptophan and bovine serum albumin as a model system. The results clearly demonstrate that binding interactions can dramatically reduce the rate of small impurity removal, leading to large increases in the required number of diavolumes. The optimal product concentration for performing the diafiltration shifts to lower product concentrations in the presence of strong binding interactions. Approximate analytical expressions for the impurity removal were developed which can provide a guide for the design and optimization of industrial ultrafiltration/diafiltration processes.

Complex Mixtures↗

PubMed2001

Small-scale bioreactor system for process development and optimization.

An agitated 12-well microtiter plate system with a working volume of 2ml was investigated for cell culture process development. Agitation assures homogeneity in wells and enhances mass transfer between the gas and the liquid phase, thus improving maximum cell density and pH stability. The pH of the NaHCO(3)-buffered system can be adjusted by altering the carbon dioxide content of the gas phase. The non-toxic, visual pH indicator phenol red was used in combination with a spectrophotometric plate reader for rapid and precise pH measurements. For high throughputs, cell growth was assessed non-invasively using stable green fluorescent protein (GFP) expressing cells and a fluorescence plate reader. The setup is simple and inexpensive. The system can be automated and allows several hundred small-scale bioreactor experiments to be run in parallel.

Journal Article↗

PubMed2005

Effect of mobile phase composition on the SMB processes efficiency. Stochastic optimization of isocratic and gradient operation.

The solvent composition was adjusted in a theoretical study in order to maximize the efficiency of a simulated moving bed (SMB) process. The isocratic realization of the process as well as the solvent gradient mode were considered. The solvent composition and the flow rates were used as decision variables in a random search optimization algorithm known to be a reliable tool for nonlinear programming problems. The results of the optimization indicate that the optimal composition of the mobile phase depends strongly on the feed concentration. The asymmetry of the internal concentration profiles, which has a negative effect on the separation efficiency, can be partly damped by an increase of the solvent strength. In the cases studied the optimal solvent strength determined for concentrated feed streams is higher than that for diluted ones. Moreover, the optimum is strongly influenced by the value of the selectivity factor and its dependency on the mobile phase composition. Different results were obtained for cases, in which the separation factor increases with increasing the modifier concentration, than for cases, in which the separation factor decreases with increasing the modifier concentration. A similar analysis was performed for a solvent gradient SMB process, in which different solvents are used at the two inlet ports: a weak solvent in the feed stream and a strong solvent in the desorbent stream. Again the optimal mobile phase composition was strongly affected by the type of the isotherms and their non-linearity. The potential of a gradient SMB process in terms of increasing the productivity and reducing the eluent consumption is exemplified.

Chromatography, Liquid↗

PubMed2004

LARES: an artificial chemical process approach for optimization.

This article introduces a new global optimization procedure called LARES. LARES is based on the concept of an artificial chemical process (ACP), a new paradigm which is described in this article. The algorithm's performance was studied using a test bed with a wide spectrum of problems including random multi-modal random problem generators, random LSAT problem generators with various degrees of epistasis, and a test bed of real-valued functions with different degrees of multi-modality, discontinuity and flatness. In all cases studied, LARES performed very well in terms of robustness and efficiency.

Algorithms↗

PubMed2006

Expression optimization and purification process development of an engineered soluble recombinant mouse linker of activation of T cells using surface enhanced laser desorption/ionization-mass spectrometry.

Protein purification development is the bottleneck of recombinant protein production therefore there is a need to shorten process development and monitoring. Surface enhanced laser desorption/ionization-mass spectrometry (SELDI-MS) was evaluated to optimize the expression and to develop the purification of a recombinant mouse protein: a transmembrane adaptor involved in T cell receptor signaling named "linker for activation of T cells" (LAT). The protein was expressed as a soluble form (S-LAT) in three strains of Escherichia coli: BL21 (DE3), Rosetta (DE3), and BL21 (DE3) pLys S. The expression of S-LAT was monitored on immobilized metal affinity chromatography (IMAC) ProteinChip arrays. The highest level of expression was found in Rosetta (DE3) with a C-terminal construct after induction at 37 degrees C. The purification scheme was elucidated using SELDI-MS: S-LAT was efficiently captured on an IMAC ProteinChip array saturated with nickel ions (Ni(2+)) and then fractionated on a Q ProteinChip array. These conditions were directly transferred to IMAC-Ni(2+) HyperCel and Q Ceramic HyperD F chromatography sorbents. After these two purification steps, S-LAT was estimated to be more than 80% pure, confirming a very good match between array and sorbent. Finally, a peptide mapping was performed on a hydrophobic array after in gel trypsin digest, verifying that the purified protein was the mouse LAT. This is the first report of a protocol for the production and purification of S-LAT. The selection of the best expression and purification strategy along with the identification were enabled in 5 days with less than 5 mL of soluble fraction of crude culture samples.

Adaptor Proteins, Signal Transducing↗

PubMed2004

[Study on extraction process of Radix Bupleuri].

The orthogonal design was used to optimize extraction process of Radix Bupleuri with content of total saponin and yield of the extract as markers. Factors that have been chosen were ethanol concentration, ethanol consumption, extraction times and extraction time. Each factor had three levels. The result showed that the optimum extraction condition was 80% ethanol, 4 times the amount of material, refluxing for 4 times, 60 minutes each time. The optimized process was stable and workable.

Analysis of Variance↗

PubMed2002

On optimality in auditory information processing.

We study limits for the detection and estimation of weak sinusoidal signals in the primary part of the mammalian auditory system using a stochastic Fitzhugh-Nagumo model and an action-recovery model for synaptic depression. Our overall model covers the chain from a hair cell to a point just after the synaptic connection with a cell in the cochlear nucleus. The information processing performance of the system is evaluated using so-called phi-divergences from statistics that quantify "dissimilarity" between probability measures and are intimately related to a number of fundamental limits in statistics and information theory (IT). We show that there exists a set of parameters that can optimize several important phi-divergences simultaneously and that this set corresponds to a constant quiescent firing rate (QFR) of the spiral ganglion neuron. The optimal value of the QFR is frequency dependent but is essentially independent of the amplitude of the signal (for small amplitudes). Consequently, optimal processing according to several standard IT criteria can be accomplished for this model if and only if the parameters are "tuned" to values that correspond to one and the same QFR. This offers a new explanation for the QFR and can provide new insight into the role played by several other parameters of the peripheral auditory system.

Animals↗

PubMed1999

Non-linear optimization of biotechnological processes by stochastic algorithms: application to the maximization of the production rate of ethanol, glycerol and carbohydrates by Saccharomyces cerevisiae.

A non-linear optimization, based on an stochastic multi-start search algorithm, has been applied to the maximization of the production rates of ethanol, glycerol and carbohydrates by Saccharomyces cerevisiae. This optimization is applied to two alternative (non-linear) model representations of the same system, namely the Michaelis-Menten and the generalized mass action forms. We find a complete agreement between the results obtained using both representations. This is, maximization of the ethanol production rate requires modulation of up to six enzymes, while modification of only one enzyme is sufficient to obtain a significant improvement in the production rate of glycerol and carbohydrates. When the results are compared with those previously obtained using an indirect linear optimization method (Torres, N.V., Voit, E.O., González-Alcón, C., Rodríguez, F. 1997. An integrated optimization method for biochemical systems. Description of method and application to ethanol, glycerol and carbohydrate production in S. cerevisiae. Biotechnol. Bioeng. 55(5), 758-772.), we find close agreement between both optimization techniques. Qualitatively, both optimization approaches render the same profile of enzymes to be modulated, while quantitatively, discrepancies arise when the objective function is the maximization of the ethanol production rate. Reasons for such discrepancies and an evaluation of the advantages of each method (linear vs non-linear) are given.

Algorithms↗

PubMed2006

The Bayesian reader: explaining word recognition as an optimal Bayesian decision process.

This article presents a theory of visual word recognition that assumes that, in the tasks of word identification, lexical decision, and semantic categorization, human readers behave as optimal Bayesian decision makers. This leads to the development of a computational model of word recognition, the Bayesian reader. The Bayesian reader successfully simulates some of the most significant data on human reading. The model accounts for the nature of the function relating word frequency to reaction time and identification threshold, the effects of neighborhood density and its interaction with frequency, and the variation in the pattern of neighborhood density effects seen in different experimental tasks. Both the general behavior of the model and the way the model predicts different patterns of results in different tasks follow entirely from the assumption that human readers approximate optimal Bayesian decision makers.

Attention↗

PubMed1998

Optimizing optical density of a Kodak mammography film-screen combination with standard-cycle processing.

The optimization of optical density in film-screen mammography is crucial in attaining good image quality. While a target range for film optical density of 1.4-1.8 has been recommended for centres participating in the National Health Service Breast Screening Programme (NHSBSP), past investigations have shown that combinations of mammography film and screen and processor conditions can have various optimum densities, some of which are outside this recommended range. The optimum optical density of the film/screen/processor conditions combination used at our institution (the Kodak MIN-RM/MIN-R combination designed for standard-cycle processing) was evaluated using a breast detail phantom study. It was found that the optimum optical density was 1.25 OD. We recommend that an individual institution determines the optimum optical density for the film-screen combination it uses and the processing conditions specific to it.

Mammography↗