Investigation of a solid-state detector for advanced computed tomography

Utilization of solid-state detectors for computed tomography (CT) has been the focus of many studies. Previous phantom and clinical experiments have shown that one of the important performance parameters for the solid-state detector is the primary speed and afterglow. In this paper, we present a detailed investigation on the signal decay characteristics of the HiLight (GE Medical Systems, Milwaukee, WI) scintillating detector. The detector primary speed and afterglow are modeled by a multiexponential function and fully characterized by a set of time constants and relative strengths. The sensitivity of these parameters to X-ray photon energy, detector aging, and radiation exposure is then established and analyzed. No statistically significant variation is observed in these parameters due to changes in the above external variables. The impact of various decay time constants on CT image quality, such as spatial resolution, noise, and artifacts, is subsequently illustrated with computer simulations and phantom experiments. Finally, an algorithmic correction scheme is derived to compensate for detector afterglow. The correction scheme employs a recursive filter to remove adverse effects of the detector decay on image quality. Experimental results have shown that the correction scheme successfully restores system spatial resolution, produces a more homogeneous noise pattern, and eliminates ring-band image artifacts due to detector afterglow. The effectiveness and robustness of the correction scheme are demonstrated by extensive phantom and clinical experiments.     

Tomographic reconstruction for tilted helical multislice CT

One of the most recent technical advancements in computed tomography (CT) is the introduction of multislice CT (MCT). Because multiple detector rows are used for data acquisition, MCT offers higher volume coverage, faster scan speed, and reduced X-ray tube loading. Recognizing its unique data-sampling pattern, several image reconstruction algorithms were developed. These algorithms have been shown to be adequate in producing clinically acceptable images. Recent studies, however, have revealed that the image quality of MCT can be significantly degraded when helical data are acquired with a tilted gantry. The degraded image quality has rendered this feature unacceptable for clinical usage. In this paper, we first present a detailed investigation on the cause of the image quality degradation. An analytical model is derived to provide a mathematical basis for correction. Several compensation schemes are subsequently presented, and a detailed performance comparison is provided in terms of spatial resolution, noise, computation efficiency, and image artifacts.     

Genetic Algorithm for Optimization of Infrastructure Investment Under Time-Resource Constraints

Abstract:   This work shows the infrastructure investment decision is essentially a 0-1, nonlinear, multiobjective knapsack problem. It argues that, without making substantial simplification on some of the practical considerations, a conventional mathematical optimization approach may not be suitable for solving the problem. Further, the use of explicit heuristics may sometimes be unwieldy dependent on the system parameters. An innovative approach based on the concept of genetic algorithms is proposed in the work to tackle the nonlinearity in the decision problem. Based on the experimental results, the proposed approach is capable of producing good quality results. The key success feature of the proposed approach resides in the unique and innovative modeling of system parameters by genetic coding in the algorithms .     

A quasi-qualitative investigation of strategies used in qualitative categorization.

This study investigates how analysts approach the task of initially categorizing qualitative data, what analysis strategies increase or decrease the testimonial validity of the categories, whether the data should be presented as a whole or in meaningful units, the effects of analysts' familiarity with the material, and the cognitive strategies associated with testimonial validity judgments. 30 upper level undergraduates (aged 19–42 yrs) analyzed essay data for "themes" while engaged in a think-aloud task. The essay writers then ranked the sets of categories in terms of overall quality and rated them on dimensions relevant to testimonial validity while thinking aloud. Think-aloud protocols for the best and worst approaches are examined. Implications for the use of qualitative research methods are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Telechelic elastomers

Telechelic elastomers, polymers with reactive terminal groups, can be prepared in emulsion and solution systems. Examples of characterization of the polymers and preparation of a mercapto telechelic copolymer in an emulsion system and of mercapto-, hydroxy-, and aziridinyl-telechelic elastomers in solution systems are given. The elastomers were cured in peroxide or sulfur-accelerator formulations. The telechelic polymers exhibited enhanced stress-strain and dynamic properties in comparision to those of the controls. In tread formulations, outstanding properties were obtained for the mercapto-and azieridinyl-telechelic butadiene-styrene copolymers.     

Sampling variability of the area under the ROC-curve and of d'e.

By computer simulation, random samples were drawn from underlying Gaussian, uniform, and negative exponential distributions which differed in terms of their mean and variance. The conditional probability of an observation of a given magnitude, or higher, was computed for each of 2 distributions. Resulting conditional probabilities for the 2 distributions trace out a receiver operating characteristic (ROC) curve. The area under the ROC-curve, which provides a distribution-free measure of performance, was calculated over a wide range of possible performances. It is shown that the sampling variability of the area measure is dependent upon its mean value and is relatively independent of the complex of conditions which lead to the given mean value. A similar conclusion is reached for the sampling variability of the intersection of the ROC-curve with the negative diagonal. This measure leads to an estimate of the sampling variability of the measure d'e, an index of O performance, often employed in the signal detectability approach to performance measurement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

High performance data compression method with pattern matching for biomedical ECG and arterial pulse waveforms

Biomedical waveforms, such as electrocardiogram (ECG) and arterial pulse, always possess a lot of important clinical information in medicine and are usually recorded in a long period of time in the application of telemedicine. Due to the huge amount of data, to compress the biomedical waveform data is vital. By recognizing the strong similarity and correlation between successive beat patterns in biomedical waveform sequences, an efficient data compression scheme mainly based on pattern matching is introduced in this paper. The waveform codec consists mainly of four units: beat segmentation, beat normalization, two-stage pattern matching and template updating and residual beat coding. Three different residual beat coding methods, such as Huffman/run-length coding, Huffman/run-length coding in discrete cosine transform domain, and vector quantization, are employed. The simulation results show that our compression algorithms achieve a very significant improvement in the performances of compression ratio and error measurement for both ECG and pulse, as compared with some other compression methods.     

Development of a whole-cell-based biosensor for detecting histamine as a model toxin

A novel whole-cell potentiometric biosensor for screening of toxins has been developed. The constructed biosensor consists of a confluent monolayer of human umbilical vein endothelial cells (HUVECs) attached to an ion-selective cellulose triacetate (CTA) membrane modified with a covalently attached RGD (arginine-glycine-aspartic acid) peptide sequence. When the HUVECs form a confluent monolayer, ion transport is almost completely inhibited, thereby reducing the response of the ion-selective electrode (ISE). When the monolayer is exposed to agents that increase its permeability (e.g., toxins), ions can diffuse through the membrane, and a potential response from the ISE is achieved. Histamine, a model toxin that increases the permeability of HUVEC monolayers, was used in this study. When the cell-based membranes are exposed to varying concentrations of histamine, the overall response increases with increasing histamine concentration. Thus, the measured potential is an indirect measurement of the histamine concentration. Further experiments were performed for a similar molecule, l-histidine, to test for selectivity. The cell permeability was unaffected by l-histidine, and the sensor response remained unchanged. This type of sensor should find multiple applications in medical, food, and environmental fields and in homeland security.