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Results for “parameter optimization”

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PubMedDate not supplied

Optimal drug and gene delivery in cancer cells by ultrasound-induced cavitation.

BACKGROUND: Lack of efficient drug and gene delivery is one of the major problems of cancer chemo- and bio-therapy. This work is focused on optimization of ultrasound-induced delivery of model macromolecular anti-cancer drugs and DNA in human cancer cells. MATERIALS AND METHODS: FITC dextrans simulated antisense oligonucleotides (10 kDa), antibodies (70 kDa), and genes (2000 kDa). Optimization of ultrasound frequency, intensity, duty cycle, time of irradiation, and concentration of Optison (ultrasound contrast agent) was performed. RESULTS: Optimal parameters provided in the MCF7 cell line 73.5+/-3.3%, 72.7+/-0.9%, and 62.7+/-2.1% delivery of 10-kDa, 70-kDa, and 2000-kDa macromolecules, respectively, 36.7+/-4.9% of cell transfection, while dead cell count was only 13.5+/-1.6%. Statistically significant drug delivery and transfection was obtained in all tested cell lines. CONCLUSION: These results suggest that optimized treatment parameters provide efficient drug and gene delivery in cancer cells and could be used for further in vivo and in vitro experiments.

Breast Neoplasms↗

PubMed2003

Optimization of ultrasound parameters for cardiac gene delivery of adenoviral or plasmid deoxyribonucleic acid by ultrasound-targeted microbubble destruction.

OBJECTIVES: This study was undertaken to optimize echocardiographic parameters for successful gene delivery to the heart and to extend the method from adenoviral to plasmid deoxyribonucleic acid (DNA). BACKGROUND: We have previously shown that ultrasound-targeted microbubble destruction can direct tissue expression of adenoviral transgenes to the heart. The optimal echocardiographic parameters for this technique have not been reported. METHODS: Adenoviral or plasmid DNA encoding the luciferase reporter gene was incorporated into liposome microbubbles and infused intravenously into anesthetized rats. We systematically evaluated the effects of ultrasound parameters known to influence microbubble destruction, including electrocardiogram (ECG) triggering, ultrasound frequency, mode of ultrasound, and mechanical index, on gene expression in rat myocardium four days after treatment. In addition, gene expression in heart, liver, and skeletal muscle were compared between adenoviral and plasmid DNA. RESULTS: Optimal ultrasound parameters for this technique include low-transmission frequency (1.3 MHz), maximal mechanical index, and ECG triggering to allow complete filling of the myocardial capillary bed by microbubbles. No difference was seen between ultraharmonics and power Doppler mode. Using adenoviral DNA, optimal ultrasound parameters yielded myocardial luciferase activity on the order of 104 relative light units/mg protein/min but with even higher liver activity. Plasmid DNA was expressed in rat myocardium at similar levels but without detectable liver expression. CONCLUSIONS: Ultrasound-targeted microbubble destruction can be used to deliver adenoviral or plasmid DNA to the myocardium. This technique holds great promise in applying the rapidly expanding repertoire of gene therapies being developed for cardiac disease.

Adenoviridae↗

PubMedDate not supplied

T2-weighted echo planar MR imaging of the abdomen: optimization of imaging parameters.

Echo planar imaging (EPI) is an ultra-fast magnetic resonance (MR) imaging method that provides strong T2-weighted contrast, which is important for the detection and characterization of various abdominal abnormalities. However, EPI may be associated with significant artifacts. The prominence of these artifacts, as well as overall image quality, is dramatically impacted by selection of imaging parameters. The purpose of this study is to demonstrate the effects of controlled alterations in operator-defined imaging parameters on image quality in breath-hold abdominal T2-weighted EPI. An understanding of these effects facilitates optimizing parameter selection for acquisition of abdominal EPI images.

Abdomen↗

PubMed2005

High-resolution MRI of the labyrinth: optimization of scan parameters with 3D-FSE.

The aim of our study was to optimize the parameters of high-resolution MRI of the labyrinth with a 3D-FSE sequence. We investigated TR, TE, Matrix, FOV, and coil selection in terms of CNR (contrast-to-noise ratio) and SNR (signal-to-noise ratio) by comparing axial images and/or three-dimensional images. The optimal 3D-FSE sequence parameters were as follows: 1.5 Tesla MR unit (Signa LX, GE Medical Systems), 3D-FSE sequence, dual 3-inch surface coil, acquisition time=12.08 min., TR=5000 msec, TE=300 msec, 3 NEX, FOV=12 cm, matrix=256 x 256, slice thickness=0.5 mm/0.0 sp, echo train=64, bandwidth=+/-31.5 kHz. High-resolution MRI of the labyrinth using the optimized 3D-FSE sequence parameters permits visualization of important anatomic details (such as scala tympani and scala vestibuli), making it possible to determine inner ear anomalies and the patency of cochlear turns. To obtain excellent heavily T2-weighted axial and three-dimensional images in the labyrinth, high CNR, SNR, and spatial resolution are significant factors at the present time. Furthermore, it is important not only to optimize the scan parameters of 3D-FSE but also to select an appropriate coil for high-resolution MRI of the labyrinth.

Ear, Inner↗

PubMed2004

Effects of surface gastric pacing on gastric myoelectrical activity and plasma motilin in a canine model of gastric motility disorders.

OBJECTIVE: To investigate the effects of surface gastric pacing on gastric myoelectrical activity and plasma motilin concentration in a canine model of gastric motility disorders. METHODS: Ten healthy mongrel dogs were divided into two groups: an experimental group of six dogs and control group of four dogs. The model of gastric motility disorders was established in the experimental group with truncal vagotomy combined with injection of glucagon. Gastric serosal myoelectrical activity was recorded with a four-channel computer analysis device. Plasma motilin concentration was measured with a radioimmunoassay (RIA) kit. Surface gastric pacing at 1.1-1.2-fold the intrinsic slow-wave frequency superimposed with a series of high frequency pulses (10-30 Hz) was performed for 45 min daily for 1 month in the conscious dogs. RESULTS: The basic electrical rhythm (BER) amplitude (2.32 +/- 0.35 mV) and propagation velocity (4.06 +/- 0.40 cm/s) of the dogs with bilateral truncal vagotomy in the fed state decreased more significantly than those of the controls (4.25 +/- 0.12 mV, 6.92 +/- 0.24 cm/s) (P < 0.03). After long-term surface gastric pacing, the BER amplitude (3.97 +/- 0.19 mV) and propagation velocity (5.57 +/- 0.48 cm/s) was increased significantly compared with before pacing (P < 0.05). Postprandial gastric dysrhythmias were provoked by large doses of glucagon; the percentage of regular slow waves of the dogs with vagotomy was markedly reduced from 67.4 +/- 6.2% at baseline to 10.0 +/- 6.7% (P < 0.001), and that of the control was also decreased from 87.1 +/- 6.9% to 35.0 +/- 11.0% (P < 0.01), but the entrainment of gastric slow waves was 100% by means of gastric pacing at optimal parameters. There was a significant increase in the plasma concentration of motilin at the phase III of the interdigestive myoelectrical complex (IMC III) in the dogs with bilateral truncal vagotomy (baseline vs vagotomy, 184.29 +/- 9.81 pg/mL vs 242.09 +/- 17.22 pg/mL; P< 0.01). However, the plasma motilin concentration (212.55 +/- 11.20 pg/mL; P < 0.02) was decreased significantly after long-term gastric pacing. Before gastric pacing the plasma motilin concentration showed an equally negative correlation with the BER amplitude, and propagation velocity in the dogs with vagotomy in the fed state (r = -0.473, r = -0.807, P < 0.04), but after long-term gastric pacing, the plasma motilin concentration showed an equally positive correlation with the BER amplitude and propagation velocity (r = 0.523, r = 0.896, P < 0.02). CONCLUSIONS: Surface gastric pacing with optimal pacing parameters is able to entrain completely propagated slow waves, improve the parameters of gastric myoelectrical activity and normalize gastric dysrhythmias induced by a pharmacological agent. Surface gastric pacing might be useful in the treatment of gastric dysrhythmia. The gastric myoelectrical activity correlated well with the plasma motilin concentration before and after pacing, which suggests that motilin could modulate the effect of gastric pacing through alteration of the gastric myoelectrical parameters.

Animals↗

PubMed2001

Basis for optimization of in vitro exposure apparatus for health hazard evaluations of mobile communications.

The main objective of this paper is to carefully study the fields induced in flasks exposed to RF electromagnetic fields. The study focuses on the widely used 60 mm Petri dishes and rectangular T-75 flasks for the two following cases: 1) cells in homogeneous suspension and 2) cell monolayers. The dependence of the coupling and the homogeneity of the SAR distribution on frequency (0.7 GHz to 2.5 GHz), polarization (E, H and k polarizations) and the amount of medium (1.9 mm to 4.7 mm medium height) is studied. In addition, the effects of the environment, meniscus and field impedance as well as the distortion of the incident field are discussed. Based on these results, advantages and disadvantages of different fundamental designs of apparatus used in the past are compared. These are TEM cells, HF chambers, radial transmission lines (RTL), waveguides and wire patch cells. Furthermore, the major optimization parameters are identified for the development of highly optimized exposure systems, enabling the conduct of high quality experiments.

Biophysical Phenomena↗

PubMed1975

Application of modified Rosenbrock's method for optimization of nutrient media used in microorganism culturing.

The Rosenbrock's procedure has been modified for optimization of nutrient medium composition and has been found to be less tedious than the Box-Wilson method, especially for larger numbers of optimized parameters. Its merits are particularly obvious with multiparameter optimization where the gradient method, so far the only one employed in microbiology from a variety of optimization methods (e.g., refs, 9 and 10), becomes impractical because of the excessive number of experiments required. The method suggested is also more stable during optimization than the gradient methods which are very sensitive to the selection of steps in the direction of the gradient and may thus easily shoot out of the optimized region. It is also anticipated that other direct search methods, particularly simplex design, may be easily adapted for optimization of medium composition. It is obvious that direct search methods may find an application in process improvement in antibiotic and related industries.

Culture Media↗

PubMed2005

Retrospective motion compensation using variable-density spiral trajectories.

PURPOSE: To develop a method of retrospectively correcting for motion artifacts using a variable-density spiral (VDS) trajectory. MATERIALS AND METHODS: Each VDS interleaf was designed to adequately sample the same center region of k-space. This central overlapping region can then be used to measure rigid body motion between the acquisition of each VDS interleaf. By applying appropriate phase shifts and rotations of the k-space data, rigid body motion artifacts can be removed, resulting in images with less motion corruption. RESULTS: Both phantom and volunteer experiments are shown, demonstrating the technique's ability to further reduce artifacts in images acquired with an already motion-resistant acquisition trajectory. Registration accuracy is highly dependent on the trajectory design parameters. This space was explored to find an optimal design of VDS trajectories for motion compensation. CONCLUSION: Using appropriately designed VDS trajectories, residual motion artifacts can be significantly reduced by retrospectively correcting for in-plane rigid body motion. An overlapping region of approximately 8% of the central region of k-space and approximately 70 interleaves were found to be near-optimal parameters for retrospective correction using VDS trajectories.

Artifacts↗

PubMed2001

Optimization of the immobilization parameters and operational stability of immobilized hydantoinase and l-N-carbamoylase from Arthrobacter aurescens for the production of optically pure l-amino acids.

2The immobilization parameters were optimized for the hydantoinase and the L-N-carbamoylase from Arthrobacter aurescens DSM 3747 or 3745, respectively. To optimize activity yields and specific activities for the immobilization to Eupergit C, Eupergit C 250 L, and EAH-Sepharose wild-type, recombinant and genetically modified ('tagged') enzymes were investigated concerning the influence of the protein concentration, the kind of support and the immobilization method. For both enzymes, the use of the recombinant proteins resulted in enhanced specific activities especially when using a hydrophilic support for immobilization such as Sepharose. In the case of a genetically modified hydantoinase carrying a His(6)-tag, affinity coupling led to a loss of activity of higher than 80%. Both enzymes were significantly stabilized by immobilization: In packed bed reactors, Eupergit C 250 L (NH(2))-immobilized hydantoinase and EAH-Sepharose-immobilized L-N-carbamoylase showed half-life times of approx. 14000 and 900 hours, respectively. Together with specific activities of the immobilized enzymes of 2.5 U/g wet carrier (hydantoinase) and 10 U/g wet carrier (L-N-carbamoylase) the newly developed biocatalysts are sufficient to fulfill industrial requirements.In comparison to the free enzymes, temperature and pH-optima were increased by 10 degrees C and one pH unit, respectively, after immobilization. The pH and temperature optima of the hydantoinase (L-N-carbamoylase) were determined to be pH 8.5-10 (pH 9.5) and 45-60 degrees C (60 degrees C).In order to provide sufficient amounts of biocatalyst for the process development in mini plant scale, a 50 fold scale-up of the optimized immobilization procedure was carried out for both enzymes. Because of the overlapping optima, both immobilized enzymes can be operated together in one reactor.

Journal Article↗

PubMed1999

Determination of the ratio of D- and L-amino acids in brewing by an immobilised amino acid oxidase enzyme reactor coupled to amperometric detection.

To determine the quantity of free amino acids, the D- and L-forms separately, is an important task in modern nutritional studies. The aim of our present work was to develop rapid, routine methods for fast determination of the different forms of free amino acids. We utilized two enzymes (L-amino acid oxidase, D-amino acid oxidase) with broad specificity. In our home-made reactors, the enzymes were immobilized in a thin-layer Plexi-cell on natural protein membrane. The enzyme-cell was built into a FIA system and the hydrogen peroxide generated during the enzymatic reaction was determined by an amperometric detector. The electrode potential was fixed at +100 mV. The parameters for the biochemical and electrochemical reactions were optimized in each case. The optimal pH value for measuring L- and D-amino acids was found ca. 8.8 and 9.5, respectively. The LAO reactor could be used for more than 900 measurements, while the DAO reactor for about 1000 measurements. The working concentration range was between 0.1-3 and 0.2-3 mM, respectively. The same standard solution (L- and D-Methionine, 1 mM) was injected 25 times sequentially and the standard deviations were 2 and 2.7%, respectively. After determining the optimal parameters, the specificity of the immobilized enzyme preparations towards different amino acids and in samples from different stages of brewing was investigated.

Amino Acid Oxidoreductases↗

PubMed2006

Testing and tuning symplectic integrators for the hybrid Monte Carlo algorithm in lattice QCD.

We examine a new second-order integrator recently found by Omelyan et al. The integration error of the new integrator measured in the root mean square of the energy difference, 1/2, is about 10 times smaller than that of the standard second-order leapfrog (2LF) integrator. As a result, the step size of the new integrator can be made about three times larger. Taking into account a factor 2 increase in cost, the new integrator is about 50% more efficient than the 2LF integrator. Integrating over positions first, then momenta, is slightly more advantageous than the reverse. Further parameter tuning is possible. We find that the optimal parameter for the new integrator is slightly different from the value obtained by Omelyan et al, and depends on the simulation parameters. This integrator could also be advantageous for the Trotter-Suzuki decomposition in quantum Monte Carlo.

Journal Article↗

PubMed2005

Dynamic motion planning for the design of robotic gait rehabilitation.

In this paper we examine a method to control the stepping motion of a paralyzed person suspended over a treadmill using a robot attached to the pelvis. A leg swing motion is created by moving the pelvis without contact with the legs. The problem is formulated as an optimal control problem for an underactuated articulated chain. The optimal control problem is converted into a discrete parameter optimization and an efficient gradient-based algorithm is used to solve it. Motion capture data from an unimpaired human subject is compared to the simulation results from the dynamic motion optimization. Our results suggest that it is feasible to drive repetitive stepping on a treadmill by a paralyzed person by assisting in torso movement alone. The optimized, pelvic motion strategies are comparable to "hip-hiking" gait strategies used by people with lower limb prostheses or hemiparesis. The resulting motions can be found at the web site http://ww.eng.uci.edu/-chwang/project/stepper/stepper.html.

Computer Simulation↗

PubMed2005

Classification of gasoline data obtained by gas chromatography using a piecewise alignment algorithm combined with feature selection and principal component analysis.

A fast and objective chemometric classification method is developed and applied to the analysis of gas chromatography (GC) data from five commercial gasoline samples. The gasoline samples serve as model mixtures, whereas the focus is on the development and demonstration of the classification method. The method is based on objective retention time alignment (referred to as piecewise alignment) coupled with analysis of variance (ANOVA) feature selection prior to classification by principal component analysis (PCA) using optimal parameters. The degree-of-class-separation is used as a metric to objectively optimize the alignment and feature selection parameters using a suitable training set thereby reducing user subjectivity, as well as to indicate the success of the PCA clustering and classification. The degree-of-class-separation is calculated using Euclidean distances between the PCA scores of a subset of the replicate runs from two of the five fuel types, i.e., the training set. The unaligned training set that was directly submitted to PCA had a low degree-of-class-separation (0.4), and the PCA scores plot for the raw training set combined with the raw test set failed to correctly cluster the five sample types. After submitting the training set to piecewise alignment, the degree-of-class-separation increased (1.2), but when the same alignment parameters were applied to the training set combined with the test set, the scores plot clustering still did not yield five distinct groups. Applying feature selection to the unaligned training set increased the degree-of-class-separation (4.8), but chemical variations were still obscured by retention time variation and when the same feature selection conditions were used for the training set combined with the test set, only one of the five fuels was clustered correctly. However, piecewise alignment coupled with feature selection yielded a reasonably optimal degree-of-class-separation for the training set (9.2), and when the same alignment and ANOVA parameters were applied to the training set combined with the test set, the PCA scores plot correctly classified the gasoline fingerprints into five distinct clusters.

Algorithms↗

PubMed2005

Automatic selection of parameters for vessel/neurite segmentation algorithms.

An automated method is presented for selecting optimal parameter settings for vessel/neurite segmentation algorithms using the minimum description length principle and a recursive random search algorithm. It trades off a probabilistic measure of image-content coverage against its conciseness. It enables nonexpert users to select parameter settings objectively, without knowledge of underlying algorithms, broadening the applicability of the segmentation algorithm, and delivering higher morphometric accuracy. It enables adaptation of parameters across batches of images. It simplifies the user interface to just one optional parameter and reduces the cost of technical support. Finally, the method is modular, extensible, and amenable to parallel computation. The method is applied to 223 images of human retinas and cultured neurons, from four different sources, using a single segmentation algorithm with eight parameters. Improvements in segmentation quality compared to default settings using 1000 iterations ranged from 4.7%-21%. Paired t-tests showed that improvements are statistically significant (p < 0.0005). Most of the improvement occurred in the first 44 iterations. Improvements in description lengths and agreement with the ground truth were strongly correlated (p = 0.78).

Algorithms↗

PubMed1989

The evolution strategy--a search strategy used in individual optimization of electrical parameters for therapeutic carotid sinus nerve stimulation.

Optimization problems, arising in the search for parameters and/or techniques of functional electrostimulation (FES), disproportionally increase when multiple electrodes, electrode configurations, electrical parameters, and stimulation modes may be applied. When computational or investigational effort precludes systematic studies in FES, we propose to apply and evaluate Rechenberg's evolution strategy, which in technical use and numerical optimization has been valid in comparison to more traditional methods. This strategy implements mutation and selection processes in analogy to biological evolution. The effect of combined multiple input variables on a quality function (Q) is experimentally evaluated. The actual computed value of Q serves as a selection criterion for those input variable combinations which lead Q to approach a target value (maximization), similar to a hill-climbing procedure. In radiofrequency controlled, therapeutic electrical carotid sinus nerve stimulation (CSNS), we varied (mutated) combinations of pulse frequency and pulse amplitude parameters, according to the evolution strategy, in individual patients. CSNS lowers blood pressure and decreases heart rate. Q was computed from blood pressure and heart rate responses to CSNS. The strategy individually optimized electrical parameters to achieve large depressor responses upon CSNS. Although, in contrast to technical usage, only two input variables were investigated, and biomedical experience with the evolution strategy is limited so far, its potential use in other fields of FES, especially when more input variables are to be optimized, is discussed and encouraged.

Algorithms↗

PubMed2006

Biodegradation of dye solution containing Malachite Green: optimization of effective parameters using Taguchi method.

In this paper, optimization of biological decolorization of synthetic dye solution containing Malachite Green was investigated. The effect of temperature, initial pH of the solution, type of algae, dye concentration and time of the reaction was studied and optimized using Taguchi method. Sixteen experiments were required to study the effect of parameters on biodegradation of the dye. Each of experiments was repeated three times to calculate signal/noise (S/N). Our results showed that initial pH of the solution was the most effective parameter in comparison with others and the basic pH was favorable. In this study, we also optimized the experimental parameters and chose the best condition by determination effective factors. Based on the S/N ratio, the optimized conditions for dye removal were temperature 25 degrees C, initial pH 10, dye concentration 5 ppm, algae type Chlorella and time 2.5h. The stability and efficiency of Chlorella sp. in long-term repetitive operations were also examined.

Animals↗

PubMed1999

High-Resolution Infrared Spectrum of nu5, nu4, nu3, nu4 + nu5, and 2nu4 Band Systems of Deuterobromoacetylene.

High-resolution vibration-rotation spectra of gas-phase deuterobromoacetylene have been recorded in the 240-990 cm-1 infrared region. The analyzed band systems are rich in hot bands and have a high density of lines. Five band systems and a total of 124 vibration-rotation bands of the isotopic species DCC79Br and DCC81Br have been rotationally analyzed. Accurate rotational parameters and vibrational wavenumbers for 33 vibrational states of each species have been obtained from the rotational analysis. l doubling and rotational l resonance have been observed on some states and the respective resonance parameters have been obtained through nonlinear least-squares optimization. A Fermi resonance block model with perturbation terms has been used for the analysis of the vibrational states. With optimized parameters, the model produces root-mean-square deviations of observed - calculated wavenumbers of about 0.3 cm-1 for both isotopic species. Copyright 1999 Academic Press.

Journal Article↗

PubMed2004

Study of the extraction procedure by experimental design and validation of a LC method for determination of flavonoids in Citrus bergamia juice.

A reversed-phase high-performance liquid chromatographic (HPLC) separation with photo-diode array detection was developed for the simultaneous determination of flavonoids extracted from Citrus bergamia juice. It employs a C18 reversed-phase column and a linear gradient elution system with methanol/water with 5% acetic acid (v/v), as mobile phase. The method was validated in terms of detection limits (LOD), quantitation limits (LOQ), linearity, precision and accuracy. Limits of detection ranged from a low of 0.007 mg ml(-1) (narirutin) to a high of 0.018 mg ml(-1) (didymin). The limits of quantitation were between a low of 0.011 mg ml(-1) (7-OH flavanone) and a high of 0.024 mg ml(-1) (didymin). An excellent linear response was observed over the range specified for all analytes, as confirmed by the correlation coefficient with ranged from 0.9982 and 0.9999. The intra-day R.S.D.% ranged from 0.11 to 3.64%. The intermediate precision R.S.D.% were not higher than 7.62%. The accuracy of the method was confirmed with an average recovery ranging, except for neoeriocitrin, between 88.07% and 102.45%. Since the extraction conditions can affect analyte recovery, a suitable optimization strategy of the procedure was needed. The experimental parameters optimized were extraction time, temperature, and solvents. A multivariate approach was used to provide direct evaluation of the selected variables and related interactions. The D-optimal design was constructed by applying the exchange algorithm. All experimental results were computed by NEMROD-W software. This methodology led us to obtain the best recovery for all the flavonoids in the least number of experiments.

Chromatography, Liquid↗