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Results for “parameter optimization”

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At least 1,189 records · Page 66Linked to original sources

PubMed2004

Assessment of different transfection parameters in efficiency optimization.

Achieving optimal transfection efficiency is the most critical step in overcoming the primary obstacle to success in nonviral-mediated gene therapy. Several transfection parameters were being examined including the effects of different types of transfection media, glucose concentration, reporter DNA concentration, and incubation time in lipotransfectant. Efficiency of transfection obtained was highest for Opti-MEM I (29 +/- 2.28%; p = 0.001) followed by M199 (24 +/- 1.54%; p = 0.009), both of which performed significantly better than DMEM (14 +/- 0.28%) as a transfection medium. The rate of transfection was affected by glucose levels in only DMEM with higher efficiency achieved using low glucose containing DMEM (17 +/- 0.38%) than its counterpart. Furthermore, transfection rate and cell viability were severely hampered by lengthened exposure to transfection complexes, leading to an overall mean efficiency of 5 +/- 0.87%. However, doubling the DNA content in the transfection mixture did not significantly change the mean rate of transfection in M199 medium (24 +/- 1.54% to 27 +/- 1.54%; p = 0.273). The overall range of mean efficiency acquired with our protocol under different transfection conditions was between 14% and 29%. Hopefully results from this study will further potential success in nonviral-mediated gene transfer.

Cells, Cultured↗

PubMed2004

Optimization of radiographic parameters for paediatric cardiac angiography.

In the paediatric cardiac catheterization laboratory the reduction of the radiation dose of diagnostic and interventional procedures is of high priority. Therefore, we performed an experimental study for optimizing the automatic exposure control (AEC) for cardiac angiography. With a Philips Integris BH 5000 system, six AEC programs were configured to acquire X-ray images of 8 cm to 18.5 cm thick PMMA phantoms at tube voltages between 50 kV and 90 kV, with 0.2 mm or 0.4 mm Cu filters and with or without an anti-scatter grid. At constant detector dose, entrance dose (ED) and image quality were evaluated as functions of the voltage. Changes in image quality were determined by the differential signal-to-noise ratio measured within regions of low (SNRb) and high (SNRd) attenuation. At equal voltages, ED saving was approximately 29% with the 0.4 mm Cu beam filtering as compared with 0.2 mm Cu, largely independent of object thickness. SNRb and SNRd were only dependent on the voltage. While SNRb was high at low voltages, SNRd showed a maximum at approximately 79 kV. Using a grid, ED increased with increasing object thickness by a factor of 1.9 to 3.5. At equal voltages, the grid led to significant image improvements, with SNRb and SNRd increasing by 27% and 11%, respectively. SNRb and SNRd are useful descriptors of the image quality in cardiac angiography. Highest image quality was found with tube voltages between 55 kV and 77 kV, independently of object thickness. To minimize dose, the thickness of the copper filter should be chosen to be as large as possible provided the tube's power limit allows keeping the voltage below the upper limit. In view of the substantial image improvement, the use of a grid is recommended for all patients, even for newborns.

Angiocardiography↗

PubMed2006

Accuracy of optimized chemical-exchange parameters derived by fitting CPMG R2 dispersion profiles when R2(0a) not = R2(0b).

The transverse relaxation rate, R2, measured as a function of the effective field (R2 dispersion) using a Carr-Purcell-Meiboom-Gill (CPMG) pulse train, is well suited to detect conformational exchange in proteins. The dispersion data are commonly fitted by a two-site (sites a and b) exchange model with four parameters: the relative population, pa, the difference in chemical shifts of the two sites, deltaomega, the correlation time for exchange, tau(ex), and the intrinsic relaxation rate (i.e., transverse relaxation rate in the absence of chemical exchange), R2(0). Although the intrinsic relaxation rates of the two sites, R2(0a) and R2(0b), can differ, they are normally assumed to be the same (i.e., R2(0a) = R2(0b) = R2(0)) when fitting dispersion data. The purpose of this investigation is to determine the magnitudes of the errors in the optimized exchange parameters that are introduced by the assumption that R2(0a) = R2(0b). In order to accomplish this goal, we first generated synthetic constant-time CPMG R2 dispersion data assuming two-site exchange with R2(0a) not equal R2(0b), and then fitted the synthetic data assuming two-site exchange with R2(0) = R2(0a) = R2(0b). Although all the synthetic data generated assuming R2(0a) not equal R2(0b) were well fitted (assuming R2(0a) = R2(0b)), the optimized values of pa and tau(ex) differed from their true values, whereas the optimized values of deltaomega values did not. A theoretical analysis using the Carver-Richards equation explains these results, and yields simple, general equations for estimating the magnitudes of the errors in the optimized parameters, as a function of (R2(0a) - R2(0b)).

Bias↗

PubMed2004

Decolorization of azo dye acid black 1 by the UV/H2O2 process and optimization of operating parameters.

An advanced oxidation process, UV/H2O2, was applied for decolorization of a di-azo dye (acid black 1). The effects of operating parameters such as hydrogen peroxide dosage, UV dosage and initial dye concentration, on decolorization have been evaluated. The acid black 1 solution was completely decolorized under optimal hydrogen peroxide dosage of 21.24 mmol/l and UV dosage of 1400 W/l in less than 1.2 min. The decolorization rate followed pseudo-first order kinetics with respect to the dye concentration. The rate increased linearly with volumetric UV dosage and nonlinearly with increasing initial hydrogen peroxide concentration. It has been found that the degradation rate increased until an optimum of hydrogen peroxide dosage, beyond which the reagent exerted an inhibitory effect. For real case application, an operation parameter plot of rate constant was developed. To evaluate the electric power and hydrogen peroxide consumption by UV/H2O2 reactor, 90% color removal was set as criteria to find the balance between both factors.

Azo Compounds↗

PubMed2006

Strike a balance: optimization of backbone torsion parameters of AMBER polarizable force field for simulations of proteins and peptides.

Based on the AMBER polarizable model (ff02), we have re-optimized the parameters related to the main-chain (Phi, Psi) torsion angles by fitting to the Boltzmann-weighted average quantum mechanical (QM) energies of the important regions (i.e., beta, P(II), alpha(R), and alpha(L) regions). Following the naming convention of the AMBER force field series, this release will be called ff02pol.rl The force field has been assessed both by energetic comparison against the QM data and by the replica exchange molecular dynamics simulations of short alanine peptides in water. For Ace-Ala-Nme, the simulated populations in the beta, P(II) and alpha(R) regions were approximately 30, 43, and 26%, respectively. For Ace-(Ala)(7)-Nme, the populations in these three regions were approximately 24, 49, and 26%. Both were in qualitative agreement with the NMR and CD experimental conclusions. In comparison with the previous force field, ff02pol.rl demonstrated good balance among these three important regions. The optimized torsion parameters, together with those in ff02, allow us to carry out simulations on proteins and peptides with the consideration of polarization.

Computer Simulation↗

PubMed1977

[Critical evaluation of clinical and hormonal parameters for the optimal timing of induction of ovulation with gonadotropins (author's transl)].

In 9 hypogonadotrophic, normoprolactinemic women with primary or secondary amenorrhea, who were infertile, 16 treatment cycles with menopausal gonadotropin and chorionic gonadotropin (HMG-HCG) were carried out. Nine treatment cycles were monitored indirectly with the cervical factor and hormonal cytology. The concomitant serum estradiol and progesterone values were later determined by radioimmunoassays. The other 7 treatment cycles were monitored by daily serum estradiol determinations. There were 4 pregnancies. Successful induction of ovulation with subsequent pregnancies was only obtained in the treatment cycles monitored by serum estradiol determinations (pregnancy rate 60%). Classical signs of overstimulation with ascites and hydrothorax occurred twice in treatment cycles which were monitored by clinical means only. Neither the maturation index nor the cervical factor reflected a quantitative overstimulation of the ovaries. The daily radioimmunological determination of estradiol prevented overstimulation of the ovaries, and permitted optimal timing of the induction of ovulation with HCG. In our experience, the maturation index determined from vaginal cytology and the clinical determination of the cervical factor are inappropriate parameters to monitor individually a successful induction of ovulation with HMG-HCG.

Adult↗

PubMed1982

Optimal inputs for parameter determination of inert gas washout from the lung.

The nitrogen washout test will yield more information about the distribution of pulmonary ventilation if a pattern of inspired gas concentrations is utilized other than the standard series of 100% oxygen breaths. The input breathing pattern which yields optimal results will vary with the specific features of the lung being studied but typically includes breaths of air, particularly in the last third of the washout. Using computerized, mathematical techniques, optimal inputs were selected for washout tests of duration 10, 20, 30 and 40 breaths for each of six lung models, ranging from a unicompartmental to a highly non-uniform 'diseased' lung. Knowing these optimal inputs we were able to devise a nominal input which was similar to the optimal inputs for all models. For a 10 breath test this nominal input pattern utilized a breath of air at breath 7. For a 20 breath test, air is utilized at breaths 12, 14, 15, 19; for 30, air at 19, 21, 22, 23, 29 and for a 40-breath test, air at breaths 19, 24, 28, 30, 31, 32 and 39. The 30-breath nominal sequence was compared with the conventional oxygen-only washout and a 31-breath pseudo-random binary (PRB) input. Comparisons were made using computer simulated washouts as well as actual tests on human subjects. The 30-breath nominal input was always superior to the standard washout and was superior to the PRB input for all models except the lung ventilated with vital capacity breaths. We conclude that a significant advantage is gained by substituting the recommended sequences of breaths in studies of the dynamics of gas exchange in the lung.

Humans↗

PubMed2005

Optimization of instrumental parameters of a near-field thermal-lens detector for capillary electrophoresis.

The optical scheme of a near-field dual-beam mode-mismatched thermal-lens detector for capillary electrophoresis with a crossed-beam configuration employing a multimode HeCd laser (325 nm) as an excitation source was optimized. It is shown that a multimode laser can be successfully used as an excitation source in thermal lensing with minimal deviations in thermal responses from Gaussian excitation sources. An equation for diffraction thermal-lens theory for near-field measurements is deduced, and the experimental results agree with the deduced equation. The temperature rise in the capillary was estimated, and the exponential decrease of the signal with time for static conditions and low flow velocities was explained. The optimum configuration of the detector from the viewpoint of the maximum sensitivity and beam sizes was found. The detector provides a significant improvement in the detection limits for model compounds absorbing at 325 nm (nitrophenols) compared to the results obtained with a commercial absorbance detector operating at the same wavelength.

Electrophoresis, Capillary↗

PubMed1988

Electric shock-mediated transfection of cells. Characterization and optimization of electrical parameters.

The effect of various parameters on the electric shock-mediated permeabilization and transfection of CHO cells has been investigated. Up to 70% of the cells can be maintained transiently permeable to erythrosin B for periods of at least 1 h at 20 degrees C. Electrical conditions optimal for transient permeabilization were also optimal for efficient DNA transfection by pSV2neo. However, the DNA must be present during exposure to the electric field for efficient transformation. The same requirement existed for voltage-induced DNA toxicity. The results suggest that DNA moves into the cells by electrophoresis, not by simple diffusion. Based on these observations a simple, rapid procedure for optimizing the conditions for electric shock-mediated DNA transfer into cells has been developed.

Animals↗

PubMed1997

[Optimization of technical parameters for processing radix Aconiti coreani].

Based on the determination of guanfu A, hypaconitine, and total alkaloids, along with the experiment of acute toxicity of sliced Radix Aconiti Coreani and in compliance with the quality standard stipulated in pharmacopeia-surface features cross section colour and odor of sliced Radix Aconiti Co-reani the technology of processing Radix Aconiti Coreani has been optimized to be steaming the drug for four hours.

Aconitine↗

PubMed2001

Using experimental design to optimize the process parameters in fluidized bed granulation.

In this study many parameters were screened for a small-scale granulation process for their effect on the yield of granules between 75 and 500 microns and the geometrical granule mean size (d50). First a Plackett-Burman design was applied to screen the inlet air temperature, the inlet flow rate, the spray rate, the nozzle air pressure, the nozzle spray diameter, and the nozzle position. The Plackett-Burman design showed that the key process parameters were the inlet flow rate and the spray rate and probably also the inlet air temperature. Afterward a fractional factorial design (2(5-2)) was applied to screen the remaining parameters plus the nozzle aircap position and the spraying time interval. The fractional factorial design showed that the nozzle air pressure was also important. As the target values for the granule yield (between 75 and 500 microns) and the geometric mean granule size (between 300 and 500 microns) were reached during the screening experiments, further optimization was not considered necessary.

Air Movements↗

PubMed2000

Optimization of chromatographic parameters for the determination of biogenic amines in wines by reversed-phase high-performance liquid chromatography.

A method suitable for the determination of eight biogenic amines (histamine, tyramine, phenylethylamine, tryptamine, cadaverine, putrescine, spermidine and spermine) in wines has been developed. The method involves derivatization of the amines by treatment with dabsyl chloride, after which the derivates were analysed by reversed-phase liquid chromatography with gradient elution and spectrophotometric detection at 446 nm. Different variables affecting separation were optimized. Validation of the method included calibration experiments, the addition of standards amines for the determination of recovery and repeatability tests. Good linearity of the responses was obtained up to 500 microg l(-1), except for putrescine (up to 2100 microg l(-1)). The detection limits ranged between 10 and 60 microg l(-1) for standard solutions. The method was successfully applied to the analysis of five Spanish wines.

Biogenic Amines↗

PubMed2004

Parameters of an optimal physiological state of the masticatory system: the results of a survey of practitioners using computerized measurement devices.

While bioelectronic instruments have been available for nearly 30 years to assist dentists in day-to-day evaluations of patients' masticatory systems, little guidance has been published to support physiological norms or ideals. An electronic questionnaire was developed and administered to an international group of dentists familiar with the use of bioelectronic instrumentation. Respondents were asked to provide feedback on the norms or ideal parameters of jaw movement, masticatory muscle function with electromyography, and joint sounds through electrosonography that they use in guiding evaluation and treatment of patients with temporomandibular disorders, neuromuscular occlusion, and orthodontics. Surveys were collated to determine areas of consensus. Out of 150 surveys, 55 responses were received from dentists representing nine different countries. Sixty percent of the respondents reported treating more than 150 cases in the past five years using bioelectronic testing. While experience ranged from 2-30 years with different types of devices, average experience was longer with mandibular/jaw tracking (mean 15.3 years) and electromyography (mean 14.1 years) than with electrosonography (mean 7.0 years). Parameters proposed as norms or ideals for electromyographic rest and clench values, and mandibular tracking (velocity, freeway space, and trajectory to closure) were very consistent. Although a smaller number of respondents reported utilization of electrosonography, their criteria for data significance and tissue-type genesis of joint sounds were consistent. While the intra-patient variability may limit the diagnostic use of bioelectronic instruments, the current study demonstrates that through decades of experience, dentists have independently arrived at very consistent definitions of an ideal physiology that can be used to guide treatment.

Biomedical Engineering↗

PubMed2005

Use of simulated annealing for optimization of alignment parameters in limited MRI acquisition volumes of the brain.

Studies suggest that clinical outcomes are improved in repeat trigeminal neuralgia (TN) Gamma Knife radiosurgery if a different part of the nerve from the previous radiosurgery is treated. The MR images taken in the first and repeat radiosurgery need to be coregistered to map the first radiosurgery volume onto the second treatment planning image. We propose a fully automatic and robust three-dimensional (3-D) mutual information- (MI-) based registration method engineered by a simulated annealing (SA) optimization technique. Commonly, Powell's method and Downhill simplex (DS) method are most popular in optimizing the MI objective function in medical image registration applications. However, due to the nonconvex property of the MI function, robustness of those two methods is questionable, especially for our cases, where only 28 slices of MR T1 images were utilized. Our SA method obtained successful registration results for all the 41 patients recruited in this study. On the other hand, Powell's method and the DS method failed to provide satisfactory registration for 11 patients and 9 patients, respectively. The overlapping volume ratio (OVR) is defined to quantify the degree of the partial volume overlap between the first and second MR scan. Statistical results from a logistic regression procedure demonstrated that the probability of a success of Powell's method tends to decrease as OVR decreases. The rigid registration with Powell's or the DS method is not suitable for the TN radiosurgery application, where OVR is likely to be low. In summary, our experimental results demonstrated that the MI-based registration method with the SA optimization technique is a robust and reliable option when the number of slices in the imaging study is limited.

Algorithms↗

PubMed1996

Decreased myocardial oxygen consumption indices in dynamic cardiomyoplasty.

BACKGROUND: To investigate the theory of decreased myocardial oxygen consumption (MVo2) in dynamic cardiomyoplasty (DCM), previous studies have calculated indices of MVo2 in DCM. These previous studies, however, used left ventricular pressure in formulas that assumed the assumed the heart to be in its native state, with the reference pressure at the epicardium assumed to be atmospheric. In DCM, however, the reference pressure at the epicardium is no longer atmospheric but rather is the compressive pressure generated by the latissimus dorsi (LD). We therefore used the transmural myocardial pressure, Pt, to calculate indices of MVo2 in DCM. METHODS AND RESULTS: A half-ellipsoidal, fluid-filled balloon was interposed between the LD and myocardium in a balloon-mediated cardiomyoplasty procedure in five goats. With commonly used LD stimulation parameters, Pt was calculated as left ventricular pressure minus balloon luminal pressure. Using Pt, the transmural tension time index (TtTI) and transmural pressure volume area (PtVA) were calculated. In another series of four goats, LD stimulation parameters were optimized and the TtTI and PtVA recalculated. With standard LD stimulation parameters, the TtTI decreased by 48%, from 15.8 to 8.2 mm Hg.s, and the PtVA by 21%, from 775 to 612 mm Hg.mL, as the LD was stimulated to contract. When the optimized parameters were used, the TtTI decreased by 45%, from 11.2 to 6.2 mm Hg.s, and the PtVA by 33%, from 1984 to 1371 mm Hg.mL. CONCLUSIONS: Our results suggest that DCM with a fluid-filled balloon decreases MVo2 as the LD contracts and that LD stimulation parameters have a determining effect on this benefit.

Animals↗

PubMed1996

Optimized sampling and parameter estimation for quantification in whole body PET.

Whole-body positron emission tomography (PET) has recently emerged as an important imaging tool for cancer detection and staging. Initial applications of the technique have been primarily qualitative. One of the major reasons is the limits imposed by kinetically undersampled data over the whole body, as opposed to the standard method of continuous dynamic sampling in one body location. In this paper, a new estimation method using weighted nonlinear least squares (WNLS) for the first bed position and Bayesian regression (BR) for subsequent positions is proposed. A general criterion for designing optimal sampling schedules which maximizes the measurement information with multiple bed positions is developed. The overall approach is illustrated with the problem of estimating the metabolic rate of glucose (MRGLu) in tumors at different axial positions (image bed positions) in the body by using computer simulations and patient data. The results show that estimates of MRGLu using sparse data and the optimized Bayesian approach are comparable with those obtained by standard methods and fully sampled data. This study demonstrates the potential of the technique described for quantification where several bed positions have to be used to image all the regions of interest (ROI).

Abdominal Muscles↗

PubMed1998

Optimization of magnetic resonance imaging parameters for left ventricular wall motion studies at 0.5 T.

Magnetic resonance cine imaging of left ventricular wall motion at rest or during stress may be used to assess myocardial function, infarction and viability, or reversible ischaemia. Whilst interpretation of the cines rests critically on image quality, there is little in the literature which systematically examines the optimal imaging parameters for such wall motion studies at rest or during stress. This study was designed to examine several imaging parameters for cine optimization using a conventional 0.5 T scanner. Gradient echo imaging was performed in two groups of volunteers with varying echo times and flip angles. The period between excitations was 80 ms (simulating a resting heart rate) in one group, and 40 ms (simulating tachycardia during stress) in the other group. Short axis imaging yielded the highest contrast between blood and myocardium for both repetition times (rest p = 0.02; stress p < 0.001) compared with the long axes, because of magnetic saturation of blood moving slowly in-plane. Contrast was higher at end-diastole than end-systole for the long axes (rest p < 0.0001; stress p < 0.0002), but not significantly different in the short axis. Increasing the echo time and flip angle resulted in increased signal but eventually caused motion artefact and magnetic saturation of blood. The optimal parameters were an echo time of 14 ms and a 45 degrees flip angle for resting heart rates, with the flip angle falling to between 35 degrees and 45 degrees for tachycardia. The choice of imaging parameters is therefore a compromise between improved signal and unwanted artefacts, although the latter are less evident in the short axis plane, which yields the best contrast results because of high blood inflow effects.

Adult↗

PubMed2006

Automatic contour propagation in cine cardiac magnetic resonance images.

We have developed a method for automatic contour propagation in cine cardiac magnetic resonance images. The method consists of a new active contour model that tries to maintain a constant contour environment by matching gray values in profiles perpendicular to the contour. Consequently, the contours should maintain a constant position with respect to neighboring anatomical structures, such that the resulting contours reflect the preferences of the user. This is particularly important in cine cardiac magnetic resonance images because local image features do not describe the desired contours near the papillary muscle. The accuracy of the propagation result is influenced by several parameters. Because the optimal setting of these parameters is application dependent, we describe how to use full factorial experiments to optimize the parameter setting. We have applied our method to cine cardiac magnetic resonance image sequences from the long axis two-chamber view, the long axis four-chamber view, and the short axis view. We performed our optimization procedure for each contour in each view. Next, we performed an extensive clinical validation of our method on 69 short axis data sets and 38 long axis data sets. In the optimal parameter setting, our propagation method proved to be fast, robust, and accurate. The resulting cardiac contours are positioned within the interobserver ranges of manual segmentation. Consequently, the resulting contours can be used to accurately determine physiological parameters such as stroke volume and ejection fraction.

Algorithms↗