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At least 1,225 records · Page 68Linked to original sources
PubMed2006

[Application of normoxic polymer gels in 3D-dosimetry for radiosurgery].

The aim of this study was to describe the manufacture of normoxic polymer gels, to characterize their dose response relationship, to optimize MR imaging parameters in order to minimize the standard deviation in the measured dose and to use the gel in a dose verification experiment in radiosurgery. The normoxic polymer gel used is simple to manufacture under normal atmospheric conditions and is characterized by a linear dose relationship up to 40 Gy. MR imaging was performed using 2-dimensional (20) single spin echo pulse sequences with two different echo times. The imaging parameters were optimized in order to minimize the standard deviation of the measured transversal relaxation rate R2 and to achieve a geometrical resolution of 1.5 mm. Comparisons of calculated and measured relative 3D dose distributions using a multi isocentric irradiation with Gamma Knife B showed a good overall agreement of both the isodose levels and the differential and cumulative dose volume histograms. The standard deviation in the measured dose was approximately 9% at 30 Gy. The evaluation according to the gamma criterion showed that 96% of the dose voxels remained within a spatial uncertainty of 1.5 mm and a dose uncertainty of 8%.

Gels↗
PubMed1988

Optimization of electrofusion parameters for efficient production of murine hybridomas.

Several factors which affect the production of murine hybridomas by electrofusion using SP2/0 myelomas were examined. These factors included the ionic composition, specific resistance and osmotic strength of the fusion medium, proteolytic pretreatment of the cells, and field strength of the single, rectangular, 15 or 20 microseconds electric pulse. Individual experiments were observed by phase microscopy, video-recorded, and subsequently analyzed. The efficiency of hybridoma formation was measured by the number of hybrid colonies which survived HAT medium selection. In most cases, the peak efficiency occurred when the pulse field was between 3 and 4 kV/cm. Ca++ and Mg++, in 0.1 and 0.5 mM concentrations, respectively, helped to prevent large-scale SP2/0 lysis following pulse application. Reduction of the osmolarity of the fusion medium allowed for an approximate two-fold increase in the hybrid production efficiency. However, other variations, including an increase of the specific resistance of the medium to 1.7 x 10(4) omega cm, and a reduction of the pulse width to 15 microseconds, allowed significantly higher efficiencies. Dispase pretreatment of the myelomas led to additional improvements when using a 15 microseconds pulse. The data suggest that for this system, the highest efficiencies are obtained by maximizing the attractive polarization forces between cells, while adjusting the ionic composition and pulse parameters to preserve myeloma viability.

Animals↗
PubMed1996

Transfecting mammalian cells: optimization of critical parameters affecting calcium-phosphate precipitate formation.

DNA-calcium phosphate co-precipitates arise spontaneously in supersaturated solutions. Highly effective precipitates for transfection purposes, however, can be generated only in a very narrow range of physico-chemical conditions that control the initiation and growth of precipitate complexes. The concentrations of calcium and phosphate are the main factors influencing characteristics of the precipitate complex, but other parameters, such as temperature, DNA concentration and reaction time are important as well. An example for this is the finding that almost all of the soluble DNA in the reaction mix can be bound into an insoluble complex with calcium phosphate in <1 min. Extending the reaction time to 20 min results in aggregation and/or growth of particles and reduces the level of expression. With improved protocols we gained better reproducibility and higher efficiencies both for transient and for stable transfections. Up to 60% of cells stained positive for beta-gal and transient production of secreted proteins was improved 5- to 10-fold over results seen with transfections using standard procedures. Similar improvements in efficiency (number of recombinant cell colonies) were observed with stable transfections, using co-transfected marker plasmids for selection. Transient expression levels 2 days after DNA transfer and titers obtained from stable cell lines, emerging weeks later, showed strong correlation.

Animals↗
PubMed2006

Optimization of nonlinear parameters in trial wave functions with a very large number of terms.

A procedure is proposed to construct highly accurate variational wave functions with large and very large numbers of basis functions. The procedure has a number of advantages in actual computations on parallel computer clusters. In particular, by using this procedure we have determined very accurate numerical values of the ground-state energies in the positronium ion Ps(-) (or e(-)e(+)e(-)) (E= -0.262 005 070 232 980 107 770 375 a.u.) and hydrogen ion infinityH(-) (E= -0.527 751 016 544 377 196 589 759 a.u.) The variational energies of the negative hydrogenlike ions (or H(-)-like ions) with the finite nuclear masses (T(-), D(-), 1H(-), and Mu(-)) are also presented. These energies are the best variational ground-state energies ever obtained for these ions.

Journal Article↗
PubMed2002

Effect of multileaf collimator leaf width on physical dose distributions in the treatment of CNS and head and neck neoplasms with intensity modulated radiation therapy.

The purpose of this work is to examine physical radiation dose differences between two multileaf collimator (MLC) leaf widths (5 and 10 mm) in the treatment of CNS and head and neck neoplasms with intensity modulated radiation therapy (IMRT). Three clinical patients with CNS tumors were planned with two different MLC leaf sizes, 5 and 10 mm, representing Varian-120 and Varian-80 Millennium multileaf collimators, respectively. Two sets of IMRT treatment plans were developed. The goal of the first set was radiation dose conformality in three dimensions. The goal for the second set was organ avoidance of a nearby critical structure while maintaining adequate coverage of the target volume. Treatment planning utilized the CadPlan/Helios system (Varian Medical Systems, Milpitas CA) for dynamic MLC treatment delivery. All beam parameters and optimization (cost function) parameters were identical for the 5 and 10 mm plans. For all cases the number of beams, gantry positions, and table positions were taken from clinically treated three-dimensional conformal radiotherapy plans. Conformality was measured by the ratio of the planning isodose volume to the target volume. Organ avoidance was measured by the volume of the critical structure receiving greater than 90% of the prescription dose (V(90)). For three patients with squamous cell carcinoma of the head and neck (T2-T4 N0-N2c M0) 5 and 10 mm leaf widths were compared for parotid preservation utilizing nine coplanar equally spaced beams delivering a simultaneous integrated boost. Because modest differences in physical dose to the parotid were detected, a NTCP model based upon the clinical parameters of Eisbruch et al. was then used for comparisons. The conformality improved in all three CNS cases for the 5 mm plans compared to the 10 mm plans. For the organ avoidance plans, V(90) also improved in two of the three cases when the 5 mm leaf width was utilized for IMRT treatment delivery. In the third case, both the 5 and 10 mm plans were able to spare the critical structure with none of the structure receiving more than 90% of the prescription dose, but in the moderate dose range, less dose was delivered to the critical structure with the 5 mm plan. For the head and neck cases both the 5 and 10 x 2.5 mm beamlets dMLC sliding window techniques spared the contralateral parotid gland while maintaining target volume coverage. The mean parotid dose was modestly lower with the smaller beamlet size (21.04 Gy v 22.36 Gy). The resulting average NTCP values were 13.72% for 10 mm dMLC and 8.24% for 5 mm dMLC. In conclusion, five mm leaf width results in an improvement in physical dose distribution over 10 mm leaf width that may be clinically relevant in some cases. These differences may be most pronounced for single fraction radiosurgery or in cases where the tolerance of the sensitive organ is less than or close to the target volume prescription.

Dose-Response Relationship, Radiation↗
PubMed1998

CT bronchoscopy: optimization of imaging parameters.

The authors evaluated the relative importance of the following scanning parameters at computed tomographic bronchoscopy in an anesthetized adult sheep's thorax: section thickness (2, 4, 8 mm), pitch (1.0, 1.5, 2.0), milliampere setting (100, 175, 250 mA), and overlap of reconstructed sections (0%, 25%, 50%, 75%). Five blinded readers ranked the images twice in comparison with photographs of the mounted specimen. Differences in image quality were significant (P < .001) with section thickness of 2 mm and a pitch of 1.0. The milliampere setting had only a minor effect on image quality, and a 50% overlap of reconstructed sections was best.

Animals↗
PubMed2006

Isolation of drug delivery from drug effect: problems of optimizing drug delivery parameters.

A recurring question in the treatment of malignant brain tumors has been whether treatment failure is due to inadequate delivery or ineffective drugs. To isolate these issues, we tested a paradigm in which the "therapeutic" agent was a toxin about which there could be no question of efficacy, provided it was delivered in adequate amounts; we used 10% formalin. We infused 10% formalin into 5- to 8-mm subcutaneous RG-2 and D54-MG gliomas at increasing rates until we achieved 100% tumor cell kill. In RG-2 gliomas, infusions of 10 microl/h x 7 days, and 2, 4, 6, and 8 microl/min x 2 h failed to kill tumors, although growth was delayed, while infusion rates of 12 microl/min x 60 min and 48 microl/min x 15 min produced 100% tumor kill. In D54-MG tumors, infusions of 4, 8, and 24 microl/min produced 100% tumor kill. 14C-Formalin autoradiographs showed a heterogeneous distribution after infusions of 2 microl/min x 2 h, whereas infusions of 48 microl/min x 15 min showed a homogeneous distribution within the tumor, but more than 95% of tissue radioactivity was found in tissue surrounding tumor. Drug delivery remains a major issue in brain tumor treatment: Distribution inhomogeneity, rapid efflux, and consequent treatment failures are likely due to high interstitial fluid pressure. Because the infusion rates being used in the treatment of human brain tumors are low and the tumors are larger, treatment failures can be expected on the basis of inadequate drug delivery alone, regardless of the effectiveness of the drug.

Animals↗
PubMedDate not supplied

Optimization of culture parameters for production of podophyllotoxin in suspension culture of Podophyllum hexandrum.

The root explants of the germinated seedlings of Podophyllum hexandrum were grown in MS medium supplemented with indole acetic acid (IAA) (2 mg/L) and activated charcoal (0.5%), and healthy callus culture was obtained after incubation for 3 wk at 20 degrees C. The cultivation of plant cells in shake flask was associated with problems such as clumping of cells and browning of media, which were solved by the addition of pectinase and polyvinylpyrrolidone. The effect of major media components and carbon source was studied on the growth and podophyllotoxin production in suspension culture. It was found that glucose was a better carbon source than sucrose and that NH4+:NO3- ratio (total nitrogen concentration of 60 mM) and PO4(3-) did not have much effect on the growth and product formation. The relative effect of culture parameters (inoculum level, pH, IAA, glucose, NH4+:NO3- ratio, and PO4(3-)) on the overall growth and product response of the plant cell suspension culture was further investigated by Plackett-Burman design. This indicated that inoculum level, glucose, IAA, and pH had significant effects on growth and production of podophyllotoxin. To identify the exact optimum concentrations of these parameters on culture growth and podophyllotoxin production, central composite design experiments were formulated. The overall response equations with respect to growth and podophyllotoxin production as a function of these culture parameters were developed and used to determine the optimum concentrations of these parameters, which were pH 6.0, 1.25 mg/L of IAA, 72 g/L of glucose, and inoculum level of 8 g/L.

Biotechnology↗
PubMed2006

MR angiography of the hand with subsystolic cuff-compression optimization of injection parameters.

OBJECTIVE: The purpose of our study was to assess the impact of various injection rates on contrast-enhanced high-resolution 3D MR angiography of the hand. MATERIALS AND METHODS: Ten healthy individuals (mean age, 24.4 years; range, 20-27 years) underwent 3D contrast-enhanced MR angiography of both hands. Starting 3 minutes before data acquisition, subsystolic upper arm cuff compression was applied unilaterally. A 1.5-T whole-body scanner with 3D gradient-echo sequence was used. Seven data sets (20 seconds) were obtained consecutively. I.v. contrast material of 0.1 mg/kg of body weight of gadobutrol was injected at rates of 0.5, 1.0, and 1.5 mL/s. For both hands, quantitative data evaluation was performed with contrast-to-noise ratio (CNR) in the radial, ulnar, palmar, and digital arteries and veins. Qualitative assessment of the arterial visualization score and venous contamination score was rated by two experienced radiologists using a 4-point scale. RESULTS: The lowest venous contamination score (CNR and reviewers' assessment) was observed with an injection rate of 0.5 mL/s (p < 0.05). For the arterial signal, the reviewers' assessment was that an injection rate of 0.5 mL/s was best (p = 0.08). Compression yielded a significantly lower venous contamination score for the compressed side than for the noncompressed side for flow rates of 0.5 mL/s and 1.0 mL/s (p < 0.05). CONCLUSION: Image quality of hand MR angiography was better with cuff compression. A flow rate of 0.5 mL/s yielded a good CNR and a significantly lower venous contamination score than the other flow rates.

Adult↗
PubMed2001

Optimization of control parameters for petroleum waste composting.

Composting is being widely employed in the treatment of petroleum waste. The purpose of this study was to find the optimum control parameters for petroleum waste in-vessel composting. Various physical and chemical parameters were monitored to evaluate their influence on the microbial communities present in composting. The CO2 evolution and the number of microorganisms were measured as the activity of composting. The results demonstrated that the optimum temperature, pH and moisture content were 56.5-59.5 degrees C, 7.0-8.5 and 55%-60%, respectively. Under the optimum conditions, the removal efficiency of petroleum hydrocarbon reached 83.29% after 30 days composting.

Bacteria↗
PubMed2001

The use of the amplification refractory mutation system (arms) in the detection of rare beta-thalassemia mutations in the Malays and Chinese in Malaysia.

Molecular characterization and prenatal diagnosis for beta-thalassemia can be carried out using the Amplification Refractory Mutation System (ARMS). The ARMS is a rapid and direct molecular technique in which beta-thalassemia mutations are visualized immediately after DNA amplification by gel electrophoresis. In the University of Malaya Medical Center, molecular characterization and prenatal diagnosis for beta-thalassemia is carried out using ARMS for about 96% of the Chinese and 84.6% of the Malay patients. The remaining 4% and 15.4% of the uncharacterized mutations in the Chinese and Malay patients respectively are detected using DNA sequencing. DNA sequencing is an accurate technique but it is more time-consuming and expensive compared with the ARMS. The ARMS for the rare Chinese beta-mutations at position -29 (A-->G) and the ATG-->AGG base substitution at the initiator codon for translation in the beta-gene was developed. In the Malays, ARMS was optimized for the beta-mutations at codon 8/9 (+G), Cap (+1) (A-->C) and the AATAAA-->AATAGA base substitution in the polyadenylation region of the beta-gene. The ARMS protocols were developed by optimization of the parameters for DNA amplification to ensure sensitivity, specificity and reproducibility. ARMS primers (sequences and concentration), magnesium chloride concentration, Taq DNA polymerase and PCR cycling parameters were optimized for the specific amplification of each rare beta-thalassemia mutation. The newly-developed ARMS for the 5 rare beta-thalassemia mutations in the Chinese and Malays in Malaysia will allow for more rapid and cost-effective molecular characterization and prenatal diagnosis for beta-thalassemia in Malaysia.

Base Sequence↗
PubMed1992

[Causes and incidence of short-life keratitis caused by dacryography. Optimization of protective parameters].

This study was aimed at investigating the changes occurring in superficial corneal epithelium (localized or diffuse, dotted or linear) as observed in 300 eyes after macrodacryography with iodate contrast media (iodized oil and water soluble non-ionic agents). In our opinion, the causes of iatrogenic short-life keratitis are: needle injury, the deposition of iodate contrast medium on the cornea and the reduction of palpebral winking, favoring dry eye, due to superficial anesthesia. The pharmacologic protection of the cornea by means of high-viscosity drugs allows both the number and the degree of keratitis to be markedly reduced. Therefore, contrast media must be chosen on the basis of anamnestic and clinical data, as well as of patient's symptoms, focusing mainly on the characteristics of the various agents--i.e., density, concentration, viscosity.

Humans↗
PubMedDate not supplied

[Optimization of energy parameters of ultrasound and laser cataract surgery with a preliminary transcorneal endocapsular YAG-laser impact exerted on the cataract lens nuclei].

The values of the main energy and time parameters of ultrasound and laser fragmentation of different-hardness cataract-lens nuclei were analyzed in patients of various age groups after a preliminary transcorneal endocapsular YAG-laser treatment of the lens. The results show, in all cases, lower key energy and time characteristics, which primarily concerns a total energy index of the ultrasound and laser effect of no less than 20% versus the ordinarily used parameters.

Adult↗
PubMed1991

[Optimization of the parameters that permit improvement in plate sorption activity for solid-phase immunoenzyme analysis].

The possibility of increasing the sorption activity of polystyrene plates with an initially low capacity for sorption has been shown. The qualitative and quantitative parameters of the process of physical modification have been ascertained. The empirical formula for achieving the highest degree of the sorption activity of plates by their definite exposure to ultraviolet radiation has been obtained.

Adsorption↗
PubMedDate not supplied

Optimization of sequence parameters in fast MR imaging of the brain with FLASH.

Owing to the intrinsically complex behavior of the signal intensity of fast gradient-refocusing MR sequences, agreement as to the clinically most useful sequence parameters has not yet been reached. This study evaluates the FLASH (fast low-angle shot) sequence for gray-white matter differentiation on normal volunteers at 1.5 T. The FLASH gradient-echo sequence is essentially T1-dependent. For very fast imaging and T1 weighting, the following parameters yield the best results: a flip angle of 30-50 degrees with TR = 20 and TE = 10. To replace T1-weighted SE by the faster FLASH sequence, the best results are achieved by a flip angle of 70-120 degrees with TR = 150-300 and TE = 10 (or shorter, if possible). The most valuable proton-density aspect is achieved by a flip angle of 30 degrees with TR = 300 and TE = 16.

Brain↗
PubMed1989

[Investigation on reduction of radiation dose and optimization of exposure parameters in radiography].

Investigation and measurement of the radiation dose level of routine X-ray diagnostic examinations were carried out on the spot, the results were as follows: Radiation dose of routine radiography: chest 0.258-1.032 x 10(-4) c/kg (0.1-0.4R); spinal and abdomen 0.774-1.806 x 10(-4) c/kg (0.3-0.7R); skull 0.774-1.032 x 10(-4) c/kg (0.3-0.4R) and gastrointestinal study 2.58-7.74 x 10(-4) c/kg (1-3R). Experiments employing different kV and mAs, and radiation exposure on 12-18 mm A1 phantoms while measuring the radiation dose and film density showed that radiation dose can be substantially reduced by improving the quality of X-ray beam for instance with the routine radiographic parameters for the chest, if the voltage is increased by 20 kV, radiation dose can be reduced to 65% or an additional 2 mm A1 filter can also reduce the dose to 60-65%.

Film Dosimetry↗