SEARCH · PubMed Health

Results for “parameter optimization”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,027 records · Page 57Linked to original sources

PubMed1996

Formulation of poly(DL-lactide-co-glycolide) microspheres and their ingestion by bovine leukocytes.

This study determined optimal parameters for producing controlled-release microspheres and examined their suitability for vaccines via ingestion by bovine leukocytes. Microspheres elicit an immune response when ingested by antigen-presenting cells and provide sustained exposure of antigen to sensitized cells. Ingestion of microspheres is determined by their size (< 10 microns), and antigen release is governed by composition. Poly(DL-lactide-co-glycolide) microspheres were prepared using different polymer concentrations, stir rates, emulsifier concentrations, and emulsifier molecular masses. Microspheres that were < 10 microns were prepared using a 6% 50:50 lactide to glycolide polymer solution emulsified at 12,000 rpm in a low molecular mass, 5% polyvinyl alcohol solution. Microspheres that were > 20 microns were prepared using a 10% 85:15 lactide to glycolide polymer solution emulsified at 1200 rpm in a low molecular mass, 3% polyvinyl alcohol solution. Small microspheres released 90% of the antigen after 7 d, and large microspheres released only 24% of the antigen after 56 d. Both monocytes and neutrophils selectively ingested small microspheres that were opsonized with normal bovine serum (heated and unheated). Ingestion of microspheres that had been opsonized with fetal bovine serum (heated and unheated) was minimal. Lymphocytes did not ingest microspheres. Ingestion of small microspheres by bovine monocytes and sustained release of antigen by large microspheres suggested that microspheres have the ability to produce a sustained immune response with a single injection.

Animals↗

PubMed2006

In vitro culture duration does not impact the ability of encapsulated choroid plexus transplants to prevent neurological deficits in an excitotoxin-lesioned rat model of Huntington's disease.

Delivery of neurotrophic molecules to the CNS is a potential treatment strategy for preventing the neuronal loss accompanying many neurological disorders. Choroid plexus (CP) epithelial cells secrete a cocktail of neurotrophic factors, and encapsulated CP transplants are neuroprotective in animal models of stroke and Huntington's disease (HD). Prior to clinical use, it is essential to identify and optimize parameters such as the length of time that transplant products such as encapsulated CP can be maintained. In the present study, neonatal porcine CP was encapsulated within alginate microcapsules and maintained in vitro for 1, 2, or 7 months. The encapsulated cells remained viable (>80%) at all time points and were transplanted unilaterally into the rat striatum. Seven days later, the same animals received unilateral injections of quinolinic acid (QA; 225 nmol) adjacent to the implant site. Separate groups of animals served as controls and received QA alone. After surgery, animals were periodically evaluated for weight loss and were tested for motor function 14 days post-QA. In controls, QA lesions produced a significant loss of body weight and impaired function of the contralateral forelimb. In contrast, implants of CP were potently neuroprotective as rats receiving CP transplants did not lose body weight and were not significantly impaired when tested for motor function. These benefits were independent of the length of time that the cells were held in vitro and demonstrate that the potential potency of alginate encapsulated CP cells can be retained for extremely long periods of time in vitro.

Alginates↗

PubMed2005

Vibrotactile intensity and frequency information in the pacinian system: a psychophysical model.

The objective of the study was to characterize the Pacinian representation of stimulus waveform. Subjects were presented with pairs of high-frequency vibrotactile stimuli that varied in intensity and/or frequency content and made same-different judgments under conditions of low-frequency adaptation designed to minimize the contribution of the RA system. We wished to infer the nature of the information conveyed by the Pacinian system about the stimuli from measured sensitivity (d') to stimulus differences. We first tested the hypothesis that the Pacinian system conveys only intensive information about vibratory stimuli and found that intensive cues could not account for much of the variance in the discrimination data. We then proposed a model characterizing the Pacinian-mediated representation of an arbitrary stimulus as a pattern of activation in a set of frequency-tuned minichannels. The model was shown to predict the discriminability of the stimulus pairs presented in the psychophysical experiments. Furthermore, the model parameters, optimized to fit the discrimination data, were compatible with analogous values obtained in other experimental contexts. One of the assumptions underlying the model is that information about individual spectral components is conveyed in parallel and quasi-independently. By simulating the response of a population of Pacinian afferents to a polyharmonic stimulus, we demonstrated that such a population can simultaneously convey information about multiple frequency components, despite having a homogeneous spectral profile.

Adult↗

PubMed2000

The generation of vibrotactile patterns on a linear array: influences of body site, time, and presentation mode.

In order to provide information regarding orientation or direction, a convenient code employs vectors (lines) because they have both length and direction. Potential users of such information, encoded tactually, could include persons who are blind, as well as pilots, astronauts, and scuba divers, all of whom need to maintain spatial awareness in their respective unusual environments. In these situations, a tactile display can enhance environmental awareness. In this study, optimal parameters were explored for lines presented dynamically to the skin with vibrotactile arrays on three body sites, with veridical and saltatory presentation modes. Perceived length, straightness, spatial distribution, and smoothness were judged while the durations of the discrete taps making up the "drawn" dotted lines and the times between them were varied. The results indicate that the two modes produce equivalent sensations and that similar sets of timing parameters, within the ranges tested, result in "good" lines at each site.

Adult↗

PubMedDate not supplied

Lamellar refractive surgery with scanned intrastromal picosecond and femtosecond laser pulses in animal eyes.

PURPOSE: To evaluate the use of scanned intrastromal picosecond and femtosecond laser pulses in lamellar refractive surgical procedures. METHODS: Intrastromal corneal photodisruption was performed in fresh porcine and primate cadaver eyes with a solid-state femtosecond laser. Laser pulses were focused 150 to 200 microns below the epithelial surface and scanned in a spiral pattern to create a plane. A flap was made by scanning an arc pattern from the plane of the spiral to the surface of the cornea. Tissue plane separation was graded using a standard scale, while internal surfaces were analyzed by scanning electron microscopy. Comparison was made to a picosecond laser system using the same delivery system device. Creation of a stromal lenticule for in situ keratomileusis was also demonstrated and compared with both laser systems. RESULTS: For femtosecond pulses, tissue separation was achieved best with pulse energies from 4 to 8 microJ and spot separations from 10-15 microns. Picosecond pulses accomplished less complete separations with pulse energies of 25 microJ and spot separations from 10 to 20 microns. Surface quality corresponded to dissection results, with high-grade dissections resulting in a smooth surface appearance, versus a more irregular surface for low-grade dissections. Although high-grade dissections could be created with picosecond pulses (with optimal parameters) in ex vivo porcine eyes, only femtosecond parameters produced similar results in ex vivo primate eyes. CONCLUSION: In contrast to previous attempts using picosecond lasers which require additional mechanical dissection, high precision lamellar refractive surgery may be practical with femtosecond laser pulses.

Animals↗

PubMed2000

Rapid detection of Salmonella typhimurium in chicken carcass wash water using an immunoelectrochemical method.

An immunoelectrochemical method coupled with immunomagnetic separation was developed for rapid detection of Salmonella Typhimurium in chicken carcass wash water. Samples of chicken carcass wash water were inoculated with Salmonella Typhimurium at different cell numbers. Possible nonspecified inhibitors in the wash water were minimized by filtration and centrifugation. An approximately 9.4% loss of Salmonella cells was found after filtration (P < 0.01). The samples were mixed with anti-Salmonella-coated magnetic beads (ASCMB) and alkaline phosphatase-labeled anti-Salmonella (APLAS) to form ASCMB-Salmonella-APLAS conjugates. The conjugates were separated from the solution using a magnetic separator and then incubated with phenylphosphate substrate to produce phenol. The number of Salmonella was determined by measuring the phenol concentration using an amperometric tyrosinase carbon paste electrode in a flow injection analysis system. Under optimized parameters (1 mM MgCl2, 0.2 microg/ml APLAS, and 1 mM phenylphosphate in pH 7.0 Tris buffer solution), Salmonella Typhimurium in chicken carcass wash water could be identified and enumerated within 2.5 h with a detection limit of 5 x 10(3) CFU/ml. A linear relationship on a log-log scale was found between Salmonella cell number and the peak current ratio for Salmonella concentrations ranging from 10(3) to 10(7) CFU/ml (R2 = 0.963). The peak currents of multibacteria samples, containing Salmonella Typhimurium, Listeria monocytogenes, and Campylobacter jejuni, were not significantly different from Salmonella-only samples (P > 0.01).

Animals↗

PubMed2002

[Development of an image processing scheme for chest radiographs using a dot printer].

The performance of dot printers has recently been improved. Images output by dot printers can provide simple, economical medical reference images if important diagnostic information is not lost. We developed an image processing scheme for chest radiographs that employed a dot printer. We used two types of pixel value conversions, a nonlinear pixel value correction using a lookup table and a linear pixel value conversion using histogram analysis. The density distribution of chest radiographs was analyzed and classified into high-density and low-density images. The two types of pixel value conversions were used depending on the density of chest radiographs. Converted pixel value had density characteristics that were adapted to the output image of the dot printer, and thus the density distributions of the lungs of radiographs became comparable. In addition, an adaptive unsharp masking technique with processing parameters optimized for each of the lungs and mediastinum was applied. An ROC study for the detection of lung nodules was carried out to evaluate the performance of dot printer images. The area under the ROC curve (A(z)) for dot printer images was 0.816, while sensitivity and specificity were 77.6% and 75.2%, respectively. The performance indicated the usefulness of our image processing scheme.

Humans↗

PubMed1995

Blastogenesis and interleukin-2 receptor expression assays in the harbor seal (Phoca vitulina).

Two in vitro functional assays were developed to evaluate mitogen-induced responses of peripheral blood mononuclear leukocytes (PBML) from free-ranging harbor seals, Phoca vitulina. Lymphocyte proliferation was measured by a standard blastogenesis assay following optimization of culture conditions including mitogen concentration, cell density, and incubation time. These optimized parameters, with the exception of incubation time, were subsequently employed to measure lymphocyte activation by analytical flow cytometry using fluorochrome-based identification of cell surface interleukin-2 receptor (IL-2r) expression. Baseline values established for free-ranging harbor seals had extensive animal variability; there was evidence that the samples were derived from a group of animals with a normal distribution. Positive correlations were observed between blastogenesis assays, and between blastogenesis and activation assays, when using pokeweed or concanavalin A as the stimulus. However, no relationship was found in the expression of the IL-2r induced by these mitogens. This result supports the contention that the two mitogens stimulate different lymphocyte subpopulations. This was observed only with the IL-2r expression assay because of its unique ability to measure the number of T lymphocytes initially activated rather than the ultimate number of progeny cells identified by blastogenesis. Both assays, used concurrently, should provide a more comprehensive representation of lymphocyte competence and serve as a measure of animal health.

Animals↗

PubMed1998

Color Doppler sonographic detection of tumor flow in superficial melanoma metastases: histologic correlation.

Color Doppler sonographic detection of tumor flow within superficial melanoma metastases was investigated to determine if tumor size, vessel size, or vessel number influences signal detection. Color Doppler imaging of 32 pathologically proved melanoma metastases was performed at 6 MHz with color Doppler imaging parameters optimized for each lesion scanned. All lesions were measured in three dimensions and the presence or absence of internal flow was documented. Seven surgically excised metastases underwent immunohistochemical staining for endothelial markers. Internal flow was detected in 21 of 32 masses and was completely absent in 11. In comparison to all masses without flow, the masses with flow had significantly greater anteroposterior dimensions (P < 0.00036) and volumes (P < 0.01). Histologically, mean vessel diameter in masses with flow was significantly greater (P < 0.05) than in those without flow, but mean vessel number was not significantly different. In conclusion, detectability of tumor blood flow in superficial melanoma metastasis may be related more to tumor size and vessel size than vessel number. Failure to detect color signal within a superficial melanoma mass does not indicate a lack of internal vascularity.

Adult↗

PubMed1999

Angiographic correlation of CT calcification in the carotid siphon.

BACKGROUND AND PURPOSE: Calcification in the coronary arteries has been correlated with significant vessel stenosis. The predictive value of calcification within the carotid siphon has not been characterized; however, stenosis in the carotid siphon is potentially important in determining management of patients with ipsilateral carotid bifurcation stenosis. The purpose of this study was to determine optimal parameters for assessing carotid siphon calcification on head CT scans and to compare the CT findings with angiographic results. METHODS: We performed a retrospective review of patients referred for diagnostic carotid arteriography. Those patients who also had undergone a head CT study at our institution were selected. The CT scans and angiograms of 64 patients (128 vessels) were reviewed. Carotid siphon calcification on CT scans was characterized on brain and bone windows as mild, moderate, or severe. Comparison was then made with angiographic findings. RESULTS: The sensitivity and specificity of CT for depicting greater than 50% angiographic stenosis in the carotid siphon were 86% and 98%, respectively, for bone windows and 100% and 0%, respectively, for brain windows. The positive predictive value (PPV) for a stenosis of greater than 50% as evidenced by severe calcification was 86% on bone windows and 11% on brain windows. The PPV for mild and moderate calcification on bone windows was 2.5% and 0%, respectively. CONCLUSION: Severe CT calcification in the carotid siphon as characterized on bone windows correlates with a carotid siphon stenosis of greater than 50% as determined angiographically. Therefore, the identification of severe calcification offers a potential noninvasive method for identifying stenosis of the carotid siphon. This information may be essential in determining management and prognosis for patients with carotid bifurcation stenosis.

Adolescent↗

PubMedDate not supplied

[Synchronous mechanical heart massage during assisted circulation].

In tests on dogs specially devised cardiac massage appliances and a monitoring system synchronizing the mechanical massage with the R wave on the ECG were used in carrying out a synchronous mechanical chest massage in conditions of an experimentally induced incompetence of the cardiac ventricles. Optimal parameters of the hemodynamics were recorded with the massage proceeding in such a manner, when mechanical action on the cardiac ventricles coincided with termination of the maximum pressure period of the myocardium. The synchronous ancillary cardiac massage effected under conditions of ventricular incompetence was found to be attended by a rise of cardiac output and increased aortic pressure, falling tension in the auricles and normalization of the acid-base equilibrium figures. Synchronization of the massaging appliance operation with cardiac contractions is an effective method of assisted circulation in acute incompetence of the heart valves.

Animals↗

PubMed1999

[Evaluation of two-dimensional thick-slice MR DSA: preliminary study].

We have used two-dimensional contrast-enhanced MR angiography for a single thick slice and called it MR DSA. This technique realizes nearly subsecond scanning per image and is therefore superior to other types of contrast-enhanced MR angiography in temporal resolution. To determine the optimal parameters of this technique, we calculated SSR (the signal of brain to the signal of contrast agent ratio) in various settings. We also obtained MR DSA images of 26 cases. We believe that MR DSA may play a supportive role in conventional MR imaging or angiography, since its high temporal resolution is of value in the evaluation of cerebrovascular diseases.

Angiography, Digital Subtraction↗

PubMed1999

[Use of diode laser in the treatment of intraocular tumors: preliminary report].

PURPOSE OF THE STUDY: The purpose of the study was to evaluate the effectiveness of diode laser transpupillary thermotherapy and to determine in what extent it may act as the only method of therapy of choroidal tumors, and when it should be used in combination with other methods. The study has preliminary character. PATIENTS: 15 eyes of 14 patients aged 38 to 82 years (mean--57 years) were treated because of intraocular tumor with the use of diode laser transpupillar thermotherapy in 13 patients primary intraocular tumor was diagnosed, and in 1 patient there was metastasis; in 13 cases tumors were localized unilaterally, whereas in 1 case they appeared in both eyes. The follow-up period (from the start of the treatment) ranged from 1 to 3 months. METHODS: All patients were treated with transpupillary thermotherapy (TTT) with the use of diode laser OcuLight SLx, IRIS Medical instruments, Inc. The power and size of the laser spots depended on the tumor size and pigmentation. Mean power used for the treatment was 600 mW, while mean exposure time was 1 minute. RESULTS: Altogether, within 15 treated eyes in 8 cases regression, in 6--stabilization and in 1--progression was stated. As to complications and side effects, visual field scotomas in the treated area as well as deterioration of visual acuity were found during the treatment. In 2 cases a slight improvement of visual acuity was found. CONCLUSIONS: In selected cases transpupillary thermotherapy (TTT) can be effective especially in regard to small tumors (height up to 4.5 mm). Probably in the future it will be the only method of treatment. Treatment of larger tumors (height more than 4.5 mm) should be connected with the use of ruthenium plaque (106Ru). All complications and side effects found in the course of treatment were not dangerous to the eye (small hemorrhage) and were relatively easily tolerated by the patients. With longer follow-up of greater group of patients probably it will be possible to establish optimal parameters, advantages and possible other complications of such therapy.

Adult↗

PubMedDate not supplied

High-resolution MR cisternography of the cerebellopontine angle, obtained with a three-dimensional fast asymmetric spin-echo sequence in a 0.35-T open MR imaging unit.

High-resolution MR cisternography performed with 3D fast asymmetric spin-echo imaging (3D fast spin-echo with an ultra-long echo train length and asymmetric Fourier imaging) was optimized in a 0.35-T open MR imaging unit. The 0.35- and 1.5-T images of the two volunteers and three patients with acoustic schwannomas were then compared. The optimal parameters for images obtained by 3D fast asymmetric spin-echo imaging at 0.35 T were as follows: field of view, 15 cm; matrix, 256 x 256 x 40; section thickness, 1 mm; echo train length, 76; and imaging time, 10 minutes 44 seconds. Scans obtained from both normal volunteers showed the facial, cochlear, and superior and inferior vestibular nerves separately in the internal auditory canal on both 0.35- and 1.5-T images. All three acoustic schwannomas were depicted on both 0.35- and 1.5-T images. Screening for disease at the cerebellopontine angle and in the internal auditory canal, without the administration of contrast material on a low-field open MR imaging unit and within a clinically acceptable imaging time, may be possible. Further controlled prospective studies are required, however, before implementation on a wide basis. If proved effective, this may be of particular value for reducing healthcare costs and for imaging claustrophobic and pediatric patients in an open system.

Cerebellopontine Angle↗

PubMedDate not supplied

Alterations of tumour cells, stroma and apoptosis in rat prostatic adenocarcinoma following treatment with histamine, interleukin-2 and irradiation.

The present study was designed to determine whether IL-2 and histamine alone, or in combination could modulate the effects of irradiation on Dunning (R3327) rat adenocarcinomas at the cellular level. Copenhagen x Fisher rats carrying bilateral tumours in the flank were used. When the tumours had a median volume of 150 mm3, one group of rats was treated with histamine alone (4 mgkg-1 subcutaneously on week days), another group with interleukin-2 (IL-2) alone (425 IU kg-1 continuous infusion) and a third group with both histamine and IL-2 during 6 weeks. Irradiation was given one week after the onset of treatment with histamine and/or IL-2, with a linear accelerator 6 MV, in a dose of 6 Gy/day for 3 days to the tumour of one side, while the other side served as control. Morphometric analyses of the amount of cystic structures, volume density for tumour epithelium, stroma and acinar lumina, the number of activated macrophages and natural killer cells (NK-cells) and in situ detection of apoptotic cells was carried out 5 weeks after the irradiation, when the experiment was ceased. The combination of IL-2 with histamine and irradiation significantly augmented the reduction of tumour cells (p < 0.002) and increased the number of apoptotic cells (p < 0.007) compared to irradiation alone. The number of cystic structures within tumour tissue increased in all tumours that received histamine, but was most pronounced in the three combination group. A strong negative correlation between the epithelial cells and the apoptotic index (rs = -0.61, p < 0.0001) and a strong positive correlation between the stroma and the apoptotic index (rs = 0.59, p < 0.001) was found. A prominent infiltration of activated macrophages was observed in the irradiated group. This infiltration was impaired by the drugs. The results suggested that the used three modality treatment could be of value in increasing the efficacy of local radiotherapy concomitantly with a most plausible effect on micrometastatic spread. The results also propose that volume measurements alone are not an optimal parameter when evaluating effects of new treatment modalities.

Adenocarcinoma↗

PubMed1999

Metaphase chromosome accumulation and flow karyotypes in rice (Oryza sativa L.) root tip meristem cells.

Highly efficient cell synchronization and metaphase chromosome accumulation in rice root tip cells were achieved. Flow cytometric analysis was performed for obtaining optimal parameters to synchronize the cell cycles. High mitotic indices (about 57.6% in root tip meristemic area) were obtained by treating seedlings with 0.5 cm length using 0.5 mM hydroxyurea at 30 degrees C for 4 h, incubating in a hydroxyurea-free solution for 30 min, and then treating with 0.3 microM trifluralin for 3 h. After trifluralin treatment, incubation in distilled water for 15 min reduced chromosome clumping on metaphase spread. Uniformity of seed germination at the time of treatment is a critical parameter for obtaining high metaphase index. Isolated rice chromosomes were suitable for flow cytometric analysis and chromosome sorting. The morphology of flow sorted metaphase chromosomes was intact.

Cell Cycle↗

PubMed1999

Biodegradation of engine oil in soil.

Laboratory experiments were conducted with the aim of bioremediation of sandy soil from engine oil in 5% concentration. Bacterial strains, active in degrading oil hydrocarbons as a sole source of carbon and energy were selected and identified. Optimal parameters, such as concentration of inorganic nutrients (expressed as C:N and C:P ratio) and the size of inoculum were established in experiments on 1% engine oil biodegradation. Process enhancing role of surfactants addition, the application of immobilized biomass and reinoculations was also evaluated.

Bacteria↗

PubMedDate not supplied

[Optimization of conditions for cultivation of the basidiomycete Coriolus hirsutus--producer of extracellular laccase].

The effects of various factors on the biosynthesis of extracellular laccase (EC 1.14.18.1) by the basidiomycete Coriolus hirsutus (Wulf.: Fr.) Quel. no. 072 during submerged cultivation were examined. Optimal parameters for cultivation in a fermenter of 10 l were determined: temperature, 28 degrees C; stirrer rotation speed, 160 rpm; and the inoculum volume, 15% of the working volume of the fermenter. The filtrate contained peroxidase, laccase, and phenol oxidase activities and displayed a high thermal stability.

Basidiomycota↗