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At least 811 records · Page 45Linked to original sources
PubMed1999

Measurement of specific gravity as a surrogate for urinary flow rate--a singular study.

About two hundred and fifty urine samples were collected some years ago in the course of experimental exposure of one individual to benzene vapor. Phenol concentrations and specific gravities were recorded, together with the volume of urine samples and the times of voiding. Review of this data shows that the reciprocal of specific gravity minus unity (SG-1) measured by refractometer correlated closely with urinary flow rate, while those using the traditional urinometer correlated much less closely. If this is valid for all workers, then refractometer measurement of specific gravity may be used as a surrogate for flow rate. More consistent interpretation of spot urine sampling results as a measure of intake of hazardous substances through occupational exposure is then possible. This is particularly the case if used in conjunction with the formula developed and tested by Araki et al. for flow rate adjustment.

Benzene↗
PubMed2000

Estimates of particle hygroscopicity during the Southeastern Aerosol and Visibility Study.

Aerosol water content was determined from relative humidity controlled optical particle counter (ASASP-X) size distribution measurements made during the Southeastern Aerosol and Visibility Study (SEAVS) in the Great Smoky Mountains National Park during summer 1995. Since the scattering response function of the ASASP-X is sensitive to particle refractive index, a technique for calibrating the ASASP-X for any real refractive index was developed. A new iterative process was employed to calculate water mass concentration and wet refractive index as functions of relative humidity. Experimental water mass concentrations were compared to theoretically predicted values assuming only ammonium sulfate compounds were hygroscopic. These comparisons agreed within experimental uncertainty. Estimates of particle hygroscopicity using a rural aerosol model of refractive index as a function of relative humidity demonstrated no significant differences from those made with daily varying refractive index estimates. Although aerosol size parameters were affected by the assumed chemical composition, forming ratios of these parameters nearly canceled these effects.

Aerosols↗
PubMedDate not supplied

Improved efficiency of budesonide nebulization using surface-active agents.

Our aim was to improve the efficiency of nebulised budesonide using surface-active agents. Cationic, anionic, and nonionic detergents were added to commercial budesonide suspension, and the particle size distribution during nebulization was measured using both cascade impaction and laser diffraction. Our results showed that the emitted dose was increased after addition of cationic (p < 0.001) and nonionic detergents (p < 0.01) compared with the commercial formulation alone. The respirable fraction was increased for all detergent formulations (p < 0.001) compared with the commercial formulation. We concluded that cationic and nonionic detergent increased the total output of budesonide from the Sidestream. All detergent formulations increased the respirable fraction of nebulized budesonide.

Administration, Inhalation↗
PubMed2005

Histochemical and topo-optical investigations on tissue-isolated and in vitro amyloid fibrils.

An improved microscopic slide preparation for staining of tissue-isolated and in vitro amyloid fibrils is described in detail. Specimens were prepared by slow drying of an amyloid fibril suspension on aminoalkyl-silanised glass slides underneath a coverglass. The purpose of this method is to obtain microscopically visible fibers. Polarization microscopy was performed on unstained fibers in different embedding media, on fibers stained with Congo red, toluidine blue, 1,9-dimethylmethylene blue, anisotropic PAS reaction and Sudan black. Results were identical in 8 tissue-isolated amyloid fibril preparations. The refractive index of amyloid was about 1.5, as expected for protein fibrils. Congo red-stained fibrils showed yellow or blue-green polarization colors, while staining with toluidine blue or 1,9-dimethylmethylene blue induced green or orange polarization colors. The latter dyes stained the fibrils even in buffers with low pH or high ionic strength, pointing to strong acidic groups like sulphates in amyloid. The anisotropic PAS reaction for selective demonstration of periodate reactive carbohydrates in tissue-isolated amyloid fibrils was positive. Thus, linearly ordered acidic groups and carbohydrate residues could be detected for the first time in tissue-isolated amyloid fibrils using an improved technique for microscopic slide preparation on one side and topo-optical reactions on the other.

Amyloid↗
PubMed2004

Study of bovine hemoglobin dissociation by multiangle laser light-scattering method.

Hemoglobin (Hb) is an oligomeric protein, composed of four monomeric subunits. Hb molecule may undergo dissociation from a single native tetramer to two dimmers, which is called hemoglobin dissociation. In this article the dissociation of bovine Hb is studied by measurment of the average MW of the samples using the multiangle laser light-scattering method. Advanced multiangle laser light-scattering technique is a powerful method to determine the absolute molecular weights of the protein in solution. Two different methods, microbatch multiangle light-scattering (MALS) and on-line size-exclusion high-performance liquid chromatography light scattering with refractive index detector, are used to measure the average molecular weight of bovine Hb in different concentration respectively. The results of the two methods are agreed well. From the results, it can be concluded that the average molecular weigh of bovine Hb will be about 54 kDa when the bovine Hb concentration is more than 1.5 mg/mL, and will be about 36 kDa when the concentration is less than 0.03 mg/mL. The other conclusion, which can be derived from these results, is that the dissociation of bovine Hb is related with the pH and the tetramer appears to be more stable in the pH range of 6-9.

Animals↗
PubMed2000

Particle size determination of a three-component suspension using a laser-scattering particle size distribution analyzer.

In this study, a rapid and accurate particle size determination method using a light-scattering particle size analyzer was developed to measure the particle size and size distribution of a suspension containing three solid components: clotrimazole, triamcinolone, and sarafloxacin, which have different refractive indices. To ensure that data represent the size distribution of the primary particles of the suspension, the optimal sonication prior to and during measurement was determined. It was found that the results obtained using the average relative refractive index (RRI) of the three components agreed with the results obtained using three individual RRIs. In addition, the results from two analysts demonstrated good reproducibility of this method. The size distribution data of the suspension were also compared to those of the bulk drugs. The results showed that the median particle size of this three-component suspension is relatively close to that of clotrimazole, which accounts for 80% of solid particles in the suspension. Furthermore, the results obtained using the light-scattering technique were comparable to those obtained using a polarized light microscope equipped with an image analyzer, indicating acceptable accuracy of this technique.

Anti-Infective Agents↗
PubMed2003

HPFP, a model propellant for pMDIs.

A novel model propellant for the study of the properties of pMDIs (pressurized metered-dose inhalers) at atmospheric pressure is proposed and extensively characterized. The reasons for the choice of this liquid, with its advantages and drawbacks, are explained and justified. Comparison with existing fluorinated propellants is also documented.

Aerosol Propellants↗
PubMed1958

An anterior-posterior gradient of refractive index in the ameba and its significance in ameboid movement.

Sustained locomotion in Amoeba proteus and Amoeba dubia results in the establishment of a measureable gradient of refractive index along the anterior-posterior axis of the cell, provided thickness of the specimens is kept constant by even compression under a selected coverglass supported by quartz beams of uniform diameter. The tail region of the ameba develops a higher refractive index, indicative of from 6 to 40 per cent more organic matter (expressed as protein) there than present in the front. This gradient fades on cessation of movement. The average protein concentrations in the crystal-free tails and fronts of 15 A. proteus were 3.9 and 3.4 per cent, respectively. In individual experiments, the tail-front difference ranged from one to eight times the accuracy of the method. Since the gradient of refractive index was shown not to result from extraction of water from the tail by the contractile vacuole, it was interpreted as displacement of water toward the anterior part of the cell during movement. It is suggested that contraction of the ectoplasm drives forward a "tide" of syncretic fluid, the anterior border of which is visible as the hyaline cap, which contains less than 1 per cent protein. The movement of the granular endoplasm into the hyaline cap would then complete the cycle by imbibition of the fluid tide. The theoretical positions of Pantin and of Dellinger have been combined in the proposal that ameba cytoplasm consists of a network of a contractile phase which is able to expel (by syneresis) a highly mobile fluid phase. Some other possible interpretations are discussed.

Amoeba↗
PubMed1979

Quantitative reflection contrast microscopy of living cells.

Mammalian cells in culture (BHK-21, PtK2, Friend, human flia, and glioma cells) have been observed by reflection contrast microscopy. Images of cells photographed at two different wavelengths (546 and 436 nm) or at two different angles of incidence allowed discrimination between reflected light and light that was both reflected and modulated by interference. Interference is involved when a change in reflected intensity (relative to glass/medium background reflected intensity) occurs on changing either the illumination wavelength or the reflection incidence angle. In cases where interference occurs, refractive indices can be determined at points where the optical path difference is known, by solving the given interference equation. Where cells are at least 50 nm distant from the glass substrate, intensities are also influenced by that distance as well as by the light's angle of incidence and wavelength. The reflected intensity at the glass/medium interface is used as a standard in calculating the refractive index of the cortical cytoplasm. Refractive indices were found to be higher (1.38--1.40) at points of focal contact, where stress fibers terminate, than in areas of close contact (1.354--1.368). In areas of the cortical cytoplasm, between focal contacts, not adherent to the glass substrate, refractive indices between 1.353 and 1.368 were found. This was thought to result from a microfilamentous network within the cortical cytoplasm. Intimate attachment of cells to their substrate is assumed to be characterized by a lack of an intermediate layer of culture medium.

Animals↗
PubMed1993

Mid- and far-infrared spectroscopy of ices: optical constants and integrated absorbances.

Laboratory spectra through the mid-infrared (4000 to 500 cm-1 [2.5-20 micrometers]) have been used to calculate the optical constants (n and k) and integrated absorption coefficients (A) for a variety of pure and mixed molecular ices of relevance to astrophysics. The ices studied were H2O, CH3OH, CO2, OCS, CH4, CO2 + CH4, CO2 + OCS, CO + CH4, CO + OCS, O2 + CH4, O2 + OCS, N2 + CH4, N2 + OCS, H2O + CH4, H2O + OCS, and H2O + CH3OH + CO + NH3. In addition, the measurements have been extended through the far-infrared (500 to 50 cm-1 [20-200 micrometers]) for the H2O, CH3OH, and H2O + CH3OH + CO + NH3 ices.

Astronomy↗
PubMed1994

A new phase function approximating to Mie scattering for radiative transport equations.

A new scattering phase function is presented to approximate the accurate phase function from Mie theory. The new phase function demonstrates much better agreement with Mie theory for biomedical media (with the mean cosine of scattering angles g > 0.8) than the Henyey-Greenstein phase function, which has been widely adopted by researchers in the biomedical optics field. Using the new phase function as the integral kernel in the radiative transport equation, an analytical result for the integral term of the equation is obtained for highly aligned beams. This may lead to a semi-analytical solution to the time-dependent radiative transport equation for time-resolved spectroscopy.

Algorithms↗
PubMed1995

The influence of glucose concentration upon the transport of light in tissue-simulating phantoms.

The effect of glucose upon the transport of light in tissue-simulating phantoms is shown and its possible application for non-invasive glucose monitoring in diabetic patients is discussed. The aim of this paper is to investigate the physical background of this effect. The presence of glucose in an aqueous solution increases its refractive index and therefore has an influence upon the scattering properties of particles suspended in solution. Experimental data on the effect of glucose upon the scattering coefficient and the phase function of aqueous suspensions of spherical polystyrene particles are presented for near-infrared wavelengths and compared to values predicted by Mie theory. The subsequent effect upon light transport in multiple scattering, tissue-simulating phantoms is demonstrated experimentally in a slab geometry and theoretically by applying diffusion theory. It is furthermore shown that optional measurements in the frequency domain allow changes of absorption and scattering coefficient to be separately determined. The possible magnitude of this glucose effect in tissue in vivo is discussed.

Glucose↗
PubMed1997

The optical properties of lung as a function of respiration.

Lung consists of alveoli enclosed by tissue and both structures contribute to volume-dependent scattering of light. It is the purpose of this paper to determine the volume-dependent optical properties of lung. In vivo interstitial fibre measurements of the effective attenuation coefficient mu eff at 632.8 nm differed during inspiration (mu eff = 2.5 +/- 0.5 cm-1) from that during expiration (mu eff = 3.2 +/- 0.6 cm-1). In vitro measurements on a piglet lung insufflated with oxygen from 50 to 150 ml showed the effective attenuation coefficient at 632.8 nm decreases as a function of oxygen volume in the lung (at 50 ml mu eff = 2.97 +/- 0.11 cm-1, at 100 ml mu eff = 1.50 +/- 0.07 cm-1, and at 150 ml mu eff = 1.36 +/- 0.15 cm-1). This was explained by combining scattering of alveoli (Mie theory) with optical properties of collapsed lung tissue using integrating sphere measurements. Theory and measured in vitro values showed good agreement (deviation < or = 15%). Combination of these data yields the absorption coefficient and scattering parameters of lung tissue as a function of lung volume. We conclude that the light fluence rate in lung tissue should be estimated using optical properties that include scattering by the alveoli.

Absorption↗
PubMed1997

Investigation of the effect of discrete absorbers upon the measurement of blood volume with near-infrared spectroscopy.

This paper derives an analytical model for investigating the effect of the distribution of absorbers upon light attenuation in a scattering medium. Results from this are found to agree with those of Monte Carlo simulations. The implications of this model are then examined for their likely effect upon the measurement of cerebral blood volume (CBV) using near-infrared (NIR) spectroscopy. We conclude that, given the small diameter of the majority of cerebral blood vessels, the distribution of the blood will have little effect upon the measurement of CBV. Where changes to the blood volume occur in the larger (> 0.2 mm diameter) vessels on the surface of the brain, NIR spectroscopy is likely to underestimate the change.

Animals↗
PubMed1999

Phase contrast enhancement of x-ray mammography: a design study.

This paper explores the application to mammography of phase contrast produced by variations in x-ray refractive index. As a spatially coherent x-ray beam propagates through an x-ray transparent medium, the phase of the incident wavefront becomes modified in a manner related to the electron density of the medium. The resulting phase gradient across the wavefront is equivalent to a small change in direction of the propagation of the wave. For a general object, the change in propagation direction will vary from point to point depending on the structures within the object. The net effect can be recorded in a radiographic image using an appropriate geometry to produce the visual appearance of edge enhancement at interfaces between materials with differing x-ray refractive indices. Normally these materials will also have differences in attenuation coefficient, so the overall effect is to increase the visibility of interfaces between materials. It is proposed that mammographic images can be subtly enhanced by the use of phase contrast information to overcome some of the known limitations of the imaging process whilst leaving the gross radiological appearance of the images substantially unchanged. The design trade-offs required to utilize phase contrast information were investigated using a conventional mammographic x-ray generator and film-screen system. The Leeds TORMAM mammographic image quality test object was then used to demonstrate a considerable improvement in image quality for the phase contrast enhanced images over those produced in the conventional geometry with no increase in radiation dose to the patient. The results are discussed in terms of their possible practical application.

Breast Diseases↗
PubMed2000

Computed tomography of x-ray index of refraction using the diffraction enhanced imaging method.

Diffraction enhanced imaging (DEI) is a new, synchrotron-based, x-ray radiography method that uses monochromatic, fan-shaped beams, with an analyser crystal positioned between the subject and the detector. The analyser allows the detection of only those x-rays transmitted by the subject that fall into the acceptance angle (central part of the rocking curve) of the monochromator/analyser system. As shown by Chapman et al, in addition to the x-ray attenuation, the method provides information on the out-of-plane angular deviation of x-rays. New images result in which the image contrast depends on the x-ray index of refraction and on the yield of small-angle scattering, respectively. We implemented DEI in the tomography mode at the National Synchrotron Light Source using 22 keV x-rays, and imaged a cylindrical acrylic phantom that included oil-filled, slanted channels. The resulting 'refraction CT image' shows the pure image of the out-of-plane gradient of the x-ray index of refraction. No image artefacts were present, indicating that the CT projection data were a consistent set. The 'refraction CT image' signal is linear with the gradient of the refractive index, and its value is equal to that expected. The method, at the energy used or higher, has the potential for use in clinical radiography and in industry.

Models, Statistical↗
PubMed2002

Towards functional 3D T-ray imaging.

We review the recent development of T-ray computed tomography, a terahertz imaging technique that allows the reconstruction of the three-dimensional refractive index profile of weakly scattering objects. Terahertz pulse imaging is used to obtain images of the target at multiple projection angles and the filtered backprojection algorithm enables the reconstruction of the object's frequency-dependent refractive index. The application of this technique to a biological bone sample and a plastic test structure is demonstrated. The structure of each target is accurately resolved and the frequency-dependent refractive index is determined. The frequency-dependent information may potentially be used to extract functional information from the target, to uniquely identify different materials or to diagnose medical conditions.

Algorithms↗