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PubMed1985

Regional and systemic effects of short-term intense muscular work on plasma concentration and content of total and ionized calcium.

Isokinetic work with one leg was carried out with maximal force for 2 min by five healthy subjects. The concentrations of plasma total calcium and of ionized calcium in the effluent from the leg increased by a mean of 13.6 +/- 1.8% (SD) and 16.2 +/- 2.0%, respectively. The corresponding rises in the resting arm were 7.7 +/- 4.3% and 8.1 +/- 3.0%. There was a close correlation (r = 0.86; P less than 0.001) between the degree of exercise-induced acidosis and the rise in plasma ionized calcium. However, the calcium values normalized both in the leg and in the arm within 5 min after the exercise and were similar at the two measuring sites despite a lower pH in the leg sample. During work there was a reduction of the plasma volume of 11.2 +/- 6.0% in the regional (femoral) and 12.4 +/- 4.2% in the systemic (antecubital) sample (P less than 0.001 compared to baseline values for both measurements). When adjustments were made for the reduction in plasma volume as well as for acidosis it was evident that, despite the apparent increases in the calcium concentrations, there was a net reduction of the plasma ionized calcium content (the total amount of plasma ionized calcium). This decrease was significantly (P less than 0.05) more pronounced in the exercising leg than in the systemic circulation but the difference could largely be explained by higher calcium-lactate complex formation in the leg.

Adult↗
PubMed1989

Effects of heparin on serum ionized calcium and haemodynamics during coronary artery surgery.

Heparin has been reported to possess hypotensive and vasodilating properties when given in 3 mg/kg bolus injection. The haemodynamic effect has been thought to be related to an acute lowering of serum ionized calcium levels. The effects of heparin on haemodynamics and ionized calcium were compared with saline in 30 patients during coronary artery surgery before the commencement of cardiopulmonary bypass. There were no significant differences in haemodynamics or ionized calcium levels between heparin or saline during the observation period of 10 min. The results are at variance with some previous findings, and suggest that the hypotensive reaction occasionally seen after heparin is given is not mediated by the reduction of serum ionized calcium.

Calcium↗
PubMed1990

Effect of fluoride addition on ionized calcium in salivary sediment and in saliva containing various amounts of solid calcium fluoride.

The aim of the present study was to estimate the fluoride concentrations necessary for the precipitation of calcium fluoride or calcium fluoride-like substances in saliva and salivary sediment, in the presence of various amounts of chemically pure calcium fluoride. Fluoride was added in increments to whole saliva to which solid calcium fluoride had been added. The ionized calcium concentration was determined immediately after centrifugation. In salivary sediments and saliva with no calcium fluoride added the ionized calcium concentration was nearly independent of the fluoride concentration added below 10 and 20 mmol/l, respectively, and at fluoride concentration above 15 and 25 mmol/l, respectively, nearly no ionic calcium was detected. In the presence of calcium fluoride the ionized calcium concentration decreased rapidly with increasing concentrations of fluoride. The more calcium fluoride added, the lower the ionized calcium concentration at a certain fluoride level. The results suggested that in the in vivo-situation, caries preventive measures based on frequent oral exposure to low concentrations of fluoride may provide calcium fluoride or calcium fluoride-like substances, which will serve as a reservoir for fluoride.

Calcium↗
PubMed1994

Clinical and histologic appearance in enamel of primary teeth in relation to neonatal blood ionized calcium values.

The purpose of this investigation was to study the relationship between low values of blood ionized calcium measured in the first days of life postpartum and the clinical and histologic appearance of enamel of primary teeth. Twenty-five healthy children selected on the basis of optimality with known blood values of ionized calcium from the first days of life participated in a dental examination at the age of 5 yr. Twenty-four of the children contributed one exfoliated tooth each, which was histologically examined. The infants had lower mean values of ionized blood calcium on days 1 and 3 than day 5 postpartum. Thirteen of the 25 children had enamel aberrations, mainly on one tooth each. The histologic examination showed normal overall enamel morphology. The neonatal line was present in all teeth, and these lines were mostly thin. The registered findings about the enamel morphology could not, in any case, be correlated with the measured values of neonatal blood ionized calcium.

Calcium↗
PubMed1980

The effect of buffer composition and deoxygenation on the concentration of ionized magnesium inside human red blood cells.

1. A method is described in which the concentration of ionized magnesium can be measured in intact red cells. The method uses an equilibrium dialysis technique originally developed by Ferreira & Lew (1976) and Flatman & Lew (1977) where the magnesium permeability of the red cell membrane is increased with the ionophore A23187. 2. The concentration of ionized magnesium in the oxygenated cells was found to be 0.39 mM and was not greatly affected by changes in the composition of the medium. 3. The concentration of ionized magnesium in deoxygenated cells showed more dependence on the composition of the medium. Values of 0.54 and 0.62 mM were found in cells incubated in Tris- and HCO3- buffered media respectively. The difference probably reflects increased competition between chloride and 2,3-diphosphoglycerate for common binding sites on haemoglobin in Tris-buffered cells. 3. Only a small increase of 0.16-0.22 mM was found in the concentration of ionized magnesium when the cells were deoxygenated. These changes are smaller than had been anticipated from estimates of the binding of ATP and 2,3-diphosphoglycerate to oxy- and deoxyhaemoglobin (Bunn, Ransil & Chao, 1971; Berger, Jänig, Gerber, Ruckpaul & Rapoport, 1973; Gerber, Berger, Jänig & Rapoport, 1973) and are unlikely to alter greatly the operation of magnesium-dependent metabolic or transport systems.

Buffers↗
PubMed2004

Determination of dose-area product from panoramic radiography using a pencil ionization chamber: normalized data for the estimation of patient effective and organ doses.

The aims of the present study were (a) to investigate the potential of pencil ionization chamber to be used for the determination of dose-width product (DWP) and dose-area product (DAP) from panoramic radiographic exposures and (b) to provide data normalized to DAP for the determination of patient effective and gonadal dose from panoramic radiography performed in any laboratory. A pencil ionization chamber commonly used to measure CT dose index (CTDI) in CT scanners was employed to determine DWP for various combinations of panoramic exposure settings at the beam exit slit of a Cranex Tome panoramic x-ray unit (Soredex, Helsinki, Finland). DWP values were also measured using an array of thermoluminescence dosimeters. Reproducibility of the DWP measurement was tested. The effect of milliamperage and kilovoltage of panoramic exposures on DWP was investigated. DAP was estimated using the value of DWP measured using the pencil ionization chamber and the beam exit slit length measured using dosimetric film attached on the beam exit slit. A Rando anthropomorphic phantom appropriately loaded with thermoluminescent dosimeters (TLDs) was used to obtain organ dose and effective dose values from panoramic radiography. Reproducibility of DWP determination using the proposed method was better than 1.5%. DWP was found to be linearly related to milliamperage (r>0.999, p<0.001) and to kilovoltage raised in a power ranging from 2.18 to 2.55. DWP measured using the pencil chamber was found to be up to 11% higher than the corresponding values determined using TLD array. The panoramic exposure obtained with settings appropriate for the typical adult patient was found to result in 0.008 mSv patient effective dose, 0.0002 mGy gonadal dose, and 11.3 cGy cm2 DAP. The use of a pencil ionization chamber is proposed for the determination of DWP and DAP from panoramic radiographic exposures. Normalized data over DAP were provided for the determination of patient effective and gonadal dose from panoramic radiography.

Body Burden↗
PubMedDate not supplied

Stem corrections for ionization chambers.

Ionization chambers often exhibit a stem effect, caused by interactions of radiation with air near the chamber end, or with dielectric in the chamber stem or cable. These interactions contribute to the apparent measured exposure. To determine the stem efffect for several common ionization chamber systems, exposures were measured with TLD capsules placed at the center of 60Co fields of various sizes. These exposure measurements then were repeated with various ionization chamber systems, including two Victoreen R meters (25- and 100-R chambers), a Capintec 192 dosimeter with a Farmer 0.6-cm3 probe, a PTW transit dose probe, and an EG and G IC-18 probe with a Keithley 610-B electrometer. From a comparison of TLD and ionization chamber measurements of the variation in exposure rate with field size, stem corrections for the different systems were determined within 1%.

Cobalt Radioisotopes↗
PubMedDate not supplied

Ionization produced by electron beams beneath curved surfaces.

Ionization produced by high-energy (6-18 MeV) electrons beneath cylindrical surfaces has been measured and compared to ionization at corresponding locations under a flat surface. Results are reported as ionization ratios over a range of depths, off-axis distances, radii of curvature, and electron energies. Phantoms with cylindrical entrance surfaces (radii 6-15 cm) were utilized to simulate patient contours. Measurements reveal that ionization ratios may depart from unity by as much as 50% and that a simple shifting of isodose curves may be insufficient to compensate for perturbation in electron dose distribution introduced by curved surfaces.

Electrons↗
PubMedDate not supplied

Sampling methods for a matrix ionization chamber system.

To achieve increased image acquisition speed or better image quality, several read-out methods for a matrix ionization chamber system have been investigated. In this device, which is applied for portal imaging in radiation therapy, 256 x 256 small liquid-filled ionization chambers are scanned by switching the polarizing voltage applied to rows of chambers. The ionization current of each column is measured by a separate amplifier. In this approach, instead of measuring row by row, more complex switching schemes can be applied for the polarizing voltage. These schemes are useful either for varying speed and spatial resolution of the imaging device or for coded sampling of the ionization signal. The former option allows for doubling or quadrupling the acquisition speed with a small loss in image quality, or for obtaining a large improvement in signal-to-noise ratio at the cost of image resolution. In the latter option, coded sampling, the image is reconstructed mathematically from the measured signals. It is shown that in this case the application of Hadamard or derived matrices for sampling leads, under certain circumstances, to a noise reduction in the reconstructed image.

Humans↗
PubMedDate not supplied

A simple method of producing depth ionization data for electron energy constancy check.

A simple method has been developed to reproduce depth ionization data of electron beams for energy determination. The method utilizes a simple set of equipment, a combination of a specially designed wedge-shaped polystyrene phantom and a linear array of detectors, to collect the necessary data. The wedge-shaped phantom provides varying depths to various detectors in the array. The ionization readings received from the detectors were corrected for off-axis ratio and plotted against corresponding ray-line depths to produce depth ionization curves. The instrument setup was fast and simple. The relevant data, for a high-energy linear accelerator with multiple electron energies, were collected in minutes. The depths of 80% and 50% ionization determined by this method were found to differ by 2 and 3 mm, respectively, at the most, with those determined by a conventional method.

Biophysical Phenomena↗
PubMed1995

General ion recombination for ionization chambers used under irradiation conditions relevant for diagnostic radiology.

General ion recombination has been studied under irradiation conditions relevant for diagnostic radiology and with four different ionization chambers. When the exposure time is appreciably shorter than the ion transit time, the exposure can be designated as pulsed irradiation. On the contrary, for relatively long irradiation times, the term continuous irradiation can be applied. Recombination was estimated by measuring the collected charge at various collecting potentials of the ionization chamber. This is a well-known method in radiotherapy, but unfortunately it cannot be used in diagnostic radiology with typical exposure meters, since they do not offer the option of varying the collecting potential. For exposures with diagnostic x-ray units, an alternative approach is to vary the exposure or exposure rate over a wide range at a constant collecting potential. Experimental and theoretical estimates of ion recombination did not yield similar values. This might be due to several causes, such as differences between the actual and the nominal dimensions and volumes of the ionization chambers, due to errors and uncertainties in the physical parameters used in the theoretical models or due to deviations of the shape of the ionization chambers from the perfect cylindrical or parallel plate geometry. For better accuracy, corrections for recombination losses should therefore be based on experimental verification rather than on theoretical models.

Gamma Rays↗
PubMed1996

kQ factors for ionization chamber dosimetry in clinical proton beams.

We discuss a formalism for clinical proton beam dosimetry based on the use of ionization chamber absorbed dose-to-water calibration and beam quality correction factors. A quantity kQ, the beam quality correction factor, is defined which corrects the absorbed dose-to-water calibration factor ND,w in a reference beam of quality Q0 to that in a user's beam of quality Q1. This study of proton beam quality correction factors used 60Co (kQ gamma) and proton (kQp) reference beams. The kQ gamma factors were measured using combined water calorimetry and ionometry for PTW and Capintec-Farmer-type ionization chambers, and were computed from standard dosimetry protocols. Agreement between measured and calculated kQ gamma values for both chambers was found within 1.2% in the plateau region for a monoenergetic 250-MeV beam and within 1.8% at the spread-out Bragg peak for a 155-MeV range-modulated beam. Comparison of absorbed doses to water determined in the range-modulated 155-MeV beam was performed with the PTW chamber using three calibration methods: Ngas calibration (AAPM Report 16), ND,w,gamma calibration in a 60Co beam in conjunction with a kQ gamma factor, and ND,w,p calibration in a proton beam in conjunction with a kQp factor. Absorbed doses to water obtained with the three methods agreed within 2% when ionization chamber dosimetry data were analyzed using the proton W-value for air from the AAPM Report 16 and the ICRU 49 proton stopping powers. The use of the proton-calibrated reference ionization chamber, in conjunction with the beam quality correction factor kQp, significantly reduced the systematic uncertainty of the absorbed dose determination.

Biophysical Phenomena↗
PubMed1998

Determination of saturation charge and collection efficiency for ionization chambers in continuous beams.

The procedure recommended by radiation dosimetry protocols for determining the collection efficiency f of an ionization chamber assumes the predominance of general recombination and ignores other charge loss mechanisms such as initial recombination and ionic diffusion. For continuous radiation beams, general recombination theory predicts that f can be determined from a linear relationship between 1/Q and 1/V2 in the near saturation region (f > 0.7), where Q is the measured charge and V the applied chamber potential. Measurements with Farmer-type cylindrical ionization chambers exposed to cobalt-60 gamma rays reveal that the assumed linear relationship between 1/Q and 1/V2 breaks down in the extreme near-saturation region (f > 0.99) where Q increases with V at a rate exceeding the predictions of general recombination theory. A comprehensive model is developed to describe the saturation characteristics of ionization chambers. The model accounts for dosimetric charge loss (initial recombination, ionic diffusion, and general recombination) and nondosimetric charge multiplication in an ionization chamber, and suggests that charge multiplication plays a significant role under typical chamber operating conditions (300 V) used in radiation dosimetry. Through exclusion of charge multiplication from the measured chamber signal Q, the model predicts the breakdown of the 1/Q vs 1/V2 relationship and shows that the final approach to saturation is governed by initial recombination and ionic diffusion which are characterized by a linear relationship between 1/Q and 1/V. Collection efficiencies calculated with this model differ by up to 0.4% from those determined through a rigorous application of general recombination theory alone.

Biophysical Phenomena↗
PubMed1999

Measured overall perturbation factors at depths greater than dmax for ionization chambers in electron beams.

In electron beam dosimetry the perturbation effect in the medium by the ionization chamber cavity is accounted for by introducing a replacement correction factor, P(repl). Another perturbation correction factor, denoted as P(wall), is due to the materials of the walls of the parallel-plate chamber differing from the phantom material. Because of the difficulties in separating these two components, we measure the overall perturbation factor, p(q) = P(repl)P(wall). A distinct advantage of parallel-plate ionization chambers over cylindrical chambers is that p(q) has been shown to be close to unity at the standard calibration depth, d(max). However, for many dosimetry applications it is necessary to know the overall perturbation factor at depths greater than d(max). We measured the overall perturbation factor at depths greater than d(max) (approximating the 95%, 90% and 50% depth dose) for a Farmer-type cylindrical ionization chamber and three parallel-plate ionization chambers. We assumed that p(q) for the NACP chamber is unity at these measurement depths. The depth dependence for the other chambers was then measured relative to the NACP chamber. The mean energy at depth, E(d), and percentage depth dose gradient ranges studied were 1.9-18.5 MeV and 0 to 4.5%/mm, respectively. For the other two parallel-plate chambers, we find p(q) to be unity at depths where the percent depth dose is greater than 90%, but it deviates from unity at deeper depths, where the dose gradients exceed about 2.5%/mm. For the cylindrical chamber, p(q) values at depths greater than d(max) were found to be in good agreement with those in TG 21, where the energy at depth, E(d), is used to evaluate p(q).

Calibration↗
PubMed2000

Use of a radioactive check device for redundancy check of ionization chambers.

The use of a radioactive check device containing Strontium 90 was investigated to carry out the redundancy checks of Farmer-type ionization chambers. It was not possible to meet the recommended tolerance limits of the redundancy checks without taking into account the angular response of the ionization chambers. The ionization chambers exhibited a maximum variation of 1% in the angular response in this check device. After accounting for the angular response the maximum variation of the short-term repeatability was 0.14% with a standard deviation of +/-0.05%. The long-term constancy checked over a period of nine months was less than +/-0.6% for measurements, taking into account the angular response of the ionization chambers. No significant effect of the background radiation levels was observed on the measurements.

Humans↗
PubMed2004

Mass spectrometry sampling under ambient conditions with desorption electrospray ionization.

A new method of desorption ionization is described and applied to the ionization of various compounds, including peptides and proteins present on metal, polymer, and mineral surfaces. Desorption electrospray ionization (DESI) is carried out by directing electrosprayed charged droplets and ions of solvent onto the surface to be analyzed. The impact of the charged particles on the surface produces gaseous ions of material originally present on the surface. The resulting mass spectra are similar to normal ESI mass spectra in that they show mainly singly or multiply charged molecular ions of the analytes. The DESI phenomenon was observed both in the case of conductive and insulator surfaces and for compounds ranging from nonpolar small molecules such as lycopene, the alkaloid coniceine, and small drugs, through polar compounds such as peptides and proteins. Changes in the solution that is sprayed can be used to selectively ionize particular compounds, including those in biological matrices. In vivo analysis is demonstrated.

Journal Article↗
PubMed1986

Combined Determination of Poly-beta-Hydroxyalkanoic and Cellular Fatty Acids in Starved Marine Bacteria and Sewage Sludge by Gas Chromatography with Flame Ionization or Mass Spectrometry Detection.

Extraction of lipids from bacterial cells or sewage sludge samples followed by simple and rapid extraction procedures and room temperature esterification with pentafluorobenzylbromide allowed combined determinations of poly-beta-hydroxyalkanoate constituents and fatty acids. Capillary gas chromatography and flame ionization or mass spectrometric detection was used. Flame ionization permitted determination with a coefficient of variation ranging from 10 to 27% at the picomolar level, whereas quantitative chemical ionization mass spectrometry afforded sensitivities for poly-beta-hydroxyalkanoate constituuents in the attomolar range. The latter technique suggests the possibility of measuring such components in bacterial assemblies with as few as 10 cells. With the described technique using flame ionization detection, it was possible to study the rapid formation of poly-beta-hydroxyalkanoate during feeding of a starved marine bacterium isolate with a complex medium or glucose and correlate the findings to changes in cell volumes. Mass spectrometric detection of short beta-hydroxy acids in activated sewage sludge revealed the presence of 3-hydroxybutyric, 3-hydroxyhexanoic, and 3-hydroxyoctanoic acids in the relative proportions of 56, 5 and 39%, respectively. No odd-chain beta-hydroxy acids were found.

Journal Article↗
PubMed2000

Ionization and photoelectric smoke alarms in rural Alaskan homes.

OBJECTIVE: To compare rates of nuisance alarms and disconnection between ionization and photoelectric smoke alarms. DESIGN: A prospective cohort study. SETTING: Four Inupiat Eskimo villages in the Northwest Arctic Borough region of Alaska, 48 km (30 mi) above the Arctic Circle. SUBJECTS: Households in 4 communities with similar populations, number of homes, mean income, size of household, and square footage per home. INTERVENTION: Two villages had photoelectric alarms installed (58 homes), and 2 other villages had ionization alarms installed (65 homes) in standard locations. Follow-up household surveys were conducted after 6 months to determine rates of false alarms and detector disconnection. All of the households that could be contacted 104/123 agreed to participate in the follow-up surveys. Main outcome measures The proportion of households experiencing false alarms and the proportion of disabled alarms in households in each of the test communities. RESULTS: Homes with ionization alarms had more than 8 times the rate of false alarms as those with photoelectric alarms. Eleven of the ionization alarms (19%) were disconnected compared with 2 of the photoelectric devices (4%). CONCLUSIONS: In small rural residences, photoelectric smoke alarms have lower rates of false alarms and disconnection. Photoelectric alarms may be the preferred choice for dwellings with limited living space or frequent false alarms.

Alaska↗