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PubMed2000

Comparison between radioactive aerosol, technegas and krypton for ventilation imaging in healthy calves.

The use of lung scintigraphy in calves necessitates the validation of a ventilation (V) imaging agent compatible with clinical applications. This study aimed at defining the value of an inhaled radioactive aerosol (99mTc-DTPA) and a 'pseudogas' (Technegas) in the assessment of regional V in healthy conscious calves by comparing 99mTc-DTPA and Technegas deposition (D) images to V(V) images obtained from the steady-state inhalation of the short half-life krypton 81 (81mKr) gas. Images were compared by analysis of radioactivity distribution in computer-generated regions of interest within the right lung and D to V ratio images were generated in order to highlight areas of mismatching between 99mTc-DTPA or Technegas and 81mKr distributions. Results of this analysis showed that the 99mTc-DTPA aerosol droplets were unable to reach the lung parenchyma because of significant particle impaction in the major conducting airways. Better definition of the ventilated lung was obtained when using Technegas because of minimal deposition in conducting airways. Furthermore, the Technegas and 81mKr distribution patterns were highly equivalent.

Aerosols↗
PubMed1979

Ventilation studies with krypton-81m.

Nuclear medicine offers well-established methods for regional lung function assessment in the preoperative evaluation of patients with lung disease. The perfusion study with Tc-99m macroaggregates is simple and can be performed without special precautions in radiation shielding. The ventilation study with Xe-133, however, requires more elaborate apparatus as well as special procedures to collect the exhaled radioactive rare gas. Nuclear medicine departments with access to short-lived radionuclides from a nearby cyclotron can use the krypton isotope Kr-81m. The physical half-life of Kr-81m is 13 s. Its gamma energy of 190 keV is optimal for gamma cameras. Kr-81m can be used as a medical isotope in spite of its short half-life. It can be eluted with a continuously flowing gas from the generator containing the mother nuclide Rb-81 which has half-life of 4.6 h. This short half-life not only simplifies radiation protection but allows repeated studies in different projections as well. Examples of comparative studies with Xe-133 and Kr-81m are presented. The importance of taking not only anterior and posterior pictures but also lateral oblique views is stressed.

Half-Life↗
PubMed2000

Effect of pressure of helium, argon, krypton, and xenon on the porosity, microstructure, and mechanical properties of commercially pure titanium castings.

STATEMENT OF PROBLEM: Porosity is a frequently observed casting defect in dental titanium alloys. PURPOSE: This study evaluated the effect of pressure of helium, argon, krypton, and xenon on the porosity, microstructure, and mechanical properties of commercially pure titanium (cp Ti) castings. MATERIAL AND METHODS: Eight groups (A-H) of 16 rectangular wax patterns each (30 mm in length, 3 mm in width, and 1 mm in depth) were prepared. The wax patterns were invested with a magnesia-based material and cast with cp Ti (grade II). Groups A, C, E, and G were cast under a pressure of 1 atm, and groups B, D, F, and H were cast under a pressure of 0.5 atm of He, Ar, Kr, and Xe, respectively. The extent of the porosity of the cast specimens was determined radiographically and quantified by image analysis. Three specimens of each group and 3 cylinders of the as-received cp Ti used as a reference were embedded in resin and studied metallographically after grinding, polishing, and chemical etching. These surfaces were used for determination of the Vickers hardness (VHN) as well. Eight specimens from each group were fractured in the tensile mode, and the 0.2% yield strength, fracture stress, and percentage elongation were calculated. Porosity was analyzed with 2-way ANOVA and the Newman-Keuls multiple range test. VHN measurements and tensile properties for specimen groups were compared with 1-way ANOVA and the Newman-Keuls multiple range test (95% significance level). RESULTS: The porosity levels per group were (%): A = 5.50 +/- 4.34, B = 0.77 +/- 1.27, C = 2.44 +/- 3.68, D = 0.06 +/- 0.12, E-H = 0. Two-way ANOVA showed that there was no detectable interaction (P<.05) between gas type and applied pressure. Metallographic examination revealed no differences in microstructure among the groups studied. A finer grain size was observed in all cast groups compared with the original cp Ti. The VHN of the as-received cp Ti was significantly greater than all the cast groups tested. Groups cast under He showed the highest VHN, yield strength, and fracture stress. No significant differences were found in percentage elongation values among the groups. CONCLUSION: Porosity and mechanical properties of cp Ti castings are dependent on the gas type and pressure, whereas the microstructure remains unaffected.

Analysis of Variance↗
PubMed1998

Measurement of krypton-85 in air at Clonskeagh, Dublin 1993-1997.

The existence of 85Kr in the air is primarily due to the reprocessing of nuclear fuel. The two major reprocessing plants in the western world are at La Hague in France and Sellafield in the UK. Prior to the commissioning of THORP at Sellafield in 1994, a programme to monitor the concentration of 85Kr in air at Clonskeagh, Dublin was commenced. While results for the measurements over the period 1993-1997 indicate that the concentration of 85Kr in the air is increasing, it has not been possible to link any particular measurement result to a krypton release from the Sellafield site. The concentration of 85Kr in air, at the existing level, does not present a significant radiological hazard. Exposure to 85Kr, which is an inert gas, results mainly in small doses to the skin. A mean annual concentration of 1.34 Bq m(-3) was calculated for 1997 which would result in a skin dose of 0.55 microSv for the year to the exposed skin of an individual.

Air Pollutants, Radioactive↗
PubMed1998

Discharges of krypton from Sellafield, 1951-1997, and the resultant doses to members of the public.

The radionulide 85Kr, which has a half-life of 10.72 years, is produced, almost exclusively, by reprocessing operations during which the fission product is released from irradiated nuclear fuel by chemical dissolution. Reprocessing plants at Sellafield, in Cumbria, have released the noble gas to atmosphere since operations commenced in 1952. Historically, krypton discharges were classified for security reasons, although these have been monitored and published by BNFL for each year since 1977. This paper reviews discharges of 85Kr from Sellafield, and consequent radiation doses, since its earliest operations. Over the past three years, discharges of 85Kr have increased due to the operation of the Thermal Oxide Fuel Reprocessing Plant (Thorp). Nonetheless, the associated annual committed effective dose to individuals remains low, peaking around 1.5 microSv a-1 to the identified critical groups, which compares with typical annual committed effective doses from natural sources of radiation of 2200 microSv. Maximum collective doses predicted from any single year of operations are 0.6 man Sv, 2 man Sv and 42 man Sv to the UK, Europe and the world respectively. Comparison may be made to natural background committed effective doses, which are of the order of 130,000 man Sva-1, 750,000 man Sva-1 and 13,000,000 man Sva-1 to the UK, EU and world populations respectively.

England↗
PubMed1976

Continuous imaging of regional myocardial blood flow in dogs using krypton-81m.

The unique physical properties of the freely diffusible gas krypton-81 m allowed continuous imaging of regional myocardial blood flow in dogs when infused into the aortic root. Regional changes in myocardial perfusion related to transient coronary artery occlusion were demonstrated both as high resolution gamma camera images and as a quantitative strip chart record.

Animals↗
PubMed1987

Right ventricular ejection fraction from equilibrium krypton-81m blood pool scans: a noninvasive predictor of pulmonary arterial hypertension.

Based on the relation between the impedance to right ventricular ejection and ejection fraction of the right ventricle (RVEF) we tested the hypothesis that radionuclide RVEF correlates inversely with pulmonary artery pressure and allows the noninvasive prediction of pulmonary hypertension. A recently developed improved equilibrium right ventricular blood pool imaging technique using ultrashort-lived krypton-81m and simultaneous right heart catheterization were combined for assessment of right ventricular systolic performance in relation to right ventricular loading in a heterogeneous group of cardiopulmonary disorders. The study group included 9 patients with pulmonary artery hypertension secondary to left ventricular dysfunction, 5 with primary pulmonary hypertension, 5 with corrected tetralogy of Fallot, and 10 normal subjects. Linear regression analysis between radionuclide RVEF and simultaneously recorded hemodynamic measurements of right ventricular loading revealed a significant inverse correlation with mean PA pressure (r = -0.87; P less than 0.001), with total pulmonary resistance index (r = -0.81; P less than 0.001) and with pulmonary vascular resistance index (r = -0.78, P less than 0.01). The sensitivity and specificity of a resting RVEF less than 40% to indicate pulmonary hypertension (mean PA pressure greater than 20 mmHg) were 71% and 100%, respectively; positive and negative predictive values were 100% and 80%, respectively. Thus, radionuclide RVEF as a parameter of right ventricular systolic performance is predominantly dependent on right ventricular afterload and has the potential for the noninvasive prediction of pulmonary hypertension in a heterogeneous group of cardiopulmonary disorders.

Humans↗
PubMed2006

Radiation damage induced by krypton ions in sintered alpha-Al2O3.

Alpha-alumina is a useful thermoluminescence (TL) dosemeter. The knowledge of its behaviour under irradiation is thus of primary importance. The purpose of this paper is to characterise the radiation damage produced by swift krypton ions using various experimental methods, namely TL, optical absorption, fluorescence and electron paramagnetic resonance (EPR). After ion irradiation, the TL intensity is shown to decrease, whereas the optical absorption rises in the whole studied wavelength range. These two phenomena seem to be related to one another. Furthermore, optical absorption measurements highlight the appearance of new absorption bands probably owing to oxygen vacancies. Induced defects are also observed in the EPR spectra of irradiated pellets. They are likely related to electronic holes trapped on oxygen ions. The concentration of these defects increases with ion fluence and fluorescence measurements indicate that some pre-existing defects such as F2(2+) centres follow the same trend up to approximately 4.1 x 10(13) ions cm(-2).

Aluminum Oxide↗
PubMed1981

Krypton-81m ventilation scintigraphy for the diagnosis of pulmonary emboli.

The value of ventilation studies in conjunction with pulmonary perfusion scintigraphies for the diagnosis of pulmonary emboli is reviewed. A retrospective study of 273 consecutive cases and comparison with 42 angiographic results provides the data base. The data are compared with previously reported results and confirm the diagnostic gain obtained by ventilation studies. Possible advantages of the use of krypton-81m for the ventilation study are suggested. Finally, with the observed prevalence of six possible scintigraphic outcomes and assuming that two outcomes are diagnostic, it can be shown that the addition of a ventilation study in the diagnostic work-up decreases the average cost of the diagnosis.

Angiography↗
PubMed1983

The evaluation of right ventricular performance using krypton-81m.

The availability of krypton-81m suitable for intravenous injection provides an easy means for assessing right ventricular function. The superimposition of the other heart chambers does not constitute a problem. The activity in the left heart is negligible and the study can be performed in the right anterior oblique position to obtain optimal separation between the right atrium and the right ventricle. Lung activity is quite high and should be corrected before computing the right ventricular ejection fraction. This correction can be accomplished by performing Tc-99m MAA perfusion scintigraphy. The measurement of the right ventricular ejection fraction appears to be reproducible with very small inter-and intraobserver variability. Good quality phase and amplitude images can be obtained with such high count rates.

Cardiac Output↗
PubMed1996

The adsorption of argon, krypton, and xenon on activated charcoal.

Charcoal adsorption beds are commonly used to remove radioactive noble gases from contaminated gas streams. The design of such beds requires the adsorption coefficient for the noble gas. Here an extension of the Dubinin-Radushkevich theory of adsorption is developed to correlate the effects of temperature, pressure, concentration, and carrier gas on the adsorption coefficients of krypton, xenon, and argon on activated carbon. This model is validated with previously published adsorption measurements. It accurately predicts the equilibrium adsorption coefficient at any temperature and pressure if the potential energies of adsorption, the micropore volume, and the van der Waals constants of the gases are known.

Adsorption↗
PubMed1983

Superimposition of Krypton-81m single photon emission CT and X-ray CT images for cerebral blood flow evaluation.

Selective arteriographic infusion of krypton-81m was used to obtain cerebral single photon emission computed tomograms. These were then superimposed on X-ray computed tomograms to assess topographically the perfusion of the entire brain. This method enhances the detecting capability for abnormal perfusion areas and has been used in 21 patients with various brain diseases.

Carotid Artery Thrombosis↗
PubMed2001

MAD phasing with krypton.

Experiments demonstrating the feasibility of Kr-edge MAD on frozen crystals as a routine method for structure determination are reported. Approximately 50% of protein crystals can be successfully derivatized by pressurization with the noble gases xenon or krypton. While Xe has produced many useful derivatives for MIR phasing over the last several years, the Xe edges (K edge = 34.6 keV, L(I) = 5.5 keV) are not easily accessible for MAD studies. As the Kr K edge (14.3 keV) is accessible on most MAD beamlines, Kr derivatization provides the additional opportunity to conduct a MAD experiment and obtain phases using only a single crystal. This paper describes the phasing of two proteins using Kr MAD: the 17 kDa Fe protein myoglobin (Mb) from sperm whale (Physeter catodon) and an 18 kDa protein (SP18) from green abalone (Haliotis fulgens). Three-wavelength data were collected at SSRL beamline 9-2 from crystals of Mb and SP18 incubated in 2.76 MPa of Kr gas for 2 min, depressurized and then flash-frozen in a stream of nitrogen gas at 100 K. MAD phases were calculated using the program SHARP and the resulting density improved with wARP. The final maps for both Mb and SP18 were of excellent quality.

Animals↗
PubMed2001

Low-resolution detergent tracing in protein crystals using xenon or krypton to enhance X-ray contrast.

Xenon and krypton show different solubilities in polar versus apolar solvents. Therefore, these noble gases should accumulate in apolar regions of protein crystals. Specifically, they should accumulate in lipid and detergent solvent regions within crystals of membrane proteins, which can be used as a basis for contrast-variation experiments to distinguish such apolar solvent regions from the aqueous phase by a low-resolution X-ray diffraction experiment. This possibility was explored with the OmpF porin, one of the general diffusion pores of the Escherichia coli outer membrane. Trigonal crystals were exposed to elevated pressures of the two noble gases (up to 10(7) Pa) for several minutes and subsequently flash-cooled to liquid-nitrogen temperatures. Both rare gases bind to a number of 'specific' sites, which can be classified as 'typical' noble-gas binding sites. Compared with a representative water-soluble protein, they are however much more abundant in OmpF. In addition, a very large number of weakly populated sites are observed which accumulate in the region of the 'detergent belt' for crystals exposed to xenon. After application of a Fourier-filtering protocol, low-resolution images of the detergent belt can be obtained. The resulting maps are similar to maps obtained from low-resolution neutron diffraction experiments on contrast-matched crystals.

Crystallography, X-Ray↗
PubMed1980

Endometrial blood flow in anaesthetized sheep as measured with krypton-85 clearance and microsphere techniques.

Uterine blood flow rates were obtained with a Krypton (85Kr) clearance technique and with radio-active microspheres in six anaesthetized, non-pregnant ewes (a total of ten comparisons). 85Kr was administered, via a catheter, into the abdominal aorta and beta-emissions were detected with a catheter-type semi-conductor detector probe situated in the lumen of a uterine horn. In seven instances, the 85Kr clearance curve had only one component while in the remaining three instances the curves could be resolved into two components. The flow rates derived from the single component curves and the mean flow rates calculated from the curves with two components were of the same order as, and highly correlated with, estimates of capillary blood flow obtained with microspheres for either the caruncles, the inter-caruncular endometrium or the total endometrium (r = 0.832, r = 0.822 and r = 0.841, respectively, P less than 0.005). There was no correlation between the flow rates obtained with the 85Kr technique and estimates of myometrial capillary blood flow obtained with microspheres.

Animals↗
PubMed1979

Photocoagulation of disciform macular lesions with krypton laser.

Ten vascular disciform mucular lesions were treated by krypton laser photocoagulation. In 8 the lesion resolved after therapy, and in 7 the retina remained flat for 6 months. On those patients treated successfully 6 had a visual acuity of 6/12 or better. The morphology of the laser lesion differed from that of the argon lesion in that there is no evidence of thermal coagulation of the inner retina near the foveola.

Adult↗