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At least 19 recordsLinked to original sources
PubMed1989

[Stable xenon CT-CBF study with measurement of end-tidal xenon concentration--correction by arterial concentration of xenon].

Non-invasive methods with monitoring end-tidal stable xenon (ETXes) are described for estimating local cerebral blood flow (LCBF) and local partition coefficient (L lambda). 30% of Xes in oxygen was inhaled for 240 sec and exhaled for 160 sec during serial CT scannings after denitrogenation with pure oxygen breathing. During the examination, serial samplings of arterial blood and continuous monitoring of ETXes were performed to determine build up range (A) and build up rate constant (K) of artery. Calculated A and K using the arterial sampling (Aa and Ka, respectively) were compared with the calculated A and K using the continuous monitoring of ETXes (Ae and Ke, respectively) in 109 patients with epilepsy, head trauma, or cerebrovascular diseases. Ae and Ke had significantly positive correlation with Aa and Ka, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Inhalation↗
PubMed1997

Theoretical Evidence for Two New Intermediate Xenon Species: Xenon Azide Fluoride, FXe(N(3)), and Xenon Isocyanate Fluoride, FXe(NCO).

The reaction behavior of xenon difluoride, XeF(2), toward HN(3), NaN(3), and NaOCN was investigated in H(2)O, aHF (anhydrous HF), and SO(2)ClF solution. The analysis of the final reaction products (XeF(2) + HN(3) (NaN(3)) in H(2)O --> HF, N(2), N(2)O, Xe; XeF(2) + HN(3) in aHF --> N(2), Xe, N(2)F(2); XeF(2) + HOCN (NaOCN) in H(2)O --> HF, N(2), N(2)O, NH(3), CO(2), Xe) indicated the intermediate formation of FXe(N(3)) and FXe(NCO) and revealed different reaction mechanisms for both compounds. Both intermediates, FXe(N(3)) and FXe(NCO), were studied on the basis of ab initio computations at HF and correlated MP2 levels using a quasirelativistic LANL2DZ pseudopotential for Xe. Both were shown to possess stable minima at HF and MP2 levels (no imaginary frequencies) with the following structural parameters (MP2/LANL2DZ). FXe(N(3)): C(s)(); d(F-Xe) = 2.051, d(Xe-N1) = 2.318, d(N1-N2) = 1.241, d(N2-N3) = 1.180 Å; angle(FXeN1) = 178.1, angle(XeN1N2) = 112.2, angle(N1N2N3) = 174.7 degrees. FXe(NCO): C(s)(); d(F-Xe) = 2.024, d(Xe-N) = 2.206, d(N-C) = 1.194, d(C-N) = 1.231 Å; angle(FXeN) = 178.7, angle(XeNC) = 125.4, angle(NCO) = 174.2 degrees. The experimentally unobserved cyanate isomer, FXe(OCN), was calculated to be higher in energy than the isocyanate isomer FXe(NCO): DeltaE = 19.8 (HF), 18.3 (MP2) kcal mol(-)(1).

Journal Article↗
PubMed2005

Dynamics of xenon binding inside the hydrophobic cavity of pseudo-wild-type bacteriophage T4 lysozyme explored through xenon-based NMR spectroscopy.

Wild-type bacteriophage T4 lysozyme contains a hydrophobic cavity with binding properties that have been extensively studied by X-ray crystallography and NMR. In the present study, the monitoring of 1H chemical shift variations under xenon pressure enables the determination of the noble gas binding constant (K = 60.2 M(-1)). Although the interaction site is highly localized, dipolar cross-relaxation effects between laser-polarized xenon and nearby protons (SPINOE) are rather poor. This is explained by the high value of the xenon-proton dipolar correlation time (0.8 ns), much longer than the previously reported values for xenon in medium-size proteins. This indicates that xenon is highly localized within the protein cavity, as confirmed by the large chemical shift difference between free and bound xenon. The exploitation of the xenon line width variation vs xenon pressure and protein concentration allows the extraction of the exchange correlation time between free and bound xenon. Comparison to the exchange experienced by protein protons indicates that the exchange between the open and closed conformations of T4 lysozyme is not required for xenon binding.

Bacteriophage T4↗
PubMedDate not supplied

Correction method for end-tidal xenon concentration in CBF measurements with xenon-enhanced CT.

PURPOSE: The goal of this work is to show how variations in respiratory rate and tidal volume affect calculated cerebral blood flow (CBF) values on xenon-enhanced CT. In xenon-enhanced CT examination, the patient often takes shallow and rapid breaths. Thus, it is less likely that end-tidal xenon concentration reflects arterial xenon concentration, and appropriate correction measures should be taken for the end-distal respiratory data to obtain reliable CBF values. METHOD: Preliminary breathing tests were performed using a lung phantom to determine the influence of respiratory volume and rate on end-tidal xenon concentration. Two xenon-enhanced CT studies were conducted of a healthy person with completely different respiratory manners between two studies. One was deep and slow respiration. The other was shallow and rapid respiration. RESULTS: The lung phantom results prove that deep and slow respiration is essential for the end-tidal method. The results of xenon-enhanced CT studies of the same person show that the direct use of end-tidal data for shallow and rapid respiration leads to CBF values much lower than the actual values. CONCLUSION: Differences in respiratory rate and tidal volume during xenon inhalation can significantly affect calculated CBF values on xenon-enhanced CT. With use of the correction methods described herein, these effects can be minimized. We have derived the end-tidal correction method on the assumption that a person's CBF values should be kept unchanged regardless of different respiratory manners.

Cerebrovascular Circulation↗
PubMedDate not supplied

The effect of xenon inhalation speed on cerebral blood flow obtained using the end-tidal method in xenon-enhanced CT.

PURPOSE: The purpose of this work is to show how variations in inhalation speed of xenon gas affect cerebral blood flow (CBF) values obtained using the end-tidal method on xenon-enhanced CT (Xe-CT). We tried to clarify whether arterial xenon concentration could keep up with end-tidal xenon concentration by evaluating the effect of xenon inhalation speed on calculated CBF values. METHOD: The same subject underwent two or three consecutive Xe-CT examinations, varying xenon inhalation speed. The rate constants of applied inhalation speeds were 0.1-0.15 min-1 (low speed), 0.25-0.3 min-1 (middle speed), and 1-2 min-1 (high speed), respectively. RESULTS: No significant difference was observed among the CBF values of the same subject obtained under different inhalation speeds. CONCLUSION: End-tidal xenon can closely reflect arterial xenon under the customary method of xenon supply. The end-tidal method can provide reliable absolute CBF values, assuming actual CBF values are substantially unchanged regardless of the inhalation speed variation applied in this work.

Administration, Inhalation↗
PubMed2001

Characterization of the effects of nonspecific xenon-protein interactions on (129)Xe chemical shifts in aqueous solution: further development of xenon as a biomolecular probe.

The sensitivity of (129)Xe chemical shifts to weak nonspecific xenon-protein interactions has suggested the use of xenon to probe biomolecular structure and interactions. The realization of this potential necessitates a further understanding of how different macromolecular properties influence the (129)Xe chemical shift in aqueous solution. Toward this goal, we have acquired (129)Xe NMR spectra of xenon dissolved in amino acid, peptide, and protein solutions under both native and denaturing conditions. In general, these cosolutes induce (129)Xe chemical shifts that are downfield relative to the shift in water, as they deshield the xenon nucleus through weak, diffusion-mediated interactions. Correlations between the extent of deshielding and molecular properties including chemical identity, structure, and charge are reported. Xenon deshielding was found to depend linearly on protein size under denaturing solution conditions; the denaturant itself has a characteristic effect on the (129)Xe chemical shift that likely results from a change in the xenon solvation shell structure. In native protein solutions, contributions to the overall (129)Xe chemical shift arise from the presence of weak xenon binding either in cavities or at the protein surface. Potential applications of xenon as a probe of biological systems including the detection of conformational changes and the possible quantification of buried surface area at protein-protein interfaces are discussed.

Amino Acids↗
PubMed1999

Xenon-131 surface sensitive imaging of aerogels in liquid xenon near the critical point.

In recent years, optically pumped xenon-129 has received a great deal of attention as a contrast agent in gas-phase imaging. This report is about the other NMR active xenon isotope (i.e., xenon-131, S = 32) which exhibits distinctive features for imaging applications in material sciences that are not obtainable from xenon-129 (S = (1/2)). The spin dynamics of xenon-131 in gas and liquid phases is largely determined by quadrupolar interactions which depend strongly on the surface of the surrounding materials. This leads to a surface dependent dispersion of relaxation rates, which can be substantial for this isotope. The dephasing of the coherence due to quadrupolar interactions may be used to yield surface specific contrast for imaging. Although optical pumping is not practical for this isotope because of its fast quadrupolar relaxation, a high spin density of liquid xenon close to the critical point (289 K) overcomes the sensitivity problems of xenon-131. We report the first xenon-131 magnetic resonance images and have tested this technique on various meso-porous aerogels as host structures. Aerogels of different densities and changing levels of hydration can clearly be distinguished from the images obtained.

Gels↗
PubMed1987

Stable-xenon-CT: effects of xenon inhalation on EEG and cardio-respiratory parameters in the human.

The effects of inhalation of a 33% Xenon-O2 mixture over a period of 5 minutes on EEG and cardio-respiratory parameters were studied in 18 human volunteers. This dosage is similar to that used clinically in Xenon-CT studies. In 4 cases no EEG power change was observed during the study. In the 14 other subjects EEG variations were seen. The most prominent change was an increase in beta EEG power. No change was observed in theta and delta EEG power. The findings seem to correlate with the early induction (excitation) phase of an anaesthetic. Hyperventilation was observed before the study and increased during the Xenon inhalation. Blood pressure remained stable while the heart rate tended to decrease a little. All these changes disappeared rapidly following the termination of the Xenon inhalation. The effects are minimal and should not reduce the clinical value of CBF measurement using the Xenon-CT method.

Administration, Inhalation↗
PubMed2005

Retention of xenon in quartz and Earth's missing xenon.

The reactivity of xenon with terrestrial oxides was investigated by in situ synchrotron x-ray diffraction. At high temperature (T > 500 kelvin), some silicon was reduced, and the pressure stability of quartz was expanded, attesting to the substitution of some xenon for silicon. When the quartz was quenched, xenon diffused out and only a few weight percent remained trapped in samples. These results show that xenon can be covalently bonded to oxygen in quartz in the lower continental crust, providing an answer to the missing xenon problem; synthesis paths of rare gas compounds are also opened.

Journal Article↗
PubMedDate not supplied

Errors in cerebral blood flow determinations by xenon-enhanced computed tomography due to estimation of arterial xenon concentrations.

Errors in the determination of xenon concentrations in arterial blood during inhalation of xenon-oxygen mixtures are used to assess errors in the derivation of regional cerebral blood flow by the xenon-enhanced computed tomography (CT) method. The results of this study indicate that approximating the arterial buildup by a single exponential introduces relatively small errors in estimated flow values. The most significant systematic error is introduced by errors in estimation of the xenon arrival time to the brain in relationship to sequential (CT) scanning times.

Cerebrovascular Circulation↗
PubMed1992

Discrepancy of xenon concentrations between end-tidal and blood collection methods in xenon-enhanced computed tomographic measurements of cerebral blood flow.

Using xenon-enhanced computed tomography for the study of cerebral blood flow, simultaneous measurements of end-tidal and arterial blood xenon concentrations using the blood collection method were performed to investigate the validity of substituting the end-tidal for the arterial blood xenon concentration. Simultaneous measurement by both methods was performed 68 times in 27 patients. There was no statistical correlation between the arterial blood accumulation rate constant obtained by arterial blood and end-tidal samples, nor between the arterial blood saturation value obtained by the two methods, even when correction was made for age. In brain tissue, all parameters calculated using the end-tidal concentration were lower than those using arterial blood. We therefore suggest that cerebral blood flow values calculated using end-tidal xenon concentration are useful only for qualitative cerebral blood flow mapping, and not applicable to absolute values of cerebral blood flow.

Adolescent↗
PubMed1998

Effect of xenon-induced flow activation on xenon-enhanced computed tomography cerebral blood flow calculations.

Computer simulations of stable xenon ((S)Xe) uptake curves were used to evaluate the effect of xenon-induced flow activation on CBF calculations by xenon-enhanced computed tomography. Estimates of flow activation were based on repeated transcranial Doppler measurements of blood velocity during 4.5 minutes of (S)Xe inhalation. The synthetic curves were generated from a generalized Kety equation that included time-varying blood flow activation. In contrast to the peak 35% increase in blood flow velocity during (S)Xe inhalation, a standard analysis of the flow-varying synthetic curves revealed only minor 3% to 5% increases in calculated CBF. It is concluded that brief xenon inhalations can provide blood flow estimates that contain minimal bias from activation.

Administration, Inhalation↗
PubMed1977

Xenon-127, a comparison with xenon-133 for ventilation studies.

In 133Xe ventilation studies the 81-keV gamma photon emitted is a major disadvantage for imaging. Using a lung model with the same attenuation coefficient as inflated lung, we compared 133Xe with 127Xe to determine the smallest "lesion" that could be imaged at different places within the lung. With the "lung lesion" directly against the collimator, the lesion had to be 10 ml in volume in order to be seen with 127Xe, but with 133Xe "lesion" had to be 30 ml. Xenon-127 gave better resolution, no matter where the lesion was placed within the lung. Xenon-127 was not better than 133Xe in resolving a lead bar phantom. When 133Xe was used with 99mTc in a model of pulmonary embolism, a "ventilation defect" was apparent even though the distribution of xenon was even throughout the model. This artifact was not seen when the 127Xe model was imaged.

Lung Diseases↗
PubMed2001

Xenon-129 MR imaging and spectroscopy of rat brain using arterial delivery of hyperpolarized xenon in a lipid emulsion.

Hyperpolarized (129)Xe dissolved in a lipid emulsion constitutes an NMR tracer that can be injected into the blood stream, enabling blood-flow measurement and perfusion imaging. A small volume (0.15 ml) of this tracer was injected in 1.5 s in rat carotid and (129)Xe MR spectra and images were acquired at 2.35 T to evaluate the potential of this approach for cerebral studies. Xenon spectra consistently showed two resonances, at 194.5 ppm and 199.0 ppm relative to the gas peak. The signal-to-noise ratio (SNR) obtained for the two peaks was sufficient (ranging from 12 to 90) to follow their time courses. 2D transverse-projection xenon images were obtained with an in-plane resolution of 900 microm per pixel (SNR range 8-15). Histological analysis revealed no brain damage except in two rats that had received three injections.

Animals↗
PubMedDate not supplied

Xenon effects on regional cerebral blood flow assessed by 15O-H2O positron emission tomography: implications for hyperpolarized xenon MRI.

Subjective and physiologic effects of 33% inhaled Xe were measured with 15O-water positron emission tomography (PET) in 3 subjects at rest and during visual stimulation. The procedure was well tolerated. Robust functional activations of the visual cortex were obtained after xenon (Xe) inhalation as well as air breathing. However, Xe inhalation was followed by smaller size, but significant decreases of regional cerebral blood flow (rCBF) in visual cortex relative to the air-breathing baseline, both during visual stimulation and at rest. No such decreases were found in other sensory or motor regions.

Adult↗
PubMed1985

A comparison of the economics of xenon 127, xenon 133 and krypton 81m for routine ventilation imaging of the lungs.

We have compared the cost of providing routine lung ventilation scintigraphy using 127Xe with other radioactive gases in 100 patients. The physical properties of 127Xe permit a logical imaging sequence where a ventilation study is only carried out if indicated by perfusion scintigraphy which is performed first. With 133Xe, all patients must be ventilated prospectively, or a preselection carried out based on radiographic appearances at the time of imaging. This results in a greater number of ventilation studies than with 127Xe. Despite the greater cost per study of 127Xe, the overall cost of providing a routine diagnostic service with this gas is no more than that of using 133Xe in selected patients. The cost of ventilating all patients prospectively with 133Xe is considerably greater than using 127Xe only when indicated by abnormal perfusion images. If ventilation imaging is to be available at all times, either isotope of xenon costs very much less than 81Krm. We conclude that 127Xe is the radiopharmaceutical of choice for routine lung ventilation scintigraphy.

Costs and Cost Analysis↗
PubMed2001

Xenon-induced flow activation in patients with cerebral insult who undergo xenon-enhanced CT blood flow studies.

BACKGROUND AND PURPOSE: Stable xenon-enhanced CT ((s)Xe/CT) has gained wide acceptance in the assessment of regional cerebral blood flow (rCBF) in patients with intracranial abnormalities. The aim of this study was to test whether the contrast medium (ie, (s)Xe) itself directly induces relevant changes in rCBF, thereby distorting any valid determination of cerebral perfusion by using (s)Xe/CT. METHODS: To characterize the degree and temporal dynamics of (s)Xe-induced flow activation, a thermal diffusion (TD)-based microprobe was placed subcortically into the frontal lobe on either hemisphere to assess rCBF (TD-rCBF) continuously in 23 patients (mean age, 55 +/- 18 years) with severe intracranial insult who were undergoing (s)Xe/CT. RESULTS: In 35, the (s)Xe/CT studies TD-rCBF rose from 25 +/- 17 mL/100 g per minute (range, 5-42 mL/100 g per minute) before (s)Xe administration to 28 +/- 21 mL/100 g per minute (range, 6-46 mL/100 g per minute) after arterial (s)Xe saturation was reached. Analysis of the flow activation curve showed a logarithmic shape with an increase in TD-rCBF between 3% and 7% within the first 76 seconds of (s)Xe wash-in (12% after 190 seconds) and showed no further augmentation until the end of the blood flow study. CONCLUSION: The observed (s)Xe-induced rCBF activation, which showed significant inter- and intraindividual variability, might lead to overestimation of rCBF in patients with severe intracranial insult. The obtained flow activation curve provides essential information that may allow subsequent refinement of the methodology, aiming to further minimize the influence of (s)Xe-induced rCBF activation on rCBF calculations when using (s)Xe/CT technology.

Administration, Inhalation↗