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At least 145 records · Page 8Linked to original sources
PubMed1990

Electroretinographic findings in panretinal photocoagulation for diabetic retinopathy. A randomized study with blue-green argon and red krypton lasers.

A total of 16 patients (16 eyes) with type II diabetes mellitus and proliferative retinopathy were studied electroretinographically before panretinal photocoagulation, during intervals between the treatment sittings, within 36 h of the final treatment and 4 months after its conclusion. Treatments were carried out with blue-green argon (eight eyes) and red krypton (eight eyes) lasers; the type of laser was randomly chosen. The analysis of the results obtained showed a significant and marked reduction in peak amplitudes of both a- and b-waves in photopic and dark-adapted conditions as early as between the multiple treatments. Electroretinograph (ERG) tracks did not change significantly at subsequent checks. Amplitude reductions were higher for scotopic b-waves and in eyes that had the less altered baseline tracks. Implicit times did not change significantly. The type of laser used did not significantly influence ERG evolution.

Aged↗
PubMed1995

The estimation of administered activity of krypton-81m for lung ventilation studies.

Measurement or estimation of the activity of krypton-81m administered to a patient during lung ventilation imaging is difficult, due to the short half-life and continuous delivery via pipework, and no satisfactory method exists. Calculations based on generator activity have the disadvantages that this activity may not be accurately known and that not all activity eluted is inhaled by the patient. The aim of this study was to develop a simple method for estimating the administered activity from the number of counts in each patient image. A formula based on the ratio of counts in 81mKr and technetium-99m lung ventilation and perfusion images was developed and reduced so that administered activity could be directly calculated from the total 81mKr counts, the 99mTc count rate, the administered activity of 99mTc and a constant representing the ratio of counts expected from equal activities of each radioisotope. The formula allows a direct calculation from the image acquisition data following an initial set of experimental work to establish the constant for a particular gamma camera and collimator system.

Administration, Inhalation↗
PubMed1993

Normal right ventricular systolic and diastolic function assessed by krypton-81m equilibrium ventriculography.

Krypton-81m equilibrium ventriculography was used to study right ventricular function in 23 healthy male volunteers. Technetium-99m lung perfusion scintigraphy was employed to subtract radionuclide activity within lung during image analysis thereby enhancing image quality. The imaging technique was used to generate a time-activity curve for the right ventricle allowing the definition of indices of normal systolic and diastolic function for the right ventricle. At rest, indices of systolic ejection and diastolic filling were comparable to those previously reported for the left ventricle. Using the imaging technique, movement artifact during exercise reduces image quality and limits accurate measurement of these indices to resting studies.

Adult↗
PubMed1986

Krypton red laser photocoagulation of peripapillary subretinal neovascular membranes.

The visual outcome of 20 eyes of 20 patients with peripapillary subretinal neovascular membranes (SRNVM) treated with krypton red laser photocoagulation (KRLP) was studied. Complete obliteration of the SRNVM was achieved in all eyes in the study. In 18 of 20 patients, the visual acuity improved or remained the same during an average follow-up of 9.9 months. There were no treatment-related complications. The efficacy of KRLP in the management of patients with peripapillary SRNVM is discussed.

Aged↗
PubMed1987

Treatment of retinal detachment with congenital optic pit by krypton laser photocoagulation.

Five patients with a congenital pit of the optic nerve and serous detachment of the macular retina were treated with krypton laser photocoagulation to the juxtapapillary region in an attempt to induce resolution of the retinal detachment. The subretinal fluid resolved after laser therapy in four of the patients. In the fifth, the retinal detachment was successfully treated with pars plana vitrectomy. One patient developed a macular hole and decreased visual acuity, despite resolution of the subretinal fluid.

Adolescent↗
PubMed1985

Evaluation of esophageal transit in children and in infants by means of Krypton-81m.

This paper presents the results of Krypton-81m esophageal transit study in a series of children and infants presenting various esophageal disorders. The advantage of Kr-81m, compared to other radionuclides, is that the radiation dose to the patient is extremely low. The study can therefore be repeated as often as necessary and a high dose can be given to ensure good quality results. The method is very easy to perform and allows a quantitative assessment of esophageal transit in physiological conditions. The method gives information about the severity of altered transit and it is particularly useful in studying the effects of treatment.

Adolescent↗
PubMed1997

Ventilation/perfusion ratios and simultaneous dual-radionuclide single-photon emission tomography with krypton-81m and technetium-99m macroaggregated albumin.

To date, there has been neither a good method to clarify the three-dimensional distribution of pulmonary ventilation/perfusion (V. A/Q.) ratios, nor a convenient way to assess V.A/Q. inequality. The purpose of this study was to develop a functional image of pulmonary V.A/Q. ratios based on data acquired with simultaneous dual-radionuclide single-photon emission tomography (SPET) and to assess V.A/Q. unevenness through the V.A/Q. histogram in patients with various pulmonary diseases. Dual-radionuclide SPET was performed with technetium-99m macroaggregated albumin (MAA) and krypton-81m, with the patient in the supine position. After correction for linear cross-talk, the total acquisition counts of both radionuclides were equalized. The V.A/Q. ratio, which was calculated in each pixel by dividing the 81mKr count by the 99mTc-MAA count, was expressed as a V.A/Q. image. A histogram of the pixel number plotted against the V.A/Q. ratios was then produced and its centre of weight (CW) and standard deviation (SD) determined. Ten healthy volunteers and 46 patients [seven with pulmonary vascular disease (PVD), nine with pulmonary emphysema (PE), 18 with bronchogenic carcinoma and 12 with miscellaneous diseases] participated in this study. In normal volunteers, V.A/Q. ratios were generally even, but were slightly lower in dorsal regions. Patients with PVD had lobar and/or segmental areas with a high V.A/Q. ratio. Low V.A/Q. areas extended widely in patients with PE. Bronchogenic carcinoma exceeding 3 cm in diameter was detected as a very low V. A/Q. area. The SD of V.A/Q. ratios had a significant positive correlation both with A-aDO2 (r=0.64, P<0.001) and with cigarette smoking history (r=0.72, P<0.001). It is concluded that the V.A/Q. ratio image produced with simultaneous dual-radionuclide SPET using 99mTc-MAA and 81mKr is a unique and simple method for demonstrating the three-dimensional distribution of V.A/Q. ratios. The unevenness of V.A/Q. distribution can be assessed through the SD of the V.A/Q. histogram.

Adult↗
PubMed1976

Definition of myocardial perfusion by continuous infusion of krypton-81m.

Krypton-81m, a radionuclide emitting a 190 kev gamma ray, has a half-life of 13 seconds. It is a radioisotope of an inert water-soluble noble gas and is produced at a constant rate by spontaneous decay of rubidium-81 in an 81Rb-81mKr generator-delivery system. Delivery is through a minibore Teflon catheter that can be threaded through a standard no. 7 or 8F angiographic catheter. The generator is eluted by 5 percent dextrose-in-water, delivered by infusion pump at 1.5 ml/min, and the eluate is infused intraarterially directly into any organ. Delivery and decay reach equilibrium within 2 minutes, producing a heterogeneous distribution that is proportional to the perfusibility of the tissue concerned and the time required to reach it. The ultrashort halflife of the radionuclide rapidly eliminates activity when delivery ceases; thus, experiments can be sequentially repeated at brief intervals. The radiation hazard for easily imaged doses is negligible. Preliminary studies in open chest dogs were visualized by scintillation camera, stored on digital data disk, processed, and displayed in dual channel, dual color mode on a video system. Images of myocardial perfusion defined relative levels of perfusion, collateral circulation between coronary arterial branches, equilibrium time of diffusible perfusion of the myocardium, focal defects in induced occlusion, collateral circulation to occlusion, and reactive hyperemia after release of induced coronary occlusion. The system and technique appear applicable to human subjects.

Animals↗
PubMed1984

Retinal pigment epithelial rip during krypton red laser photocoagulation.

In three patients (two women, 73 and 74 years old, and one man, 74 years old), a pigment epithelial rip occurred near the edge of a hypopigmented, partly organized choroidal neovascular membrane at the time of its treatment with krypton red photocoagulation. In all three cases, final visual acuity was 20/200.

Aged↗
PubMed1978

Topographical distribution of VA/Q in elderly subjects using Krypton-81m.

The topography of ventilation-perfusion (VA/Q) ratios was measured in seven elderly (aged 58--69) subjects, seated erect, using the short-life (t1/2 = 13 sec) radioisotope Krypton-81m. 81mKr was inhaled (for ventilation) or infused intravenously (for perfusion) continuously for 1--2 min periods, during spontaneous ventilation, while radio-activity was recorded on a large-field gamma camera interfaced to a computer. The VA/Q ratio was computed for 15 horizontal slices of the left lung. VA/Q distribution was similar to that of young subjects. No decrease of basal VA/Q was seen; thus, if there are any changes of ventilation in the lower part of the lung in the elderly, they are matched by equal alterations of perfusion. There was no significant change when 60% oxygen was breathed. The progressive fall in arterial oxygen tension which occurs in erect subjects with increasing age does not appear to be caused by inter-regional differences of ventilation and perfusion.

Aged↗
PubMed2004

Krypton laser-induced photothrombotic distal middle cerebral artery occlusion without craniectomy in mice.

Recent advances in genetical engineering of the mouse have highlighted the importance of reproducible and less invasive models of cerebral ischemia in mice. In this paper, we developed minimally invasive and reproducible model of distal middle cerebral artery (MCA) occlusion in mice using krypton (Kr) laser-induced photothrombosis. C57BL/6 or BALB mice (n=8 each) were anesthetized with halothane. The skin was cut, the temporal muscle was retracted, and the right distal MCA was observed through the skull. A Kr laser beam of wavelength 568 nm was focused onto the MCA over the intact skull. Upon laser irradiation, intravenous administration of a rose bengal solution was begun. After 4 min of irradiation, the laser beam was refocused on the MCA just proximal to the first spot, and another 4-min irradiation was performed. Then, the right common carotid artery (CCA) was ligated. Three days later, the brain was removed, and infarct volume was determined. Infarction confined almost solely to the cortical area was produced in each mouse. Mean infarct volume in C57BL/6 mice was 25.2+/-13.7 mm3. The BALB mice group showed significantly larger and more reproducible infarction (44.1+/-5.2 mm3; the coefficient of variation was 12%) than did C57BL/6 mice (P<0.005). Our photothrombosis model of stroke in mice can be performed without craniectomy, and its reproducibility is satisfactory when using BALB mice.

Animals↗
PubMed1984

Complications of krypton red laser photocoagulation to subretinal neovascular membranes.

The use of krypton red laser photocoagulation (KRLPC) to treat subretinal neovascular membranes (SRNVM) is increasing. The complications of this treatment in a large series of patients have not been reported. Over a 15-month period, 195 patients had KRLPC to SRNVM of the following etiologies: senile macular degeneration (151), presumed ocular histoplasmosis (33), miscellaneous (11). Fourteen patients had the following complications attributable to KRLPC: choroidal hemorrhage (9), retinal pigment epithelial tears (3), choroidal ischemia (1) and choroidal folds (1). The visually significant complication rate was 3.6%. Proper patient selection and treatment technique may decrease the risk of complications.

Choroid↗
PubMed1984

Krypton red laser photocoagulation of subretinal neovascular membranes located within the foveal avascular zone.

Fifty-one eyes with senile macular degeneration and a well-defined subretinal neovascular membrane located within 250 microns from the center of the foveal avascular zone were treated with krypton red laser photocoagulation. Follow-up ranged from 8 to 18 months (mean, 10 months). The eyes were divided into two groups based upon the location of the neovascular membrane. Group I (juxtafoveal membrane 1 to 250 microns from the center of the foveal avascular zone) contained 26 eyes. Following treatment the visual acuity in 16 of the 26 eyes (62%) improved by two or more lines on the Snellen chart or stabilized. Group II (subfoveal membrane present under the center of the foveal avascular zone) contained 25 eyes. Following treatment only 7 of 25 eyes (28%) improved by two or more Snellen lines or maintained their pretreatment visual acuity. Of 16 eyes that had a pretreatment visual acuity of 20/100 or better, only 2 eyes (12%) remained in this group following treatment.

Aged↗
PubMed1986

Cellular processes causing defects in Bruch's membrane following krypton laser photocoagulation.

Krypton laser photocoagulation of the posterior fundus of the rat created white retinal lesions comparable with therapeutic burns in the human. Twenty-four hours after injury, the retinal pigment epithelium was destroyed and the majority of the endothelial cells survived. The choriocapillary lumen was occluded. Bruch's membrane was not fractured nor had it undergone thermal lysis in any area studied but choriocapillary endothelial cell buds invaded the choroidal side of Bruch's membrane. After seven days, cellular protrusions arising from retinal pigment epithelial cells traversed Bruch's membrane through full-thickness defects and entered the choroid. Although intense laser burns may destroy Bruch's membrane, we conclude from this data that many so-called "breaks" in Bruch's membrane following laser therapy are formed by cellular processes and are not caused primarily by laser coagulation.

Animals↗
PubMed1987

Krypton red laser photocoagulation for branch retinal vein occlusion.

Krypton red (647 nm) laser photocoagulation may offer distinct advantages in the treatment of branch retinal vein occlusion (BRVO), particularly in eyes with extensive intraretinal hemorrhage or in the presence of media opacities such as vitreous hemorrhage or cataract. Twenty-three eyes were followed for a minimum of 6 months (range, 6-38). Of 19 eyes treated for macular edema, 17 (89%) had complete resolution of their edema, one (5%) had reduction of its edema, and one (5%) was unchanged. Of five eyes treated for retinal neovascularization of the disc or retina, all eyes had complete elimination of neovascularization. The authors were unable to demonstrate any statistical correlation between final visual acuity and the following factors: duration of symptoms, cystoid macular edema (CME), degree of paramacular nonperfusion, and contiguous intraretinal hemorrhage extending into the foveal avascular zone (FAZ).

Edema↗
PubMed1990

Argon green (514 nm) versus krypton red (647 nm) modified grid laser photocoagulation for diffuse diabetic macular edema.

Between 1984 and 1988, 225 eyes of 132 patients were entered in a prospective, randomized clinical trial to determine if any significant differences exist between treatment with argon green (514 nm) and krypton red (647 nm) modified grid laser photocoagulation for patients with diffuse diabetic maculopathy with or without cystoid macular edema. At the 12- and 24-month follow-up visits, no statistically significant difference was found between the two groups with respect to all of the following: reduction or elimination of macular edema, improvement in visual acuity, worsening of visual acuity, number of treatments per eye, and effect on the visual field. At the 12-month follow-up visit, none of the following factors statistically affected the visual outcome in either of the two groups: a history of systemic hypertension, systemic vascular disease, cystoid macular edema, or initial poor visual acuity.

Adult↗
PubMed2003

Hydration of krypton and consideration of clathrate models of hydrophobic effects from the perspective of quasi-chemical theory.

Ab initio molecular dynamics (AIMD) results on a krypton-water liquid solution are presented and compared to recent XAFS results for the radial hydration structure for a Kr atom in liquid water solution. Though these AIMD calculations have important limitations of scale, the comparisons with the liquid solution results are satisfactory and significantly different from the radial distributions extracted from the data on the solid Kr/H(2)O clathrate hydrate phase. The calculations also produce the coordination number distribution that can be examined for metastable coordination structures suggesting possibilities for clathrate-like organization; none are seen in these results. Clathrate pictures of hydrophobic hydration are discussed, as is the quasi-chemical theory that should provide a basis for clathrate pictures. Outer shell contributions are discussed and estimated; they are positive and larger than the positive experimental hydration free energy of Kr(aq), implying that inner shell contributions must be negative and of comparable size. Clathrate-like inner shell hydration structures on a Kr atom solute are obtained for some, but not all, of the coordination number cases observed in the simulation. The structures found have a delicate stability. Inner shell coordination structures extracted from the simulation of the liquid, and then subjected to quantum chemical optimization, always decomposed. Interactions with the outer shell material are decisive in stabilizing coordination structures observed in liquid solution and in clathrate phases. The primitive quasi-chemical estimate that uses a dielectric model for the influence of the outer shell material on the inner shell equilibria gives a contribution to hydration free energy that is positive and larger than the experimental hydration free energy. The 'what are we to tell students' question about hydrophobic hydration, often answered with structural clathrate pictures, is then considered; we propose an alternative answer that is consistent with successful molecular theories of hydrophobic effects and based upon distinctive observable properties of liquid water. Considerations of parsimony, for instance Ockham's razor, then suggest that additional structural hypotheses in response to 'what are we to tell students' are not required at this stage.

Hydrophobic and Hydrophilic Interactions↗
PubMed2000

Spectra and structure of small ring compounds. LXVII vibrational spectra, variable temperature FT-IR spectra of krypton solutions, conformational stability and ab initio calculations of 1-bromosilacyclobutane.

The infrared (3,200-30 cm(-1) spectra of gaseous and solid 1-bromosilacyclobutane, c-C3H6SiBrH, have been recorded. Additionally, the Raman spectra of the liquid (3,200- 30 cm(-1) with quantitative depolarization values and the solid have been recorded. Both the equatorial and the axial conformers have been identified in the fluid phases, Variable temperature ( - 105 to - 150 degrees C) studies of the infrared spectra of the sample dissolved in liquid krypton have been carried out. From these data the enthalpy difference has been determined to be 182 +/- 18 cm(-1) (2.18 +/- 0.22 kJ/mol) with the equatorial conformer the more stable rotamer and only conformer remaining in the annealing solid. At ambient temperature there is approximately 22% of the axial conformer present in the vapor phase. A complete vibrational assignment is proposed for both conformers based on infrared contours, relative intensities, depolarization values and group frequencies. The vibrational assignments are supported by normal coordinate calculations utilizing the force constants from ab initio MP2/6-31G(d) calculations. From the frequencies of the Si-H stretch, the Si-H bond distance of 1.483 A has been determined for both the equatorial and the axial conformers. Complete equilibrium geometries have been determined for both rotamers by ab initio calculations employing the 6-31G(d) and 6-311 +/- G(d,p) basis sets at levels of Hartree Fock (RHF) and/or Moller- Plesset with full electron correlation by the perturbation method to the second order (MP2). The results are discussed and compared to those obtained for some similar molecules.

Cyclobutanes↗