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At least 19 recordsLinked to original sources
PubMed1992

Comparison of photocoagulation with the argon, krypton, and diode laser indirect ophthalmoscopes in rabbit eyes.

PURPOSE: The purpose of this study is to compare photocoagulation with the argon green, krypton red, and diode infrared laser indirect ophthalmoscopes in an experimental setting. METHODS: Photocoagulation was performed with each of the laser indirect ophthalmoscopes in a grid pattern within one sector of the same eye of 14 Dutch-belted rabbits. Treatment was performed either with or without scleral depression. Measurements of the retinal burn diameters were performed after hemisecting the globes, and the burns were examined with light microscopy. RESULTS: Variation in burn intensity and diameter (10% to 28%) was common with all 3 laser indirect ophthalmoscopes. Five times more output energy was required to make equivalent burns with the diode laser indirect ophthalmoscope than with the argon or krypton laser indirect ophthalmoscopes. Choriovitreal hemorrhages only occurred during scleral depression. Histopathologically, the argon green laser indirect ophthalmoscope burns spared the choroid and inner sclera, while the intense krypton and diode burns had full-thickness choroidal involvement and even thermal injury to the inner sclera. Scleral depression reduced the mean energy required to create equivalent burns with all three laser indirect ophthalmoscopes. There was a 10% to 40% reduction in the mean retinal burn diameter with scleral depression (argon green, P < 0.0005; krypton red, P < 0.0005; and diode, P < 0.025). CONCLUSION: Photocoagulation with the argon green, krypton red, or diode infrared laser indirect ophthalmoscopes is a safe and effective method of retinal ablation. Decreasing the posterior nodal distance of the eye with scleral depression will produce a smaller spot on the retina with the laser indirect ophthalmoscope.

Animals↗
PubMed1992

An evaluation of Technegas as a ventilation agent compared with krypton-81 m in the scintigraphic diagnosis of pulmonary embolism.

A ventilation agent that provides good quality lung images, which is cheap, easy to use and non-toxic, with a low radiation dose, has long been sought. Technegas, an ultrafine aerosol of technetium-99m-labelled carbon, was developed with these qualities in mind. We have studied Technegas in a clinical setting to evaluate some of these qualities. Twenty-five patients referred with a diagnosis of suspected pulmonary embolism were investigated during the same study using both krypton-81 m and Technegas as ventilation agents in conjunction with 99mTc-macroaggregated albumin as a perfusion agent. Technegas provided images which were of satisfactory quality. Images were obtained relatively easily and without discomfort to the patient, and Technegas has the advantage of always being available. A semi-quantitative regional assessment was employed which showed a good correlation (r = 0.499, P less than 0.001) between Technegas and krypton-81 m ventilation. We report on an effect not previously found to be significant, that is lung regions were better ventilated with Technegas than with krypton-81 m. This altered the diagnostic probability rating of pulmonary embolism in a number of patients (n = 3, 12%) compared with krypton-81 m. This effect was also noted in a further 8 patients (32%) without a change in the diagnostic probability. We offer possible explanations for this phenomenon.

Female↗
PubMed1979

Assessment of coronary venous bypass graft function using krypton-81m.

Fifteen patients with intractable angina pectoris underwent coronary angiography and coronary arterial bypass graft surgery. After the operation, a continuous infusion of krypton-81m was delivered into each graft. A gamma camera and multichannel analyzer were used to record the regional myocardial distribution of perfusion provided by each graft. The disappearance of myocardial activity at the end of each infusion was used to calculate the flow per unit volume in the myocardial distribution provided by each vessel. Myocardial perfusion provided by the grafts to all the major coronary arteries were recorded individually as high spatial resolution images. Myocardial flow rates in the distribution of each graft were measured using the washout of krypton-81m. The rates were 0.5 to 2.0 ml/g per min in the 13 patients with no evidence of previous myocardial infarction. Krypton-81m was infused into grafts to the left anterior descending coronary artery in two patients with a history and electrocardiographic evidence of previous anterior myocardial infarction. The grafts provided poor perfusion to the anterior and apical portions of the ventricles. An experimental model of myocardial perfusion was used to demonstrate that the washout of krypton-81m can be used to measure flow per unit volume within or above the physiologic range.

Angina Pectoris↗
PubMed1979

Krypton-81m in the physiologic assessment of coronary arterial stenosis in man.

Fifteen patients with frequent anginal chest pain underwent diagnostic cardiac catheterization. After coronary arteriography a specially designed cardiac catheter was seated in the aortic root, permitting the continuous infusion of krypton-81m into the right and left aortic sinuses. A gamma camera, areas of interest and a visual display unit were used to record images and the regional myocardial equilibrium of activity before, during and after a standarized atrial pacing test. The unique physical properties of krypton-81m allowed the continuous imaging and recording of moment to moment changes in regional myocardial perfusion. This investigation revealed that when the coronary arteriogram was normal or revealed lumonal stenosis of less than 50 percent, regional myocardial perfusion was uniform at rest and during stress. Two patients with a previous history of myocardial infarction had defects of regional perfusion at rest and during stress. Krypton scintigraphy demonstrated reversible regional defects in myocardial perfusion during stress in seven patients with greater than 70 percent stenosis of one or more coronary arteries. Alterations in regional myocardial perfusion occurred within 30 seconds of the start of atrial pacing in all the patients and preceded the onset of electrocardiographic signs of ischemia or chest pain.

Adult↗
PubMedDate not supplied

Saturation curve in gases of high atomic number at pressures up to 8 atm. I. Krypton and xenon.

The saturation curve has been studied in xenon and in krypton up to a pressure of 8 atm. An empirical formula has been found that describes the fraction of current collected over a wide range of voltages, pressures, ionization intensities, and electrode spacings. This is of practical value in the design of ionography chambers. For krypton the collection fraction fKr = (1 + 0.25eta-1.74)-1, and for xenon fXe = (1 + 0.16eta-1.88)-1, where eta = Fp-0.7Vd-2q-1/2 with F = 3.61 X 10(-7) and 2.50 X 10(-7) for krypton and xenon, respectively. The ranges of the variables covered in the experiments were p = 1-8 atm, V = 5-25000 V, d = 0.3-1.3 cm, and q = 4 X 10(-9)-6 X 10(-8) A/cm3.

Atmospheric Pressure↗
PubMed1979

A comparative histopathological study of argon and krypton laser irradiations of the human retina.

A series of comparative exposures to both argon and krypton lasers have been made at 3 locations in a human retina--the fovea, the macula, and intraretinal vessels. In the fovea argon irradiations resulted in damage to both the inner and outer retinal layers as a result of absorption within the pigment epithelium and the macular pigment, while krypton exposures damaged the outer retina and the choroid. In the macula both systems resulted in damage to the outer retina, and again sufficient krypton radiation passed into the choroid to induce blood vessel occlusion, haemorrhage, and oedema. When intraretinal vessels were irradiated, only with argon was sufficient energy absorbed within the vessels to damage them or their surroundings in the inner retina. The implications of these findings are discussed in relation to the therapeutic uses of lasers.

Argon↗
PubMed1977

The determination of the diffusion coefficient of krypton in rabbit ocular tissue.

The validity of the inert gas clearance method for measuring choroidal blood flow has recently been demonstrated by studying the diffusion of krypton in ocular tissue. In this study the diffusion coefficients of krypton in rabbit ocular tissue were calculated from measurements of the diffusion coefficients of xenon. The mean values for the diffusion coefficients of krypton obtained in this study were 1.6 X 10(-5), 0.76 X 10(-5), 0.80 X 10(-5), and 1.2 X 10(-5) cm.2 per second for the sclera, choroid, retina, and vitreous, respectively.

Animals↗
PubMed1990

Krypton laser photocoagulation for idiopathic neovascular lesions. Results of a randomized clinical trial. Macular Photocoagulation Study Group.

The Idiopathic Neovascularization Study--Krypton Laser is a multicenter randomized controlled clinical trial conducted to determine whether krypton red laser photocoagulation is useful in preventing or delaying loss of visual acuity in eyes that have either choroidal neovascularization 1 to 199 microns from the center of the foveal avascular zone or choroidal neovascularization 200 microns or farther from the foveal avascular zone center with associated blood and/or blocked fluorescence extending within 200 microns of the foveal avascular zone center in the absence of any other clinically significant eye disease. Eligible lesions could have blood or blocked fluorescence that extended through the entire avascular zone. Patients were assigned to laser photocoagulation (n = 24) or to observation only (n = 25). With 65% of these patients followed up for 5 years and 85% for 3 years, there is evidence that krypton laser treatment is beneficial. After 3 years of follow-up, 2 (10%) of 20 treated eyes in comparison with 7 (37%) of 19 untreated eyes had lost six or more lines of visual acuity (P = .15). Furthermore, more untreated eyes than treated eyes had experienced such losses at each point in follow-up after the 3-month examination. The findings from this trial taken with findings of other trials conducted by the same investigators for lesions similar in appearance and location but secondary either to age-related macular degeneration or to ocular histoplasmosis support the conclusion that patients with idiopathic parafoveal neovascularization benefit from laser treatment.

Adult↗
PubMed1990

Krypton laser-induced lens opacity as a complication of retinal photocoagulation.

Lens opacification is a well-documented complication of argon laser photocoagulation, particularly in eyes with preexisting cataracts. In eyes with media opacity, the krypton laser is frequently used for its superior penetrating qualities. To date, lens opacification from krypton application has not been documented. We report such a case in a cataractous eye with a vitreous hemorrhage undergoing panretinal photocoagulation. Factors previously implicated in the etiology of laser-induced lens damage were not present. The opacities were similar to those produced by the argon laser. We present a mechanism for understanding laser-induced lens damage and speculate on the difference between the interaction of argon versus krypton laser energy with lens constituents.

Cataract↗
PubMedDate not supplied

Saturation curve in gases of high atomic number at pressures up to 8 atm. Part II: Freon 13-B1, and mixtures of Freon with xenon and krypton.

The saturation curve has been studied in Freon 13-B1 (CF3Br) and in mixtures of Freon with xenon and krypton up to a pressure of 8 atm. The enhanced initial recombination due to the electron affinity of Freon has been evaluated and an empirical formula constructed that describes the fraction of current which escapes initial recombination over a wide range of voltages, pressures, and electrode spacings. After correction for this initial recombination, the general saturation curve for Freon and for mixtures of this gas with krypton and xenon has been derived and, again, convenient empirical formulae established which allow the current collection efficiency to be calculated for any given parameters within the range investigated. These formulae are of practical value in the design of image-forming ionization chambers.

Chlorofluorocarbons, Methane↗
PubMed1990

Krypton laser photocoagulation for neovascular lesions of age-related macular degeneration. Results of a randomized clinical trial. Macular Photocoagulation Study Group.

The Age-Related Macular Degeneration Study-Krypton Laser (AMDS-K) is a multicenter controlled clinical trial designed to determine whether krypton red laser photocoagulation is of value in preventing visual acuity loss in eyes with macular degeneration that have either choroidal neovascularization 1 to 199 microns from the center of the foveal avascular zone or choroidal neovascularization 200 microns or farther from the foveal avascular zone center with blood and/or blocked fluorescence extending within 200 microns of the foveal avascular zone center. Recruitment ended in December 1987 after 247 patients had been assigned to photocoagulation and 249 patients had been assigned to no treatment. At 3 years after randomization, 49% (86/174) of treated eyes, in contrast to 58% (98/169) of untreated eyes, had lost six or more lines of visual acuity. The average visual acuity of treated and untreated eyes at that time was 20/200 and 20/250, respectively. The benefit of laser treatment was largest among patients without evidence of hypertension and diminished to no apparent benefit among patients who had highly elevated blood pressure and/or used antihypertensive medication. Treatment of lesions meeting the AMDS-K eligibility criteria in eyes of patients with no hypertension is recommended. However, treatment cannot be recommended uniformly for patients with definite hypertension having lesions similar to those of patients enrolled in the AMDS-K.

Age Factors↗
PubMed1990

Persistent and recurrent neovascularization after krypton laser photocoagulation for neovascular lesions of age-related macular degeneration. Macular Photocoagulation Study Group.

The persistence and recurrence of choroidal neovascularization after initial treatment with laser photocoagulation have been shown to be major contributors to loss of visual acuity. The 247 eyes assigned to krypton red laser photocoagulation in the Age-Related Macular Degeneration Study-Krypton Laser were examined to describe the incidence, timing, visual impact, and potential risk factors for persistence and recurrence. Persistent neovascularization detected within 6 weeks of initial treatment was observed in 32% of treated eyes, and recurrent neovascularization was estimated by life-table methods to develop in an additional 47% over a 5-year period. Both persistence and recurrence were accompanied by an increased frequency of severe visual loss. The persistence rate among eyes having 10% or more of the foveal side of the neovascular membrane not covered by treatment was twice as high as in eyes having more extensive coverage. Patients having a fellow eye with a neovascular membrane or scar, a fellow eye with 20 or more drusen in the central macula, or a fellow eye with nongeographic atrophy at initial visit had more recurrences than patients without these characteristics. Ophthalmologists treating similar lesions may be able to reduce persistent neovascularization and the associated visual loss by covering the entire lesion with treatment.

Age Factors↗
PubMed1991

Transcleral contact krypton-laser photocoagulation of the retina in rabbits.

Transcleral contact retinal krypton laser photocoagulation of the retina was studied in rabbit eyes. The laser application was performed under indirect ophthalmoscope visual control with indentation of the sclera by the laser probe. Retinal lesions were produced with powers ranging from 0.2 to 0.3 W and application times between 1 and 2 sec. The lesions were studied histologically 2, 5, 10, 12, 20, 30 and 70 days after treatment. Histopathological examination of the lesions showed damage of mainly the outer retinal layers in light lesions, and to all layers of the retina in the more intense lesions. No scleral damage was observed in the light lesions, whereas transient oedema of the inner sclera was seen in the intense lesions. Studies with enucleated rabbit eyes showed that indentation of the sclera by the laser probe substantially decreased the power needed to produce a retinal lesion. It is concluded, that when used with scleral indentation, transscleral krypton laser photocoagulation of the retina can be performed with minimal damage to the sclera.

Animals↗
PubMed1992

[Krypton laser therapy. Use in secondary serous detachment of the retinal pigment epithelium and in multiple idiopathic serous detachments of the retinal pigment epithelium].

Two variants of serious detachments of the retinal pigment epithelium (RPE) are demonstrated with reports of typical cases: (1) secondary serous detachment of the RPE; (2) idiopathic serous detachment of the RPE (pigment epithelium detachment not associated with any other retinal or choroidal disease). Fluorescein angiographic criteria for differential diagnosis and the resulting different techniques of krypton laser coagulation are portrayed: (a) focal krypton laser coagulation of the total area of the pigment epithelium detachment; (b) circular, one-row laser coagulation at the detachment borders. The advantages of circular, one-row laser coagulation of idiopathic serous RPE detachment over coagulation of the total area of the RPE detachment are described: first, these are fewer scotomas following coagulation; second, fewer laser foci are required; and third, the risk of subretinal bleeding is lower. These findings emphasize the efficiency of circular, one-row laser coagulation at the detachment borders in the treatment of idiopathic serous RPE detachments.

Adult↗
PubMed1990

Krypton filled flashlamp: a possible new light source for near infrared spectroscopy in vivo.

We have designed a reliable and flexible low cost instrument for NIR spectroscopy. A krypton filled flashlamp was used as inexpensive light source. Providing a number of suitable emission peaks in the NIR, this flashlamp is ideal for NIR spectroscopy. Application to other NIR spectroscopy systems, e.g. to CCD (Charge Coupled Device) spectrophotometers, should be possible. The introduced system was tested on human arm tissue during arterial occlusion. Results equivalent to those described by other authors could be obtained by this new technical approach.

Adult↗
PubMed1977

The measurement of spleen perfusion in man: a non-invasive method using the ratio between Rubidium-81 and its decay product Krypton-81m.

A non-invasive method has been developed for measuring spleen perfusion in man. This involves recording the gamma-ray energy spectra over the spleen following the localisation of Rubidium-81 within the organ by injecting intravenously labelled heat denatured red cells. The spectra are analysed to provide the ratio of Rubidium-81 to its radioactive decay product Krypton-81 m. This ratio is dependent on the rate of perfusion through the organ. The difficulties encountered in applying this steady state method for monitoring tissue perfusion are illustrated and practical means for their solution presented. The results of applying this method to patients with various splenic disorders are presented and compared with those obtained by other workers using different monitoring techniques.

Humans↗
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↗
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↗