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PubMed1980

Limitations of radioactive microspheres as tracers for bone blood flow and extraction ratio studies.

Radioactive microspheres have been used for measuring bone blood flow and the extraction ratios of bone-seeking radionuclides, but we have shown that the technique is not completely valid. Bone uptake of 18F and 85Sr was compared with that of microspheres simultaneously injected into the heart or aorta of rats and rabbits under a variety of conditions. In single-passage experiments with quick killing to avoid recirculation, attention was focused on the tibiae and femora which could be dissected quickly to avoid post-mortem migration. For the rest of the skeleton, the effect of the latter was minimized by allowing recirculation for 5 min and comparing blood flow determinations in conjunction wit a cardiac output measurement. The apparent extraction ratio of 18F was variable and always exceeded unity in the single-passage experiments. With recirculation, there were significant differences between the extraction ratios for some bones, and the ratios sometimes exceeded unity. Extraction ratios for 85Sr were similarly variable, but lower. When 85Sr was compared directly with 18F, the relative extraction ratio was 0.8, with little variation between bones or animals. It is concluded that the flux of microspheres entering the vasculature of bone is not representative of blood flow, owing to the removal of some microspheres in pre-osseous capillary beds. Microspheres are therefore not a satisfactory standard for the determination of extraction ratios.

Animals↗
PubMed1975

Coronary hemodynamics during reperfusion following acute coronary ligation in dogs.

The coronary hemodynamic effects of re-establishing blood flow to ischemic myocardium and the regional distribution of myocardial flow during reperfusion were studied in anesthetized open-chest dogs. A large portion of the left ventricular wall was rendered ischemic by occlusion of the left anterior descending coronary artery for 2 hours. During reperfusion of the LAD, coronary resistance in the reperfused vasculature increased progressively for the first 3 hours, while resistance in the intact LC vasculature was unchanged. Minimal resistances in the reperfused vascular bed, calculated from mean aortic pressure and peak coronary reactive hyperemic blood flow following a 90 sec. LAD occlusion, were elevated significantly during reperfusion. The increased minimal resistance values, which reflect the passive physical component of resistance, indicate structural changes in the reperfused vascular bed which were evident shortly after the initiation of reperfusion and persisted throughout the experimental period. Coronary resistances (RH) in the reperfused (LAD) and intact (LC) vasculatures during the reactive hyperemia following 10 sec. coronary occlusions were evaluated. During reperfusion, RH in the reperfused vasculature increased progressively while RH in the intact bed was unchanged. The marked increase in RH in the LAD indicates that the reactive hyperemic flow response to a consistent period of coronary occlusion progressively diminished, and reflects a gradual reduction in the vasodilatory potential of the reperfused coronary circulation. The regional distribution of myocardial blood flow following 5 minutes, 2 hours, and 4 hours of reperfusion was measured with multiple injections of radioactive microspheres. These measurements demonstrated a progressive reduction of blood flow to the reperfused myocardium with no significant change in flow to the control myocardium. In contrast to the uniform transmural distribution of flow in the normal myocardium, the reperfused region showed a distinctly nonuniform distribution of flow after 2 hours and 4 hours of reperfusion, with more severe reduction of flow to the endocardial layer. These studies would suggest that rechannelling blood flow distal to an acute coronary occlusion in human subjects might not in itself be capable of reversing the myocardial injury. It is hoped that additional therapeutic measures might be applied to salvage the injured myocardium.

Animals↗
PubMed1984

Disposition of 3-, 7-, and 13-microns microspheres instilled into lungs of dogs.

This study examined the lung retention and clearance of particles which differed only in their size. Radiolabeled polystyrene microspheres 3, 7, and 13 microns in real size, were instilled into the lungs of beagle dogs. A fiberoptic bronchoscope was used to distribute a 10-ml saline suspension of the microspheres among lung lobes of 24 dogs. The retention and clearance patterns of the microspheres were observed for 128 days after instillation. Tissue and excreta content of the radiolabel provided the basis for defining the fate of the microspheres or radiolabel dissolved from the microspheres. Approximately 2 to 3% of each size of the microspheres cleared the lung within a few days after the instillation procedure, primarily via the mucociliary escalator. Thereafter, the 3-microns microspheres cleared the lung with a biological retention half-time of 820 +/- 54 days; 7- and 13-microns microspheres were retained with biological retention half-times in excess of several thousand days and too long to be determined in this study. Approximately 1.7% of the instilled burden of 3-microns microspheres translocated to tracheobronchial lymph nodes during this 128-day study. Approximately 0.2% of the 7-microns microspheres and none of the 13-microns microspheres accumulated in tracheobronchial lymph nodes. From these data, it was concluded that microspheres or particles 7 microns or more real diameter may be retained indefinitely in the lungs of dogs after deposition by instillation. Similar results are predicted for humans for large particles deposited in the lung by inhalation.

Animals↗
PubMed1986

Cardiac cryosurgery: regional myocardial blood flow of ventricular cryolesions.

Cryosurgery is one of three methods introduced recently for the treatment of ventricular tachyarrhythmias. Cryothermic exposure ablates arrhythmogenic ventricular myocardium, and produces a dense fibrous scar with a sharp border to histologically normal tissue. Myocardial blood flow in the region of the cryolesion, however, has not been quantitated. The purpose of this study was to measure regional blood flow within and around the cryolesion in an attempt to identify ischemic zones that might become arrhythmogenic. Left ventricular cryolesions were created in eleven adult dogs. Two weeks later, the animals underwent radioactive tracer microsphere injection for quantitation of regional myocardial blood flow. The fibrotic cryolesion demonstrated a significantly depressed blood flow (0.44 +/- 0.07 ml/min/g) compared to blood flow in control tissue (1.36 +/- 0.12 ml/min/g) (P less than 0.001). A 1-mm strip of myocardium immediately adjacent to the cryolesion, as well as other myocardium surrounding and subjacent to the cryolesion, did not show a significant decrease in regional blood flow. The border between the fibrotic cryolesion and the surrounding myocardium is, therefore, sharply defined not only in terms of histology but also in regards to regional blood flow. These data lend further support to the safe clinical use of cryothermia in the treatment of refractory ventricular tachycardia.

Animals↗
PubMedDate not supplied

Dose mapping of porcine coronary arteries using an optical fiber dosimeter.

BACKGROUND: This study is about the measurement of radiation dose contribution to the coronary arteries during intravascular brachytherapy with beta and gamma emitters utilizing in vivo optical fiber dosimeters. METHODS AND MATERIALS: Domestic pigs were used. With each measurement, catheters were introduced into two different coronary arteries, including the left circumflex (LCX), the left anterior descending (LAD), the first diagonal, and/or the right coronary artery (RCA). A radioactive source (192Ir, 90Sr/Y, or 32P) and the dosimeter were loaded in each of these catheters. Data were collected as the dosimeter was being retracted at a constant rate via computer control. RESULTS: The radiation dose was normalized to 100% at a 2-mm radial distance from the source. When radiating a branching artery, the dose to the bifurcation at 5 mm from the source was 35%, 10%, and 3% for the 192Ir (10 seeds), 90Sr/Y (40 mm), and 32P sources, respectively. When utilizing a 23-seed 192Ir source, the dose is 40% at a 5-mm distance. However, radiation of the RCA did not result in dosing to the LAD or LCX using any source. CONCLUSIONS: The dose to adjacent artery segments is less with beta than with gamma emitters. Significant dose exposition is noted when using gamma emitters at a distance of 5 mm. The results can serve as a guideline for establishing prescription doses and safety margins for the treatment of bifurcation lesions and retreatment of the arteries.

Animals↗
PubMed2006

Transfer factors of 137Cs and 90Sr from soil to trees in arid regions.

Transfer factors of (137)Cs and (90)Sr from contaminated soil (Aridisol) to olive, apricot trees and grape vines were determined under irrigated field conditions for four successive years. The transfer factors (calculated as Bqkg(-1) dry plant material per Bqkg(-1) dry soil) of both radionuclides varied among tree parts and were highest in olive and apricot fruits. However, the values for (90)Sr were much higher than those for (137)Cs in all plant parts. The geometric mean of the transfer factors in olives, apricots and grapes were 0.007, 0.095 and 0.0023 for (137)Cs and 0.093, 0.13 and 0.08 for (90)Sr, respectively, and were negligible in olive oil for both radionuclides. The transfer factors of both radionuclides were similar to, or in the lower limits of, those obtained in other areas of the world. This could be attributed to differences in soil characteristics: higher pH, lower organic matter, high clay content, and higher exchangeable potassium and calcium.

Cesium Radioisotopes↗
PubMed2006

Treatment of radioactive liquid waste by sorption on natural zeolite in Turkey.

Liquid radioactive waste has been generated from the use of radioactive materials in industrial applications, research and medicine in Turkey. Natural zeolites (clinoptilolite) have been studied for the removal of several key radionuclides ((137)Cs, (60)Co, (90)Sr and (110m)Ag) from liquid radioactive waste. The aim of the present study is to investigate effectiveness of zeolite treatment on decontamination factor (DF) in a combined process (chemical precipitation and adsorption) at the laboratory tests and scale up to the waste treatment plant. In this study, sorption and precipitation techniques were adapted to decontamination of liquid low level waste (LLW). Effective decontamination was achieved when sorbents are used during the chemical precipitation. Natural zeolite samples were taken from different zeolite formations in Turkey. Comparison of the ion-exchange properties of zeolite minerals from different formations shows that Gordes clinoptilolite was the most suitable natural sorbent for radionuclides under dynamic treatment conditions and as an additive for chemical precipitation process. Clinoptilolite were shown to have a high selectivity for (137)Cs and (110m)Ag as sorbent. In the absence of potassium ions, native clinoptilolite removed (60)Co and (90)Sr very effectively from the liquid waste. In the end of this liquid waste treatment, decontamination factor was provided as 430 by using 0.5 mm clinoptilolite at 30 degrees C.

Adsorption↗
PubMed1999

Anthropogenic radionuclides in seawater of the Far Eastern Seas.

Large quantities of radioactive wastes have been dumped in the Far Eastern Seas by the former Soviet Union and the Russian Federation, and small amounts of radioactive wastes have been dumped by Japan and the Republic of Korea. In order to investigate the concentrations of anthropogenic radionuclides in the nine dumping areas, a second expedition was conducted in 1995 by Japan, the Republic of Korea, the Russian Federation and IAEA, following the first expedition in 1994. The results show that 137Cs, 90Sr and 239 + 240Pu concentrations in surface and bottom waters at dumping areas do not significantly differ from the values observed in background areas, and from historical values. There is no clear effect of possible contamination due to radioactive waste dumping. The concentrations and water column inventories of 137Cs, 90Sr and 239 + 240Pu in the Far Eastern seas are controlled by physical oceanic processes such as horizontal transport and biogeochemical processes such as scavenging.

Cesium Radioisotopes↗
PubMedDate not supplied

Application of intravascular brachytherapy: utilization of beta-irradiation source delivery systems within a community-based cardiac center.

PURPOSE: There are numerous clinical studies ongoing to assess the outcome, physics, and radiobiology of intravascular brachytherapy and its effect on the reduction of the rate of restenosis after balloon angioplasty procedures. The present study reports on the experience of two different delivery systems as utilized in the community hospital setting. METHODS AND MATERIALS: Patients were enrolled into one of four ongoing trials at our institution: the Novoste Beta-Cath trial, the Novoste Stents and Radiation Therapy trial (START), the Novoste START 40/20 trial, and the Guidant Intimal Hyperplasia Inhibition with Beta In-stent Trial (INHIBIT). The Novoste studies utilized the Novoste Beta-Cath System with 90Sr/Y, and the Guidant INHIBIT trial used 32P. Enrollments into the various trials were determined by inclusion and exclusion criteria specified by each protocol. Randomization was conducted per criteria as determined by the participating study protocol. RESULTS: Forty-two patients were enrolled in total. Thirty-four were included in the Novoste trials and eight in the Guidant study, according to availability of the trial. Assessment of practicality of treatment was dependent primarily on treatment duration and extension of time of catheterization procedures by the addition of intravascular radiation. Average dwell time within the Novoste trials was 3 min 40 s, and 7 min 46 s for patients in the Guidant study. No acute complications were observed in any of the trials. CONCLUSIONS: Intravascular brachytherapy can be performed in the community hospital setting without compromising the efficiency of balloon angioplasty procedures. Pending long-term outcome data and FDA approval for specific delivery systems, endovascular brachytherapy in community hospital cardiac catheterization laboratories can be realized in an efficient and timely manner.

Aged↗