Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Background Radiation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20Linked to original sources
PubMed2000

Correlation between quantitative salivary gland scintigraphy and salivary secretion rates in children and young adults treated for hematological, malignant and metabolic diseases.

OBJECTIVES: To study the correlation between whole salivary secretion rates and different variables from the radionuclide time-activity curve and to determine a reliable region for background correction in salivary gland scintigraphy. METHODS: Salivary gland scintigraphy (SGS) was performed before bone marrow transplantation or more than 4 years later in 23 patients aged 13.5 (s.d. 4.9) years. Unstimulated and stimulated whole salivary secretion rates were measured before SGS. Six different methods for background correction were evaluated. RESULTS: The unstimulated secretion rate was significantly correlated (P < 0.05) with the percentage stimulated secretion (S) and reaccumulation-slope (RS) after stimulation. The stimulated secretion rate was significantly correlated with RS, S and down-slope (DS). The temporal region above the parotid glands and the area above the thyroid gland was used for subtraction of background radiation for the parotid and submandibular glands respectively showed a strong correlation between repeated measurements of the variables analysed. The mean maximum uptake was 0.73-1.34% of total dose injected. CONCLUSIONS: The salivary scintigraphic variables which correlated more strongly with salivary secretion rates were RS, S and DS. The temporal region above the parotid gland and the area above the thyroid gland can be used reliably for correction background radiation in the analysis of the time-activity curve in SGS of the parotid and submandibular glands respectively.

Adolescent↗
PubMed2000

Natural radioactivity and radiation exposure at the Minjingu phosphate mine in Tanzania.

In this paper the results of studies on activity and ambient radiation background around the Minjingu phosphate mine in Tanzania are presented. The outdoor dose rate in air and the activity levels of samples from and outside the mine were determined by thermoluminiscent dosimeters and a gamma spectrometer system with a Hyper Pure germanium detector system respectively. The determination of activity was made for the 226Ra, 228Ra, 228Th and 40K radionuclides. High concentrations of radium-226 were observed in phosphate rock (5760+/-107 Bq kg(-1)), waste rock (4250+/-98 Bq kg(-1)), wild leaf vegetation (650+/-11 Bq kg(-1)), edible leaf vegetation (393+/-9 Bq kg(-1)), surface water (4.7+/-0.4 mBq l(-1)) and chicken feed (4+/-0.1 Bq kg(-1)) relative to selected control sites. These findings suggest a radiation health risk particularly when the samples are ingested, because the internal exposure may give rise to an effective dose exceeding 20 mSv which is the annual limit of intake of natural radionuclides recommended by the ICRP. On the other hand, the radiation dose from ambient air over five years at the phosphate mine ranges from 1375 to 1475 nGy h(-1) with an average of 1415 nGy h(-1). The average is about 28 times that of the global average background radiation from terrestrial sources, and about 12 times the allowed average dose limit for public exposure over five consecutive years. Future investigations on the occupancy factor, external dose rate and radon and radon progeny exposure in drinking water, buildings and activity content in the locally grown foodstuffs are proposed, for the realistic quantification of the overall exposure of workers and public at Minjingu, and remedial measures for future radiation safety.

Environmental Exposure↗
PubMed2001

Some case studies of skewed (and other ab-normal) data distributions arising in low-level environmental research.

Three general classes of skewed data distributions have been encountered in research on background radiation, chemical and radiochemical blanks, and low levels of 85Kr and 14C in the atmosphere and the cryosphere. The first class of skewed data can be considered to be theoretically, or fundamentally skewed. It is typified by the exponential distribution of inter-arrival times for nuclear counting events for a Poisson process. As part of a study of the nature of low-level (anti-coincidence) Geiger-Muller counter background radiation, tests were performed on the Poisson distribution of counts, the uniform distribution of arrival times, and the exponential distribution of inter-arrival times. The real laboratory system, of course, failed the (inter-arrival time) test--for very interesting reasons, linked to the physics of the measurement process. The second, computationally skewed, class relates to skewness induced by non-linear transformations. It is illustrated by non-linear concentration estimates from inverse calibration, and bivariate blank corrections for low-level 14C-12C aerosol data that led to highly asymmetric uncertainty intervals for the biomass carbon contribution to urban "soot". The third, environmentally, skewed, data class relates to a universal problem for the detection of excursions above blank or baseline levels: namely, the widespread occurrence of ab-normal distributions of environmental and laboratory blanks. This is illustrated by the search for fundamental factors that lurk behind skewed frequency distributions of sulfur laboratory blanks and 85Kr environmental baselines, and the application of robust statistical procedures for reliable detection decisions in the face of skewed isotopic carbon procedural blanks with few degrees of freedom.

Journal Article↗
PubMedDate not supplied

[The radioecological problem of radon].

Radon and its daughter decay products are the main part of natural radiation background. The review presents the information on indoor radon radiation level, radon sources, exposure doses and effects on human health. In addition to radioecological aspects, the radon effects should be considered as the important problem of low-dose radiation biology.

Background Radiation↗
PubMed2001

Use of low-dose technetium Tc 99m sulfur colloid to locate sentinel lymph nodes in melanoma of the head and neck: preliminary study.

OBJECTIVES/HYPOTHESIS: Because sentinel lymph nodes are the first lymph nodes that drain a primary cancer site, results of sentinel lymph node (SLN) biopsy indicate status of the regional lymph nodes. Preoperative lymphoscintigraphy and intraoperative combined application of the handheld gamma probe and blue-dye technique (i.e., the "combined technique") was used previously to accurately identify the SLN, mostly in melanoma of the extremities and trunk and, sometimes, in melanoma of the head or neck, which is anatomically complex. Because of this complexity, melanoma in the head or neck is inherently problematic to treat: Localization of the SLN can be difficult or impossible because the primary cancer site can be near or overlapping the nodal basin. The objective of the present study was to determine the technical modifications and other considerations that can make SLN localization feasible in cases of melanoma occurring near or overlapping the nodal basin in the head or neck. STUDY DESIGN/METHODS: In a retrospective study of clinical records containing our database of melanoma diagnoses made between January 1996 and December 1999, we identified 27 patients diagnosed with stage I or II primary melanoma of the head or neck with clinically negative neck nodes who also had had preoperative lymphoscintigraphy. Of the 27 patients (17 male and 10 female patients; mean age, 54 y), 24 had SLN biopsy by intraoperative localization using both the handheld gamma probe and the blue-dye technique. RESULTS: Among the 27 patients who had SLN mapping, a median Breslow thickness of 1.8 mm was noted. Sentinel lymph node was noted at preoperative lymphoscintigraphy in 26 (96%) of the 27 patients. Activity of technetium Tc 99m (Tc-99m) sulfur colloid injected ranged from 10 to 1000 microCi (0.37 to 37 megabecquerel [MBq]). Intraoperative use of the combined technique for sentinel lymphadenectomy was successful in 92% of patients. Sentinel lymph nodes were identified in all 14 patients who received Tc-99m sulfur colloid at an activity level less than 60 microCi (2.2 MBq); mean activity level of injected TC-99m sulfur colloid was 28 microCi (1.04 MBq). Sentinel lymph nodes were identified in 8 (80%) of 10 patients who received Tc-99m sulfur colloid at an activity level greater than 100 microCi (3.7 MBq); mean activity of injected Tc-99m sulfur colloid in these patients was 482 microCi (17.8 MBq). A mean number of 1.4 sentinel lymph nodes per patient was identified at preoperative lymphoscintigraphy, and a mean number of 3 sentinel lymph nodes per patient was identified intraoperatively using the combined technique. Tumor recurrence was seen in 2 (10%) of the 19 patients who had cancer-free SLN at mean follow-up of 18 months (range, 1 to 47 mo). Sentinel lymphadenectomy of the parotid region did not injure the facial nerve in any patients. CONCLUSIONS: For patients with primary melanoma that is near or overlaps the nodal basin in the head or neck, SLN biopsy can be accurately performed using Tc-99m sulfur colloid at low activity levels (10 microCi to 60 microCi [0.37 to 2.2 MBq]. However, background radiation from the primary injection site can incorporate the SLN, making localization at preoperative lymphoscintigraphy difficult if not impossible; therefore, the high doses commonly used for melanoma of the extremities and trunk (500 to 2000 microCi [18.5 to 74 MBq]) should not be used for melanoma of the head or neck if the primary site is near or overlaps the nodal basin. In addition, absorption of Tc-99m sulfur colloid by salivary glands increases background radiation in the nodal basin; therefore, use of the handheld gamma probe for intraoperative localization of SLN can be problematic in regions where lymph nodes are adjacent to or within the substance of the salivary gland (i.e., the submandibular and parotid glands).

Female↗
PubMed1991

[Cytogenetic analysis of the peripheral blood lymphocytes in people residing in regions of the Kaluga Oblast polluted with radionuclides].

In order to reveal possible genetic effects of the Chernobyl accident for human populations, a cytogenetic survey of 33 agricultural workers from 2 areas of the Kaluga Region with different radiation backgrounds (villages of Mladensk and Ogor) was conducted in 1989. At the time of investigation a dose of 137Ce for Mladensk was 3.7 ci/km2, that for Ogor--1.17 ci/km2. Lymphocyte cultivation was performed after the standard semimicromethod for 50 hours; about 155-300 cells were analyzed for chromosome aberrations of each individual, the total number of metaphase plates in 2 groups being 9360. One-factor dispersion analysis has shown that the rate of exchanges of a chromosome type, specific for radiation, was higher in the workers of the village of Mladensk than in the workers of Ogor (p less than 0.05). Thus statistically significant differences in the rate of metabolic aberrations of a chromosome type were revealed in the two study groups with different radiation backgrounds. A high sensitivity of cytogenetic analysis for population biological indication of irradiation was shown.

Accidents↗
PubMed2001

Characteristics of a new fully programmable blood sampling device for monitoring blood radioactivity during PET.

The first performance tests of a new fully programmable blood sampling device for monitoring blood radioactivity during positron emission tomography (PET) are described. Blood is withdrawn through 1-mm internal diameter tubing using an infusion pump which can be operated at rates varying from 0 to 600 ml/h. Activity in blood is measured by a 6-cm-thick bismuth germanate crystal connected to a photomultiplier tube and multichannel analyser (MCA) which are positioned within 6 cm lead shielding. Positioning of the tubing is an exact and simple procedure. The minimal readout time of the MCA is 1 s. Two independent energy windows can be set. Operation of the pump and MCA is fully controlled by a PC, i.e. sampling time, interval time and pump rate can be varied at any time during the PET scan by user-defined scripts. A number of characteristics of the new system were studied, such as sensitivity, dead time, linearity, effect of background radiation and pump rate as a function of input pressure. In addition, dispersion was measured as a function of pump rate. Finally, first clinical results were compared with manual samples. The sensitivity equalled 0.7 and 0.2 cps/Bq for 511- and 1022-keV 30% energy windows, respectively, and the system dead time was 500 ns. The system remained linear within 2% with activity concentrations up to 2.5 MBq/cc. Short-term reproducibility was better than 3% for a 1-h period. Long-term reproducibility was about 5% (ISD), which was mainly caused by variation in the diameter of the tubing. If the device was positioned in such a way that maximum shielding was directed towards the patient, the effects of background radiation from the patient on the measured activity concentration for clinically relevant conditions was minimal (<3%). Pump rate varied with input pressure, but remained constant for a given pressure. Dispersion constants smaller than 0.14 s(-1) were observed for pump rates higher than 300 ml/h, indicating that the system dispersion is small. Clinical data showed an excellent agreement to within 3% (ISD) between the results obtained with the new system and manual samples. With the continuous blood sampler radioactivity in blood can be measured accurately during the entire course of the PET scan. Furthermore, the system is fully programmable allowing adjustment of all parameters during a single PET scan.

Algorithms↗
PubMed1974

NUCLEAR-FUELED CIRCULATORY SUPPORT SYSTEMS IV: RADIOLOGIC PERSPECTIVES.

If an implantable artificial heart can be developed, it should prove beneficial to a significant group of patients. A variety of energy sources, such as biologic, electromagnetic, and nuclear, are under evaluation. Currently, biologic fuel cell technology is not sufficiently advanced to permit its extrapolation to the power levels required for implantable circulatory support systems. Electromagnetic systems have the disadvantage of heavy batteries of considerable bulk requiring frequent recharging. Radioisotope-fueled thermal engine systems have the potential of providing degrees of freedom not possible with rechargeable units. However, radiosotope circulatory support systems subject their recipients to prolonged intracorporeal radiation, add to environmental background radiation, and constitute an exceedingly small, but finite, hazard due to possible violation of fuel containment.

Journal Article↗
PubMed1984

Radiation induced cancer: risk assessment and prevention.

A number of factors have to be considered in defining the cancer risk from ionizing radiation. These include the radiation sensitivity of the target tissue(s), the temporal pattern of risk, the shape of the dose-incidence curve, the effects of low dose rates, host susceptibility factors, and synergism with other environmental exposures. For the population as a whole the largest sources of radiation exposure are natural background radiation and medical/dental radiation. Radiation exposures in the medical field make up the largest volume of occupational exposures as well. Although new technologies offer opportunities to lower exposures, worker training, careful exposure monitoring with remedial feedback, and monitoring to prevent unnecessary radiodiagnostic procedures may be even more important means of reducing radiation exposure. Screening of irradiated populations can serve a useful preventive function, but only for those who have received very high doses.

Dose-Response Relationship, Radiation↗
PubMed1994

[Radiation-induced constrictive pericarditis. Associated cardiac lesions, therapy and follow-up].

OBJECTIVES: To evaluate the diagnostic and therapeutic problems that occur in managing patients with radiation-induced constrictive pericarditis. BACKGROUND: Radiation therapy of the chest and mediastinum can damage all cardiac structures, the pericardium being the most frequently involved one. It is little appreciated, however, that radiation-induced constrictive pericarditis can be associated with significant involvement of coronary arteries, myocardium and valves. METHODS: Retrospective evaluation of clinical, hemodynamic, surgical and postoperative data in 8 patients, (7 women, 1 man, aged 26-67 years, mean 44), who had received 30-50 Gy to the chest because of Hodgkin's disease, lymphoma, or breast cancer 7-23 years before the diagnosis of constrictive pericarditis. RESULTS: Six patients had symptoms related to the pericardial disease, one had angina and syncope, one was in congestive heart failure. Hemodynamic signs of constriction were obvious in 6, and were revealed by volume load in 2. All patients had mitral regurgitation, 5 had also tricuspid insufficiency and 5 had aortic regurgitation. The degree of the valvular regurgitation was > or = 3+ in four instances. Critical coronary arterial stenoses were discovered in 3 cases. The coronary ostia were involved in 5 cases (2 critical, 3 non critical). A diagnosis of restrictive cardiomyopathy was arrived at in 4 instances, always after pericardiectomy. Seven patients were operated on: there were 6 pericardiectomies, associated with either valvular surgery or myocardial revascularization or both in 3. One patient underwent myocardial revascularization only. The remaining patient is being treated medically. One patient died at surgery, two died 16 and 72 months thereafter. The remaining 5 have mild symptoms 11-60 months (mean 29) after the discharge from the hospital. CONCLUSIONS: Radiation-induced pericardial constriction is frequently associated with coronary artery disease, mostly silent, with valvular insufficiency, and with myocardial disease. Thorough cardiac evaluation in such patients is mandatory. Surgical treatment frequently uncovers an underlying restrictive myopathy that presents a serious diagnostic and therapeutic challenge.

Adult↗