Two experimental positron emission tomography (PET) camera modules were constructed using (1) two 5-cm*5-cm*2.5-cm detector stacks made of parallel 0.5- and 1.0-mm-diameter scintillating fibers and ...(2) two 5-cm*5-cm*5-cm detector stacks made of alternating x and y layers of 0.5-and 1.0-mm diameter scintillating fibers. Each stack was viewed by Hamamatsu R2486 position sensitive photomultipliers. The time resolution of the coincidence system was 10 ns. The spatial resolution and efficiency of the PET modules was tested using an approximately 1 mu Ci 0.5-mm-diameter Na-22 source. The best results were achieved with the 1.0-mm parallel fiber stacks: 2.0-mm spatial resolution (FWHM) and 2.3% efficiency. Possibilities to improve the characteristics of this agreement and, particularly, the alternating x and y layer stacks are discussed.< >
The EGS4 (Electron Gamma Shower 4) Monte Carlo program was used to investigate the angular and energy response of double Compton scattering telescopes using plastic scintillating fibers coupled to ...position-sensitive photomultipliers. The program allows the optimization of important parameters for telescopes under development. The influence of the parameters on the efficiency, and the angular, position, and energy resolution of the telescope was studied. Preliminary results are presented.< >
The use of nuclear photoactivation in conjunction with positron emission analysis techniques to quantify the spatial distribution of elements in bone is considered. A realistic model of bone ...composition and a simplified model of bremsstrahlung spectral intensity have been used to calculate the activation yields obtainable with medical linear accelerators. The results of activation experiments performed using a linac-produced 18-MV X-ray beam have been compared with the predictions of this model to assess the feasibility of obtaining the relative amounts of the different elements from the analysis of the time dependence of the decay. It is concluded that photonuclear activation in conjunction with positron emission analysis techniques has the potential for noninvasively determining the elemental composition of bone. Because this process will also have the unique signature used in positron emission tomography (PET), it provides an approach to imaging the distribution of elements within bones.< >
The authors studied 100 patients who had been exposed to toxic molds in their homes. The predominant molds identified were Alternaria, Cladosporium, Aspergillus, Penicillium, Stachybotrys, ...Curvularia, Basidiomycetes, Myxomycetes, smuts, Epicoccus, Fusarium, Bipolaris, and Rhizopus. A variety of tests were performed on all, or on subgroups of, these patients. Sensitivities and exposures were confirmed in all patients by intradermal skin testing for individual molds (44-98% positive), and by measurement of serum antibodies. Abnormalities in T and B cells, and subsets, were found in more than 80% of the patients. The findings of trichothecene toxin and breakdown products in the urine, serum antibodies to molds, and positive intradermal skin tests confirmed mycotoxin exposure. Respiratory signs (e.g., rhinorrhea, sinus tenderness, wheezing) were found in 64% of all patients, and physical signs and symptoms of neurological dysfunction (e.g., inability to stand on the toes or to walk a straight line with eyes closed, as well as short-term memory loss) were identified in 70% of all patients. Objective abnormal autonomic nervous system tests were positive in all 100 patients tested. Brain scans, conducted using triple-head single photon emission computed tomography, were abnormal in 26 (86%) of 30 (subgroup of the 100) patients tested. Objective neuropsychological evaluations of 46 of the patients who exhibited symptoms of neurological impairment showed typical abnormalities in short-term memory, executive function/judgment, concentration, and hand/eye coordination.
The authors report on further development and testing of a Compton telescope composed of scintillating fibers and position-sensitive photomultipliers. Initial tests of the telescope showed a better ...than 1-mm (RMS) position resolution and a 17.5-mrad (RMS) angular resolution for 1.2-MeV photons from a collimated /sup 60/Co gamma source. This type of device can be used for constructing large-area telescopes for gamma-ray astronomy. It was shown that this gamma ray telescope worked successfully.< >
Effects of hadron irradiation on scintillating fibers Abbott, B.; Adams, D.; Armstrong, T. ...
IEEE Transactions on Nuclear Science (Institute of Electrical and Electronics Engineers); (United States),
08/1993, Letnik:
40, Številka:
4
Journal Article, Conference Proceeding
Recenzirano
Trackers based on scintillating-fiber technology are being considered by the Solenoidal Detector Collaboration at SSC and the DO collaboration at Fermilab. Some 600 fibers in the Fermilab Tevatron CO ...area were irradiated, thereby obtaining a hadronic irradiation at realistic rates. Four-meter-long samples of ten Bicron polystyrene-based fibre types, maintained in air, dry nitrogen, argon, and vacuum atmospheres within stainless-steel tubes, were irradiated for seven weeks at various distances from the accelerator beam pipes. Maximum doses, measured by thermoluminescence detectors, were about 80 krad. Fiber properties, particularly light yield and attenuation length, were measured over a one-year period. A description of the work together with the results is presented. At the doses achieved, corresponding to a few years of actual fiber-tracking detector operation, little degradation was observed. Recovery after several days' exposure to air was noted. Properties of unirradiated samples kept in darkness show no changes after one year.< >
Fifty chemically sensitive patients with vascular, asthmatic and arthritic signs, ranging in age from 21 to 61, were exposed to double-blind challenges of ambient doses of inhaled toxic chemicals in ...a specially designed booth in an Environmental Control Unit (ECU). Primary signs and symptoms were recorded before and after challenge with five chemicals and three placebos. Inhaled challenges included phenol (less than .0025 ppm), petroleum-derived ethyl alcohol (less than .5 ppm), formaldehyde (less than .2 ppm), chlorine (less than .3 ppm), and pesticide (2, 3,-D at less than .0034 ppm). Placebos were water or saline. A set on testing criteria were evaluated for maximizing the likelihood of well-defined, reproducible information from these ambient-dose double-blind challenges. For best results, these testing criteria include: Before testing, the patient must be housed in a chemically less polluted environment. The individual must have been de-adapted to food, air, and water pollutants by means of a water fat for three to four days. At the time of the challenge, the patient must be on food and water previously determined to be safe. An enclosed non-pulluted challenge booth must be used for these chemical exposures. Sign and symptom scores appropriate for that patient must be recorded, before and after challenge. Appropriate doses of the chemical in question (determined by air concentration and length of exposure) are necessary to investigate a particular problem. The conclusion of the study is that in these patients, chemical sensitivity clearly does exist (pulse rate differences between positive responses and placebo - p .001).
The blood levels of organochlorine pesticides and chlorinated hydrocarbon solvents were measured in 200 and 114 chemically sensitive patients respectively, and compared with blood concentrations of ...standard medication (non- chlorinated substances. Clonidine, Haloperidol) of comparable toxicity after therapeutically effective dosage, and with reference levels of highly potent chemicals in the blood such as hormones. It was shown that the average blood levels of the most toxic environmental pollutants are comparable with the therapeutic steady state average blood levels of medications which have similar toxicities in the animal model. In addition the toxicity levels of xenoestrogens are at least an order of magnitude higher than normal plasma estrogen or progesterone levels. These findings suggest the possibility of additive or synergistic effects of these chlorinated compounds and the aforementioned medications. Also, these findings suggest the possibility of hormone deregulation from exposure to the aforementioned toxic chlorinated compounds.
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