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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 629 (1991), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 199 (1967), S. 25-40 
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An iron-free intermediate-imageβ-ray spectrometer was used to investigate theβ-decay of208T1 in coincidence with the 2.615 MeVγ-ray of208Pb. Fourβ-groups were found, three of which were previously known. The fourth group has an endpoint energy of 0.64±0.03 MeV and an intensity of (4.5±1.5)%. It is supposed that this transition is still complex and feeds a group of levels around the known 4.3 MeV level of208Pb. Noβ-ray of maximum energy 1.032 MeV to the 3.961 MeV level could be found.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 108 (1938), S. 200-203 
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Zusammenfassung Dieser wird erzeugt von den Erweiterungen eines hyperkomplexen Zahlsystems 1), welches der Verfasser als Angelpunkt aller quantenmechanischen Matrizensysteme erkannt hat. Die neue Raum-Zeit-Struktur wird angegeben. Zu ihrer Eichung benötigt man drei Meßwerte (g, cm, sec). Die physikalischen Konstanten sind hierauf theoretisch berechenbar. Im besonderen werden Eigenschaften der Elementarteilchen quantitativ erfaßt.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 106 (1937), S. 329-342 
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Zusammenfassung Es wird ein Verfahren angegeben, so allgemein, daß jedes Austauschproblem damit erfaßt wird, dabei so einfach, daß mancherlei Antworten sofort abzulesen sind.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1619-7089
    Keywords: 11C-Butanol ; Tumor perfusion ; Tumor trans-plants ; Positron emitters ; Blood-flow tracer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract 1-11C-n-Butanol produced semiatomatically using a cyclotron was employed to investigate the whole-body distribution and kinetics of the label of this compound. Following the administration of 11C-butanol into the aorta of two dogs, more than 80% of the activity was cleared from the blood within 1 min. The activity distribution mirrored the cardiac output distribution as determined using 121I microspheres. Within 25 min p.i., a significant release of decay-corrected activity was only observed for the liver, spleen, and kidneys. Muscle and whole-body activity showed constant levels during this period. In 45 tumor transplants from rats, the dynamic behavior of the label was studied. The tissue retention of activity following injection into the a. femoralis was approximately 100% during the 1st 15 s for both tumor and muscle (n=6). The activity release by tumors during the 1st 10 min after intra-aortic injection was 18%±4.5% (n=39; decay corrected). In five different tumor lines (n=10), the initial 11C-butanol uptake was related to that of muscle, and the results were correlated with the tumor-to-muscle retention of 121I-microspheres (r =0.89). In 17 tumors, the correlation between 11C-butanol uptake and the washout rate of 133Xe resulted in a correlation coefficient of 0.96. Tumor-to-muscle uptake ratios could be equally determined using intra-aortic and intravenous injection, as evaluated by intraindividual comparison in 12 rats (y=0.01+0.98x;r=0.98). 11C-Butanol appears to be an appropriate radiotracer for the assessment of blood supply to malignant tumors relative to muscle.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1619-7089
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract L-(13N)-glutamate (4–8 mCi) was administered IV to 27 patients with coronary artery disease and to 12 control subjects. Quantitative whole body imaging of the 13N label was performed in 31 individuals at different time intervals following the injection. Initial uptake of the total myocardium was estimated to be 5.0±0.88% of the dose. Standardized areas of reduced size on the projection plane contained 2.38±0.41% of the total dose in control subjects and 2.67±0.49% in coronary patients. Subsequent imaging exhibited significant differences in the dynamic behavior of both groups: 13N activity loss within 10 min was 3.2±4.2% of the initial value in control subjects and 16.0±9.8% in coronary patients. In individual cases a high myocardial accumulation of the 13N label was observed in regions of reduced 201Tl uptake. The findings are explained by an augmented extraction efficiency in cases of flow reduction. Glutamate utilization may be involved in metabolic adaptations of the myocardium to chronic or repetitive ischemia and may be worthy of further investigation by positron emission tomography.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1619-7089
    Keywords: Key words: Positron emission tomography ; Spatial resolution ; Image restoration ; Animal studies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. The purpose of this work was to improve of the spatial resolution of a whole-body positron emission tomography (PET) system for experimental studies of small animals by incorporation of scanner characteristics into the process of iterative image reconstruction. The image-forming characteristics of the PET camera were characterized by a spatially variant line-spread function (LSF), which was determined from 49 activated copper-64 line sources positioned over a field of view (FOV) of 21.0 cm. This information was used to model the image degradation process. During the course of iterative image reconstruction, the forward projection of the estimated image was blurred with the LSF at each iteration step before the estimated projections were compared with the measured projections. The imaging characteristics of the high-resolution algorithm were investigated in phantom experiments. Moreover, imaging studies of a rat and two nude mice were performed to evaluate the imaging properties of our approach in vivo. The spatial resolution of the scanner perpendicular to the direction of projection could be approximated by a one-dimensional Gaussian-shaped LSF with a full-width at half-maximum increasing from 6.5 mm at the centre to 6.7 mm at a radial distance of 10.5 cm. The incorporation of this blurring kernel into the iteration formula resulted in a significantly improved spatial resolution of about 3.9 mm over the examined FOV. As demonstrated by the phantom and the animal experiments, the high-resolution algorithm not only led to a better contrast resolution in the reconstructed emission scans but also improved the accuracy for quantitating activity concentrations in small tissue structures without leading to an amplification of image noise or image mottle. The presented data-handling strategy incorporates the image restoration step directly into the process of algebraic image reconstruction and obviates the need for ill-conditioned ”deconvolution” procedures to be performed on the projections or on the reconstructed image. In our experience, the proposed algorithm is of special interest in experimental studies of small animals.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    European journal of nuclear medicine 15 (1989), S. 722-726 
    ISSN: 1619-7089
    Keywords: Positron emission tomography ; Attenuation correction measurement ; Transmission ; Masked Source ; Random and scattered events
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Accurate attenuation correction is a prerequisite for the determination of exact local radioactivity concentrations in positron emission tomography. Attenuation correction factors range from 4–5 in brain studies to 50–100 in whole body measurements. This report gives an overview of the different methods of determining the attenuation correction factors by transmission measurements using an external positron emitting source. The long-lived generator nuclide68Ge/68Ga is commonly used for this purpose. The additional patient dose from the transmission source is usually a small fraction of the dose due to the subsequent emission measurement. Ring-shaped transmission sources as well as rotating point or line sources are employed in modern positron tomographs. By masking a rotating line or point source, random and scattered events in the transmission scans can be effectively suppressed. The problems of measured attenuation correction are discussed: transmission/emission mismatch, random and scattered event contamination, counting statistics, transmission/emission scatter compensation, transmission scan after administration of activity to the patient. By using a double masking technique simultaneous emission and transmission scans become feasible.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1619-7089
    Keywords: Positron emission tomography ; Spatial resolution ; Image restoration ; Animal studies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The purpose of this work was to improve of the spatial resolution of a whole-body positron emission tomography (PET) system for experimental studies of small animals by incorporation of scanner characteristics into the process of iterative image reconstruction. The image-forming characteristics of the PET camera were characterized by a spatially variant line-spread function (LSF), which was determined from 49 activated copper-64 line sources positioned over a field of view (FOV) of 21.0 cm. This information was used to model the image degradation process. During the course of iterative image reconstruction, the forward projection of the estimated image was blurred with the LSF at each iteration step before the estimated projections were compared with the measured projections. The imaging characteristics of the high-resolution algorithm were investigated in phantom experiments. Moreover, imaging studies of a rat and two nude mice were performed to evaluate the imaging properties of our approach in vivo. The spatial resolution of the scanner perpendicular to the direction of projection could be approximated by a one-dimensional Gaussian-shaped LSF with a full-width at half-maximum increasing from 6.5 mm at the centre to 6.7 mm at a radial distance of 10.5 cm. The incorporation of this blurring kernel into the iteration formula resulted in a significantly improved spatial resolution of about 3.9 mm over the examined FOV As demonstrated by the phantom and the animal experiments, the high-resolution algorithm not only led to a better contrast resolution in the reconstructed emission scans but also improved the accuracy for quantitating activity concentrations in small tissue structures without leading to an amplification of image noise or image mottle. The presented data-handling strategy incorporates the image restoration step directly into the process of algebraic image reconstruction and obviates the need for ill-conditioned ”deconvolution“ procedures to be performed on the projections or on the reconstructed image. In our experience, the proposed algorithm is of special interest in experimental studies of small animals.
    Type of Medium: Electronic Resource
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