[en] The method of ß-ß-coincidence scintigraphy allows for superposition free reproduction of selected planes of the body without numerical image reconstruction. In this paper the development of a coincidence system with a scintillation camera and a layer isolated apparatus is described and suitable isotopes as Se-75 (cascade radiation) are proposed. Based on phantom measurements an improvement in image contrast is demonstrated for the detection of cold and hot regions in extended object with realistic activity concentrations. Using a pin hole collimator, acceptable measuring times can be obtained. (orig./HP)

[en] In order to determine if and to which extent diagnostic radiation exposure may add to the risk of acquiring leukaemia it is first of all necessary to estimate the dose absorbed by the red bone marrow during X-ray examinations. The organ doses received by a patient subjected to diagnostic radiography can generally be calculated with a high degree of accuracy, provided that the parameters of exposure and related patient parameters have been documented for each individual examination. Before any further steps are taken to analyze the X-ray procedure chosen, an estimation is made of the bone marrow dose to be expected for usual exposures and state-of-the-art examination techniques and equipments. The results thus obtained are then adjusted using correction factors to take account of the state of the art at the time of examination, while the examination technique used is presumed to have been adequate. Subsequently, account is also taken of scattered radiation which, even though undesirable, is likely to occur in examinations performed on a day-to-day basis. (orig./MG)

[en] Two problems in the γ-γ-coincidence method for depth discrimination in scintigraphy are discussed. Firstly, the FW(1/e)M of the distribution function of time differences between 'coincident' pulses has been calculated to be the optimum resolving time for measurement of true coincidences. Secondly, the improvement of time resolution of such an apparatus by substituting a large volume NaI(Tl) crystal by an array of many small ones has been analysed. It was shown that such arrays have no practical advantage since the loss in efficiency is of the same order of magnitude as the gain in time resolution. (author)

[en] The method described for use in nuclear medicine optimises a system of slit collimators in an opposite arrangement with reference to a maximum mean sensitivity for line sources over the screened layer. The program contains quality factors for the variation of the thickness of the layer and deviations from the mean efficiency. Restrictions can be assigned for both quality factors as well as for the penetration through the collimator septa. Collimators used in an auxiliary system for screening layers by means of γ-γ-coincidence scintigraphy are optimised with the aid of the program. Collimators designed by the program with a separation of 240mm have a higher sensitivity than those designed by Schmitz-Feuerhake with a separation of 180 mm. As the program only considers absorption and not scattering in material, there are deviations in the response in comparison with the computed response, dependent on the width of the energy window in the pulse height analysis. Experimental results enable one to estimate the broadening of the screened layer by scattering and to include the broadening by further optimisations. In profile scanning, scattering effects are of little importance once small energy windows are employed. The method can therefore be applied without restrictions. (author)

[en] To simplify routine gain adjustment of the detectors, and in order to achieve good long-term stability, a digital method of gain adjustment applying high-voltage control has been developed. The required control and computer functions are carried out by a microcomputer system, TM 990/189. Calibration proceeds in two steps: After starting the program by entering the energy of the calibration peak, all 16 photomultiplier signals are separately adjusted to a uniform mean pulse height. Fine adjustment of the four detector summation signals is achieved by re-adjusting the respective four photomultiplier signals. The process is constantly repeated during the operating pauses, thus guaranteeing a reliably good stability of the energy calibration of the measured spectra. (orig./HP)

No abstract available

[en] A low-level gamma spectrometer, placed in a shield of low background lead is described. The three detectors of the system, a 70cm³ Ge(Li) with 15.5% relative efficiency, a 30'' diam. x 15'' annular plastic scintillator, and a 70mm diam. x 3'' NaJ(TI) are combined either as an anticoincidence spectrometer or as a Ge(Li)-NaJ(TI) coindence spectrometer with Compton suppression. In the presence of Compton background from γ-rays of higher energy, the two modes of detection described in this paper provide a sensitivity quite higher than that of the single Ge(Li) spectrometer. (orig.)

[en] A 3D-scanner for direct three-dimensional imaging using a γ-γ-coincidence technique is presented. The characteristics of the system were demonstrated by isoresponse curves and modulation transfer functions. A phantom study showed the possibility of detecting cold nodes when they are invisible in normal scans in large subjects because of masking by overlying activity. (orig.)

[en] Only multiple X ray diagnostics could be identified as a common risk factor in a leukaemia cluster that appeared between 1985-1989 in the municipality of Sittensen in northern Germany. In order to judge if the effect could be explained by irradiation dose, estimates were done in two of the leukaemia cases and seven former patients of a practice where some of the leukaemia cases had been treated for orthopaedic reasons. The methods used for the reconstruction of doses were physical simulation and biological dosimetry by dicentric chromosomes in peripheral lymphocytes. Compared to the Bremen laboratory control the mean frequency of dicentric chromosomes in the lymphocytes of the seven volunteers was significantly elevated. An overexposure of about 12-fold could be derived compared to state of the art X raying. At least two cases of the leukaemia cluster in Sittensen can therefore be correlated to an overexposure by diagnostic X rays. (author)

[en] A scintigraphic system consisting of an Anger camera and additional detectors is presented which allows imaging of an object by measuring ß-ß-coincidences. The additional detectors are in opposite arrangement, each with a focussing slit collimator viewing a plane parallel to the camera head. Imaging of hot spots and cold nodes in extended objects in this way will result in considerable contrast enhancement, which is shown by phantom studies. The sensitivity of the system will be significantly increased by using pinhole collimators. (author)