[en] The effects of the angular range of data taking in reconstructions in planar positron cameras using the deconvolution method and the matrix method, respectively, are investigated. It is found that in the absence of any a priori information there are undetermined components in the reconstruction if the field of view of the positron camera is limited. However, most of the undetermined components are recovered in the case in which the transverse spacing of the object is discrete, and all of them are recovered if the fact that the object extent is finite is utilized. It is concluded that the two reconstruction methods are mathematically equivalent. The results obtained can be applied to other transmission and emission imaging devices

No abstract available

[en] Positron cameras using two opposed area detectors for the coincidence detection of 511 keV annihilation photons have been available for some time. Image reconstruction from the collected annihilation data in this camera configuration is usually based on focal plane tomography. However, this method suffers from structured background existing in the images from the contribution of off-focal plane activity, resulting in low contrast, poorly resolved images. A method which reduces this off-focal plane background through an iterative approach which weights individual picture elements according to the activity computed by the previous iteration. 12 refs

[en] Results of computer simulations showed that the use of Anger cameras with collimators for 511 keV is possible. In combination with a conventional crystal, a yield of almost 30% may be expected compared with Tc-scintigraphy. The transfer properties are reduced in this case. If the cutoff frequency of the MTF for Tc-collimators is slightly above ν = 1 cm^-1, a value around ν = 0.5 cm^-1 is reached by high-energy collimators. (orig./HP)

[en] The efficiency and the width of the line spread function of parallel hole collimators for single crystal and multicrystal cameras can be assessed using simple approximations. All colimators are treated in a formally identical way, irrespective for the form and arrangement of the holes. The method cannot predict the penetration and the complete line spread function. Examples of optimized lead and tungsten collimators are presented. Tungsten collimators have higher efficiencies and may easier be matched to the detector of single crystal cameras. (orig.)

[en] Positron imaging systems provide a unique and powerful means to examine the spatial and temporal course of radiopharmaceuticals in the body to observe normal and abnormal physiology in vivo. The information so obtained in conventional or transverse section mode complements the information on structure obtained from conventional x-ray and computerized tomography (CT) imaging. Powerful instruments are now available to provide high resolution conventional and transverse section positron images

[en] The localized depression of activity in the centre of images from the MK 11 positron camera (MUP-PET) has been identified by modelling as one feature of an artefact which is the result of the non-uniform sensitivity of lines-of-response (LOR) due to their variable pathlength though the detectors and thus detection efficiency. By recalculating the rotational weights incorporating this effect an accurate correction can be achieved without any increase in processing time. This correction does not account for those LOR which exit from the superior and inferior sides of the detectors, the polar angle threshold required for Fourier image reconstruction diminishing the necessity for this component. However, if more oblique LOR were to be incorporated into the backprojection (Defrise et al 1988) a more complete correction may be required. (author)

No abstract available

[en] A positron imaging system and method are described, in which two opposed Auger cameras are employed on opposite sides of an organ to be imaged. The cameras include a planar unitary scintillation crystal approximately one inch in thickness, and the electronics which process the signals from the camaras include pulse shaping circuitry to reduce both the duration and the integration time of pulses resulting from radioactive events. Both cameras exclude collimators to enable radiation incident upon them at many angles to be accepted, and means are included to rotate the opposed cameras about the organ of interest to enable transverse tomographic imaging. (C.F.)

[en] The principles of operation of the Anger Gamma Camera and its main applications are reviewed. New developments at Elscint include the removal of Compton scattered events from the image and attenuation correction in Single Photon Emission Tomography (SPECT) using external sources. The Positron Emission Tomography (PET) method and its current implementation on Gamma Cameras is also discussed. (author)