THEORETICAL-STUDIES OF IMAGE ARTIFACTS AND COUNTING LOSSES FOR DIFFERENT PHOTON FLUENCE RATES AND PULSE-HEIGHT DISTRIBUTIONS IN SINGLE-CRYSTAL NAL(TL) SCINTILLATION CAMERAS

  • 1 January 1980
    • journal article
    • research article
    • Vol. 21  (3) , 264-275
Abstract
Using computer simulations a theoretical model was developed to explain the correlation between counting losses and image artifacts in single-crystal NaI(Tl) scintillation cameras. The theory, valid for scintillation cameras of the Anger type, is based on the physical properties of the NaI(Tl) crystal. Based on a statistical model using random numbers, pulse trains of the light pulses from scintillations were simulated. Pulse-height distributions for different event rates were calculated with Compton distributions. Images of point sources and line sources were generated. Counting losses and image artifacts were dependent on the shape of the pulse-height distribution. The calculated counting losses decreased with larger Compton distributions, due to increasing numbers of pileup events in the energy window; this caused severe image distortion. The improvement of the spatial resolution with pileup rejection was demonstrated. In modern cameras, the decay time of the scintillation apparently determines the amount of pileup and the resolving time of the electronics governs the count rates. In some modern cameras the limits of the count-rate capacity in Anger cameras may be reached.

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