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Image Artifacts at High Photon Fluence Rates in Single-Crystal NaI(Tl) Scintillation Cameras

Lasarettet, S-221 85 Lund, Sweden

Correspondence: For reprints contact: Sven-Erik Strand, Radiation Physics Dept., Lasarettet, S-221 85 Lund, Sweden.

ABSTRACT

A method that simulates a clinically relevant situation is used to measure the amount of pulse pileup in the gamma image by distinguishing between correctly and incorrectly positioned events. Comparison was then made between responses from different cameras. These investigations show the influence of pileup rejection on counting rate. Pileup effects can be determined for some cameras at such low count rates as about 10,000/sec with a 30% energy window. Parameters affecting the total count rate of the scintillation camera—such as scattering media, source geometry, collimator, and energy window—have been investigated. It is shown that the energy distribution of the photon fluence striking the crystal determines the counting losses and image distortion, rather than the counting rate in the energy window.

The approach described here might fulfill the requirements for a new method to compare scintillation cameras. It is important to note that measurements without scattering medium yield results irrelevant for clinical situations.