Time-of-flight positron emission tomography: status relative to conventional PET.

Abstract

Summary An advantage of using the TOF information in PET is the sensitivity gain that can be calculated as the ratio of the total counts required to obtain the same random noise in the image, with and without the TOP information. This gain ranges from one to about eight and depends on the TOF performance, activity distribution, and the relative efficiency of the available detectors. This sensitivity gain is a driving force for time-of-flight technology; however, the gains are not quite as good as one would expect in the practical imaging situation wherein a priori distribution occupies only a limited number of resolution elements, and the efficiency of the available crystals for TOF might lead to a reduction in the sensitivity relative to conventional PET. Inherent in TOFPET is the ability to perform very high count rate experiments for fast dynamic studies (e.g., 15O, 82Rb, 122I). In addition, random coincidences are lower than in non-TOFPET. Finally, an important attribute of TOFPET is the fact that the low random coincidences at high count rates allow transmission data to be obtained more efficiently than in conventional PET. At present, due to lack of availability of small and highly efficient, crystal-phototube detectors, TOFPET does not have the high spatial resolution capabilities of non-TOFPET.

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