QUANTITATIVE PET WITH POSITRON EMITTERS THAT EMIT PROMPT GAMMA-RAYS

The purpose of this work was to determine the feasibility of using pos itron emitting isotopes that emit prompt gammas to acquire quantitativ e positron emission tomography (PET) data using standard PET instrumen tation. Prompt gammas can contaminate PET data by: increasing dead tim e, converting singles into invalid coincidences, and producing multipl e coincidences which can lead to the replacement of valid coincidences by invalid coincidences. The measurements in this work were made by s canning point sources containing F-18, Na-22, and Co-60 and studying t he effects of the prompt gammas on the PET data. We found that for the Na-22 point source, the annihilation photon coincidence rate was abou t 25 times the prompt gamma-annihilation photon coincidence rate in th e entire active volume of the scanner. With scatter, the Na-22 prompt gamma-annihilation photon coincidence rate was 1.3 times higher than t he F-18 scatter coincidence rate. The most significant effect of the p rompt gamma was to increase dead time; the dead time correction factor for Cu-60 was 2.4 times higher than the correction factor for N-13 fo r the same source activity. We conclude that, in many cases, quantitat ive PET data can be readily obtained with isotopes that emit prompt ga mmas, using standard PET 2-D instrumentation. However there are some c ases, such as 3-D PET, where prompt gammas could significantly contami nate the PET data.