Optimized protocols in terms of equalizing the true and accidental coincidences of each bed position in static multiple bed position carbon-11 PET studies and a target single bed position study

Quantitative carbon-11 (C-11) positron emission tomography (PET) is gaining more attention in oncological applications. In addition, it was discovered that accidental coincidences (randoms) can play an important role in studi es such as partial volume effects correction without needing to use anatomi cal information. However, because of the short half-life of C-11, a homogen eous multiple bed position C-11 image is hard to obtain. This study aimed t o determine whether innovative pseudogating, optimized pseudogating and opt imized double-up methods could match the true counts and randoms to each be d position and to a target single bed position study. A long cylindrical ph antom filled with [C-11]acetate was scanned by a dedicated PET scanner usin g six protocols: whole body, frame-duration-compensated whole body, double- up, optimized double-up, pseudogating, and optimized pseudogating. The diff erences between the protocols are in the initial activity, frame duration a nd frame number for each bed position. The parameters for pseudogating were determined according to the theory that true counts and randoms are propor tional to the radioactivity and its square, respectively. The results show that the stated goals could only be achieved by pseudogating and optimized pseudogating. We conclude that pseudogating or optimized pseudogating must be applied for a critical quantitative study. However, optimized double-up and double-up methods are good alternatives for semi-quantitative and quali tative studies, respectively. ((C) 2001 Lippincott Williams & Wilkins).