Optimized protocols in terms of equalizing the true and accidental coincidences of each bed position in static...

Quantitative carbon-11 (11C) 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 studies such as partial volume effects correction without needing to use anatomical information. However, because of the short half-life of 11C, a homogeneous multiple bed position 11C image is hard to obtain. This study aimed to determine whether innovative pseudogating, optimized pseudogating and optimized double-up methods could match the true counts and randoms to each bed position and to a target single bed position study. A long cylindrical phantom filled with [11C]acetate was scanned by a dedicated PET scanner using six protocols: whole body, frame-duration-compensated whole body, double-up, optimized double-up, pseudogating, and optimized pseudogating. The differences between the protocols are in the initial activity, frame duration and frame number for each bed position. The parameters for pseudogating were determined according to the theory that true counts and randoms are proportional 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 qualitative studies, respectively.