Advances in scatter correction for 3D PET/CT

We report on several significant improvements to the implementation of image-based scatter correction for 3D PET and PET/CT. Among these advances are: a new algorithm to scale the estimated scatter sinogram to the measured data, thereby largely compensating for external scatter; the ability to handle CT image truncation during this scaling; the option to iterate the scatter calculation for improved accuracy; the use of ordered subset estimation maximization (OSEM) reconstruction for the estimated emission images from which the scatter contributions are simulated; reporting of data quality parameters such as scatter and randoms fractions, and noise equivalent count rate (NECR), for each patient bed position; and extensive quality control output. Scatter correction (2 iterations, OSEM) typically requires 15-45 sec per bed. Very good agreement between the estimated scatter and measured emission data for several typical clinical scans is reported for CPS Pico-3D and HiRez LSO PET/CT systems. The data characteristics extracted during scatter correction are useful for patient specific count rate modeling and scan optimization