Gamma camera PET with low energy collimators: characterization and correction of scatter

Imaging of myocardial viability with FDG is possible with PET and with SPECT. The image quality from SPECT is not as good but is reported to provide clinical information comparable to PET. Studies have just begun to appear using gamma camera PET and either axial slat collimators or open frame graded absorbers to image myocardial viability. Alternatively, it may be possible to use standard low energy collimators when detecting coincidences. Although image quality may suffer, it is may be possible to devise methods such that no clinical information is lost. Such an approach also paves the way for dual isotope simultaneous imaging of coincidence and single photons. Here we characterize the scatter fraction and scatter distribution of gamma camera PET with low energy collimators, and investigate the improvements possible with a convolution-subtraction type scatter correction scheme. The scatter fraction was found to be almost identical to that obtained with axial slat collimators on a triple head Marconi Irix scanner. Images acquired with low energy collimators were degraded but still of good quality compared to acquisitions using axial collimation. The scatter correction scheme showed a degree of improvement over reconstructions without scatter correction. This approach is useful not only towards making the simultaneous imaging possible, but may also be useful to save time in a busy clinic that does both SPECT scans and cardiac FDG studies, since collimators would not need to be changed.