Dependence of image quality on acquisition time for the PET/CT Biograph mCT

The impact of acquisition time on reconstructed PET image quality is analyzed for different acquisition times (1, 2, 3 and 4min). Image quality was tested according to the National Electrical Manufacturers Association (NEMA) NU 2-2007, the evaluation for the signal to noise ratio (SNR) and the reconstructed activity ratio (RAR) for three algorithms, i.e. OSEM, TrueX and TOF applying different effective iteration numbers. The present work shows that the image quality of 3 and 4min acquisition time for spherical lesions of 10mm diameter are not significantly different between TrueX, TOF and OSEM. The 2min acquisition time should be used carefully for the TrueX and OSEM algorithms in small lesions, because the levels of background noise are high compared to 3 or 4min measurements. Also, the reconstructed activity ratio is underestimated to be approximately half of the expected value. For large lesions the three algorithms perform similarly for all acquisition durations, however, OSEM has the advantage of a more accurately reconstructed activity ratio compared to TrueX and TOF, which are more strongly influenced by noise.