Evaluation of the HD and HD+TOF reconstructions for Siemens' Biograph-mCT TOF PET scanner

We describe an evaluation of the HD and HD+TOF reconstructions in terms of contrast vs noise, precision vs accuracy, and inter-realization variation on Siemens' Biograph-mCT time-of-flight (TOF) PET scanner. The HD-PET reconstruction is the 3D-OSEM with point-spread-function (PSF) modeling, and the HD+TOF is the HD-PET with the time-spread-function (TSF) modeling based on the TOF information acquired from the scanner. A chest-spine phantom was scanned, and the data were reconstructed using the HD and HD+TOF methods. Hot contrast as well as cold contrast from regions with different densities was evaluated as a function of the voxel-noise in the images. The coefficient of variation (COV) in contrast was evaluated over 10 realizations at low statistics and plotted as a function of the bias in contrast. The standard deviation (STD) images were also compared between the HD and HD+TOF reconstructions. It was observed that the HD+TOF reconstruction outperforms the HD method in terms of hot contrast vs noise as well as cold contrast in the low density regions. However, for the high density regions the HD+TOF showed slightly worse results as compared to the HD method. Consistent results were also observed in terms of precision vs accuracy. The STD image comparison showed similar results between the HD and HD+TOF reconstructions. Additionally, the phantom data were also reconstructed with various methods and parameters for both Biograph-mCT (mCT) and Biograph-40 (B40), and the contrast vs noise evaluation showed that the same reconstruction method with the same or similar parameters on both scanners performs similarly (e.g. HD reconstruction with 2 iterations and 2 mm Gaussian smoothing).