Original paper| Volume 75, P85-91, July 2020

The impact of time-of-flight, resolution recovery, and noise modelling in reconstruction algorithms in non-solid-state detectors PET/CT scanners: – multi-centric comparison of activity recovery in a 68Ge phantom


      • The ability of reconstruction algorithms to correct for partial volume effect is controversial.
      • Iterative reconstructions with and without TOF achieve activity recovery in the 22 mm sphere.
      • Resolution recovery and noise modelling algorithms achieved considerable activity recovery in the intermediate spheres (in particular in the 17 mm diameter sphere).
      • There is no activity recovery gain in the smallest sphere (6 mm diameter) using neither PSF, nor TOF nor BPL.


      The reconstruction algorithms implemented on PET/CT scanners offer gain in activity recovery of small lesions at an extent that is not full known yet.


      A cylindrical phantom with warm background and hot spheres filled with a 68Ge epoxy was acquired with four non-state-solid-detectors PET/CT scanners: mCT, Ingenuity TF, Discovery 710, and IQ. Images were reconstructed switching on and off time-of-flight (TOF), point spread function (PSF) modelling, and Bayesian penalised likelihood (BPL). Images were reconstructed with the default parameters recommended by the manufacturers. The recovery coefficient (RCmax), defined as the ratio of the measured maximum activity concentration in each sphere and the actual one, and the coefficient of variation (CoVBAC) defined as the ratio of the standard deviation and the average of background activity concentration were measured.


      While with IR alone, complete recovery of the activity concentration is achieved down to the 22 mm diameter’s sphere, with TOF, TOF + PSF and BPL it is achieved down to the 17 mm diameter one. At smaller dimensions, the difference among the various studied reconstruction algorithms is substantial for the 13- and 17-mm diameters’ spheres for all scanners and for all reconstructions with a considerable gain in RCmax when PSF and BPL are used. At 10 mm diameter’s sphere the difference among the algorithms is significantly reduced, except for BPL which still guarantees a gain in RCmax.


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