Aim: The subject of our study is to investigate the accuracy of a typical PET/CT system
applying 18F-FDG to determine activity of small, hot volumes (HV) by phantom measurements under
the impact of reconstruction techniques (RT) with and without Time-of-flight-Mode (TOF), activity
concentration ratios into the phantom (ACR), density variations and relevant analysis parameters.
Methods: We investigated a body phantom containing up to 7 spheres (d = 6-37mm) on a topical
PET/CT system (SIEMENS BIOGRAPH mCT40). Recovery coefficients (RC) of small HVs dependent
on the ACR and several RTs (iterative default (IT), iterative high-definition including the system
Point-Spread-Function (HD), HD+TOF (UHD), filtered backprojection (FBP) and FBP+TOF (FBPT) were analysed. In
addition, we determined RCs with respect to the matrix size, number of iterations, filter settings and a phantom insert of
lung and bone density equivalent material. Results: The application of UHD in particular reproduces true activities of
small volumes best, followed by HD, IT, FBPT and FBP. Lung and bone equivalent density inserts reduce the RCs by up
to 19%. Especially for small HVs the RC can be raised by increasing the matrix size and iterations. Conclusions: Novel
technology and analysis have a strong impact on the quantification. Hence, new guidelines are required enabling comparisons
to other, prior systems. In order to get a precise activity determination of small structures, we recommend the UHD
algorithm, high resolution matrix and high number of iterations with respect to acquisition time and administered activity.