Comparison of clinical data sets acquired on different tomographs using 6-18F-L-dopa.

Longitudinal positron emission tomography (PET) studies of 6-18F-L-dopa uptake in the striatum are used to assess the progression of Parkinson's disease or the survival of neuronal cells grafted in parkinsonian patients. These studies are performed over several years, and data analysis may suffer from the change from old tomographs to new machines with better sensitivity and spatial resolution. Furthermore, such studies on parkinsonian patients may be accomplished in either 2D or 3D acquisition mode. The aforementioned improvements offer great benefits for the study of neurodegenerative diseases, especially those affecting the striatum. However, direct comparison of data is not straightforward owing to variation in scanner characteristics. In this study, we assessed the feasibility of comparing the 6-18F-L-dopa striatal uptake values (Kc) measured in two groups of healthy subjects using two tomographs of different generations. We re-studied and compared acquisitions performed on 14 healthy subjects using 6-18F-L-dopa. Half of these studies had been performed in 2D acquisition mode using an ECAT 953B. The other half had been performed in 3D acquisition mode using an ECAT EXACT HR+. Different reconstruction protocols were used and the Kc values obtained were statistically compared. The results showed that lowering the transverse spatial resolution of images obtained with the scanner having the better spatial resolution, so that it more closely matched that of the other machine, allowed similar KC values to be obtained in healthy subjects. This study shows that quantitative results of 6-18F-L-dopa scans can be matched between different scanners with different intrinsic resolutions. This can be accomplished using adequate modifications of the reconstruction parameters. Such modifications can be used to help in the longitudinal monitoring of parkinsonian patients using different tomographs.