A new approach to neuroreceptor quantification from fast activity curves sampling with a three-headed SPECT system

Recently we applied the direct reconstruction of region-of-interest (ROI) to three-projection data sets acquired in fast mode with a three-headed SPECT system. In this study, we evaluated whether the fast sampling of the time-activity curves (TACs) in regions of specific (striata) and non-specific (cerebellum) binding could allow for quantitative estimation of the binding potential (BP) in human ¹²³I-FPCIT dopamine receptor studies. Numerical simulations and phantom studies showed that this TACs-based method estimates regional concentrations better than using the ROI contents taken on expectation maximization (EM) reconstructed images. Moreover, it allows for an estimation of the statistical uncertainty. In the phantom study, the TACs-based method reproduced the real target-to-background ratio within about 10%; the ratio evaluated on EM images underestimated the real value of about 45%. Indeed, partial volume effect (PVE) correction is naturally embedded in the method. The approach was also applied in a patient DATSCAN study. The TACs were used to describe the evolution of the specific-to-nonspecific ratio (R) in time. The R values retrieved on EM images were about a 40% of the estimates obtained on TACs. The higher accuracy of TACs in measuring receptor density should allow for better clinical performance of receptor SPECT in Parkinson´s disease. The drawback of the method resides in a higher sensibility to region segmentation errors with respect to the conventional procedure.