Validity of a Simple Spillover Correction for Positron Emission Tomography Measurements in the Cerebrospinal Fluid Region

Objective Positron emission tomography (PET) measurements in the cerebrospinal fluid (CSF) region may be overestimated because of spillover artifacts from surrounding radioactivity. In this study, we proposed a simple spillover correction method (the subtraction method) and evaluated its validity. Methods A cylindrical phantom simulating brain ventricles was used to compare the subtraction method with a partial volume effect (PVE) correction method, specifically the geometric transfer matrix (GTM) approach. The subtraction method was then applied to dynamic PET images using three radiotracers, [¹⁸F]fluorodeoxyglucose (FDG), [¹⁸F]fluorodopa (FDOPA), and [¹¹C]raclopride (RAC), in one healthy individual, and [¹⁵O]H₂O (H₂O) in another case. None of these tracers were expected to diffuse into the CSF within a short timeframe. The effects of spillover correction on CSF measurements were assessed. Results Both the subtraction and GTM methods effectively reduced spillover artifacts in the phantom study. In dynamic PET images, all four radiotracers showed an immediate increase in radioactivity within the CSF region following intravenous administration. FDG, FDOPA, and RAC demonstrated similar radioactivity trends in the CSF and surrounding regions, whereas H₂O showed a distinct pattern. After spillover correction, time-activity curves for FDG, FDOPA, and RAC approached near-zero levels in the CSF, whereas H₂O continued to show increasing activity over time. Conclusions We developed a subtraction method to correct PET signal overestimation in the CSF region attributed to spillover effects. This approach effectively reduced artifacts, comparable to the GTM method, and offers the advantages of simpler volume-of-interest (VOI) settings and straightforward calculation procedures.