Single time point quantitation of cerebral glucose metabolism by FDG-PET without arterial sampling

BACKGROUND: Until recently, quantitation of the net influx of 2-[(18)F]fluorodeoxyglucose (FDG) to brain (K(i)) and the cerebrometabolic rate for glucose (CMR(glc)) required serial arterial blood sampling in conjunction with dynamic positron emission tomography (PET) recordings. Recent technical innovations enable the identification of an image-derived input function (IDIF) from vascular structures, but are frequently still encumbered by the need for interrupted sequences or prolonged recordings that are seldom available outside of a research setting. In this study, we tested simplified methods for quantitation of FDG-K(i) by linear graphic analysis relative to the descending aorta IDIF in oncology patients examined using a Biograph Vision 600 PET/CT with continuous bed motion (Aarhus) or using a recently installed Biograph Vision Quadra long-axial field-of-view (FOV) scanner (Bern). RESULTS: Correlation analysis of the coefficients of a tri-exponential decomposition of the IDIFs measured during 67 min revealed strong relationships among the total area under the curve (AUC), the terminal normalized arterial integral (theta((52–67 min))), and the terminal image-derived arterial FDG concentration (Ca((52–67 min))). These relationships enabled estimation of the missing AUC from late recordings of the IDIF, from which we then calculated FDG-K(i) in brain by two-point linear graphic analysis using a population mean ordinate intercept and the single late frame. Furthermore, certain aspects of the IDIF data from Aarhus showed a marked age-dependence, which was not hitherto reported for the case of FDG pharmacokinetics. CONCLUSIONS: The observed interrelationships between pharmacokinetic parameters in the IDIF measured during the PET recording support quantitation of FDG-K(i) in brain using a single averaged frame from the interval 52–67 min post-injection, with minimal error relative to calculation from the complete dynamic sequences.