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An Alternative Method to Normalize Clinical FDG Studies

Department of Radiation Physics, University Hospital, Lund, Sweden

Correspondence: For correspondence or reprints contact: Anders Sandell, MSC, Department of Radiation Physics, University Hospital, S-221 85 Lund, Sweden.

ABSTRACT

An alternative method of determining the integrated input function, necessary in the quantitative [¹⁸F]fluorodeoxyglucose (FDG) autoradiographic model, has been developed. Using erythrocytes as reference tissue, researchers require only one blood sample after injection of FDG to obtain the integrated input function. Methods: The amount of FDG-6-PO₄ in the erythrocytes is proportional to their exposure to FDG, that is, the integrated input function. Free FDG is removed by washing the erythrocytes twice. Inter- and intraindividual differences of the metabolic rate of erythrocytes are corrected for by an in vitro incubation with a known amount of FDG. Results: Validation of the proposed method was done by correlating the integrated input function, based on the glucose metabolism of the erythrocytes, to the integrated input function obtained by multiple venous blood samples. The new method provides the integrated input function with an accuracy better than ±8%. Conclusion: By usingerythrocytes as a reference tissue, researchers can determine the integrated input function in the quantitative FDG autoradiographic model with an accuracy sufficient for clinical PET studies. The simplicity of the method also makes it suitable for FDG studies on small children. With two samples, the method can also be used for a simplified graphical Patlak analysis.

Key Words: erythrocytes • fluorine-18-fluorodeoxyglucose • integrated input function • normalization