Attenuation correction in PET-transmission vs. contour finding in the study of [11C]raclopride binding

Attenuation correction is of major importance for accurate quantification by PET. In this study analyses were performed on the uptake curves for [¹¹C]raclopride binding in 11 healthy subjects. The images were reconstructed by applying two different methods for attenuation correction, estimated attenuation correction by an external transmission source and attenuation correction by using a contour finding algorithm with a fixed attenuation value (μ=0.096 cm ^-1). The PET instrument used was the Scanditronix PC 2048-15B brain tomograph. Radioactivity was determined for the putamen and the cerebellum and the putamen to cerebellum ratios were calculated. The attenuation values measured in the transmission images was μ=0.096 cm ^-1 for the cerebellum but lower for the putamen (μ=0.092 cm^-1). For the skull bone the attenuation factor was lower (μ=0.119 cm^-1) than expected (μ=0 092 cm^-1). The difference in putamen to cerebellum ratios between the two attenuation methods was 7%