VALIDATION OF POSTINJECTION TRANSMISSION MEASUREMENTS FOR ATTENUATIONCORRECTION IN NEUROLOGICAL FDG-PET STUDIES

Accurate estimation of local cerebral metabolic rate of glucose utiliz ation (LCMRGlu) with PET requires a separate measurement of photon att enuation using a transmission source that extends study duration. The feasibility of postinjection transmission (PIT) scanning has been demo nstrated but not previously validated in humans. Methods: Preinjection and postinjection transmission scans were performed in 26 patients un dergoing routine [F-18]fluorodeoxyglucose (FDG) neurological PET. The PIT data were processed with two methods: One estimated emission conta mination using an independent emission scan (PITInd; the other estimat ed the contamination directly from the PIT scan, using simultaneously acquired emission data for subtraction (PITsim). These methods were co mpared with measured attenuation correction (AC) using preinjection tr ansmission data (AC(pre) and calculated AC (AC(calc)). After reconstru ction, image data were reformatted to fit a standard brain atlas to fa cilitate analysis of the region of interest and to allow subtraction o f datasets averaged over all subjects. Results: The ratios of LCMRGlu values with respect to those obtained by the AC(pre) method ranged fro m 0.98 to 1.06 (mean +/- s.d., 1.01 +/- 0.02) for PITind, from 0.96 to 1.04 (mean 0.99 +/- 0.02) for PITsim and from 0.77 to 1.12 (mean 0.96 +/- 0.07) for AC(calc). Both PIT methods agreed well with the AC(pre) method, whereas AC(calc) gave rise to appreciable bias in structures near thick bone or sinuses. Conclusion: Accurate quantitative estimate s of LCMRGlu can be obtained using PIT measurements. The PIT methods s horten study duration and increase patient throughput. The PITsim meth od has the further advantage that it is not affected by tracer redistr ibution and can therefore be applied to tracers with relatively rapid kinetics in vivo.