Application of Simultaneous Emission and Transmission Scanning to Quantitative Cerebral PET

This chapter investigates the impact of simultaneous emission and transmission (SET) on the accuracy of quantification in tracer kinetic studies of the brain. Accurate quantification of brain function with positron emission tomography (PET) requires a separate transmission scan to correct for photon attenuation, which extends the duration of the study. Alternatively, emission and transmission measurements can be performed simultaneously, at the potential cost of bias due to increased scatter and dead time. Scatter and dead time correction errors in SET are measured as functions of the emission count rate. The effective scatter fraction for SET was –1 (11.8 vs. 10.6%), but increased with decreasing emission count rate. In contrast, dead time correction error was –5% at 30 kcounts . sec –1 and became worse with increasing count rate. The net effect was to overestimate activity at low count rates and underestimate activity at high count rates. As a result, estimates of glucose metabolic rate using SET were lower than those from conventional acquisition, and the bias was greater in gray matter than in white matter. However, in both cases, the bias was small relative to measurement noise. It has been concluded that quantitative cerebral PET studies can be performed with acceptable bias and reduced study duration using SET.