Influence of cross-contamination on PET values for simultaneous emission/transmission acquisition using the mask technique

For the quantitative accuracy of simultaneous emission/transmission (SET) acquisition using the mask technique, we confirmed the contamination of photons that spilled over from the transmission source into the emission data, and evaluated the influence of decay correction with different half-lives of the transmission source and emission source. First, to confirm the contamination of photons from the transmission source, SET scans were performed with a cold phantom and blank status in the field of the gantry. Second, to evaluate the quantitative accuracy of the PET values obtained by the decay correction, serial scanning with SET and conventional scanning were carried out with the same frame time. All of the data were reconstructed with the decay correction based on the same scan start time, and counts of ROI on the reconstructed images were evaluated. For SET acquisition, contamination of photons from the transmission source into the emission data due to the scattered photons, which were from the object and spillover fraction through the mask window, was shown. The intensity of this contamination was dependent on the activity of the transmission source. Quantitative accuracy was affected by the decay correction of the SET data. The effect was emphasized by increasing the emission activity or reducing the transmission activity. It is suggested that the effect of attenuation correction is based on the transmission data, which are subtracted from the emission data. These characteristics should be carefully considered for the quantitative estimation of SET acquisition. (author)