Simultaneous transmission and emission scans in positron emission tomography

Transmission scans are performed using a point source of Ge-68 masked by lead into a fan beam of annihilation photons in each scanning plane of the tomograph. As the source orbits the patient, section detector pairs collinear with it accept data for the transmission scan. Data from detector pairs nearly collinear with the source are rejected, while those far from collinear record an emission scan from activity in the patient slice. While this reduces the tomograph´s emission event efficiency by 30% (7% transmission, 23% rejected), slice registration errors are eliminated, and scanning time is reduced. There is no significant difference in measured activity concentrations from independent and simultaneous emission scans over a 110:1 activity concentration or in regional attenuation coefficients measured before and after isotope injection