Cardiac gating of transmission data is unnecessary for attenuation compensation of double-gated emission scans

Respiratory motion produces differences in PET attenuation maps from different phases of a respiratory-gated cardiac transmission acquisition. The effect of the contraction of the heart on the attenuation map is assumed to be small, but has not yet been investigated. The authors acquired list mode transmission data from two normally breathing humans while monitoring both respiration and the cardiac waveform. The data were retrospectively analyzed; first dividing them into separate time frames to check for gross patient motion, then into respiratory frames to isolate respiratory motion. A large, nearly motionless respiratory dataset is available near end expiration. These data were divided into 100 msec cardiac frames and reconstructed. Though up to 20 mm of respiratory motion was seen in the attenuation map, no discernible motion was detected between cardiac frames. The authors' finding implies that cardiac gating of the PET transmission map is unnecessary, and that only compensation for respiratory motion need be considered when correcting double-gated emission data for attenuation effects.