Fig. 4.

Retrospective analysis of SG signals from the “SPACE SWL+SG” scans in all eight human subjects (V1 – V7) determines the number of TRs that have motion present. The left and right bars of each subject represent those numbers when the real-time “SG-reference update” was performed and not performed (using the SG line from the 6^th TR only as the reference profile), respectively. The real-time “SG-reference update” occurred once or twice in subjects #1, #3, and #6, as indicated by the numbers above the left bars. Omission of this procedure would give rise to a drastic increase in scan times, presumably because the data acquisition could be stalled with an “outdated” reference profile. With the “SG-reference update” activated, the numbers of TRs with motion detected respectively by SG₁ and SG₂ were calculated, as shown in the stacked left bars. In all subjects, swallowing motion was not always detected simultaneously by both SG₁ and SG₂, suggesting the necessity of the dual-gate procedure.