Figure 3.

Schematic of integration with the gating system: linking the superior–inferior movement of the projected motion kernel with the gating mechanism that detects anterior–posterior movement of surrogate markers. (a) Maximum exhalation creates the most posterior marker position, and (b) maximum inhalation creates the most anterior marker position (analogous to movement of structures in the lung vs. position of markers on a breathing belt). $\text{IR}=\text{infrared}$.