Fig. 1

Using bellows for respiratory motion. Respiratory bellows are placed over the diaphragm or abdomen where excursion is greatest from respiratory motion, and are attached with a Velcro strap (a, arrowhead). A corrugated pneumatic tube (a, arrow) expands and contracts with each respiration, and pressure changes from within the tube are transmitted to a transducer through rubber tubing. b demonstrates a representation of a bellows tracing. Breathing at rest has decreased excursion of the diaphragm that is periodic. During breath-hold imaging, patients take a breath deeper and hold their diaphragm location for an extended period of time (15–30 s), measured as decreased pressure within the tubing during inspiration (b, breath hold). The goal of respiratory gating is to collect data that is acquired during the quiescent phase, which is closest to end expiration (b, quiescent phase)