Respiratory compensation reduces motion artifacts due to breathing. The approach is to reassign the echoes that are sensitive to respiratory motion in the central region of k-space. The outer lines of phase encoding normally contain the echoes where the motion from expiration is the greatest. The central portion of k-space will have encoded the echoes where inspiration and expiration are minimal. By a bellows device fixed to the abdomen, monitoring of the diaphragm excursion is possible. Respiratory compensation does not increase scan time with most systems.
An advantage of very fast sequences is the possibility of breath holding during the acquisition to eliminate motion artifacts. Breath hold is commonly used on most abdominal studies where images are acquired using gradient echo-based sequences during a brief inspiratory period (20-30 seconds). To enhance the breath holding endurance of the patient, connecting the patient to oxygen at a 1-liter flow rate via a nasal cannula has been shown to be helpful.
Also called PEAR, Respiratory Trigger, Respiratory Gating, PRIZE, FREEZE, Phase Reordering.

See also Phase Encoding Artifact Reduction, Respiratory Ordered Phase Encoding.

Respiratory gating is a respiratory motion reduction technique with reordering of the phase encoding matrix.

See Gating.

Respiratory synchronization that acquires image data at regular times independent of the respiratory cycle, but chooses the sequence of phase encoding data acquisition so as to minimize the respiratory motion-induced artifacts in the resulting image. For example, choosing the sequence of phase encoding such that adjacent samples in the final full data set have minimal differences in respiratory phase will minimize the spacing of ghosting artifacts in the final image.

The resorting of data collected over several acquisitions to create an image where all phase encoding lines are acquired with the object at the same spatial location of the respiratory cycle.

The respiratory phase can be used to control imaging either by only acquiring the image data during a particular portion of the respiratory cycle (which increases image acquisition time) or by adjusting the sequence of image data collection according to the phase of the respiratory cycle in such a way as to minimize motion-induced artifacts in the reconstructed image.

See also Respiratory Ordered Phase Encoding.