Comparison of respiratory triggering and gating techniques for the removal of respiratory artifacts in MR imaging.

Abstract

Respiratory movement degrades magnetic resonance (MR) images of the chest and abdomen by increasing noise through the production of "ghost" artifacts and by decreasing edge sharpness in moving structures. Respiratory gating, which limits data acquisition to end-expiration, is successful in restoring edge sharpness and reducing ghosts but increases imaging time two to three times, which limits its use to sequences with short repetition times (TRs). To overcome this limitation, an alternative technique, respiratory triggering, was developed, which triggers the acquisition of an MR section at a fixed point on the respiratory cycle. This technique restores edge sharpness and reduces ghosts, but unlike gating, it can be used to produce an image at any phase of the respiratory cycle. Triggering requires long TRs since the TR is limited to the respiratory period (TP) or one-half of TP, depending on whether the same section is triggered once or twice during a single respiratory cycle. Gating and triggering were evaluated and compared for single-section and multi-section imaging of both volunteers and patients. The authors conclude that when a chest or abdominal survey is required, triggering takes less time than gating if TRs are required that exceed one-fifth of TP.

Contrast-Enhanced Abdominal MRI for Suspected Appendicitis: How We Do It

“…SSFSE is remarkably motion insensitive, and, for this reason, the inability to breath-hold is not a contraindication for MRI to evaluate for appendicitis. We recommend that breath-holding be performed at end-tidal volume using the instructions, “breathe in, breathe out, stop breathing.” Imaging at end-inspiration is also effective, but the position of the diaphragm is less reproducible and can lead to misregistration of slices or sequences acquired in different breath-holds [29, 30]. …”

Magnetic Resonance Imaging of Renal Disease: Recent Developments and Future Applications

“…Respiratory triggering, however, initiates the acquisition of an MRI section at a fixed point of the respiratory cycle, restoring sharpness and reducing ghost artifacts. Unlike gating, triggering can be used to produce an image at any phase of the respiratory cycle, but it requires the use of longer TR [15]. An elaborate technique used to suppress respiratory motion uses respiratory gating with MRI navigators [16, 17].…”

Amplitude demodulation of the electrocardiogram signal (ECG) for respiration monitoring and compensation during MR examinations

“…Triggering of MR imaging sequences of the heart is often less demanding since artifacts between triggering pulses are acceptable. Respiration compensation (17,18) on the other hand requires a signal that is correlated with the position of the diaphragm and that shows no delay or drift. While a delay of less than 1 s can generally be accepted, a drift of the signal is less tolerable.…”