To maximize navigator performance and efficiency, localization of the navigator at the dome of the right hemidiaphragm is important. Since the 3D shape of the diaphragm is individually dependent, identification of the dome on 2 orthogonal planes is advised. Localization of the navigator with 1/3 above the lung-liver interface and 2/3 below is recommended. Caudal 'drift' of the end-expiratory diaphragmatic position is sometimes observed which may adversely affect the efficiency of the scan. However, this is often related to sleep apnea or a low frequency pattern overlaid to the respiration, and in most cases the end-expiratory diaphragmatic position returns to its original position. On average, the navigator efficiency should approach ~50% which prolongs the nominal scanning time by a factor of 2. Navigator efficiencies below 20% and above 80% are suboptimal meaning that the localization of the navigator may need to be adapted. Stopping and restarting the scan may help in some cases. General patient motion can be minimized by specifically informing the patient that changing the position of the legs (crossed vs. non-crossed) should be avoided during the scan session. Asking the patient to go to the restroom prior to the MR exam helps to minimize general patient motion and improves the respiratory pattern.
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