MR navigator‐echo monitoring of temporal changes in diaphragm position: Implications for MR coronary angiography

Abstract

Temporal changes in respiration could influence navigator-echo (NE)-gated MR coronary angiography (MRCA), but systematic investigation of the effects of such variations and how to limit them has not been performed. We addressed these issues by studying the influence of time in the magnet on diaphragm position and respiratory patterns using NE diaphragm monitoring in volunteers and a phantom model. NE diaphragm monitoring was performed at .5 T in 10 subjects over a total period of 35 minutes. The end-expiratory position was sustained for longer (1.1 vs .4 seconds, P < .001) and with greater position stability (SD 1.9 vs 5.9 mm, P = .01) than the end-inspiratory position. Drift of the end-expiratory position occurred over time, causing a fall in scan efficiency (44-28%, P = .01). Up-drift of the end-expiratory position was most common. Loss of scan efficiency was worse with up-drift because of loss of the end-expiratory pause from the NE window (up-drift 10% mm-1, down-drift 7% mm-1, both P = .03). Scan efficiency also was reduced during sleep (to a nadir of 0%), secondary to loss of the end-expiratory pause, periodic breathing with oscillating end-expiratory position, and periods of apnea. The phantom model used actual diaphragm traces to evaluate the artifact resulting from diaphragm motion during acquisition. Artifact was considerably reduced by NE adaptive motion correction compared with NE gating alone (ghosting ratio 2.0 vs 2.8, P < .01). Artifact also was significantly reduced with up-drift if scan efficiency was maintained above 35% (P = .05). For optimal NE-gated MRCA, the following features are important: the NE window should be placed around the end-expiratory position; subjects should not sleep; scan efficiency should be monitored and the NE window should be repositioned if scan efficiency falls below 35%; and adaptive motion correction should be used.

Magnetic Resonance Angiography

“…Imaging during free (unrestricted) breathing offers obvious advantages over breathholding. A novel technique for minimizing respiratory-related motion is with the use of real-time navigator echoes 25,27,[212][213][214][215][216][217] that interrogate an interface such as the diaphragm-lung or heart-lung. 25 Positional changes of this interface along the axis of the navigator can then be followed through the normal respiratory cycle.…”

Coronary artery motion with the respiratory cycle during breath‐holding and free‐breathing: Implications for slice‐followed coronary artery imaging

“…However, during prolonged studies drifting of the respiratory pattern leads to a corresponding fall in efficiency (2), resulting in registration errors between scans and a frequent need to reposition the acceptance window. Real-time slice-following (3) has the potential to increase the scan efficiency and reduce the sensitivity to respiratory drift by allowing the implementation of a larger navigator acceptance window.…”

Comparison of Diagnostic Performance of Multi Detector CT Angiography with Conventional Coronary Angiography for Assessment of Coronary Artery Disease

“…The navigator echo procedure appears to have more application in clinical practice, as the breath hold method is not generally possible for patients with congestive heart failure, CAD, and chronic obstructive pulmonary disease [79,80]. Nonetheless, in those cases the nature of images might be debased because of conflicting breathing patterns and patient developments [82]. The other option systems incorporate magnetic resonance subtraction techniques, which incorporate particular labeling of blood in the aortic root and suppression of the foundation tissue.…”