Magnetic resonance navigator echo diaphragm monitoring in patients with suspected diaphragm paralysis

Real-time magnetic resonance (MR) navigator echo (NE) monitoring of the diaphragm is now possible. Using this technique, temporal changes in diaphragm position can be analyzed in a non-invasive fashion, without x-ray exposure. In this preliminary study, we have optimized three NE parameters (the NE column area, the NE repeat time, and the location of the NE on the diaphragm surface), and demonstrated the clinical application of MR NE diaphragm monitoring in patients with suspected diaphragm paralysis. The NE parameters were defined in 10 healthy volunteers, and diaphragm traces were scored for variance in NE diaphragm position registration. Using the optimal NE column parameters, we investigated four patients with diaphragm paralysis, one of whom required positive pressure ventilation while in the MR scanner, to show the utility of this technique. The NE diaphragm position registration was significantly affected by the area of the NE column, with poor position registration for the smallest column area (2.25 cm2 vs. 4 cm2 vs. 6.25 cm2, variance 6.3 vs. 0.6 vs. 0.3, P = 0.006). Diaphragm position registration was also significantly affected by the NE repeat time, with misregistration for the shortest repeat time (250 msec vs. 500 msec vs. 1000 msec, variance 11.9 vs. 0.6 vs. 1.0, P = 0.02), and data clipping, with loss of end-expiratory and end-inspiratory position registration, for the longest repeat time. Finally, if the NE was positioned too anteriorly, the diaphragm traces were of poor quality (anterior vs. dome vs. posterior, variance 11.8vs. 0.6vs. 3.2, P < 0.001). Application of the technique confirmed diaphragm paralysis in all four patients. The technique can be applied during positive pressure ventilation if necessary. The optimal NE parameters for diaphragm monitoring at 0.5 T were: column area, 400 mm2; NE repeat time; 500 msec; NE column positioned on the diaphragm dome. MR NE diaphragm monitoring provides a safe, non-invasive method of assessing diaphragm motion in patients with suspected diaphragm paralysis and may prove useful for long-term follow-up and monitoring of therapeutic interventions in these subjects.